DISORDERS CAUSED BY ALTITUDE - Medicine for Mountaineering and Other Wilderness Activities - page 337

rise again. At extreme altitudes the muscles of respiration may tire more rapidly than those
of the legs and arms.
Changes in pH
Increased breathing depletes carbon dioxide from blood, making the pH higher and the
blood more alkaline. Increased alkalinity stimulates the excretion of bicarbonate in the ur-
ine, which tends to restore the pH of the blood toward normal, a process called renal (kid-
ney) compensation. The drug acetazolamide (Diamox®) increases bicarbonate excretion,
and the lungs compensate by increasing breathing. Acetazolamide has been called the “ar-
tificial acclimatizer” because it causes the same physiologic responses as acclimatization
but in reverse order (the kidneys excrete bicarbonate and then the lungs increase breathing,
instead of the lungs increasing breathing and then the kidneys excreting bicarbonate).
Figure 24-1. Blood oxygen content (saturation) under varying working conditions at an altitude of
19,000 feet
Figure 24-2. Decline of maximum heart rate with altitude