Altitude and the human body
What happens at altitude: Air pressure
At sea level, we have about one bar of air pressure at the surface – exactly 1013.25 millibars. This pressure is also called atmospheric pressure, because it really indicates exactly one thing: The pressure of the atmosphere that weighs on us.
The air pressure decreases with increasing altitude, since only a smaller part of the earth’s atmosphere is above us. On the first km this drop is almost linear, in the area that we are interested in when diving, you can roughly calculate that the pressure drops by 0.1 bar every 1000m.
Of course, this is not entirely correct: the air at the very bottom is denser than that at altitude, so you experience much higher absolute pressure differences at the beginning than several km above sea level.
The human organism and height
In principle, the human organism is adapted to life at moderate altitudes. Anyone who has ever been in somewhat higher mountain regions may have been able to feel it themselves: Already at 2000m there can be a significant drop in performance, from about 2500m symptoms of altitude sickness are possible, even higher up there is an increased risk of e.g. pulmonary edema. The most important reason for this is the lower partial pressure of oxygen (pO2). Although the composition of the air we breathe is the same, if the total pressure is lower, the pO2 is correspondingly lower. Our body is used to and adjusted to a certain pressure. If this falls, certain adjustments take place. To ensure that enough oxygen is still available, the heart beats a little faster: the resting pulse increases and breathing is also somewhat accelerated. Over time, the body adapts, and after a week of adaptation, all problems are usually resolved.
People can adapt to an astonishing extent. The highest major city, for example, is La Paz in Peru at 3879m – an altitude that travelers do not always endure without complications, but where, with appropriate adaptation, many people live permanently. A real limit, above which human life is really no longer possible without an additional oxygen supply, even for a short time, is higher than the highest peaks in the world: above 13km, sufficient oxygen saturation can no longer be achieved. The hard limit, however, is at an even lower pressure of 63 hPa at an altitude of 19 km, the so-called “Armstrong limit”: here, the boiling point of the water in our body fluids is already 37 degrees Celsius. As a result, water vapor would constantly form in our 37°C warm lungs, for example, and its escape would prevent oxygen uptake and thus make survival impossible.
Diving usually doesn’t involve such extreme heights. The much dived mountain lakes in Montana (USA) are around 1000m altitude; in Switzerland it may well go up to around 2000m – but beyond that, dives at higher altitudes quickly take on an expedition character.
Perhaps the most famous extreme altitude dive site is Lake Titicaca in Peru. It plays an important role in the history of diving: Jacques Cousteau undertook an expedition in 1968, during which his team discovered a special species of frog. And even today, diving is sometimes done there, but not regularly. At such altitudes, what also applies to mountain hiking on the subject of altitude adaptation becomes quite important: you should take a few days to be in good physical condition when you expose yourself to the stress of a dive at this altitude.
With a small change in altitude before diving, altitude adjustment is not necessary, but a little caution can not be wrong.