Pulmonary gas exchange and cardiac output in open-chest dogs with varied inflation of the lungs.

Abstract

In anesthetized dogs artificially ventilated at constant volume and frequency pulmonary gas exchange and circulatory parameters were measured under alternating conditions of closed and open chest.All parameters of pulmonary gas exchange were the same with closed and open chest when the mean transpulmonary pressure (or lung inflation) was identical. Reduction of the mean transpulmonary pressure with open chest increased the venous admixture and alveolar dead space ventilation.Cardiac output was similar with open and closed chest when the mean intrapulmonary pressure was the same in both conditions. Increase of the mean intrapulmonary pressure up to normal inflation of the lungs under open chest conditions caused a reduction of cardiac output and stroke volume.With open chest an optimum O2 transport rate to the body is achieved when the lungs are subnormally inflated.