Altitude sickness (also known as altitude hypoxia) is negative health effect of high altitude, caused by acute exposure to low amounts of oxygen at high altitude. It can occur as a result of decrease of the oxygen pressure in the mountains, as well as when flying on aircrafts, that are not equipped with sealed cabins (such as paragliders, hang gliders, hot air balloons, gondolas, etc.). People have different susceptibilities to altitude sickness. For some acute altitude sickness can begin to appear at around 2,000 metres above sea level.
Mountain sickness is a type of altitude sickness which is caused by the lack of oxygen, as well as several aggravating factors such as physical fatigue, illness, dehydration, ultraviolet radiation, severe weather conditions (such as downpours), sudden temperature changes during the day (from +30 ° C in the daytime to -20 ° C at night), etc. But the main pathological factor of the mountain sickness is hypoxia.
It is possible to adapt to the high-altitude hypoxia. Athletes specifically train their bodies in order to improve their sports achievements. The maximum possible height for a long-term adaptation to hypoxia (from hours to dozens of hours) is considered the level of around 10,000 meters. A longer stay of a person at such altitudes without breathing through oxygen devices is impossible: it will cause death.
The height at which mountain sickness can occurs varies based on numerous individual and climatic factors.
The following individual factors influence the occurrence of mountain sickness:
The following factors provoke development of mountain sickness, and reduce tolerance to high altitudes:
The following climatic factors contribute to the development and faster progression of mountain sickness.
The above-mentioned factors prove the fact that the height of the mountain sickness is individual, and varies based on a person and conditions. Some begin to suffer from oxygen deficiency already at an altitude of 2000 m, while others do not feel its effect even at 4000 m.
Most of the healthy non-acclimatized residents of lowlands begin to feel the effect of altitude of 2500-3000 m, while with intense physical work it can be felt at lower altitudes. At an altitude of about 4000 m even absolutely healthy people have slight malaise, and acute mountain sickness is registered in 15-20% of the ascent participants. At altitudes of 6,500-7,000 m, complete acclimatization, apparently, is impossible. However, participants in the expeditions to 8,000-meter mountains obtain numerous functional disorders and signs of mountain sickness. In high-altitude mountaineering, there is the term called “lethal zone” or, in other words, “death zone”. The term was brought by the head of the Swiss expedition of 1952 to Everest E. Viss-Dunant, who expressed the opinion that there are boundaries, crossing beyond which is lethal for mountaineers.
At altitudes of more than 8000 m a person can live at the expense of internal reserves no more than 2-3 days, gradually losing resistance to the altitude effect. Nevertheless, the experience of recent Himalayan expeditions, during which many participants did not use oxygen-delivery devices due to successful acclimatization, somewhat broadens our understanding of the limits of adaptation to oxygen deficiency.
The height of the onset of the occurrence of mountain sickness depends on the climate and humidity of the mountains:
In the mountains of humid maritime climate:
In the mountains of dry continental climate:
The human body functions best at the sea level, where the atmospheric pressure is 101.325 Pa (roughly 14.6959 pounds per square inch). The concentration of oxygen (O2) in the air at sea level is 20.9% at a partial pressure of O2 (PO2) of 21.2 Pa. In healthy peoples’ bodies, haemoglobin is saturated with oxygen, which binds to red blood cells. After a person ascends to an altitude of about 2100 meters above the sea level, the body’s saturation with oxy-haemoglobin (a protein of hemoglobin bound to oxygen) begins to fall.
Atmospheric pressure decreases exponentially with increasing altitude, while the proportion of O2 remains unchanged to about 100 km, which means that PO2 also decreases exponentially with increasing altitude. At the height of the base camp on Mount Everest, at 5000 m above sea level, the PO2 pressure is about half of the PO2 pressure at sea level and only a third at the summit of Everest of the PO2 pressure at sea level, at an altitude of 8,848 m. When PO2 falls, the human body responds through its adaptive mechanisms, which is called ‘altitude acclimatization’.
Adaptive reactions aim to maintain the sufficient oxygen supply to organs and tissues, as well as to manage a more economic expenditure of energy and in the conditions of oxygen starvation. Such compensatory reactions include:
There are also reactions at the tissue level:
When climbing to an altitude of 2000-4000 m, oxygen deficiency in healthy people is compensated without any (at least visible) harm to health.
As a result of hyperventilation of the lungs, the content of carbon dioxide decreases in the blood, as a result of which respiratory alkalosis develops (plasma of blood and body fluids acquire an alkaline reaction). Due to the “washing away” of CO2, the regulation of breathing is disturbed, since the excess of carbon dioxide in the blood excites the respiratory centre. This leads to breathing disorders, due to the suppression of the activity of the respiratory nervous system of the organism at low concentrations of CO2. While a person is awake, his consciousness signals to inhale. In a dream, when consciousness control weakens, a phenomenon called periodic breathing or Cheyne-Stokes breathing occurs: for a few seconds (up to 10-15), breathing stops, and then resumes, at first with redoubled force. The first event is connected with the brain’s reaction to the lack of CO2, the second one: with the reaction to the critically low level of O2. In practice, it looks like a person wakes up because he/she feels suffocated. Climbers describe this feeling as extremely unpleasant.
However, having recovered, the person comes to the senses and can continue to sleep easily. Despite the unpleasant feeling this is a normal reaction of the body to the altitude, and this symptom itself is not a sign of mountain sickness.
Mechanisms of the onset of oedema
With further ascent, hypoxia increases, since the compensatory functions of the body no longer provide sufficient compensation. The lack of oxygen in the air leads to a decrease in the partial pressure of oxygen in the lungs and to a decrease in the saturation of the arterial blood with oxygen, as a result of which there is oedema of the lungs and brain.
Some believe that the basis of clinical manifestations of mountain sickness is the increasing oedema of the brain.
In the human body the most sensitive and vulnerable parts to hypoxia are the brain tissue and the pulmonary alveolar tissue, since the latter receive oxygen directly from the air. It is the insufficient supply of oxygen to these tissues that causes development of oedematous processes in them.
The main sources of pulmonary and brain oedema:
There are other mechanisms that join the hypoxic mechanism:
Therefore, at low temperatures, oedema of the lungs or brain occurs more rapidly – at high altitudes and with a high frost this period can last only 8-12 hours instead of the usual 24 hours.
Oedema of the brain is an excessive accumulation of water in the brain tissues, and the source of water is mainly blood flowing through micro vessels and brain capillaries.
Oedema of the lungs is the accumulation of light blood plasma in the tissues of the lungs, and then in the lumens of the alveoli: when inhaling, the plasma filling the lumens foams, sharply reducing the useful volume of the lungs.
Normally, oedema of the brain and oedema of the lungs develop at night (the peak of the crisis usually occurs at 4 am), which is due to:
This brings us to the conclusion that:
The death with oedema of the brain is caused by the squeeze of the swollen cortex of the brain with the cranial vault, wedging the cerebellum into the trunk of the spinal cord. The death with pulmonary oedema is caused by massive foaming, which causes asphyxia of the respiratory tract.
The reason for the transience of the lethal outcome is that they develop on the principle of a vicious circle, when the subsequent stages aggravate the original cause, and the original cause – aggravates the consequence (for example, compression of the veins of the brain leads to a stronger oedema and vice versa).
Changes in other bodies and systems
The digestive system
At high altitudes, the appetite significantly changes, the absorption of water and nutrients decreases, the secretion of gastric juice leads to disruption of digestion of food, especially fats. As a result, a person abruptly loses weight (up to 15-22 kg in 6-7 weeks at an altitude of 6000 m). At the height, a person can feel an imaginary feeling of fullness of the stomach, nausea, diarrhoea, not amenable to drug treatment.
At altitudes of about 4500 m, normal visual acuity is possible only at a brightness of 2.5 times as much as the usual for plain conditions. At these altitudes, there is a narrowing of the peripheral field of vision and a visible “blurring” of vision as a whole. At high altitudes, the accuracy of focus and correctness of the distance determination are also reduced. Even in mid-mountain conditions, night vision weakens, and the period of adaptation to darkness is prolonged.
Dehydration of the body
The release of water from the body is known to be carried out mainly by the kidneys (1.5 litters of water per day), skin (1 litter), lungs (about 0.4 litters) and intestines (0.2-0.3 litters), which makes up about 3 litters of water per day. With increased muscular activity, especially in the heat, the release of water through the skin increases sharply (sometimes up to 4-5 litters). Intense muscular work performed in high altitude conditions, due to the lack of oxygen and dry air, dramatically increases pulmonary ventilation and thus also increases the amount of water released through the lungs. All this leads to the fact that the total loss of water among participants in hard high-altitude travel can reach 7-10 litters per day.
As the pace of hypoxia decreases, pain sensitivity reduces until to its complete loss.
Many climbers talk about the influence of height on the human psyche. For example, the expeditionary doctor points out a climber, who is mentally stable on a lowland, at the height of a glass that is torn apart. Reinhold Messner (height 8200 m, anoxic single ascent to Everest in 1980) reported an increasing sense of the presence of an invisible companion, up to the point that he shared food with him. The first climber from the Soviet Union to have ascended to Mount Everest, Mikhail Turkevich, reported that Edward Myslovsky, during the descent, refused to go any further after his oxygen ran out, saying that he was well and wanted to stay in the mountains.
The acute form of a mountain sickness occurs with the rapid movement (for several hours) of non-acclimatized people in the highlands, usually at a height of more than 3500 m. Clinical symptoms of it develop rapidly. In subacute form of mountain sickness, they do not develop so quickly and last longer (up to 10 days). The clinical manifestations of both forms of mountain sickness generally coincide.
Acute mountain sickness
Symptoms of a mild degree of mountain sickness appear within 6-12 hours (and sometimes even earlier) after lifting to a new height. At a higher altitude, the symptoms are detected earlier. In many, they are manifested by deterioration of health, a certain lethargy. A newbie in the mountains experiences malaise, rapid heartbeat, mild dizziness, slight dyspnoea with physical exertion, drowsiness and at the same time does not sleep well. 3-4 days later, these symptoms either increase or disappear. There are no clear and objective clinical/neurological symptoms of this form of mountain sickness.
All of the above-mentioned symptoms are not specific and can be a consequence of many other diseases. Nevertheless, it is believed that an un-acclimatized person who has risen to a height of more than 2500 m has an acute mountain sickness, if their head starts to ache and when at least one of the above-mentioned symptoms appears. If the above-mentioned symptoms appear 36 hours after well-being, then you must exclude the presence of another diseases.
At the altitudes of 2500-3500 m, some people may have euphoria: good mood, excessive gesticulation and speechlessness, accelerated speech, fun and laughter without any reason.
Later, the euphoric state is replaced by decline in the mood, apathy, melancholy, dull interest in the surrounding.
At altitudes of 4000-5000 m the state of health worsens. One can have a moderate and even severe headache. Sleep becomes restless, anxious, with unpleasant dreams, some fall asleep with difficulty and often wake up from a feeling of suffocation (periodic breathing). With physical effort, breathing and palpitation immediately increase, dizziness occurs. There is a loss of appetite, nausea, which is intense and can end up with vomiting. The affected individual mainly prefers sour, spicy or salty food (which is partly explained by dehydration and violation of the water-salt balance). Dryness in the throat causes thirst. The nose might bleed.
The final degree
At altitudes of 5000-7000 m and above, people rarely feel well, often unsatisfied. There is general weakness, fatigue, heaviness in the whole body. There is a moderate, and sometimes severe pain in the temples; frontal, occipital part of the head. With sudden movements and inclinations or after work, dizziness occurs. A person falls asleep with great difficulty, often awakens, some suffer from insomnia. A mountain-sick person is not able to do physical exercises for a long time due to dyspnoea (“the breath of a stalked dog”) and palpitation, working capacity drops. For example, at an altitude of 8000 m there remains 15-16% of the working capacity at sea level altitude.
Dryness in the throat increases resulting a constant feeling of thirstiness. Many people dry coughs. Appetite normally is either goes down or disappears. The number of cases of nausea and vomiting during food intake increases. Often there are pains in the abdominal area and gastrointestinal tract, there is a feeling of bloating. The rhythm of breathing is disturbed during the night sleep (Cheyne-Stock’s breathing). The skin of the face, especially the lips, become pale, often cyanotic, tint as a result of insufficient oxygenation of the arterial blood, which loses its scarlet colour. The body temperature rises by 1-2 ° C, chills occur. There are frequent incidents of nose, mouth, lungs (haemoptysis), and sometimes gastric bleeding.
Under certain conditions, starting from 4000 m, dangerous forms of mountain sickness can arise due to the failure of adaptation mechanisms and the development of more serious pathologies: pulmonary oedema and cerebral oedema.
High-altitude oedema of the lungs
Along with severe mountain sickness unexpected stagnant phenomena can evolve in the small circle of blood circulation along with pulmonary oedema, as well as acute heartburn.
As a matter of fact, the symptoms of high-altitude oedema of the lungs, appear on 2-3 days of stay at high altitude. The liquid comes out from the capillaries of the lungs and enters the lumen of alveoli, disturbs the with gas exchange. As a result, hypoxia increases and the sickness progresses.
If one does not take measures from the beginning, three hours after the first symptoms occur, they can end up with death. Its development is enhanced by previous diseases of the respiratory and circulatory organs, chronic or acute respiratory tract infections (e.g., angina, bronchitis, pneumonia, chronic purulent dental diseases), excessive physical exertion performed before the onset of sustainable adaptation.
Out of all the mountain-specific diseases high-altitude oedema of the lungs is the most common cause of death. At an altitude of 2,700 m, the incidence of high-altitude pulmonary oedema is 0.0001% and increases to 2% at 4000 m.
Alpine oedema of the lungs has the following three stages of development:
The first stage
The following symptoms are also characteristic for pulmonary oedema:
The second stage
Usually, 8-12 hours after the first symptoms occur, the second stage of pulmonary oedema commences:
The third stage
It develops after 6-8 hours and 4-8 hours before the death:
Without proper treatment, there is a drop in the pressure, collapse, coma, cardiac arrest.
High-mountain oedema of the brain
High-altitude oedema of the brain can be considered as an extreme manifestation of acute mountain sickness. A liquid comes out from the capillaries of the brain, the latter increases in volume. In this case, the tissues of the cerebellum are wedged into the trunk of the spinal cord, the vital centres that are in it are destroyed, and death occurs.
A participant in one of the expeditions to Everest, Dale Cruise describes his condition with a brain oedema:
“It felt like I was very drunk. I could not go without stumbling and completely lost the ability to think and speak. I had a few words in my head, but I could not figure out how to say them.”
There are three stages of cerebral oedema:
The first stage
Because of changes in the brain, specific symptoms occur:
The second stage
Usually starts in 8-12 hours after the appearance of the first symptoms:
The third stage
Starts 6-8 hours later and 4-8 hours before the death:
Signs of significant dehydration: thirst;
At the end of the third stage, there is a loss of consciousness, the breathing and heartbeat stop.
The most acute form of mountain sickness
The most acute form of mountain sickness is hypoxic suffocation, which sometimes occurs right after people land on high altitudes by helicopters, airplanes, motor transport or as they ascend fast.
Suddenly there is a feeling of emptiness when inhaling, strong pain in the whole body, ripples and darkening in the eyes, prostration, there is a fear of death, loss of consciousness (for example, when the cockpit of a plane is depressurized, the pilot loses consciousness after 2 minutes). However, with rapid descent and the provision of necessary medical care, the pilot immediately starts feeling well.
Chronic mountain sickness
Chronic mountain sickness was descovered in 1829 by the famous Peruvian scientist Carlos Monge, which is why it is called Monge’s disease. Chronic mountain sickness is much less common; it affects a small part of mountaineers living at altitudes above 3500-4000 m.
It is characterized by a decrease in physical and mental performance, with prevailing changes in the central nervous system. Because of the increase in hypoxemia (fall of the oxygen content in the blood), there is an increase in the volume of circulating blood, its volume in the lungs, there is an increase in the size of the right side of the heart and liver. The thorax becomes barrel-shaped, it is often possible to observe the thickening of the fingers (“drumsticks”), well-expressed cyanosis.
Patients with chronic mountain sickness often complain about coughing, haemoptysis, dyspnoea, pain in the right hypochondria, bleeding occurs in the food canal. An important diagnostic symptom of Monge’s disease is its almost complete disappearance after the descent into a flat terrain. In severe manifestations of chronic mountain sickness, the same measures and medications are used, as in acute mountain sickness.
There are three “golden rules” for the prevention of mountain sickness:
To prevent the acute mountain sickness there should be an active step-by-step acclimatization. There should also be a rational selection of climbers who would go through a physical and psychological preparation, have a previous high-altitude experience, and pharmacological prophylaxis.
The basic principles of acclimatization:
Both for the prevention and treatment of acute mountain sickness the same medicines are usually used. When ascending to a height of more than 3000 m, the following medicines are recommended (the recommended daily doses are indicated in brackets):
Vitamins, microelements and amino acids:
Carbohydrates increase the resistance to hypoxia. Thus, to prevent mountain sickness at high altitudes, you need to use more glucose, sugar and other easily digestible carbohydrates, but not more than 300-400 g per day. Canned orange juice, warm lemon juice in powder will do as drinks. Very strong tea is not recommended. It irritated the nervous system and thus causes insomnia.
Coke in the form of tea and chewing leaves, in contrary to widespread prejudice, contains very little cocaine and, in a moderate amount, promotes acclimatization. Therefore, being in the Andes, do not neglect the advice of guides offering to drink it.
The preventive efficacy of the following drugs has not been proven:
The following drugs are ineffective for the prevention of mountain sickness: Spironolactone, Furosemide, Codeine.
Alcohol at a height of more than 3000 m reduces the respiratory rate and increases hypoxia even in small doses. So, the use of alcoholic beverages in the highlands should be prohibited.
Treatment of acute mountain sickness
Light and medium degree
It should be emphasized that the mild degree of mountain sickness, in spite of unpleasant feeling, is usually only a condition that physically restricts a person without any protracted consequences. The basic treatment of mild mountain sickness:
Normally, the symptoms usually go away after 2-4 days.
Treatment of pulmonary oedema
It is important to know that no drug manipulation should serve as a excuse for the descent.
Oedema of the lungs can very quickly cause a development of inflammatory diseases of the respiratory tract (sore throats, pneumonia), so when these signs occur, it is necessary to descend and take medicine based on the symptoms.
Treatment of cerebral oedema
The Medications for oedema of the brain play a rather auxiliary role, but, nevertheless, they should not be neglected. To reduce the symptoms and facilitate evacuation, Dexamethasone is used (at first 8 mg, then 4 mg every 6 hours inside or parenterally).
Vasodilators (Nitroglycerin, Nifedipine, Trental), and medicine increasing the pressure (caffeine, adrenaline) shall not be used when having as oedema of the brain. Any increase in pressure or vasodilation will enhance the oedema of the brain. Now also do not recommend using diuretics.
The symptoms do not immediately after the descent, and the patient must be transferred under the supervision of medical workers.