Oxygen Transport, Circulation and Respiration in Healthy Subjects at Simulated Altitudes of 16,000–18,000 Feet

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Abstract
21 healthy adult subjects were tested at sea level and at simulated altitudes of 16,000 and 18,000 ft. in a low pressure chamber. The subjects sat in a ballistocardiograph built in the shape of an airplane pilot''s seat. Blood pressure, respiration and arterial oxygen saturation (oximeter) were measured and cardiac output and pulse rate were estimated from the ballistocardiograms. All these estimations could be made simultaneously or nearly so. Excluding a few subjects who collapsed, the avg. changes at altitude and the standard deviations about the mean were as follows: Arterial O2 saturation, -21% [plus or minus] 7%; pulse rate, +23% [plus or minus]9%; volume of respiration, +32% [plus or minus]19%; cardiac output per beat, +14% [plus or minus]9%; cardiac output per min. +39% [plus or minus]16%; oxygen transport, +8% [plus or minus]13%. Changes in blood pressure were small and inconsistent. The arterial oxygen saturation between 2 normal subjects breathing the same rarefied air differed on the avg. by 4.1%. Voluntary hyperventilation promptly increased the oxygen saturation of all subjects at altitude, but the long-continued differences in level could not be explained by differences in involuntary respiration or in circulation.