THE EFFECT OF PULMONARY VENTILATION ON ANOXEMIA

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Abstract
Increase in pulmonary ventilation is a normal response to O2 lack and tends to increase pO2 in alveolar air and arterial blood. In this study, deliberate hyperventilation was used during anoxia in an attempt to quantitate the relation of ven-tilatory volume to arterial oxygenation. Ten resting subjects breathed 10.5% O2 in N at sea level, adjusting respiratory min. vol. at various levels between 10 and 30 l./min. HbO2 saturation was measured by a Coleman-Millikan oximeter, and in a number of expts. arterial pO2, pCO2 and pH were detd. directly in samples drawn from the brachial artery. HbO2 saturation increased markedly with increased ventilation. An increase of 2-3 l./min. above the resting ventilation increased HbO2 saturation by 10-20% units. Doubling the resting ventilation increased saturation by 20-30% units, an increase not exceeded by much larger ventilatory vol. Arterial pO2 increased in direct proportion to increase in ventilation. Alveolar pO2 rose about 1.5 times as fast as pCO2 fell with increasing ventilation. It is again stressed that arterial oxygenation cannot be predicted accurately from the level of inspired pO2. Clinical applications on O2 lack (such as the anoxemia test of coronary insufficiency) should be based, therefore, on arterial HbO2 saturation or arterial pO2 rather than on a certain inspired pO2.