Pulmonary Diffusion of Carbon Dioxide

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Abstract
Changes of O2 and CO2 pressures and concentrations of blood passing through the lungs have been calculated for one specific case, assuming normal values for the physiological parameters involved, constant alveolar pressures of O2 and CO2, and validity of the diffusion hypothesis. It is concluded that CO2 does not diffuse as rapidly as is generally assumed, the rate being initially about 25 times the mean rate, then decreasing gradually to about half the mean rate and finally increasing to the mean rate. As a result of these rates of CO2 diffusion in relation to the rate of diffusion of O2, there is no overshooting of pH beyond the arterial limit. The change of pH during passage of the blood through the last 90% of the length of the pulmonary capillaries is not greater than 10% of the venous-arterial (pH) difference, so a regulatory function of the pH upon perfusion might be ascribed to a direct physicochemical action on the walls of the capillaries.