About all

Can high altitude cause shortness of breath: The request could not be satisfied


Symptoms, Diagnosis, Treatment & Prevention


What is altitude sickness?

If you’ve ever hiked up a mountain and felt yourself getting nauseous or lightheaded, you may have experienced altitude sickness, also called mountain sickness. This condition happens when you travel to a high altitude (elevation) too quickly.

It doesn’t happen only to hikers. Just visiting a high-altitude location can cause problems for some. Symptoms happen when your body tries to adjust to the lower air pressure and lower oxygen levels at high altitudes.

Who is at risk for altitude sickness?

Anyone can get altitude sickness. Your age, sex and general health don’t seem to affect your risk. You may be at higher risk if you:

  • Have a lung or heart condition: Your healthcare provider may recommend avoiding high altitudes if possible.
  • Are pregnant: Talk to you provider before traveling to a high-altitude location.
  • Live at low elevation: Since your body isn’t used to higher altitudes, you have a greater risk for symptoms. If you’re planning a trip to a high-altitude location, be aware of the symptoms of altitude sickness and how to treat it.
  • Previously had altitude sickness: Talk to your provider about prevention and treatment before your next trip.

What is considered a “high elevation” in terms of getting altitude sickness?

Climbing to these elevations can bring on symptoms of altitude sickness:

  • High altitude: 8,000 to 12,000 feet above sea level.
  • Very high altitude: 12,000 to 18,000 feet.
  • Extremely high altitude: 18,000+ feet.

For context, New York City is at an elevation of 33 feet above sea level. Denver (known as the “Mile High City”) sits at 5,000 feet, and many Rocky Mountain ski slopes are at 11,000 feet or higher. The Grand Canyon is 6,600 feet above sea level. The summit of Mount Everest is over 29,000 feet.

How common is altitude sickness?

Altitude sickness may occur in up to half of people who climb to elevations above 8,000 feet.

What are the different forms of altitude sickness?

Most people who get altitude sickness get AMS, acute mountain sickness. Higher than 10,000 feet, 75% of people will get mild symptoms . There are three categories of AMS:

  • Mild AMS: Symptoms, such as mild headache and fatigue, don’t interfere with your normal activity. Symptoms improve after a few days as your body acclimates. You can likely stay at your current elevation as your body adjusts.
  • Moderate AMS: Symptoms start to interfere with your activities. You may experience severe headache, nausea and difficulty with coordination. You’ll need to descend to start to feel better.
  • Severe AMS: You may feel short of breath, even at rest. It can be difficult to walk. You need to descend immediately to a lower altitude and seek medical care.

Two severe forms of altitude illness occur less frequently but are more serious. Both can be life-threatening. You need to descend immediately and receive medical treatment for:

  • HAPE (High-altitude pulmonary edema): HAPE produces excess fluid on the lungs, causing breathlessness, even when resting. You feel very fatigued and weak and may feel like you’re suffocating.
  • HACE (High-altitude cerebral edema): HACE involves excess fluid on the brain, causing brain swelling. You may experience confusion, lack of coordination and possibly violent behavior.

Symptoms and Causes

What causes altitude sickness?

Altitude sickness results from a rapid change in air pressure and air oxygen levels at higher elevations. You may have symptoms if you travel to a high elevation without giving your body time to adjust to less oxygen. Even if you’re physically fit, you can still experience altitude sickness.

In addition, high altitude and lower air pressure can lead to fluid leaking from blood vessels. Researchers don’t understand exactly why this happens. This leakage causes fluid to build up in your lungs and brain. Ignoring moderate or severe symptoms can lead to a life-threatening situation.

What are the symptoms of altitude sickness?

You’ll likely feel nauseous and lightheaded. You may vomit and have a headache. Different levels of altitude sickness have different symptoms:

Symptoms of mild, short-term altitude sickness usually begin 12 to 24 hours after arriving at high altitude. They lessen in a day or two as your body adjusts. These symptoms include:

  • Dizziness.
  • Fatigue and loss of energy.
  • Shortness of breath.
  • Loss of appetite.
  • Sleep problems.

Symptoms of moderate altitude sickness are more intense and worsen instead of improve over time:

  • Worsening fatigue, weakness and shortness of breath.
  • Coordination problems and difficulty walking.
  • Severe headache, nausea and vomiting.
  • Chest tightness or congestion.
  • Difficulty doing regular activities, though you may still be able to walk independently.

Severe altitude sickness is an emergency. The symptoms are similar to moderate AMS, but more severe and intense. If you start experiencing these symptoms, you must be taken to a lower altitude immediately for medical care:

  • Shortness of breath, even when resting.
  • Inability to walk.
  • Confusion.
  • Fluid buildup in the lungs or brain.

HAPE, when fluid builds up in the lungs, prevents oxygen from moving around your body. You need medical treatment for HAPE. Symptoms include:

  • Cyanosis, when your skin, nails or whites of your eyes start to turn blue.
  • Confusion and irrational behavior.
  • Shortness of breath even when resting.
  • Tightness in the chest.
  • Extreme fatigue and weakness.
  • Feeling like you’re suffocating at night.
  • Persistent cough, bringing up white, watery fluid.

HACE happens when the brain tissue starts to swell from the leaking fluid. You need medical treatment for HACE. Symptoms include:

  • Headache
  • Loss of coordination.
  • Weakness.
  • Disorientation, memory loss, hallucinations.
  • Psychotic behavior.
  • Coma.

Diagnosis and Tests

How is altitude sickness diagnosed?

If you get a headache and at least one other symptom with 24 to 48 hours of moving to a higher elevation, it’s most likely altitude sickness. If you’re climbing, a more experienced climber may recognize symptoms of altitude sickness and guide you to get help.

If you have severe altitude sickness, a healthcare provider will ask about your symptoms, activities and location. The provider may perform a physical exam, including listening to your chest.

Will I need tests to diagnose altitude sickness?

You may need a chest X-ray to see if there is any fluid in your chest. In severe cases, your healthcare provider may order a brain MRI or CT scan to check for fluid in the brain.

Management and Treatment

How is altitude sickness treated?

The main treatment for altitude sickness is to move to a lower elevation as quickly and safely as possible. At the very least, do not go higher. If symptoms are mild, staying at your current elevation for a few days might be enough to improve the symptoms.

Other treatments depend on how severe the symptoms are:

  • Mild altitude sickness: Over-the-counter medicines can relieve headaches. Other symptoms will improve once your body adjusts or you move to a lower altitude.
  • Moderate altitude sickness: Symptoms should improve within 24 hours once you are 1,000 to 2,000 feet lower than you were. Within three days, you should feel completely better.
  • Severe altitude sickness, HACE and HAPE: If you have severe symptoms, you must be taken immediately to an elevation that’s no higher than 4,000 feet. Get to a healthcare provider as soon as possible. You may need hospitalization.

What treatments are available for severe altitude sickness?

Treatments depend on your symptoms:

  • For fluid in the brain (HACE), you may need dexamethasone, a steroid that helps reduce swelling in the brain. Dexamethasone is sometimes prescribed as a preventive medication.
  • For fluid in the lungs (HAPE), you may need oxygen, medication, a lung inhaler or, in severe cases, a respirator.
  • If you need more oxygen, a provider might prescribe acetazolamide, which increases your breathing rate, so you take in more oxygen. The medicine helps your body adjust faster to the higher elevation and reduces symptoms of altitude sickness.


How can altitude sickness be prevented?

The best way to prevent altitude sickness is to go slow — called acclimatization. This process allows your body time to adjust to the change in oxygen levels. Take your time when traveling up. For instance, spend a day at a point midway up before continuing to ascend.

You can also talk to your healthcare provider about taking acetazolamide before your trip. Taking it 24 hours before traveling to a high altitude and continuing for five days can help prevent altitude sickness. Dexamethasone can also be used preventively, but it can have serious side effects. Talk to your provider before your trip.

Outlook / Prognosis

What’s the outlook for someone with altitude sickness?

Most people who get altitude sickness get the mild form. Once you return to a lower elevation (or stay at your current elevation without climbing higher), symptoms improve.

Are there long-term effects of altitude sickness?

If you take care and move to a lower elevation when you feel symptoms, altitude sickness has no long-term negative effects. You’ll recover within a few days. Once you feel better, you can continue to travel to higher elevations, as long as you do so slowly and carefully.

Can altitude sickness be fatal?

In rare cases, altitude sickness can be life-threatening. If you develop HAPE or HACE, you are at risk for complications such as coma or even death. Get treatment as soon as possible to reduce your risk.

Can altitude sickness be cured?

Altitude sickness is temporary. Once you return to a lower altitude, you’ll feel better. When you begin your ascent again (or on your next climb), make sure to travel slowly to let your body acclimate.

Living With

If I’m planning a hike to a very high elevation, how can I hike safely without getting altitude sickness?

These steps can help your body acclimate:

  • Walk up: Start below 10,000 feet and walk to a high altitude instead of driving or flying. If you drive or fly to an elevation higher than 10,000 feet, stay at your first stop for at least 24 hours before going higher.
  • Go slow: Once above 10,000 feet, don’t increase your altitude more than 1,000 feet a day.
  • Rest: Build a rest day into your schedule for every 3,000 feet you climb.
  • “Climb high and sleep low”: If you climb more than 1,000 feet in a day, come down to sleep at a lower altitude.
  • Know your body: Recognize the signs and symptoms of altitude sickness. Move to a lower altitude (or avoid climbing higher) if you notice any symptoms.
  • Stay hydrated: Drink 3-4 quarts of water per day.
  • Avoid alcohol: Alcohol can dehydrate your body. It also has stronger effects at higher elevations, which can impair judgment.
  • Eat carbs: Eat a diet that’s more than 70% carbohydrates.
  • Know the “don’ts”: Avoid tobacco and depressant drugs, such as sleeping pills and tranquilizers.

What should I ask my doctor?

If you’re planning to travel to high altitudes, ask your healthcare provider:

  • Should I take a preventive medication to avoid altitude sickness?
  • Do I have any risk factors that would prevent me from visiting high elevations?
  • What other steps can I take to prevent altitude sickness?
  • What steps should I take if I start to feel symptoms during my climb?

A note from Cleveland Clinic

Altitude sickness symptoms can range from uncomfortable to life-threatening. But with some planning and precautions, you can avoid this condition. The best way to prevent it is to move at a slower pace and let your body adjust. If you notice symptoms at high elevation, don’t push yourself to go farther. Get back down to a lower elevation and let your body adjust before moving up, slowly and carefully.

Altitude Illness — Institute For Altitude Medicine

Acute Mountain Sickness

AMS can afflict any visitor sleeping higher than 6000 feet. In Colorado, between 15 and 40% of visitors sleeping at 8000 ft or higher get AMS, with the incidence the highest at the highest resorts. Most folks visiting these areas travel in one day from low to high altitude; if an intermediate day is spent in Denver or a similar altitude, the incidence of AMS is much lower. One survey done at a Colorado ski resort at 9800 ft found that 60% of visitors developed a headache, the first sign of AMS, and also called high altitude headache. To meet the definition of AMS, other symptoms need to develop, such as loss of appetite, sometimes vomiting, weakness, dizziness, fatigue, and difficulty sleeping.  AMS feels exactly like a bad hangover. Symptoms can occur as early as 2 hours after arrival to altitude, or be delayed for 24 hours or so. Symptoms of AMS do NOT develop after 2 days of feeling well, unless one has moved to a higher altitude. . Therefore, a person who has been doing well at altitude and then gets sick after two or three days needs to be evaluated for other conditions.

What causes AMS?

We have to admit that the exact cause of AMS is still not clear. Of course, AMS is due to low oxygen, but the steps between low oxygen and AMS are fuzzy. Current thinking is that hypoxia (low oxygen) in the air and blood causes the blood vessels of the brain to dilate in an attempt to get more oxygen. Something about this vasodilation causes the headache. And because there is more blood in the brain, the brain is slightly swollen. Although everyone going to high altitude has slight brain swelling, it is worse in those who develop AMS. This swelling causes pressure on the brain as it is squeezed against the skull, and the pressure might be the cause of the symptoms. Some researchers think that AMS is more like a migraine headache, and indeed, AMS and migraine have some similarities, but they are not identical. Rarely, AMS will go on to a more severe form of altitude illness, high altitude cerebral edema (HACE). While very unusual in Colorado ski resorts, being aware of this condition, recognizing symptoms early, and seeking treatment will easily avoid severe illness.

How is AMS diagnosed?

Diagnosis of AMS is based on the classic symptoms in someone who has been at high altitude for less than 2 or 3 days. Headache is the cardinal symptom, but is not always present. Other symptoms include dizziness, feeling chilled, trouble sleeping, loss of appetite or nausea, fatigue, and sometimes irritability. The Lake Louise Score is a scoring system of symptoms developed by experts at a conference in Lake Louise, Canada. A score of 4 or more is considered diagnostic for AMS for research purposes. However, a bad headache by itself may be sufficient for the diagnosis of AMS in mountain clinics.

Have you, a family member, or friend had altitude illness in the past?

If you have had altitude illness in the past you may be at risk to get it again, since there is a significant genetic component to altitude illness. People are generally susceptible or resistant to altitude illness, and this is generally reproducible on multiple trips to high altitude if the ascent rate is similar, but as always, there are exceptions. Having been to altitude once without problems should not encourage too great a sense of optimism that you will never get sick in the future. And even though you have had altitude illness in the past, you can safely return to altitude without getting sick again if you educate yourself on altitude illness and follow recommended guidelines.

How can I prevent altitude illness?

As with any illness, prevention is always the best approach. These are things you can do to improve your chances of not getting altitude illness.

  • Slow ascent to altitude is the key to prevention. Almost anyone can get altitude illness if they go too high, too quickly. Because of the individual differences, a preventive rate of ascent for one person may be too slow or fast for another.
  • An overnight stay at an intermediate altitude such as Denver (5280 ft) or preferably a bit higher prior to further ascent into the mountains is very helpful. If traveling to Telluride, overnighting in Ridgway, Ouray, Placerville or Durango would be helpful, especially if the destination is Mountain Village.
  • Staying hydrated is important as it aids your body in acclimatizing.
  • Avoid use of alcohol or sleeping agents of the benzodiazepine family, since they both suppress breathing and result in lower blood oxygen. Other sleeping pills like Ambien® or Lunesta® do not affect breathing at high altitude and are safe. Avoid over-exertion for 1-2 days after arrival to altitude.
  • Acetazolamide (Diamox®) taken 24 hours prior to arrival to altitude and the first 2 days at altitude is 75% effective in preventing AMS. It speeds up the acclimatization process in the body, stimulates breathing, raises blood oxygen and increases urination.
  • Gingko biloba, according to some studies was effective in preventing AMS when started 5 days prior to ascending to altitude, at a dose of 100 mg twice a day.

What are the risk factors for AMS?

Several factors increase your risk for getting AMS:

  • Your genetic makeup
  • A history of previous AMS
  • Residence at an altitude below 3000 ft
  • Obesity
  • Current respiratory infection
  • Most importantly, fast rate of ascent
  • Over-exertion the first day or two at altitude
  • Alcohol the first night at altitude

How do you treat AMS?

  • AMS usually resolves by itself, within 6 to 48 hours. In one study in Colorado, it lasted an average of 16 hours. However, certain actions can help or hinder its resolution.
  • Do not proceed to a higher altitude if you have AMS. You must stay at the same altitude and rest at a minimum, or you can descend to a lower altitude; this always works, but is often not necessary. If you are getting very ill, then you must go to a lower elevation, or start on oxygen. Descent to 1000 ft lower is generally adequate. At a ski resort, seeking medical attention is the best option.
  • The headache of AMS improves with rest, and medications such as ibuprofen (Motrin) or acetaminophen (Tylenol®) are often sufficient.
  • Oxygen breathing will improve symptoms rapidly, usually within minutes.
  • Acetazolamide (Diamox®) is a prescription medication that increases breathing, raises the blood oxygen level, speeds up acclimatization and therefore resolves AMS. The usual dosage is 125 mg twice a day for a few days.
  • Dexamethasone (Decadron®) is a prescription steroid medication that reduces swelling in the brain and improves symptoms, but it is generally reserved for moderate to severe illness. Dosage is 4 mg every 6 hours, usually for 24 hours.
  • A hyperbaric bag is a portable pressurized bag which simulates going to a lower altitude. It is mainly used in remote areas where oxygen and descent are less available options.  

Effects of High Altitude on Sleep and Respiratory System and Theirs Adaptations

ScientificWorldJournal. 2013; 2013: 241569.

* and

Turhan San

1Department of Otolaryngology-Head and Neck Surgery, Istanbul Medeniyet University, Faculty of Medicine, 34100 Istanbul, Turkey

Senol Polat

2Department of Otolaryngology-Head and Neck Surgery, Acibadem University, Faculty of Medicine, 34742 Istanbul, Turkey

Cemal Cingi

3Department of Otolaryngology-Head and Neck Surgery, Osmangazi University, Faculty of Medicine, 26020 Eskisehir, Turkey

Gorkem Eskiizmir

4Department of Otolaryngology-Head and Neck Surgery, Celal Bayar University, Faculty of Medicine, 45010 Manisa, Turkey

Fatih Oghan

5Department of Otolaryngology-Head and Neck Surgery, Dumlupinar University, Faculty of Medicine, 43100 Kutahya, Turkey

Burak Cakir

6Sisli Etfal Training and Research Hospital, Department of Otolaryngology-Head and Neck Surgery, 34371 Istanbul, Turkey

1Department of Otolaryngology-Head and Neck Surgery, Istanbul Medeniyet University, Faculty of Medicine, 34100 Istanbul, Turkey

2Department of Otolaryngology-Head and Neck Surgery, Acibadem University, Faculty of Medicine, 34742 Istanbul, Turkey

3Department of Otolaryngology-Head and Neck Surgery, Osmangazi University, Faculty of Medicine, 26020 Eskisehir, Turkey

4Department of Otolaryngology-Head and Neck Surgery, Celal Bayar University, Faculty of Medicine, 45010 Manisa, Turkey

5Department of Otolaryngology-Head and Neck Surgery, Dumlupinar University, Faculty of Medicine, 43100 Kutahya, Turkey

6Sisli Etfal Training and Research Hospital, Department of Otolaryngology-Head and Neck Surgery, 34371 Istanbul, Turkey

Academic Editors: I. Ozcan, K. M. Ozcan, and A. Selcuk

Received 2013 Jan 6; Accepted 2013 Mar 20.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article has been cited by other articles in PMC.


High-altitude (HA) environments have adverse effects on the normal functioning body of people accustomed to living at low altitudes because of the change in barometric pressure which causes decrease in the amount of oxygen leading to hypobaric hypoxia. Sustained exposure to hypoxia has adverse effects on body weight, muscle structure and exercise capacity, mental functioning, and sleep quality. The most important step of acclimatization is the hyperventilation which is achieved by hypoxic ventilatory response of the peripheral chemoreceptors. Hyperventilation results in increase in arterial carbondioxide concentration. Altitude also affects sleep and cardiac output, which is the other determinant of oxygen delivery. Upon initial exposure to HA, the resting pulse rate increases rapidly, but with acclimatization, heart rate and cardiac output tend to fall. Another important component that leads to decrease in cardiac output is the reduction in the stroke volume with acclimatization. During sleep at HA, the levels of CO2 in the blood can drop very low and this can switch off the drive to breathe. Only after the body senses a further drop in O2 levels breathing is started again. Periodic breathing is thought to result from instability in the control system through the hypoxic drive or the response to CO2.

1. Introduction

Modern travel facilities and mountain tours now permit access to high mountains previously visited only rarely by hardy climbers. Traveling to elevations over 2500 meters may lead to signs and symptoms of HA illness [1]. Effects of high-altitude (HA) depend on several factors, including the rate of ascent to altitude, final altitude reached, altitude at which a person sleeps, and individual physiology [2–4].

On arriving at HA, lowlanders will be incapable of as much physical exertion as they were at sea level. Further, they may not feel well and may have impaired mentation. These effects are ultimately due to hypoxia. Fortunately, human body has a series of physiological adjustments to compensate this hypoxia including increase in ventilation, hemodynamic and hematologic changes, and metabolic changes which are usually termed as acclimatization [2, 3].

The time required for these adaptations varies with the individual physiology, with the altitude ascended and with the speed of ascent [4]. This paper reviews the effects of HA, as well as the adaptations to the changes associated with HA.

2. Oxygen at HA

HA that reflects the lowered amount of gases including O2 in the atmosphere is defined as [5]:

  1. intermediate altitude: 1500–2500 m;

  2. HA: 2500–3500 m;

  3. very HA: 3500–5800 m;

  4. extreme altitude: above 5800 m.

Air is a mixture of gases and the principal gases are O2 and nitrogen whose summated partial pressures equal the barometric pressure (BP). Their concentrations are essentially constant over earth terrestrial elevations [3]. Thus, the amount of O2 in the atmosphere, 20.93 percent, remains constant at any given altitude. However, the surface of earth oceans, which we call sea level, is also the bottom of an ocean of air and air, unlike water, is compressible.

The partial pressure of O2 (PaO2) in the atmosphere falls as BP falls. Therefore, the change in BP at HA is the basic cause of decrease in the amount of O2 leading to hypobaric hypoxia (HH) [6, 7]. Atmospheric pressure and the PaO2 decrease at increasing altitude in a logarithmic fashion. The atmospheric PaO2 is 159 mm Hg at sea level and 53 mm Hg on the summit of Mount Everest [8, 9]. Although the major determining factor of PaO2 is BP, the PaO2 is also lowered towards the poles of the earth at any given altitude. It should also be noted that BP is known to fluctuate with changing weather systems [2].

3. Effects of HA

When the climbers are exposed to HH, they experienced different reactions to the effects of altitude. The basis of pathophysiological changes is tissue HH. The greater the hypoxic stress, the less time the body has to adapt to it and the greater the adverse effects of HA.

4. Maximal Oxygen Consumption (VO

2 max)

VO2 max⁡ is the maximum capacity of an individual’s body to transport and use O2 during exercise, which reflects the physical fitness of the individual. The point at which O2 consumption plateaus defines the individual’s maximal aerobic capacity. This capacity varies among the individuals and can be improved to a level with training. Genetics plays a major role in a person’s VO2 max⁡, and heredity can account for up to 25–50% of the variance seen between individuals [6].

VO2 max⁡ begins to decrease significantly above an altitude of 1600 m. For every 1000 m above that VO2 max⁡   drops by approximately 8–11%. At the summit of Everest, an average sea level VO2  max⁡ of 62 mL/kg/min can drop to 15 mL/kg/min. Anyone with a VO2 max⁡ lower than 50 mL/kg/min would struggle to survive at the summit of Everest without supplemental O2 [7].

Since at altitude the transfer of O2 to the active muscles is reduced, particularly during whole body exercise, fatigue occurs at lower work rates [4, 8]. The reduced VO2 max⁡ at HA is usually ascribed to the reduction in mitochondrial PO2, which interferes with the function of the electron transport chain responsible for providing cellular energy [3, 8]. Although arterial O2 content increases to values of sea level with acclimatization VO2 max⁡ capacity remains reduced [3, 9]. The reason was proposed to be the unproportionate delivery of O2 to the tissues; while under sea level conditions O2 is more directed to contracting muscles during exercise, at HAs greater proportion of the O2 is directed to noncontracting tissues during exercise. Thus exercise performance is reduced. There is little evidence that the pulmonary hypertension of HA limits VO2 max⁡ [10].

5. Skeletal Muscle and Body Weight

Sustained exposure to severe hypoxia has detrimental effects on muscle structure. Chronic hypoxia of altitude leads to a marked decrease in muscle fiber density [4, 11]. Similarly, there is a decrease in mitochondrial volume by up to 30% [12]. The changes in mitochondrial volume are accompanied by significant decrease in the activity of enzymes responsible for aerobic oxidative metabolism and muscle oxidative capacity and are found to be moderately reduced by exposure to altitude. In contrast, proteins involved in the cellular transport of bicarbonate, protons, and lactates are increased in both skeletal muscle and red blood cells (RBCs) [13, 14]. Prolonged exposure to HH which causes reduction in maximal rate of O2 uptake was proposed as the main reason for decrease in muscle cross-sectional area and in muscle oxidative activity [12]. These changes correlate with body weight and overall muscle mass decline at HA.

Hypoxia also causes diaphragm and abdominal muscle contractile fatigue which results in exercise performance limitations at HAs [15]. Despite these negative effects of HH, Edwards et al. [16] suggested that in response to HA hypoxia, skeletal muscle function is maintained in humans, although there is a significant muscle atrophy. The proposed causes of weight loss (WL) at HA are decreased food intake due to loss of appetite, changes in endocrine parameters controlling homeostasis, imbalance of energy intake and expenditure, increased basal metabolic rate and high activity levels, impaired intestinal function, change in body composition including loss of fat mass or loss of muscle mass, and decrease in body water [17–19]. Although it was suggested that body water was gradually lost through increased ventilation and decreased water intake or altered metabolism, some other studies concluded that water balance is maintained at altitude, via increased intake or metabolic water formation, and does not account for WL [17, 18, 20]. From these suggested mechanisms for WL at HAs it is obvious that there is a negative energy balance due to a combination of decreased energy intake and an increased energy expenditure [21]. Loss of appetite with altitude was thought be due to increased leptin levels which is a protein hormone secreted from adipose tissue in response to food intake and affects the satiety center of hypothalamus [17, 18]. However, some studies could not be able to prove this increase and even some other studies showed a decrease in the level of leptin levels at HAs [22]. Changes in body composition result from hypoxia-related suppression of muscle protein synthesis results in WL [17, 20]. Hypoxia-induced intestinal dysfunction contributes to WL especially above 5500 m, and the reason was suggested to be changes in the intestinal flora due to hypoxia [17, 23].

During the study period of the Operation Everest (OE)-II project, weight was found to be reduced by 7.44 kg, which constituted overall 8.9% decline in the body weight [4, 24]. In the same study, in 6 subjects, total muscle area of the thigh and upper arms was calculated via CT scans and the results showed decrease of 13% and 15%, respectively. Weight was reduced by an average of 5 kg in the study participants during the study period of the OE-III which evaluated the long-term effect of HH on appetite using a hypobaric chamber and simulating the ascent of Everest during a 31-day period [25]. They concluded that exposure to HH appeared to be associated with a change in the attitude towards eating and with a decreased appetite and food intake.

6. Mental Performance (MP)

HAs of more than 3.000 m produce physiological disorders and adverse changes in moods and cognitive/motor performance of nonacclimatized individuals [3]. It is known that exposure to HA can produce adverse effects in motor skills, mental efficiency, and mood states, including anxiety depending on the altitude level reached, the speed of the ascent, and the time spent at HA [26, 27]. Most people working at an altitude of 4000 m experience an increased number of arithmetic errors, reduced attention span, and increased mental fatigue. Visual and auditory sensitiveness and short-term memory are negatively affected by exposure to an altitude of nearly 2500 m.

The molecular and cellular mechanisms responsible for impaired MP during hypoxia are poorly understood. The brain normally accounts for approximately 20% of the body’s total O2 consumption, and the O2 is almost entirely used for the oxidation of glucose. Suggested mechanisms for the impairment of nerve cell function during hypoxia include altered ion homeostasis, changes in calcium metabolism, alterations in neurotransmitter metabolism, and impairment of synapse function [3, 26, 27]. Cardiovascular and respiratory functions also affect MP and may cause a condition like organic brain syndrome during climbing to HA [28]. Environmental factors, air condition, exercise, and individual differences during climbing to altitude also can have some negative effects on MP [3, 28].

7. Sleep

At altitude, the reduced oxygen content of the blood induces breathing instability, with periods of deep and rapid breathing alternating with central apnea. This breathing pattern is called high-altitude periodic breathing (PB). It occurs even in healthy persons at altitudes above 6000 ft. It may lead to sleep disturbances with frequent awakenings and a feeling of lack of air [29]. De Aquino Lemos et al. found that hypoxia reduced total sleep time, sleep efficiency, slow-wave sleep, and rapid eye movement. Depressive mood, anger, and fatigue increased under hypoxic conditions. Vigor, attention, visual and working memory, concentration, executive functions, inhibitory control, and speed of mental processing worsened. Changes in sleep patterns can modulate mood and cognition after 24 h [30]. People at HA often wake frequently, have arousals, and do not feel refreshed in the morning and during day, and they experience somnolence [31]. The periodic breathing (PB) that occurs in most of the people at altitudes above 4000 m is probably the main causative factor [32, 33]. Latshang et al. described that at high altitude, nocturnal periodic breathing affects males more than females. In this study, females started to present a significant number of central sleep apneas only at the highest reached altitude. After 10 days at 5400 m gender differences in the apnea-hypopnea index similar to those observed after acute exposure were still observed, accompanied by differences in respiratory cycle length [34].

PB involves alternating periods of deep breathing and shallow breathing. Typically, three to five deep breaths will be followed by a couple of very shallow breaths or even a complete pause in breathing which is called apnea [32]. During sleep at HA, the levels of CO2 in the blood can drop very low and this can switch off the drive to breathe. Only after the body senses a further drop in O2 levels breathing is started again. PB is thought to result from instability in the control system through the hypoxic drive or the response to CO2 [31, 32]. Weil [31] stated that the sleep disorder of altitude was largely due to respiratory disturbance arising from the physiologic ventilatory dilemma of acute ascent, where stimulation by hypoxia alternates with inhibition by hypocapnic alkalosis. The OE-II decompression chamber studies found severe sleep fragmentation and PB at all altitudes was studied but especially at the HAs. These brief 2- to 5-second arousals from sleep increased from an average of 22 times per hour at sea level to 161 times per hour at 25,000 ft [35, 36]. Although total sleep time was reported to not change, it was found that there was a strong shift from deeper to lighter sleep stages and a marked increase in frequency of brief arousals [37]. Experienced trekkers and mountain climbers often recommend climbing high but sleeping mitigates these problems. The cold, the wind, noisy, or smelly tent companions and long distance travel can also disturb the sleep. Nussbaumer-Ochsner et al. concluded that in healthy mountaineers ascending rapidly to high altitude, sleep quality is initially impaired but improves with acclimatization in association with improved oxygen saturation, while periodic breathing persists. Therefore, high-altitude sleep disturbances seem to be related predominantly to hypoxemia rather than to periodic breathing [38].

8. Acclimatization

8.1. Oxygen Transport

O2 must continuously be transported from the air to the mitochondria in sufficient quantities in order to meet tissue demands. Because the O2 amount falls sequentially and progressively, transport can be regarded as a series of steps in a cascade from alveolus to the cells mitochondria [9].

Because the atmospheric PaO2 is lower at HAs, gradient driving O2 transport at this higher point is considerably less than at sea level. It is obvious to consider that the PaO2 fall at each consecutive step in the O2 transport cascade is less at HAs than at sea level. Indeed, most of the humans have a great capacity for physiological adjustments to compensate for this reduced pressure gradient.

8.2. Pulmonary Ventilation

The most important feature of acclimatization is the increase in depth and rate of breathing, which results in an increase in alveolar ventilation that may reach 5-fold of the values at sea level [3, 9]. This is achieved by hypoxic ventilatory response (HVR) of the peripheral chemoreceptors, mainly the carotid bodies which are situated just above the bifurcation of the common carotid artery in response to the low O2 concentration in the arterial blood [4, 9]. The HVR is the reflex response to hypoxic stimulation of carotid body chemoreceptors. Ventilatory acclimatization to hypoxia includes the time-dependent increase in the HVR that occurs during hours to weeks of hypoxic exposure [3, 9]. Two major mechanisms have been described to explain the increase in the HVR during hypoxia [39]. First, the sensitivity of the carotid body glomus cells to O2 increases during chronic hypoxia. Second there is an increase in the CNS responsiveness to afferent input from the carotid body. Afferent fibers from the O2-sensing glomus cells of the carotid body reach to the brain via the carotid sinus nerve whose afferents project to the nucleus of the solitary tract. In turn, the nucleus of the solitary tract contains neurons that project to the phrenic motor nucleus. The phrenic nerve innervates the diaphragm and stimulates hyperventilation.

Hyperventilation increases partial pressure of alveolar (PPA) and PaO2 and decreases PPA and arterial CO2. In a study by West et al. [7], pulmonary gas exchange was studied on members of the American Medical Research Expedition to Everest at altitudes of 8,050 m, 8,400 m, and 8,848 m, respectively. Their results showed that the PPA of CO2 was reduced to 7 to 8 mm Hg, about one-fifth of its normal sea level value of 40 mm Hg. The alveolar PaO2 is then maintained near 35 mm Hg and arterial pH was 7.7 on the summit. Although some members of expedition had a much HVR to hypoxia at these extreme altitudes than others, there was approximately fivefold increase in the ventilatory rate when compared to resting levels.

Upon initial exposure to HAs the vital capacity and residual lung volume are reduced, but after about 4 weeks of residency, the values are maintained to a level that they are comparable to those measured at low altitudes [3, 37]. In a recent study, Sonmez et al. [40] measured vital capacity at different altitudes and the results showed that there was no statistically significant difference in vital capacity values after the measurements are taken at 1520 m, 3200 m, and 4200 m during one-week long climbing to Mountain Ararat (5138 m). The O2 pulmonary diffusing capacity remains unchanged at HAs when compared to the capacity attained at sea level [41].

9. Hematological Adaptations

Transport of O2 in the blood is mainly carried out by hemoglobin (Hb) which is present in RBCs. Upon initial exposure to HA, initial transient increase in erythrocyte concentration can be seen which is caused by a reduced plasma volume, not by an increased rate of erythrocyte production [3]. Tannheimer et al. investigated the influence of water distribution on Hb and hematocrit values during a long-term exposure at HA. Their results showed that the main reason for the observed rapid massive increase of Hb and hematocrit at altitude was an intravascular hemoconcentration effect provoked by a shift of fluid to the interstitium [42]. Reduced plasma volume is caused due to dehydration that is very common at HA, partly because of the great insensible fluid loss mainly caused by the large ventilation of cold dry air. A reduced fluid intake and probable diuresis may also be other factors causing initial plasma volume reduction. Krzywicki et al. [43] studied water metabolism during acute HA exposure during 6 days of HA (4,300 m). Their results showed that total body water was significantly decreased, extracellular water appeared to increase but not significantly, and intracellular water was significantly decreased at altitude. They concluded that with heavy physical activity prior to and during altitude exposure, it appeared that hypohydration and a diuresis still occurred during acute altitude exposure [43]. Over a course of a week in response to the hypoxia, the bone marrow is stimulated by erythropoietin to increase the production of RBCs. Erythropoietin (EPO) is a glycoprotein, which stimulates RBCs production. It is produced primarily in the kidney in response to hypoxia and/or endurance training. Athletes either live or sleep in artificial or natural hypoxic conditions with the aim to increase serum erythropoietin concentrations, which are thought to improve maximum oxygen uptake and thus exercise performance [44]. Erythropoiesis is central to optimizing performance at HA. During ascent to moderate or HAs, serum EPO levels typically peak within 24 to 48 h and then decline to near baseline levels within approximately one week [13, 45]. An increase in RBC mass is measurable after 3-4 weeks and further increases have been reported for up to 9 months of continuous altitude residence. For subjects who remain at HA for less than a week, the change in RBCs mass may not be considerable and would not make a significant contribution to the acclimatization process [46]. O2 concentration in the blood is also maintained with the changes in the affinity for O2. The affinity for O2 depends mainly on the acid-base status and the total concentration of organic phosphates in the erythrocyte, mainly 2,3-diphosphoglycerate (DPG) and ATP [46, 47]. DPG binds to Hb and decreases its affinity for O2 on exposure to HA. It was shown to increase slower and seems to reach a plateau only after the subjects spent several days at HA. While increased blood pH shifts the curve leftward reflecting increased affinity of Hb for O2, accumulation of RBC-DPG shifts the curve rightward reflecting decreased affinity for O2 [47]. It was found that RBC-DPG increased, but the predicted rightward shift was counterbalanced by an increasing blood pH with increasing altitude. O2 concentration remained relatively unchanged up to an altitude of 6300 m. Beyond this altitude, the curve progressively shifted leftward and the O2 concentration decreased because of the stronger effect of the high blood pH [48]. Relative increasing in capillary bed may lead to better blood perfusion and, thus, O2 could more readily diffuse despite the relatively low O2 concentration [3, 48]. Increases in skeletal muscle myoglobin levels have been reported following a relatively brief exposure to HA [49]. These increased levels may be another important factor for the availability of O2 in the tissues at HAs. These findings are compatible with the hypothesis that hypoxic training potentates skeletal muscle angiogenesis [49].

10. Metabolic Compensation

At HA, the cost of meeting tissue O2 requirement is competitive with other body functions that may become progressively impaired by alkalosis. The final situation represents a compromise between the respiratory stimuli, which is aimed at increasing blood alkalosis in order to optimize the O2 transport system and the metabolic adjustment, which is aimed at reestablishing normal blood pH. In other words, although hyperventilation is adaptive since it increases the arterial O2 levels, it is also nonadaptive because the hypoxia-induced decrease in PaCO2 at the alveolar level induces blood alkalization. Prolonged alkalosis, however, is not compatible with normal body homeostasis, as it impairs several functions, including those of the CNS [50]. Fortunately, the pH of the cerebrospinal fluid (CCF) changes towards normal by movement of bicarbonate out of the CCF, and the pH of the arterial blood moves towards normal by renal excretion of bicarbonate, after 2 or 3 days. By the help of this metabolic compensation, pH of the medullary chemoreceptors is lowered and the original relationship between the pH of the CCF and the blood is restored to sea level values. It is the maintenance of this equilibrium that enables the lowlanders to sustain increased ventilation at HAs without the risks of alkalosis or hypocapnia. The rate and extent of the metabolic compensation depend on the altitude being slower and less complete at very HAs [3, 50].

11. Cardiac Output (COP)

Altitude also affects COP, which is the other determinant of O2 delivery. Upon initial exposure to HA, the resting pulse rate increases rapidly from an average of 70 beats per minute to as much as 105 beats per minute in an attempt to compensate for the reduced O2 content of the blood [10, 51]. These changes are thought to be because of hypoxia-induced increase in sympathetic nerve activity and stimulation of beta adrenergic receptors of myocardium via both sympathetic fibers and circulating adrenaline resulting in abrupt augmentation of the COP [51, 52]. Another proposed mechanism for the increase in heart rate at HA is the partial parasympathetic withdrawal [53]. Underlying mechanism of the sympathetic overactivity unexplained and administration of O2 has been reported to have only minor effect on the elimination of chemoreflex activation [51, 53]. But increase in sympathetic nerve activity remains persistent even in well-acclimatized subjects [52]. With acclimatization, despite the increase in sympathetic nerve activity, heart rate and COP tend to fall [2]. This decline in COP appears to be associated with a decrease in heart rate which usually remains above sea level values and has been attributed to increased vagal input and to downregulation in the number of adrenergic receptors [2, 51, 52]. Another important component that leads to decrease in COP is the reduction in the stroke volume with acclimatization [9, 36]. Upon prolonged exposure to altitude, stroke volume clearly declines over time, stabilizing after 1-2 weeks. While the factors responsible for this alteration in stroke volume are unknown, hypoxic pulmonary artery vasoconstriction and loss of plasma volume which result in the reduction of preload may play a role in this decline [2, 36]. Despite the fall in COP discussed previously, the performance of the heart is well maintained even at extreme altitudes. There is no electrocardiographic evidence of myocardial ischemia, and cardiac contractility as assessed by ultrasound is well maintained despite the extreme conditions [12, 54]. During OE-II cardiac function was appropriate for the level of work performed and COP was not a limiting factor for performance.


2. Palmer BF. Physiology and pathophysiology with ascent to altitude. The American Journal of the Medical Sciences. 2010;340(1):69–77. [PubMed] [Google Scholar]3. West JB. The physiologic basis of high-altitude diseases. Annals of Internal Medicine. 2004;141(10):789–800. [PubMed] [Google Scholar]4. Howald H, Hoppeler H. Performing at extreme altitude: muscle cellular and subcellular adaptations. European Journal of Applied Physiology. 2003;90(3-4):360–364. [PubMed] [Google Scholar]6. Bouchard C, Dionne FT, Simoneau JA, Boulay MR. Genetics of aerobic and anaerobic performances. Exercise and Sport Sciences Reviews. 1992;20:27–58. [PubMed] [Google Scholar]7. West JB, Hackett PH, Maret KH, Milledge JS, Peters RM, Jr., Pizzo CJ, et al. Pulmonary gas exchange on the summit of Mount Everest. Journal of Applied Physiology Respiratory Environmental and Exercise Physiology. 1983;55(3):678–687. [PubMed] [Google Scholar]8. Mizuno M, Savard GK, Areskog NH, Lundby C, Saltin B. Skeletal muscle adaptations to prolonged exposure to extreme altitude: a role of physical activity? High Altitude Medicine and Biology. 2008;9(4):311–317. [PubMed] [Google Scholar]9. Calbet JAL, Lundby C. Air to muscle O2 delivery during exercise at altitude. High Altitude Medicine and Biology. 2009;10(2):123–134. [PubMed] [Google Scholar]10. Naeije R. Physiological adaptation of the cardiovascular system to high altitude. Progress in Cardiovascular Diseases. 2010;52(6):456–466. [PubMed] [Google Scholar]11. Green HJ, Sutton JR, Cymerman A, Young PM, Houston CS. Operation Everest II: adaptations in human skeletal muscle. Journal of Applied Physiology. 1989;66(5):2454–2461. [PubMed] [Google Scholar]12. Hoppeler H, Vogt M. Muscle tissue adaptations to hypoxia. Journal of Experimental Biology. 2001;204(18):3133–3139. [PubMed] [Google Scholar]13. Saunders PU, Pyne DB, Gore CJ. Endurance training at altitude. High Altitude Medicine and Biology. 2009;10(2):135–148. [PubMed] [Google Scholar]14. Juel C, Lundby C, Sander M, Calbet JAL, van Hall G. Human skeletal muscle and erythrocyte proteins involved in acid-base homeostasis: adaptations to chronic hypoxia. Journal of Physiology. 2003;548(2):639–648. [PMC free article] [PubMed] [Google Scholar]15. Verges S, Bachasson D, Wuyam B. Effect of acute hypoxia on respiratory muscle fatigue in healthy humans. Respiratory Research. 2010;11(article 109) [PMC free article] [PubMed] [Google Scholar]16. Edwards LM, Murray AJ, Tyler DJ, Kemp GJ, Holloway CJ, Robbins PA, et al. The effect of high-altitude on human skeletal muscle energetics: P-MRS results from the Caudwell Xtreme Everest expedition. PLoS One. 2010;,5(5, article 10681) [PMC free article] [PubMed] [Google Scholar]17. Westerterp KR, Kayser B. Body mass regulation at altitude. European Journal of Gastroenterology & Hepatology. 2006;18(1):1–3. [PubMed] [Google Scholar]18. Rejc E, Lazzer S, Antonutto G. Energy expenditure and dietary intake of athletes during an ultraendurance event developed by hiking, cycling and mountain climbing. The Journal of Sports Medicine and Physical Fitness. 2010;50(30):296–302. [PubMed] [Google Scholar]19. Ge RL, Wood H, Yang HH, Liu YN, Wang XJ, Babb T, et al. The body weight loss during acute exposure to high-altitude hypoxia in sea level residents. Acta Physiologica Sinica. 2010;62(6):541–546. [PubMed] [Google Scholar]20. Richalet JP, Robach P, Jarrot S, et al. Operation Everest III (COMEX ’97): effects of prolonged and progressive hypoxia on humans during a smulated ascent to 8,848 m in a hypobaric chamber. Advances in Experimental Medicine and Biology. 1999;474:297–317. [PubMed] [Google Scholar]21. Macdonald JH, Oliver SJ, Hillyer K, et al. Body composition at high altitude: a randomized placebo-controlled trial of dietary carbohydrate supplementation. The American Journal of Clinical Nutrition. 2009;90(5):1193–1202. [PubMed] [Google Scholar]22. Sierra-Johnson J, Romero-Corral A, Somers VK, Johnson BD. Effect of altitude on leptin levels, does it go up or down? Journal of Applied Physiology. 2008;105(5):1684–1685. [PubMed] [Google Scholar]23. Kleessen B, Schroedl W, Stueck M, Richter A, Rieck O, Krueger M. Microbial and immunological responses relative to high-altitude exposure in mountaineers. Medicine and Science in Sports and Exercise. 2005;37(8):1313–1318. [PubMed] [Google Scholar]24. MacDougall JD, Green HJ, Sutton JR, et al. Operation Everest II: structural adaptations in skeletal muscle in response to extreme simulated altitude. Acta Physiologica Scandinavica. 1991;142(3):421–427. [PubMed] [Google Scholar]25. Westerterp-Plantenga MS, Westerterp KR, Rubbens M, Verwegen CRT, Richelet JP, Gardette B. Appetite at “high altitude” [Operation Everest III (Comex-’97)] a simulated ascent of Mount Everest. Journal of Applied Physiology. 1999;87(1):391–399. [PubMed] [Google Scholar]26. Dykiert D, Hall D, van Gemeren N, et al. The effects of high altitude on choice reaction time mean and intra-individual variability: results of the edinburgh altitude research expedition of 2008. Neuropsychology. 2010;24(3):391–401. [PubMed] [Google Scholar]27. Lowe M, Harris W, Kane RL, Banderet L, Levinson D, Reeves D. Neuropsychological assessment in extreme environments. Archives of Clinical Neuropsychology. 2007;22(1):89–99. [PubMed] [Google Scholar]28. Sevre K, Bendz B, Hankø E, et al. Reduced autonomic activity during stepwise exposure to high altitude. Acta Physiologica Scandinavica. 2001;173(4):409–417. [PubMed] [Google Scholar]29. Lombardi C, Meriggi P, Agostoni P, Faini A, Bilo G, Revera M, et al. High-altitude hypoxia and periodic breathing during sleep: gender-related differences. Journal of Sleep Research. 2013 [PubMed] [Google Scholar]30. de Aquino Lemos V, Antunes HK, dos Santos RV, Lira FS, Tufik S, de Mello MT. High altitude exposure impairs sleep patterns, mood, and cognitive functions. Psychophysiology. 2012;49(9):1298–12306. [PubMed] [Google Scholar]31. Weil JV. Sleep at high altitude. High Altitude Medicine and Biology. 2004;5(2):180–189. [PubMed] [Google Scholar]32. Johnson PL, Edwards N, Burgess KR, Sullivan CE. Sleep architecture changes during a trek from 1400 to 5000 m in the Nepal Himalaya. Journal of Sleep Research. 2010;19(1):148–156. [PubMed] [Google Scholar]33. Cingi C, Erkan AN, Rettinger G. Ear, nose, and throat effects of high altitude. European Archives of Oto-Rhino-Laryngology. 2010;267(3):467–471. [PubMed] [Google Scholar]34. Latshang TD, Bloch KE, Lynm C, Livingston EH. Traveling to high altitude when you have sleep apnea. JAMA. 2012;308(22, article 2418) [PubMed] [Google Scholar]35. Anholm JD, Powles ACP, Downey R, 3rd, et al. Operation Everest II: arterial oxygen saturation and sleep at extreme simulated altitude. The American Review of Respiratory Disease. 1992;145(4 I):817–826. [PubMed] [Google Scholar]36. Groves BM, Reeves JT, Sutton JR, et al. Operation Everest II: elevated high-altitude pulmonary resistance unresponsive to oxygen. Journal of Applied Physiology. 1987;63(2):521–530. [PubMed] [Google Scholar]37. Reite M, Jackson D, Cahoon RL, Weil JV. Sleep physiology at high altitude. Electroencephalography and Clinical Neurophysiology. 1975;38(5):463–471. [PubMed] [Google Scholar]38. Nussbaumer-Ochsner Y, Ursprung J, Siebenmann C, Maggiorini M, Bloch KE. Effect of short-term acclimatization to high altitude on sleep and nocturnal breathing. Sleep. 2012;35(3):419–423. [PMC free article] [PubMed] [Google Scholar]39. Wolff CB. Cerebral blood flow and oxygen delivery at high altitude. High Altitude Medicine and Biology. 2000;1(1):33–38. [PubMed] [Google Scholar]40. Sonmez GT, Ozen S, Yuktasir B, Yalcin B, Ozen G, Sonmez S, et al. The effects of high altitude climbing on respiratory parameters. Medicina Sportiva. 2009;13(1):49–53. [Google Scholar]41. Dill DB, Hillyard SD, Miller J. Vital capacity, exercise performance, and blood gases at altitude as related to age. Journal of Applied Physiology. 1980;48(1):6–9. [PubMed] [Google Scholar]42. Tannheimer M, Fusch C, Böning D, Thomas A, Engelhardt M, Schmidt R. Changes of hematocrit and hemoglobin concentration in the cold himalayan environment in dependence on total body fluid. Sleep and Breathing. 2010;14(3):193–199. [PubMed] [Google Scholar]43. Krzywicki HJ, Consolazio CF, Johnson HL, Nielsen WC, Jr., Barnhart RA. Water metabolism in humans during acute high-altitude exposure (4,300 m) Journal of applied physiology. 1971;30(6):806–809. [PubMed] [Google Scholar]44. de P, Niebauer J. Effects of high altitude training on exercise capacity: fact or myth. Sleep and Breathing. 2012;16(1):233–239. [PubMed] [Google Scholar]45. Sawka MN, Young AJ, Rock PB, et al. Altitude acclimatization and blood volume: effects of exogenous erythrocyte volume expansion. Journal of Applied Physiology. 1996;81(2):636–642. [PubMed] [Google Scholar]46. Basu M, Malhotra AS, Pal K, et al. Erythropoietin levels in lowlanders and high-altitude natives at 3450 m. Aviation Space and Environmental Medicine. 2007;78(10):963–967. [PubMed] [Google Scholar]47. Mairbäurl H, Oelz O, Bärtsch P. Interactions between Hb, Mg, DPG, ATP, and Cl determine the change in Hb-O2 affinity at high altitude. Journal of Applied Physiology. 1993;74(1):40–48. [PubMed] [Google Scholar]48. Windsor JS, Rodway GW. Research at the extremes: lessons from the 1981 American medical research expedition to Mt Everest. Wilderness & Environmental Medicine. 2007;18(1):54–56. [PubMed] [Google Scholar]49. Olfert IM, Breen EC, Mathieu-Costello O, Wagner PD. Skeletal muscle capillarity and angiogenic mRNA levels after exercise training in normoxia and chronic hypoxia. Journal of Applied Physiology. 2001;91(3):1176–1184. [PubMed] [Google Scholar]50. Hornbein TF. The high-altitude brain. The Journal of Experimental Biology. 2001;204:3129–3132. [PubMed] [Google Scholar]51. Mazzeo RS, Bender PR, Brooks GA, Butterfield GE, Groves BM, Sutton JR, et al. Arterial catecholamine responses during exercise with acute and chronic high altitude exposure. American Journal of Physiology. 1991;261(4, part 1):E419–E424. [PubMed] [Google Scholar]52. Hansen J, Sander M. Sympathetic neural overactivity in healty humans after prolonged exposure to hypobaric hypoxia. Journal of Physiology. 2003;546(3):921–929. [PMC free article] [PubMed] [Google Scholar]53. Hopkins SR, Bogaard HJ, Niizeki K, Yamaya Y, Ziegler MG, Wagner PD.
β-Adrenergic or parasympathetic inhibition, heart rate and cardic output during normoxic and acute hypoxic exercise in humans. Journal of Physiology. 2003;550(2):605–616. [PMC free article] [PubMed] [Google Scholar]54. Windsor JS, Rodway GW, Montgomery HE. A review of electrocardiography in the high altitude environment. High Altitude Medicine and Biology. 2010;11(1):51–60. [PubMed] [Google Scholar]

Know if you have altitude sickness and when to worry

“Many people in Colorado experience various stages of altitude sickness every day. You can get it even just going from Denver to 10,000 or 11,000 feet,” said Bull, a Grand Junction native.

Though it is fairly common, it often is not identified as altitude sickness, he said, which makes it hard to establish how often it really happens.

“It is difficult to put exact numbers to this,” Bull said, although “reported incidence in visitors sleeping 8,000 feet or higher is between 15 and 40 percent. The incidence depends on how high people are going (and from what starting altitude) and how fast they ascend.”

Dr. Todd Bull, medical director of the UCHealth Comprehensive Lung and Breathing Program

Milder symptoms include headache, insomnia and nausea, but victims can also suffer more serious consequences.

Altitude sickness can become acute mountain sickness, which includes cerebral edema (HACE) or pulmonary edema (HAPE), both of which can be life-threatening, he said.

The risk factors are related to rate of ascent.

“If someone comes from Florida or Texas and goes right up to Winter Park or Vail, it’s more likely to happen than if they acclimate more slowly,” he said. If coming from sea level, he suggested the visitor stop in Denver or Colorado Springs or somewhere along the Front Range for a night to acclimate to that altitude first. About 24 hours should be sufficient.

“That helps decrease the incidence and severity,” he said.

He also suggested avoiding significant alcohol intake during the first 24 to 48 hours, because it can exacerbate the problem. Also avoid sedatives, such as benzodiazepines—“They can sometimes worsen it, as well.”

Who gets altitude sickness?

There’s no definitive answer to that, he said. It doesn’t seem to be related to age or sex, although people with underlying heart and lung issues may be more vulnerable.

“Other than that, there doesn’t seem to be any other pre-defining risks we can identify at this point,” Bull said, though it is an active area of investigation at the University of Colorado. “And if you’ve had it before, the likelihood of getting it again is higher.”

The principle behind altitude sickness is simple, though there are many aspects that remain poorly understood.

“What’s really going on here is you see lower levels of oxygen and air pressure—almost anyone can be vulnerable, given the right conditions. There is local vasoconstriction due to local hypoxia (or low oxygen). This can induce both the mild forms of the condition and also the more severe effects. And the faster and higher you go, the higher the risk.”

UCHealth has a High Altitude Clinic specifically for the assessment of altitude sickness.

“Patients from all over the world come here,” he said. “We’ve had patients who have tried to climb Everest and couldn’t who are looking for help. “

In fact, he added, “Our cardiovascular and pulmonary research program helped define much of what we now know about the pulmonary vascular effects of high altitude.”

Are you less likely to experience problems at 10,000 feet if you already live at 5,000 or 6,000 feet?

“We are less likely. People who come here from lower altitudes are more susceptible, of course,” he said. Visitors can even get altitude sickness on the Front Range, but the symptoms are usually mild and don’t last long. “Serious issues really rarely occur at this altitude.”

How can I prevent altitude sickness?

Hydration: “Staying hydrated is good and avoid alcohol at first.”

Acclimation: Go up in increments, allowing the body time to adjust to each level before moving up to the next.

Exertion: “As you are acclimating, limiting your level of exertion can help. Also, get plenty of rest.”

Medications: “There are medications we can give to patients who we think are high risk. Discuss this with your physician.”

Oxygen: “If the situation is acute, then oxygen can be administered.”

Descent: “Get back to a lower altitude. This is the most important and most effective treatment always. Getting to a lower altitude is most imperative in severe cases—and oxygen should be administered as a temporizing measure at the same time.”

To learn more about the High Altitude Clinic offered through the Comprehensive Lung and Breathing Program in Metro Denver, call 855.586.4824.

Altitude Illness – Injuries and Poisoning

Descent to lower elevation is the best treatment for all forms of acute altitude illness.

  • For mild symptoms, stopping the ascent and treating with fluids and, in some cases, drugs

  • For severe or slow-to-resolve acute mountain sickness, descent to a lower altitude and treating with drugs

  • For high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE), immediate descent to a low altitude and drugs (if descent is not feasible, drugs and supplemental oxygen or a portable hyperbaric chamber)

People who have swelling of the hands, feet, and face do not need treatment. The swelling goes away on its own after a few days or following descent. Poor sleep is a common problem at high altitude, even among healthy people, and, by itself, is not a reason to descend to lower elevation.

People with mild acute mountain sickness (AMS) must stop their ascent and rest. They should not ascend to higher altitudes until symptoms disappear. Other treatment includes fluids and acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) to help relieve headache. Fluids do not treat AMS, but do eliminate dehydration, the symptoms of which can imitate those of AMS. Most people with AMS improve within a day or two. Sometimes, acetazolamide or dexamethasone is given to help relieve symptoms.

If AMS symptoms are more severe, or if symptoms persist or worsen despite treatment, the person should descend to a lower altitude, preferably 1,650 to 3,200 feet (500 to 1,000 meters) lower. The descent often provides rapid relief. The person is also given fluids, acetaminophen or NSAIDs, and acetazolamide or dexamethasone.

People with HAPE should immediately descend to a low altitude. Oxygen should be given if it is available. The drug nifedipine may temporarily help by decreasing blood pressure in the arteries to the lungs. Heavy exertion should be avoided during descent as this can worsen pulmonary edema. People who promptly descend usually recover from HAPE within 24 to 48 hours. Most people who develop HAPE are admitted to a hospital, but some (for example, those in areas with adequate medical resources such as a ski resort community) can be discharged with supplemental oxygen if they have family or friends who can monitor them.

If HACE develops, the person should immediately descend as far down as possible. Oxygen and dexamethasone should be taken. Acetazolamide may be added.

OA Guide to High Altitude: Acclimatization and Illnesses

OA Guide to High Altitude: Acclimatization and Illnesses

by Rick Curtis, Director, Outdoor Action Program

Last Page update 07/07/1999


Traveling at high altitude can be hazardous. The information provided here is
designed for educational use only and is not a substitute for specific training or
experience. Princeton University and the author assume no liability for any individual’s
use of or reliance upon any material contained or referenced herein. This paper is
prepared to provide basic information about altitude illnesses for the lay person. Medical
research on high altitude illnesses is always expanding our knowledge of the causes and
treatment. When going to altitude it is your responsibility to learn the latest
information. The material contained in this article may not be the most current.
Copyright 1995 Rick Curtis, Outdoor Action Program, Princeton University.

High altitude-we all enjoy that tremendous view from a high summit, but there are risks
in going to high altitude, and it’s important to understand these risks. Here is a classic
scenario for developing a high altitude illness. You fly from New York City to a Denver at
5,000 feet (1,525 meters). That afternoon you rent a car and drive up to the trailhead at
8,000 feet (2,438 meters). You hike up to your first camp at 9,000 feet (2,745 meters).
The next day you hike up to 10,500 feet (3,048 meters). You begin to have a severe
headache and feel nauseous and weak. If your condition worsens, you may begin to have
difficulty hiking. Scenarios like this are not uncommon, so it’s essential that you
understand the physiological effects of high altitude.

What is High Altitude?

Altitude is defined on the following scale High (8,000 – 12,000 feet [2,438 – 3,658
meters]), Very High (12,000 – 18,000 feet [3,658 – 5,487 meters]), and Extremely High
(18,000+ feet [5,500+ meters]). Since few people have been to such altitudes, it is hard
to know who may be affected. There are no specific factors such as age, sex, or
physical condition that correlate with susceptibility to altitude sickness. Some people
get it and some people don’t, and some people are more susceptible than others. Most
people can go up to 8,000 feet (2,438 meters) with minimal effect. If you haven’t been to
high altitude before, it’s important to be cautious. If you have been at that altitude
before with no problem, you can probably return to that altitude without problems as long
as you are properly acclimatized.

What Causes Altitude Illnesses

The concentration of oxygen at sea level is about 21% and the barometric pressure
averages 760 mmHg. As altitude increases, the concentration remains the same but the
number of oxygen molecules per breath is reduced. At 12,000 feet (3,658 meters) the
barometric pressure is only 483 mmHg, so there are roughly 40% fewer oxygen molecules per
breath. In order to properly oxygenate the body, your breathing rate (even while at rest)
has to increase. This extra ventilation increases the oxygen content in the blood, but not
to sea level concentrations. Since the amount of oxygen required for activity is the same,
the body must adjust to having less oxygen. In addition, for reasons not entirely
understood, high altitude and lower air pressure causes fluid to leak from the capillaries
which can cause fluid build-up in both the lungs and the brain. Continuing to higher
altitudes without proper acclimatization can lead to potentially serious, even
life-threatening illnesses.


The major cause of altitude illnesses is going too high too fast. Given time, your body
can adapt to the decrease in oxygen molecules at a specific altitude. This process is
known as acclimatization and generally takes 1-3 days at that altitude. For example, if
you hike to 10,000 feet (3,048 meters), and spend several days at that altitude, your body
acclimatizes to 10,000 feet (3,048 meters). If you climb to 12,000 feet (3,658 meters),
your body has to acclimatize once again. A number of changes take place in the body to
allow it to operate with decreased oxygen.

  • The depth of respiration increases.
  • Pressure in pulmonary arteries is increased, “forcing” blood into portions of
    the lung which are normally not used during sea level breathing.
  • The body produces more red blood cells to carry oxygen,
  • The body produces more of a particular enzyme that facilitates
  • the release of oxygen from hemoglobin to the body tissues.

Prevention of Altitude Illnesses

Prevention of altitude illnesses falls into two categories, proper acclimatization and
preventive medications. Below are a few basic guidelines for proper acclimatization.

  • If possible, don’t fly or drive to high altitude. Start below 10,000 feet (3,048 meters)
    and walk up.
  • If you do fly or drive, do not over-exert yourself or move higher for the first 24
  • If you go above 10,000 feet (3,048 meters), only increase your altitude by 1,000 feet
    (305 meters) per day and for every 3,000 feet (915 meters) of elevation gained, take a
    rest day.
  • “Climb High and sleep low.” This is the maxim used by climbers. You can climb
    more than 1,000 feet (305 meters) in a day as long as you come back down and sleep at a
    lower altitude.
  • If you begin to show symptoms of moderate altitude illness, don’t go higher until
    symptoms decrease (&quotDon’t go up until symptoms go down”).
  • If symptoms increase, go down, down, down!
  • Keep in mind that different people will acclimatize at different rates. Make sure all of
    your party is properly acclimatized before going higher.
  • Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need
    to drink lots of fluids to remain properly hydrated (at least 3-4 quarts per day). Urine
    output should be copious and clear.
  • Take it easy; don’t over-exert yourself when you first get up to altitude. Light
    activity during the day is better than sleeping because respiration decreases during
    sleep, exacerbating the symptoms.
  • Avoid tobacco and alcohol and other depressant drugs including, barbiturates,
    tranquilizers, and sleeping pills. These depressants further decrease the respiratory
    drive during sleep resulting in a worsening of the symptoms.
  • Eat a high carbohydrate diet (more than 70% of your calories from carbohydrates) while
    at altitude.
  • The acclimatization process is inhibited by dehydration, over-exertion, and alcohol and
    other depressant drugs.

Preventive Medications

  • Diamox (Acetazolamide) allows you to breathe faster so that you metabolize more
    oxygen, thereby minimizing the symptoms caused by poor oxygenation. This is especially
    helpful at night when respiratory drive is decreased. Since it takes a while for Diamox to
    have an effect, it is advisable to start taking it 24 hours before you go to altitude and
    continue for at least five days at higher altitude. The recommendation of the Himalayan
    Rescue Association Medical Clinic is 125 mg. twice a day (morning and night). (The
    standard dose was 250 mg., but their research showed no difference for most people with
    the lower dose, although some individuals may need 250 mg.) Possible side effects include
    tingling of the lips and finger tips, blurring of vision, and alteration of taste. These
    side effects may be reduced with the 125 mg. dose. Side effects subside when the drug is
    stopped. Contact your physician for a prescription. Since Diamox is a sulfonamide drug,
    people who are allergic to sulfa drugs should not take Diamox. Diamox has also been known
    to cause severe allergic reactions to people with no previous history of Diamox or sulfa
    allergies. Frank Hubbell of SOLO recommends a trial course of the drug before going to a
    remote location where a severe allergic reaction could prove difficult to treat.
  • Dexamethasone (a steroid) is a prescription drug that decreases brain and other
    swelling reversing the effects of AMS. Dosage is typically 4 mg twice a day for a few days
    starting with the ascent. This prevents most symptoms of altitude illness. It should be
    used with caution and only on the advice of a physician because of possible serious side
    effects. It may be combined with Diamox. No other medications have been proven valuable
    for preventing AMS.

Acute Mountain Sickness (AMS)

AMS is common at high altitudes. At elevations over 10,000 feet (3,048 meters), 75% of
people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the
rate of ascent, and individual susceptibility. Many people will experience mild AMS during
the acclimatization process. Symptoms usually start 12-24 hours after arrival at altitude
and begin to decrease in severity about the third day. The symptoms of Mild AMS are
headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed
sleep, and a general feeling of malaise. Symptoms tend to be worse at night and when
respiratory drive is decreased. Mild AMS does not interfere with normal activity
and symptoms generally subside within 2-4 days as the body acclimatizes. As long as
symptoms are mild, and only a nuisance, ascent can continue at a moderate rate. When
hiking, it is essential that you communicate any symptoms of illness immediately to others
on your trip. AMS is considered to be a neurological problem caused by changes in the
central nervous system. It is basically a mild form of High Altitude Cerebral Edema (see

Basic Treatment of AMS

The only cure is either acclimatization or descent. Symptoms of Mild AMS can be
treated with pain medications for headache and Diamox. Both help to reduce the severity of
the symptoms, but remember, reducing the symptoms is not curing the problem. Diamox allows
you to breathe faster so that you metabolize more oxygen, thereby minimizing the symptoms
caused by poor oxygenation. This is especially helpful at night when respiratory drive is
decreased. Since it takes a while for Diamox to have an effect, it is advisable to start
taking it 24 hours before you go to altitude and continue for at least five days at higher
altitude. The recommendation of the Himalayan Rescue Association Medical Clinic is 125 mg.
twice a day (morning and night). (The standard dose was 250 mg., but their research showed
no difference for most people with the lower dose, although some individuals may
need 250 mg.) Possible side effects include tingling of the lips and finger tips, blurring
of vision, and alteration of taste. These side effects may be reduced with the 125 mg.
dose. Side effects subside when the drug is stopped. Contact your physician for a
prescription. Since Diamox is a sulfonamide drug, people who are allergic to sulfa drugs
should not take Diamox. Diamox has also been known to cause severe
allergic reactions to people with no previous history of Diamox or sulfa allergies.

Frank Hubbell of SOLO in New Hampshire recommends a trial course of the drug before
going to a remote location where a severe allergic reaction could prove difficult to

Moderate AMS

Moderate AMS includes severe headache that is not relieved by medication,
nausea and vomiting, increasing weakness and fatigue, shortness of breath, and decreased
coordination (ataxia). Normal activity is difficult, although the person may still be able
to walk on their own. At this stage, only advanced medications or descent can reverse the
problem. Descending even a few hundred feet (70-100 meters) may help and definite
improvement will be seen in descents of 1,000-2,000 feet (305-610 meters). Twenty-four
hours at the lower altitude will result in significant improvements. The person should
remain at lower altitude until symptoms have subsided (up to 3 days). At this point, the
person has become acclimatized to that altitude and can begin ascending again. The best
test for moderate AMS is to have the person “walk a straight line” heel to toe.
Just like a sobriety test, a person with ataxia will be unable to walk a straight line.
This is a clear indication that immediate descent is required. It is
important to get the person to descend before the ataxia reaches the point
where they cannot walk on their own (which would necessitate a litter evacuation).

Severe AMS

Severe AMS presents as an increase in the severity of the aforementioned symptoms,
including shortness of breath at rest, inability to walk, decreasing mental
status, and fluid buildup in the lungs. Severe AMS requires immediate
descent to lower altitudes (2,000 – 4,000 feet [610-1,220 meters]).

There are two other severe forms of altitude illness, High Altitude Cerebral Edema
(HACE) and High Altitude Pulmonary Edema (HAPE). Both of these happen less frequently,
especially to those who are properly acclimatized. When they do occur, it is usually with
people going too high too fast or going very high and staying there. The lack of oxygen
results in leakage of fluid through the capillary walls into either the lungs or the

High Altitude Pulmonary Edema (HAPE)

HAPE results from fluid buildup in the lungs. The fluid in the lungs prevents effective
oxygen exchange. As the condition becomes more severe, the level of oxygen in the
bloodstream decreases, and this can lead to cyanosis, impaired cerebral function, and
death. Symptoms include shortness of breath even at rest, “tightness in the
chest,” marked fatigue, a feeling of impending suffocation at night, weakness, and a
persistent productive cough bringing up white, watery, or frothy fluid. Confusion, and
irrational behavior are signs that insufficient oxygen is reaching the brain. One of the
methods for testing yourself for HAPE is to check your recovery time after exertion. If
your heart and breathing rates normally slow down in X seconds after exercise, but at
altitude your recovery time is much greater, it may mean fluid is building up in the
lungs. In cases of HAPE, immediate descent is a necessary life-saving
measure (2,000 – 4,000 feet [610-1,220 meters]). Anyone suffering from HAPE must
be evacuated to a medical facility for proper follow-up treatment.

High Altitude Cerebral Edema (HACE)

HACE is the result of swelling of brain tissue from fluid leakage. Symptoms can include
headache, loss of coordination (ataxia), weakness, and decreasing levels of consciousness
including, disorientation, loss of memory, hallucinations, psychotic behavior, and coma.
It generally occurs after a week or more at high altitude. Severe instances can lead to
death if not treated quickly. Immediate descent is a necessary life-saving
measure (2,000 – 4,000 feet [610-1,220 meters]). There are some medications that may be
prescribed for treatment in the field, but these require that you have proper training in
their use. Anyone suffering from HACE must be evacuated to a medical
facility for proper follow-up treatment.

Other Medications for Altitude Illnesses

  • Ibuprofen is effective at relieving altitude headache.
  • Nifedipine rapidly decreases pulmonary artery pressure and relieves HAPE.
  • Breathing oxygen reduces the effects of altitude illnesses.

Gamow Bag (pronounced ga mf)

This clever invention has revolutionized field treatment of high altitude illnesses.
The bag is basically a sealed chamber with a pump. The person is placed inside the bag and
it is inflated. Pumping the bag full of air effectively increases the concentration of
oxygen molecules and therefore simulates a descent to lower altitude. In as little as 10
minutes the bag can create an “atmosphere” that corresponds to that at 3,000 –
5,000 feet (915 – 1,525 meters) lower. After a 1-2 hours in the bag, the person’s body
chemistry will have “reset” to the lower altitude. This lasts for up to 12 hours
outside of the bag which should be enough time to walk them down to a lower altitude and
allow for further acclimatization. The bag and pump weigh about 14 pounds (6.3 kilos) and
are now carried on most major high altitude expeditions. Bags can be rented for short term
trips such as treks or expeditions.

Cheyne-Stokes Respirations

Above 10,000 feet (3,000 meters) most people experience a periodic breathing during
sleep known as Cheyne-Stokes Respirations. The pattern begins with a few shallow breaths
and increases to deep sighing respirations then falls off rapidly. Respirations may cease
entirely for a few seconds and then the shallow breaths begin again. During the period
when breathing stops the person often becomes restless and may wake with a sudden feeling
of suffocation. This can disturb sleeping patterns, exhausting the climber. Acetazolamide
is helpful in relieving the periodic breathing. This type of breathing is not
considered abnormal at high altitudes. However, if it occurs first during an illness
(other than altitude illnesses) or after an injury (particularly a head injury) it may be
a sign of a serious disorder.

  • Mountain Sickness, Peter Hackett, The Mountaineers, Seattle, 1980.
  • High Altitude Illness, Frank Hubble, Wilderness Medicine Newsletter, March/April 1995.
  • The Use of Diamox in the Prevention of Acute Mountain Sickness, Frank Hubble, Wilderness
    Medicine Newsletter, March/April 1995.
  • The Outward Bound Wilderness First Aid Handbook, J. Isaac and P. Goth, Lyons &
    Burford, New York, 1991.
  • Medicine for Mountaineering, Fourth Edition, James Wilkerson, Editor, The Mountaineers,
    Seattle, 1992.
  • Gamow Bags – can be rented from Chinook Medical Gear, 34500 Hwy 6, Edwards, Colorado
    81632, 970-926-9277. www.chinookmed.com
Additional Reading:
  • Altitude Illness Prevention & Treatment, Steven Bezruchka, The Mountaineers,
    Seattle, 1994.
  • Going Higher, Charles Houston, Little Brown, 1987.
  • High Altitude Sickness and Wellness, Charles Houston, ICS Books, 1995.
  • High Altitude Medicine and Physiology, Ward Milledge, West, Chapman and Hall, New York,

This article is written by Rick Curtis, Director, Outdoor Action Program. This material
may be freely distributed for nonprofit educational use. However, if included in
publications, written or electronic, attributions must be made to the author. Commercial
use of this material is prohibited without express written permission from the author.
Copyright 1998 Rick Curtis, Outdoor Action Program, Princeton University.

Altitude Sickness: Prevention & Symptoms

The elevations of some of the communities we serve can reach up to 12,000 feet, which means the air is thinner and contains less oxygen than at lower elevations. If you’re coming from a state where elevations are much lower, you may experience altitude sickness (also called altitude illness) while traveling to elevations of 8,000 feet or above.

If at all possible, it is suggested you spend an extra day or two at an elevation of 5,000-7,000 feet before attempting activities at higher elevations. This adjustment period will give your body a chance to adapt to the change in altitude gradually. 

The symptoms of mild altitude sickness are similar to the flu and can last three or four days before clearing up.

Symptoms can include:

  • Headache
  • Loss of appetite
  • Nausea
  • Difficulty sleeping
  • Dizziness or light-headedness
  • Shortness of breath
  • Swelling of hands and feet
  • Rapid pulse
  • Trouble sleeping

If you feel you’re suffering from the symptoms of altitude sickness, see a doctor immediately.

Extreme altitude sickness may result in life-threatening conditions caused by fluid accumulation in the lungs (high-altitude pulmonary edema, or HAPE) or swelling of the brain (high-altitude cerebral edema, or HACE). HAPE is characterized by breathlessness and can also cause a high fever and coughing up of frothy saliva. HACE can cause uncharacteristic behavior, excessive emotion or violence, drowsiness and the loss of consciousness. If you experience severe symptoms or are feeling seriously ill, go to lower altitude immediately and seek medical attention.

Preventing or lessening altitude sickness

Altitude sickness can affect anyone, regardless of age or health. To avoid or lessen your symptoms of altitude sickness, try to avoid alcohol, sleeping pills, caffeine and narcotic pain medicine during your first days at higher elevations. Alcohol and drugs can escalate symptoms of altitude sickness. Drink plenty of fluids and try to acclimate to the altitude. For headaches, mild analgesics such as acetaminophen, ibuprofen or naproxen can help, or a doctor may prescribe you medication to reduce your symptoms. Note: Vigorous physical exercise can increase your risk of developing altitude sickness.

Your risk of suffering a severe sunburn also increases at higher elevations because of decreased oxygen. To protect yourself, always use sunscreen with an SPF of at least 15, and wear a hat and sunglasses.

If you develop a more severe case of altitude sickness, you’ll be treated with oxygen therapy and you may need to be transported to a lower elevation.

90,000 Pulmonologists told what diseases can cause shortness of breath

Shortness of breath with coronavirus may indicate a large amount of lung damage. Thus, the body signals a lack of oxygen, said Pavel Prokin, therapist of the Doctor Nearby service.

“Shortness of breath is a compensatory response to oxygen deprivation. With COVID-19, shortness of breath usually develops against the background of a fairly significant lung damage. That is why it is an alarming symptom, that is, it may indicate an increasing respiratory pathology, ”the expert explained.

In this case, shortness of breath can also occur due to a mild or asymptomatic course of the coronavirus. Although in this case the disease is practically invisible, the lungs can still be affected, noted Natalya Vereshchagina, a pulmonologist at SM-Clinic.

“Then a full gas exchange becomes impossible. Even with an asymptomatic course of the disease, doctors often observe signs of viral pneumonia on an X-ray. As a result of the destruction of the inner layer of the alveoli, the vacated space is filled with pathological cells, lymphocytes and erythrocytes.Lung ventilation is impaired. Clinically, this is manifested by severe shortness of breath. On the X-ray images, darkened areas are visualized, which are called “frosted glass”, ”the expert said.

Medic added that elderly people, patients with reduced immunity and severe concomitant pathologies are most susceptible to such complications.

In addition to the appearance of shortness of breath against the background of the asymptomatic course of the coronavirus, the patient may have a decrease in the volume of the respiratory surface.Because of this, there is a risk of developing fibrosis.

“With a decrease in the volume of the respiratory surface between the pulmonary lobules, dense“ partitions ”are formed, consisting of connective tissue. This complication is considered very dangerous. It leads to fibrosis. The bronchi also suffer: the volume of inhalation and exhalation is disturbed, which is manifested by shortness of breath both at rest and during physical activity, ”Vereshchagina summed up.

According to Prokin, shortness of breath against the background of an asymptomatic course of the disease is rare.However, you should only worry if the course of the disease was mild and a similar symptom arose a few days after the condition improved.

“You should be worried and seek medical help just if the course of the disease was mild and even there were signs of improvement (after 5-7 days of illness), and then suddenly the state of health worsened: weakness, shortness of breath, fever appeared. There is a high likelihood of lung damage with the involvement of a significant volume.To assess the volume of lung damage, CT of the chest organs is used; to assess the degree of hypoxia – pulse oximetry (measurement of tissue oxygen saturation), ”the doctor added.

In addition, neuralgic problems can also cause shortness of breath with or after coronavirus. This is due to the fact that the infection affects all body systems, says pulmonologist Rustem Nasretdinov.

“For example, a patient may feel short of breath, chest congestion, the inability to” breathe “or take a deep breath.At the same time, he may have normal oxygen levels in the blood, improvements are also visible on the tomography – but such symptoms are still observed. That is, these are not lungs, but neurology, ”the expert noted.

The physician warns that the appearance of shortness of breath does not exclude other diseases in addition to coronavirus infection. That is why, when such a symptom occurs, a full diagnosis of the body should be carried out.

“Do not take every shortness of breath as a manifestation of the coronavirus – this symptom can speak of other diseases.For example, people with bronchial and lung disease, heart failure, and other heart conditions may have shortness of breath.

Also, shortness of breath can appear at a temperature or against the background of emotional stress, “- said Nasretdinov.

It is important not to overestimate this symptom, emphasized therapist Prokin. “Against the background of constant conversations, rumors, and cases of acquaintances, some impressionable people exaggerate the degree of respiratory disorders. And some (especially those with chronic lung or cardiovascular disease) may underestimate the increase in symptoms.Pulse oximetry should be used to objectify the degree of violations, ”he concluded.

Central City Clinical Hospital №6

Views: 92735


After a successful recovery, the coronavirus can again remind of itself.

Statistics appeared: patients who were treated for COVID-19, during the illness itself, felt more or less normal, although CT showed pneumonia.They were successfully cured, but after a month or two, the disease reminded of itself again: shortness of breath, pressing feeling in the chest, cough, sore throat.

The journalist of the city portal e1 Elena Pankratyeva asked what to do with the head of the city outpatient consultative department of allergology and immunology of our hospital.

Why is this happening? Will it get through? Anna Petukhova, candidate of medical sciences, pulmonologist, allergist-immunologist.

Our hospital began admitting patients with coronavirus in the midst of a pandemic. Now, on the basis of the 6th hospital, there is a rehabilitation center, where patients who have recovered from COVID-19 are sent. For three months of work, the center has received more than 500 adult patients. All these people have recovered, but they continue to be monitored by a pulmonologist to recover.

– You know, the most important rule that we have clearly learned over these months is that the covid does not play by the rules. The course of the disease and its complications can vary from patient to patient.As soon as you allow yourself to think that you have finally understood the essence, that there is a certain standard scheme, the patient comes to the appointment and the previous conclusions immediately break down. For example, I see a patient who has been diagnosed with a large volume of lung lesions – 80, 90 percent. In this case, it is clear and understandable to me why, after recovery, he complains of shortness of breath. Because a significant volume of the lungs is “turned off” from the breathing process. This part of the lung tissue is functionally inactive. Dropped out of the breathing process. But, you see, we also have a lot of patients, one in three, probably, whose lung lesions are very small, or who have completely resolved pneumonia.But the shortness of breath remained. Or they complain of chest congestion, uncomfortable breathing. At the same time, there is no organic substrate, that is, changes in the lungs!

– Outwardly, the lungs are clean, why then does the disease remind of itself again?

– We have identified three main causes of shortness of breath after suffering covid pneumonia. The first reason is postcoid lesion of the lung tissue, in fact, this is covid pneumonia, or rather, viral damage to the lung tissue.The second point is psychogenic shortness of breath.

– Psychosomatics?

– Yes, psychosomatic shortness of breath. And this is a very large part of our patients. We test all of our patients on the scale of anxiety and depression. And I very rarely see normal readings. I honestly did not expect that we will face this. There are two factors why this shortness of breath occurs. The main factor is social: fears associated with the occurrence of the disease itself. People hear a lot about this disease, they know about unfavorable outcomes, so they are afraid.The second factor is, to one degree or another, a pronounced damage to the nervous system. By the way, the characteristic loss of smell in COVID is nothing more than a lesion of the olfactory nerve. Today we know that another target for the coronavirus is the central nervous system and the brain in particular. In simple terms, the center of stress and the center of respiration in the brain are located close to each other. And the excitement of one center is transferred to another center. This is how psychogenic shortness of breath is formed.In simple terms,

Yesterday a woman came to me for a consultation, everything in her lungs had resolved, the CT scans are perfect. But right at the reception, I hear her noisy, demonstrative breathing with deep breaths and occasional yawning. The patient is very anxious, she herself is exhausted, but cannot cope with it. There was a breakdown, a failure in the breathing technique.

– And the third reason?

– Decompensation of chronic diseases. For example, the patient had previously suffered from high blood pressure.And it worsened after the postponed coronavirus infection. The coronavirus is insidious, it is capable of infecting not only the lungs, but also other organs and systems of the body. Heart failure, which before the illness was in a dormant (compensated) state, may decompensate. This is manifested by increasing shortness of breath. Moreover, this virus is capable of provoking the onset of a new disease: heart damage – heart attacks, impaired arterial circulation – strokes, diseases of the endocrine system – diabetes mellitus.All of these diseases can also lead to shortness of breath in the patient.

– Can the coronavirus cause diabetes?

– Yes. We see such cases.

– Why are there usually no such consequences after bacterial pneumonia, it is also difficult to bear?

– The coronavirus is several times more conducive to the formation of blood clots in small vessels – in the vessels of the lungs than, for example, the usual influenza virus. And there is a fundamental difference between bacterial and viral pneumonia.Viral pneumonia cannot even be called pneumonia. Correctly say: viral lung damage. This injury consists of tissue edema and thrombosis. Edema plus thrombosis. Viral pneumonia has a faster spread through the lung than bacterial pneumonia. For example, a patient initially has a CT scan at the first symptoms of 15–20 percent of the lesion, after a week already seventy. We are trying to treat with antiviral drugs, but covid may not respond to this treatment, so it is very important to prevent and treat the complications of coronavirus infection.For example, for the prevention of thrombosis in covid, most patients are shown drugs that prevent blood clotting – heparin, for example. Now tell me, how often do you hear that classical bacterial pneumonia is treated with heparin?

Covid is not an inflammation of the lung tissue in its classical sense, like bacterial pneumonia, which can be stopped with antibiotics – and in 14 days you are healthy. At the same time, the symptom of “frosted glass” (“frosted glass” is a medical x-ray term, such an effect on an x-ray gives alveolar damage to the lung tissue, associated with edema of the alveolar wall due to a violation of vascular permeability.- Approx. ed. ), characteristic of viral pneumonia, will resolve from three to six months. Depending on the degree of lung damage. Therefore, after a seemingly successful recovery, patients complain of shortness of breath or chest pressure.

What is the absurdity of the situation? We see patients who do not have pneumonia but have shortness of breath. And we see patients who have a change in the lung tissue, but no shortness of breath. The clinical manifestation and the picture on the x-ray may not be combined.The patient feels great, but the x-ray shows a terrible picture.

– Could it last a lifetime? In general, is it true or myth that covid pneumonia simply goes into remission and will constantly remind of itself?

– Myth. Yes, there is a group of patients whose consequences will last for life. But these are people with chronic diseases or who had a large lesion of the lung tissue, they were on mechanical ventilation for a long time. They are at risk of developing pulmonary fibrosis. But this is a very small proportion of patients.Fibrosis is a scar on the lung tissue. That is, it is an area of ​​functionally inactive lung tissue. Therefore, it is important to start pulmonary rehabilitation in order to prevent fibrosis and scar formation as early as possible, already at the stage of inpatient treatment and even in the conditions of the intensive care unit.

– How long does it take for a scar to form?

– It’s hard to say. But we observed patients who were in the intensive care unit and came to us for rehabilitation, already having fibrotic changes.If frosted glass and consolidation (hardening of the lung tissue) go away without a trace, then it is difficult to predict about fibrosis. The larger the affected area, the less likely it will disappear. You see, this is the transformation of lung tissue into connective tissue. But, fortunately, according to our observations, according to the observations of Moscow and European colleagues, such a lesion as fibrosis occurs in a very small number of patients. In our center, this is about eight percent of patients. Moscow colleagues speak about 10-12 percent, European doctors – about 18 percent.Yes, at first there was a certain panic that all those who had recovered from the changes [of the lung tissue] would go into fibrosis. But in practice, this is only a very small fraction of patients.

– Doctors have repeatedly said that changes in the lungs on CT were observed even in asymptomatic patients. Can it happen that a person suffered a coronavirus, without even knowing about it, of course, did not undergo any rehabilitation, and he developed fibrosis?

– No. Still, the body cannot be fooled. Pulmonary fibrosis is formed when there is a large amount of lung damage.In this case, there will be clinical manifestations in the form of shortness of breath. Small changes in the lungs dissolve to zero, without consequences. We have not seen a single asymptomatic patient with severe, severe lung changes. As well as not seen the lungs of patients who would have formed fibrosis.

– Would it be right if, after suffering covid pneumonia, start playing sports again as before in order to restore the lungs?

– Not really, after any acute illness that is accompanied by damage to the lung tissue, you need to increase physical activity gradually.Swimming in the pool is very useful for such patients, while the respiratory muscles work. But the basis of rehabilitation is the restoration of correct breathing. The first thing we teach in our consultations is breathing exercises, in particular, diaphragmatic breathing.

It is with this type of breathing that the maximum saturation of the lungs with oxygen occurs. In fact, this is a very physiological type of breathing. This is how babies breathe, with age it is lost. This is our most important recommendation, it is suitable for patients with psychogenic shortness of breath, and for those who have changes in the lungs.It is also imperative to do physical exercises: for the upper muscle group – exercises with dumbbells, exercises for muscle endurance, walking up stairs is also useful, at home you can use step platforms (steppers). We in our center, having several rehabilitation programs, try to approach each patient individually, solving his breathing problems. All the techniques we offer are developed by federal experts in the field of respiratory rehabilitation and experts from the World Health Organization.On average, exercise should be 20-30 minutes a day at least five times a week. Exercise increases blood flow, diaphragmatic breathing saturates the lungs with oxygen. All this prevents the formation of fibrous tissue in the lungs.

– How do you know if you have enough physical activity or not?

– There is a simple methodology from WHO experts. For example, at the height of physical activity, cross, say any phrase, sentence. Anyone: “Playing sports is very good for me.”If you cannot pronounce the sentence without stopping, in its entirety, then the physical activity is excessive. If you pronounce the phrase with ease, the load is not enough. If stopping slightly, after two or three words, this is an adequate load. But I repeat, if you have not run cross-country before, you should not start doing it immediately after suffering a coronavirus infection. The most ideal thing that suits, in addition to our professional rehabilitation complexes, is walking. It is available to everyone. We recommend walking for 30 minutes to two hours a day.Moreover, we recommend planning all physical exercises and walks in the afternoon. This gives pleasant fatigue and promotes deeper and more fulfilling sleep. And proper sleep is a very important part of any rehabilitation technique. It is in a dream that the body is restored after a disease. We tell our patients a lot about quality sleep: complete darkness, all windows are curtained, a comfortable temperature in the room is 19-23 degrees. The duration of a night’s sleep should be at least 7-8 hours.And very important: falling asleep between 22 and 23 hours. This is the key to quality sleep and full recovery.

In conclusion, I would like to say that if a person who has had a covid disease will carefully and carefully treat himself, will follow all the doctor’s recommendations, then for the majority everything will end with a complete victory over the disease.

Source: https://www.e1.ru/news/spool/news_id-69442636.html

90,000 what is it and how does it help you get enough oxygen?

Erythropoietin helps our cells get enough oxygen, and also allows us to achieve success in sports.We figure out how this substance works, why its deficiency is dangerous, and what does genetics have to do with it.


What is erythropoietin?

Erythropoietin is a hormone that helps the body maintain optimal oxygen levels. To do this, it stimulates the production of red blood cells or red blood cells.

Red blood cells provide oxygen to our tissues and remove carbon dioxide. When oxygen levels drop, erythropoietin helps replace the loss by increasing the production of red blood cells and hemoglobin.Here’s how it works:

There are specialized cells in the kidneys that can detect when the oxygen level in the blood is low. If so, the kidneys make more erythropoietin. The hormone triggers the maturation of hematopoietic stem cells in the bone marrow. These are precursors of erythrocytes, which are converted into full-fledged cells with the help of erythropoietin.

Why is the lack of erythropoietin dangerous?

If the production of erythropoietin is reduced or impaired, the oxygen level in the blood remains low or will fall further.This is dangerous because it leads to several pathologies, including anemia and hypoxia. With them, the tissues of the body receive an insufficient amount of oxygen and cannot function normally.

Symptoms of anemia:

  • fatigue
  • dizziness
  • shortness of breath
  • weakness
  • headaches
  • pale skin
  • rapid heart rate

Diseases such as AIDS, inflammatory diseases and some cancers can cause decreased erythropoietin levels. Lack of oxygen can worsen the course of these and other chronic diseases.

Mild cases of anemia may not require any treatment, especially if no symptoms are present. However, in more severe cases, iron supplementation or erythropoietin-stimulating drugs may be required. Erythropoietin therapy has been shown to be an effective treatment for anemia in patients with chronic kidney disease, as well as in patients with cancer, HIV, and organ transplants.

What is an excess of erythropoietin?

An increase in erythropoietin levels causes the bone marrow to produce more red blood cells. A constantly elevated level of this hormone signals a chronic lack of oxygen in the blood, for example, due to iron deficiency anemia. Also, an increase in erythropoietin levels can cause a tumor that secretes the hormone. For example, renal cell carcinoma.

In rare cases, too many red blood cells can cause a condition known as secondary polycythemia.It is associated with a number of serious health risks:

  • increased blood viscosity
  • less efficient blood supply and oxygenation
  • high blood pressure in the lungs
  • life-threatening blood clots
  • stroke

Should erythropoietin be used in sports?

In recent decades, professional athletes have discovered significant benefits of erythropoietin. This hormone significantly increases tissue oxygen uptake, which can increase endurance and performance.

Erythropoietin belongs to the group of doping blood products that are banned by the Medical Commission of the International Olympic Committee (IOC) and the World Doping Agency. One of the reasons for the ban was the high health risk.

The use of erythropoietin for doping results in an abnormally high number of red blood cells. Blood clots and increases the risk of serious side effects:

  • allergic reactions
  • blood clots
  • flu-like symptoms
  • heart attack
  • high blood pressure
  • pulmonary embolism
  • stroke
  • ?

    This is what contributes to a decrease in blood oxygen levels and increased production of erythropoietin:

    High Altitude

    At high altitudes, the air pressure is lower, which means that there is less oxygen in each breath.The body compensates for this by increasing the production of erythropoietin and red blood cells to maintain stable oxygen levels in the blood. This response helps fight the symptoms of altitude sickness caused by low oxygen levels.

    ☝️When adapting to high altitudes, different people have big differences: some quickly produce more erythropoietin, others much more slowly.

    The body’s response to high altitude is determined in part by genetics. Populations that have traditionally lived at high altitudes for thousands of years, such as the Himalayan Sherpas, produce more erythropoietin and have on average more red blood cells than people living at sea level.


    The level of erythropoietin depends on the genetic makeup of a person. The EPO gene encodes a protein called erythropoietin. When oxygen levels are low, the activity of this gene is increased and the production of erythropoietin is increased.

    A 2015 study found that a variant (rs7776054) located near the MYB gene is associated with erythropoietin levels. The MYB gene regulates the formation of blood cells, and is also involved in the maturation of red blood cells.

    Genetic Test Atlas will help you find out what level of erythropoietin is normal for you based on genetics.

    90,000 reasons, dangers and ways to help

    Cat owners need to know that nature has endowed these small predators with a very sensitive respiratory system. The lungs of animals are their weak point. If your pet has difficulty breathing, take this fact seriously.

    Symptoms of respiratory distress

    Signs and ailments that may cause concern:

    strange noises when breathing an animal;

    cat excitement, unusual posture;

    rapid breathing;

    grabbing air with an open mouth;

    Bluish tinge to lips and gums or excessive pallor;

    heavy breathing with difficulty breathing in and out.

    In frequent cases, if a cat breathes through an open mouth, it means that he has a violation of the respiratory system. As an exception, there may be a non-standard state of the animal after a long game. Obese cats usually grab air through their mouths after physical exertion (running, jumping, and so on). But fat animals are already unhealthy in themselves.

    For mammals, lack of oxygen can be life threatening. The reason for this is the fact that their bodies are not adapted to make oxygen stores.Therefore, if a cat has difficulty breathing, it is necessary to immediately take the animal to the veterinarian. A sharp deterioration in the condition of the pet may occur – the gums and lips turn blue, shortness of breath worsens. What do they do in such cases?

    Home help for a cat

    Under no circumstances should an animal be disturbed. Any anxiety can be fatal. Provide your pet with peace, while trying to protect it from various stresses that affect the respiratory system.You should not give your cat water and try to lay it down more comfortably. The use of medicines intended to normalize the functioning of the respiratory tract is not allowed. This can only harm the animal. Aim to see your doctor as soon as possible.

    Veterinarian actions

    First of all, the task of a specialist is to provide oxygen to the patient’s body. There are several ways to manipulate:

    put an oxygen mask on the cat

    animals are sent to the oxygen chamber;

    carry out artificial ventilation of the lungs;

    is doing an urgent operation.

    When providing emergency care, diagnostics are performed in parallel, which will help to establish the cause of the pathology.

    Causes of breathing problems and troubleshooting

    Difficulty breathing occurs due to the lack of air supply to the lungs or insufficient air volume.

    A foreign body trapped in the upper layer of the respiratory system (plant, food, small toy) may be a barrier to air inflow into the body.

    Non-entry of air into the body occurs with injuries of the respiratory tract.

    Difficulties with the passage of air occur with swelling of the neck.

    It is imperative to normalize the work of the upper part of the respiratory system. To do this, you should take care of the unobstructed patency of the airways. The goal of the doctor is to remove the foreign object, with the help of medicines to remove the puffiness. In extreme cases, the veterinarian performs tracheal intubation (the procedure involves placing a tube in the trachea, which is inserted through the mouth).

    If the upper respiratory tract is damaged and prevents air from entering the body, they resort to a tracheostomy (a hole is made below the injured place and a tube is inserted into the trachea).The doctor performs these actions on the cat under anesthesia.

    If the lungs are damaged, the blood does not receive the required volume of oxygen, and gas exchange in the body fails. The source of the problem can be pneumonia (inflammation of the lungs), trauma caused by bruising, pulmonary edema. Breathing difficulties in cats can be caused by bronchial asthma that has not been treated in the past. Usually, in such cases, animals experience rapid breathing with great difficulty.

    Shortness of breath is possible with diseases of the cardiovascular system, when the heart cannot fully provide blood circulation through the vessels.There is stagnation of fluid that enters the lungs.

    Animals suffering from lung pathology should be hospitalized and enhanced treatment should be prescribed. Artificial ventilation may be required.

    Difficulty breathing also occurs when the chest is damaged (accumulation of air or fluid, hip fracture). Before helping a patient, you need to get rid of the underlying cause of the disease. For example, when falling from a height, free air accumulates in the chest cavity of a cat, which enters the area of ​​the injured lungs and interferes with breathing.To remove air from the chest, the doctor may puncture the chest wall. In some situations, you cannot do without a special tube for removing the collected air, as well as a drainage installation. Animals with such a diagnosis should also be monitored by a specialist until complete recovery.

    Diseases of cats associated with the respiratory system cannot be cured without the help of a veterinarian. Therefore, be vigilant and make sure that pets do not put yourself in danger.

    Vash Doctor Veterinary Clinic is always happy to help you.Make an appointment:

    (812) 607-68-62, (931) 322-14-22.

    We see patients from 10:00 to 21:00!