The simple truth is that hiking at high altitudes have other issues over and above the physical terrain itself. Short of slipping, tripping or simply falling off the mountain or into a crevasse, your body can take a physical pummelling at higher altitudes. To counter the physical effect, one must condition one’s body to cope with the physical demands of high altitude hiking; but conditioning your body is by no means the only thing to worry about. The higher the altitude, the less dense the air, hence less oxygen is present in every breath taken in at high altitudes, leading to what is commonly known to deep sea divers as the “bends”. Knowledge of the effects of low oxygen on your body will help you to beat the “bends” when ascending.

The composition of oxygen in the air is roughly the same between 0 meters and 21,000 meters i.e 21%, but as the altitude increases the pressure decreases causing the air to be less dense (sparse). It is the increased space between the air particles that results in less oxygen being drawn in with every breath. The effects of low oxygen on the human body is directly related to the  fitness of the person, the rate of ascent and the altitude itself.

Using the base that the available oxygen is 100% and the measure of atmosphere is 1 at the accepted mean sea level (amsl), i.e. 0 meters, then the following will hold true as the altitude increases;

Between 1,500 thru 3,500 meters, which is categorised as High Altitude (0,75 atmosphere), there is between 87% and 66% of the oxygen available at sea level. At these altitudes, one can start to feel the effects of low oxygen with a tingling sensation in the extremities of the limbs and the onset of headaches. Note that these effects wear off after a few days and the body acclimatises pretty well at these heights.

Between 3,500 and 5,500 meters, which is categorised as Very High Altitude (0,60 atm), there is between 66% and 53% of the oxygen available at sea level. At these heights, headaches and the tingling sensation become more pronounced. To adapt to these conditions, the “walk high, sleep low” technique is employed. This allows the body to be pushed to the limit in low oxygen conditions and then returned to a “lower” altitude to recover.

At altitudes greater than 5,500 meters, which is categorised as Extreme Altitude (<50 atm), there is less than half of the oxygen available at sea level. Above 6,000 meters, the progressive degrading effect of low oxygen outstrips the ability of the human body to acclimatise. In essence, any time spent at altitudes above 6,000 meters without supplementary oxygen means that the human body begins to succumb to the effects of low oxygen. It is also the reason why no permanent human dwellings are built above 5,500 meters.

Returning to the subject of this piece i.e. HAPE and HACE; these are the result of acute mountain sickness brought about by exposure to low oxygen environments.

HAPE stands for High Altitude Pulmonary Edema and HACE stands for High Altitude Cerebral Edema. So both are caused by exposure to high altitudes and low oxygen environment that exist at these altitudes. Pulmonary relates to the lungs while Cerebral relates to the brain and is obviously the more serious condition while both can lead to fatality.

So what is an edema and why does this occur?

Research is still at odds on exactly why the body retains excess fluids in response to low oxygen environments but the net effect is that there is an increased fluid retention which seeps out of the cells and locates between the cells, which results in the swelling. It is this swelling that leads to HAPE and HACE. The eventual bursting of the cells in the extremities of the limbs leads to the blackened “frost-bite” symptoms that is commonly seen on mountaineers. When water freezes, it increases in size and is eventually too large for the cells to hold, hence they burst causing the blood to seep out and freeze.

But all is not lost. People climb to high altitudes everyday and this is down to excellent conditioning of one’s body, a keen understanding of the symptoms of low oxygen and understanding the techniques to identify, remedy and reverse any symptom. There are also drugs available on the market to assist with the acclimatisation process. These drugs mimic the production of carbon dioxide in the body to which the body responds with deeper and quicker inspirations thus allowing for the hiker to acclimatise.

In conclusion, ascending to high altitudes is all about attitude. If you think that because you are in great physical condition that ascending quickly will not hurt you; be careful not to fall into the trap of ascending too quickly for the body to acclimatise. The Tanzanian’s use a term “Pole-Pole” which they teach their guests every time you ascend one of their mountains. Pole in Swahili means slowly; so a rough translation of “Pole-Pole” is slow and easy or slowly, slowly. It is a wise term, one that is applicable on all mountains.

Happy hiking