Figure 7.08. Comparison of P80 of Quechua (Andes Mountains) inhabitants with Western Europeans (sea level) under normal conditions and after pH is lowered from 7.4 to 6.7. "Double effect" rightward shifts of Quechuas aids unloading of oxygen from blood to tissues.
When people go to high altitude the oxygen dissciation curve shifts to the right due to respiratory alkalosis. This results from CO2 being blown off as the result of hyperventilation stimulated by the rarified air. Alkalosis stimulates the increased synthesis of 2,3-diphophoglyceric acid in red blood cells (erythrocytes). The DGP in turn decreases the affinity of hemoglobin for oxygen. This acts to promote oxygen unloading at the tissues.
This strategy by the body works well at intermediate altitudes where loading of oxygen on the "shoulder" is not a problem. At extreme altitude (ie. above 20,000 ft.) this strategy becomes counterproductive, as loading of oxygen is now significantly impaired.
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