EFFECTS OF CHANGES IN BLOOD PC02 ON BRAIN OXYGENATION AT 147 MM HG AMBIENT PRESSURE (39,000 FEET)
PENNSYLVANIA UNIV PHILADELPHIA PHILADELPHIA United States
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Hyperventilation during the breathing of 100 percent oxygen elevates the PO2 of alveolar gas by the same amount that it lowers its Pco2. Since the development of arterial hypocapnia causes cerebral vasoconstriction, brain oxygenation is drastically decreased even while arterial oxygenation is improved by the hyperventilation. Administration of 30 percent CO. with oxygen at an ambient pressure equivalent tothat at 39,000 feet altitude prevented alkalemia and, in spite of hyperventilation, restored central oxygenation to a level at least equivalent to that found when pure oxygen was breathed at rest at the same altitude. The respiratory minute volume during administration of C02 with 02 was greater than when 02 alone was breathed at the reduced ambient pressure., Since neither arterial Po2 nor central Pco2 values differed in these two experimental situations, the respiratory stimulation may represent the quantitative demonstration in man of a respiratory effect of carbon dioxide which is mediated solely by the chemoreceptors exposed to arterial blood and which acts in the absence of a change in direct central stimulation by C02.