Influence of carbon dioxide on pulmonary vasculature

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Abstract
The single-breath CO diffusing capacity (Dl) and pulmonary vascular resistance (PVR) were measured in isolated perfused cat lungs exposed to varying concentrations of CO2. Ventilation of the lungs with 5–10% CO2 produced a significant rise in D1 and PVR compared to contro1 values breathing room air. Perfusion of five lungs with blood equilibrated with 5–10% CO2 while breathing room air produced a significant rise in PVR but inconsistent changes in D1. When the direction of perfusion was reversed so that blood entered the lungs through the pulmonary veins, ventilation with 7.5–10% CO2 increased both D1 and PVR while perfusion with blood equilibrated with 10% CO2 only increased PVR. These findings indicate: 1) arteries and veins can constrict independently when directly exposed to elevated CO2 tensions; and 2) if the capillaries and downstream vessels are exposed to elevated CO2 tensions, D1 is increased. A likely mechanism is that constriction downstream from the capillaries produces a rise in their transmural pressure, which in turn causes an increase in capillary blood volume. Among alternative explanations for the change in D1 is the possibility that CO2 increases the speed of the uptake of CO by erythrocytes. Submitted on June 18, 1963

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