Measurement of Total Gas Pressure in Blood

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Abstract
The microtonometer method of Krogh has been modified for the determination of the total gas pressure of arterial and mixed venous blood. In the anesthetized dog it was found that the average arterial blood was 19 mm Hg less and the mixed venous blood was 54 mm Hg less than the alveolar or atmospheric gas pressure. In addition O2, CO2 tension and by difference from the total gas pressure the N2 tension was determined in the arterial and venous blood and the alveolar air. The arterial and mixed venous N2 tension average out to be the same, but are significantly greater than the mixed alveolar N2 by 8 mm Hg. This confirms previous findings of an arterial-alveolar N2 difference resulting from distribution of alveoli with different ventilation-perfusion ratios. Preliminary results indicate that when pure O2 is breathed, the arterial O2 pressure is 50–150 mm Hg less than atmospheric pressure. Submitted on November 15, 1956
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