Many things contribute to our health and wellbeing and some of these things are not as obvious as others. For example, simply being at a great height can cause a range of different symptoms and in the worst case scenarios may even be fatal. You could be hiking up a mountain and feeling fine one moment, only to start feeling terribly ill and pass out moments later.
This is altitude poisoning, also sometimes referred to as altitude 'sickness' or 'acute mountain sickness' and it's a very real phenomenon that anyone going mountain trekking needs to take into account. Read on and we'll take a look at how something as seemingly harmless as 'being high up' can have such profound implications for your health.
What Is Altitude Sickness?
When you are affected by altitude sickness, it is not the height or the gravity itself that causes the problem but rather the thinness of the air. As we get higher up, air pressure becomes lower as the particles of oxygen become more and more spaced out. What this then means is that you no longer get the same amount of oxygen into your lungs with each breath, so you can end up gasping for air and still only taking a very small amount in each time.
The result is a low amount of oxygen in your blood which in turn triggers 'non-specific' symptoms that resemble having a flu combined with a hangover as the body is starved of oxygen. Dehydration may also contribute to symptoms as water vapour is lost from the lungs. Ultimately this can progress to high-altitude pulmonary oedema which is a life-threatening accumulation of fluid in the lungs, or high-altitude cerebral oedema in which the brain accumulates fluid and swells up (likely due to local vasodilation widening of the blood vessels).
Generally altitude poisoning will begin to take effect at 2,400 metres (8,000 feet) and above. This is because the oxygen content remains at a similar level (21%) at altitudes all the way up to 21,000 metres.
Interestingly though, different people will be affected differently and not everyone will be affected as early as other people. This appears to be connected to the 'end-tidal pCO2' which is the lowest amount of carbon dioxide present at the end of a person's respiratory cycle. People who have more carbon dioxide in their systems will have higher saturations of oxygen as standard and appear to be less susceptible to mountain sickness.
The primary symptom of altitude sickness is headache which may also be exacerbated by related dehydration. On top of this, other symptoms include: nausea, lack of appetite, tiredness, fatigue, vomiting, dizziness, light-headedness, pins and needles, nosebleeds, drowsiness, flatulence, malaise, peripheral oedema (swelling in the hands and feet), rapid pulse rate and shortness of breath during exertion. Generally it is wise to proceed with caution if you notice any two of these symptoms in conjunction.
As sufferers persist symptoms may become more severe at which point they may include bronchitis-type symptoms, a dry cough, coughing up sputum, shortness of breath (while resting), poor balance, retinal haemorrhage, loss of coordination, partial paralysis, bowel dysfunction and fever. Under these circumstances it's important to descend and seek medical attention. These symptoms suggest high-altitude cerebral or pulmonary oedema respectively, and the latter is often rapid to progress leading to fatalities. The former if left untreated can also result in coma and death.
The best prevention against mountain sickness is to ensure you ascend slowly and take it easy on the way up. This will allow your body more time to acclimatise and after the first 24 hours you should find yourself significantly less likely to suffer from the condition. If you are planning a large climb, then a good precaution is to use a strategy known as 'climb-high, sleep-low'. Here you will spend a few days at a base camp, then ascend part of the way (slowly while avoiding intense exertion) and returning to base camp. Next you return to the second point and spend the night there before returning back and recovering. You repeat this process a number of times and each time the aim is to increase the amount of time spent at the higher point. Then, once acclimatised, you start repeating the whole process while increasing the altitude of the second camp each time until you eventually reach the peak of your climb.
The general rule to follow here is not to ascend more than 300 metres (1,000ft) each day when sleeping. For instance you might climb from 3,000 metres to 4,500 metres, but must then return to 3,300 to stay the night. The process must not be rushed. Over time you will produce additional red blood cells thus increasing the amount of oxygen in your system.
Treatment and Management
The drug acetazolamide can be used to help some making rapid descents to avoid the symptoms of mountain sickness by stimulating the kidneys to secrete extra bicarbonate through the urine, acidifying blood and increasing the depth and frequency of respiration. In those already suffering it can also be used to help manage early symptoms of altitude poisoning. That said, the Everest Base Camp Medical Centre advises against using acetazolamide as a substitute for the right acclimatisation program. One unwanted side effect is a reduction in aerobic performance.
For those suffering with high-altitude cerebral oedema, dexamethasone may be able to provide temporary relief allowing the sufferer to continue their descent. In any case, descending as soon as possible is the best course of action. Supplemental oxygen can also be used to counteract hypoxia-related effects of altitude sickness through the use of an oxygen concentrator or nasal cannula. Anther recommendation is to increased fluid consumption to avoid dehydration (while being weary of over-hydration).
Above a certain height acclimatisation becomes impossible. This is true at heights above 5,500 metres (18,000ft) where progressive deterioration will outstrip the capacity to adapt. This is why there are no permanent human settlements beyond this height.
A different but related condition is 'chronic mountain sickness' which affects people who have been exposed to high altitudes for a longer period of time. This is also known as 'Monge's Disease' and usually affects those living above 3,000 metres.