Measurement of Total Gas Pressure in Blood

¹ From the Department of Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York

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.