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Unformatted text preview: II. IMMEDIATE AND LONGER ADJUSTMENTS TO ALTITUDE HYPOXIA A. Cardiovascular System V02 = (HR X SV) X (C302 - CV02) With increasing altitude, C302 progressively decreases. To compensate, cardiac output initially increases during rest and submaximum exercise due to an increase in heart rate. Over the first week at altitude, cardiac output falls to or below sea level values for the same V02 and there is a progressive increase in 02 extraction --> more efficient method of delivering 02_ The most important long-term adaptation to altitude is an increase in the blood's oxygen carrying capacity. Hemoglobin concentration starts to increase during the first two days at altitude due to a decrease in plasma volume and an increase in RBC production by bone marrow. These hematological changes during acclimatization are dependent on an adequate iron intake In some high altitude natives and well-acclimatized sojourners, hemoglobin concentration may be increased 40 - 50% above normal. Concentration of 2,3 DPG within RBC increases --> shift 02 dissociation curve to right --> unload more 02 at the tissues for a given capillary P02. Even after several months of acclimatization, V02 max. still remains significantly below sea- level values. B. Pulmonagy System Decreased alveolar P02 --> decreased arterial P02 --> stimulation of aortic and carotid chemoreceptors --> increase in ventilation --> increase in P A02 and Pa02 Hyperventilation --> decreased P AC02 and PaC02 --> increase in blood pH (respiratory alkalosis) --> plasma bicarbonate levels decrease during first two days because the kidneys excrete excess HC03 to compensate pH. After the acid-base balance is corrected, hyperventilation persists during acclimatization. Within a week at high altitude, a new level for VB is attained - 40 to 100% above sea level values. ...
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