Pulmonary hemodynamics and gas exchange were studied in four physicians during 72 hr acclimatization to 12,470 ft. Pulmonary catheters were left in three subjects for 72 hr. Resting mean pulmonary arterial pressure (P̄ĀP̄) rose progressively during the first 24 hr from 10.3 ±1.0 to 21.1 ±4.0 torr and remained at this level. During this same 24 hr period cardiac output increased from 7.1 ±1.4 to 8.4 ±2.0 liters/min and total pulmonary resistance rose from 122 ±16 to 209 ±40 dynes·sec/cm-5. Excercise at 60 w after 24 hr of hypoxia increased P̄ĀP̄ to 28.8 ±5.1 torr and decreased total pulmonary resistance to 155 ±25. Shunt fractions were 11 ±3.8% after 24 hr at altitude and fell to 7 ±0% after 72 hr. Alveolar to arterial O2 difference (P(A-a)O2) breathing oxygen fell from 116 ±10.8 to 92 ±33.3 torr during the same period of acclimatization, whereas dead space to tidal volume ratio (VD/VT) rose from 33 ±4.0% to 40 ±5.3% and P(A-a)O2 breathing ambient air rose from 8 ±2.6 to 11 ±3.0 torr. Inspiratory static lung compliance decreased significantly from a control of 176 ±8 to 141 ±8 ml/cm H2O after 72 hr of hypoxia.
Richard S. Kronenberg, Peter Safar, Joseph Lee, Fred Wright, William Noble, Eric Wahrenbrock, Robert Hickey, Edwin Nemoto, John W. Severinghaus
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