THE INTERACTION OF CHANGES IN PULMONARY HEMODYNAMICS AND VENOUS RETURN FOLLOWING PULMONARY THROMBOEMBOLISM
Acute experiments with rabbits were used to study changes in pulmonary haemodynamics in a model of pulmonary artery thromboembolism under intact circulatory conditions and upon volumetric clamp perfusion of the lungs. Under intact circulatory conditions, blood pressure in the pulmonary artery increased upon thrompoembolism to a lesser degree than under perfusion of the lungs, because pulmonary blood flow decreased. In both cases, pulmonary vascular resistance increased equally. Upon caudal vena cava stenosis, blood pressure and flow decreased in the pulmonary artery, the later decrement being the same as in the case of thromboembolism. At the same time, upon caudal vena cava stenosis, pulmonary vascular resistance increased two time less than in response to pulmonary artery thromboembolism. Under pulmonary artery thromboembolism, blood pressure in the artery depended on changes in pulmonary blood flow and pulmonary vascular resistance. Changes in blood flow through the pulmonary artery were caused by changes in venous return and myocardial contractility and did not correlate with pulmonary vascular resistance.