The atmosphere that sorrounds our planet is composed of approximately 79% Nitrogene and 21% Oxygene at sea level, and the atmospheric pressure is averagely 1013,25 mbar (760 mmHg). However, both the atmospheric pressure, the oxygen content, and the temperature all fall with increasing height, and at 5500 metres of altitude the oxygen content is reduced to 10% and the atmospheric pressure is halved. On the highest point of the Earth, the Mount Everest, which is 8850 metres, the oxygen content of the air is reduced to 7-8%, and may even be lower at low pressure. At this altitude the atmospheric pressure is reduced to 1/3 of the pressure at sea level. In addition to altitude, the temperature is also dependent on variables such as atmospheric pressure and air vapour. A rule of thumb states that the temperature falls 6,5 degrees C for every 1000 metres of altitude.
Passengers in air flights travelling at high altitude are protected against the surrounding pressure by the pressure-cabines of the air flight. Here, the temperature is kept below 20 degrees C, and the air-pressure at 999,9 mbar (750 mmHg), which corresponds to the pressure at 2500 metres.
The amount of damaging ultraviolet radiation also increases with altitude.
When humans engage on adventures in high altitude, the lower oxygen level, hydrostatic pressure, and the lower air vapour will influence important body functions.
The bone marrow will start producing increased amounts of red blood cells, which are responsible for the transportation of oxygen to the hungry cells. The pH (acidity) and the electrolyte balance will be influenced. The pulmonary arteries will begin squeezing larger amounts of blood into the lungs, and one reacts by taking deeper breaths following the decrease in the oxygen content of the circulating blood.
Symptoms at high altitude
Headaches which are often aggravated at nighttime and in the early morning, nausea, irritability, loss of appetite, non-expectorative cough, vomiting, dizziness, oedema of the face, hands and feet, dysuria, a weight on the chest, unsecure gait, dehydration, cramps, bleeding of the retina and visual disturbances, amnesia, confusion, hallucinations and loss of consciousness. The most serious symptoms are cramps, oedema of the brain and lungs, and embolies.
The low temperature aggravates the symptoms and altitude takes many lives on the highest mountains.
Someone who is fuddled and confused because of hypoxia, may also make dangerous choices, that may be deleterious to him/herself and the peole who travels with him/her.
Visible signs of hypoxia are blue-coloured appearences of the nails, lips, and ears.
It is a widespread belief that anybody can get accustomed to staying in altitude, but that some require longer acclimatization than others. Ventures to 3500 metres and more can require many weeks of acclimatization.
In some cases acute aggravation is seen rather than acclimatization. Such cases require acute treatment.
The number and severity of symptoms increase proportionally with altitude, and the risk of aquirering acute mountain sickness is generally higher under the following conditions:
- The younger you are
- If one has a history of AMS
- The faster you travel in altitude.
- If the haemoglobin percentage is too low.
- If you suffer from chronic diseases as asthma, sleep-apnea, and cardio-vascular disease.
Relations between altitude and AMS can roughly be devided into the following risk-zones:
Zone 0: sea level (0) to 2400 metres (0 - 8000 feet)
AMS does not occur in this altitude.
Zone I: 2.400 to 3.600 metres (8.000 - 12.000 feet)
Mild altitude related symptoms are possible.
Zone II: 3.600 to 5.500 metres (12.000 - 18.000 feet)
At this altitude many will experience AMS symptoms, although they most often disappear within a few days. The air vapour of this altitude is generally low.
Zone III: 5.500 to 7.000 metres (18.000 - 23.000 feet) The risk of AMS is pronounced. People staing in this altitude will experience gradual weakening in spite of getting sufficient nourishment, enough to drink, and adequate sleep. Complete acclimatization to this altitude is not possible, one can only get accustomed to staying in this altitude for short periods of time, and acclimatization is not permanent. The air vapour is practically zero.
Zone IV: 7.000 metres (23.000 feet) and more
This altitude is referred to as the death zone, because one assumes that man can only survive for about 5 days and nights in this altitude.
Breathing
When staying in altitudes close to sea level, we averagely take about 12 breaths a minut. At 5000 metres the respiratory frequency has increased to about 20-30 breaths a minut, and on the top of mount everest we averagely take about 50 breaths a minut.
Cheyne-Stokes breathing
Trouble falling asleep and bad quality of sleep is familiar to trekkers and mountaineers, who stay overnight at altitudes above 3000 metres. When staying in this altitude many experience what is known as Cheyne-Stokes breathing. Cheyne-Stokes breathing occurs when sleeping, and is characterized by a number of weak respiratory efforts followed by deep, gasping inspirations and sudden arrest of respiration. Sleep-apnea may follow; which is periods of respiratory arrest, lasting up to 30 seconds. Sleep-apnea will often cause the affected person to wake up with a feeling of suffocation, and instead of feeling rested one will awake after a night like this with feelings of exhaustion. Mild incidences of Cheyne-Stokes breathing are considered as a normal symptom to altitude and will disappear when the body aquires complete acclimatization, but this respiration is normally associated with severe illnes, where the patient does not aquire acclimatization with accompaning failure of the cardiac pump, renal failure, medicinal poisoning, or brain damage.
Fluid balance
We lose fluid with expiration. Since we breathe more often with increasing altitude, and the air gets increasingly dry, our need for fluid increases proportionally. In zone III one will typically need a fluid-intake of about 3-4 litres to make up for the fluid-loss and in zone IV between 4 and 6 litres of fluid is lost with expiration. Fluid lost in the urine and sweat, or because of diarrhoea will increase the dehydration. The dry air interferes with natural feelings of thirst, and we are therefore not reminded to drink by our body. The increased concentration of red blood cells in the blood vessels causes the bloodstream to move slower, and if the body is also stressed by fluid loss, the circulatory flow is reduced. This increases the risk of dehydration, tiredness, confusion, embolies, and frost-bites.
Acute Mountain Sickness - AMS
Symptoms appear few hours after the arrival. Mild symptoms are general discomfort, tiredness, dizziness, headache, shortness of breath, tachycardia, nausea, sometimes vomiting, loss of apetite, and dificulty sleeping. Symptoms normally disappear within 3 days because of acclimatization.
Moderate Mountain Sickness
Symptoms are similar to those of acute mountain sickness, but of course more pronounced. Medicine offers no visible symptom relief. Gait is unsteady. Fast descent to lower altitude and if neccesary medical treatment will relieve the symptoms and restore the possibility for further ascent. Untreated the condition may progress into severe mountain sickness.
Severe Mountain Sickness
In severe mountain sickness the symptoms are further aggravated. The person will no longer be able to walk on his/her own and the symptoms are of the more serious kind.
Lung- and heart oedema may also occur with varying severity and may occur without prior warning already from within 24 hours of the arrival in high altitude. These are typical symptoms of too high and too fast ascent. Both conditions are life-threatening, and therefore require fast intervention.
High Altitude Pulmonary Edema - HAPE
Also known as water in the lungs. In lung edema fluid is transferred into the interstitial space of the lungs, interfearing with the exhange of oxygen and carbon dioxide. This causes the body to become hypoxic and carbon dioxide pools into the blood. Respiration is affected and accompanied by a boiling sound. The affected person must not lie down.
High Altitude Cerebral Edema - HACE
In severe hypoxia and hypercapnia (increased concentration of carbon dioxide in the blood) fluid may pool into the brain cells. The pressure against the inside of the skull causes the brain to become squeezed and interferes with the oxygen supply. The pressure to the brain may cause changes in personality and result in loss of consience.
