COMPARISON BETWEEN THE TIME AVAILABLE AND THE TIME REQUIRED FOR CO2 EQUILIBRATION IN THE LUNG*

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Abstract
The factors determining whether CO2 equilibration will occur in the lungs are the rate of the reactions leading to CO2 evolution and the time the bicarbonate ions spend in contact with the gas exchange surface. If the rate of the reactions involved in CO2 liberation is slowed gradually by repeatedly giving small doses of acetazolamide, a point will be reached where the evolution of CO2 cannot be completed in the time the blood spends in the pulmonary capillaries, and the amount of CO2 produced decreases sharply. In applying this principle, we used a body plethysmograph as a manometer to determine the rate and magnitude of CO2 evolution, and we found that the bicarbonate ions spend an average of 2.2 seconds in contact with the gas exchange surface in dogs, a much longer time than the erythrocyte transit time through the pulmonary capillaries. We think that this prolongation of bicarbonate transit time is caused by the presence of a large pericapillary dilution and reaction space for the bicarbonate-CO2 system, and we suspect that this prolongation plays a role in the completion of CO2 equilibration in the lungs.