Altitude (HB)

Altitude illnesses are all caused by a change in air pressure and the actual concentrations of oxygen.

The air we breathe contains about 21% oxygen, even though we only use a small percent of it with each breath. As we exhale, we blow out around 16% oxygen and any carbon dioxide exchanged in the lungs.

The pressure on top of Denali (18,000 feet) is about one-half of sea level pressure, but it still contains 21% oxygen. There is less available oxygen in the same space because of the decreased pressure. The higher we go, the more we need to breathe to get the oxygen we need; however, the more we breathe, the more carbon dioxide we exhale, and this is the problem.

The brain measures the amounts of oxygen and carbon dioxide in your system. The amount of oxygen to carbon dioxide influences the pH (acidity of your system). One of the ways your body manages the acidity is via respirations. When you start exhaling too much carbon dioxide, your blood becomes alkalotic, and your body will take steps to try and restore the pH. Generally, it does this by using your kidneys to balance via urination—which is why hydration is critically important.

Over time (two to three weeks), your body will acclimatize by creating more red blood cells, enabling you to carry more oxygen, and becoming more efficient in a few other ways. Some people are better at adapting than others, and some people that have adapted well in the past may have problems in the future. Overexertion and alcohol consumption (as well as a few medical conditions) inhibit the body’s ability to acclimate.