Abstract
When venous return to the right heart was acutely impeded in anesthetized dogs with intact vagus nerves by inflating a balloon in the right atrium, the mean circulatory pressure rose, indicating a decrease in the capacitance of the circulatory system, thus confirming the present author's earlier observation. Since this response could be elicited to an equal extent after the elimination of the carotid sinus reflex, this response is probably due to mechanisms other than the carotid sinus reflex. When venous return to the left heart was impeded similarly by a balloon in the left atrium, the mean pulmonary arterial wedge and left atrial pressure rose, in the absence of appreciable changes in the volume of blood measured as existing between the pulmonary artery and left atrium, suggesting a decrease in the capacitance of the pulmonary circulatory system. An equation was derived that gives, under several simplifying assumptions. the slope (static) compliance. ΔV/ΔP, of the pulmonary "venous" system in terms of hemodynamic parameters measurable from pulmonary arterial wedge pressure tracings. On this basis, relative distensibility, (ΔV/ΔP)/V, of the pulmonary "veins" of anesthetized dogs was tentatively estimated to be about 0.026 (mmHg)-1 at mean pulmonary artery wedge pressure of about 8 mmHg.
