The Effect of Pulmonary Vascular Pressures on the Mechanical Properties of the Lungs of Anesthetized Dogs1

Abstract

Since the experiments of von Basch (1) it has been recognized that pulmonary vascular congestion influences the mechanical behavior of the lungs. A number of studies in patients with chronic congestive failure have demonstrated marked changes in pulmonary elasticity (2-6). It has not been possible to determine in such patients the relative contributions of pulmonary edema, other parenchymal changes, and vascular congestion per se to the observed changes. Experiments with acute congestion in man or living animals (7-10) and isolated lungs (11) have yielded conflicting results.The purpose of the present study was to examine in the living animal the effects of acute changes in pulmonary arterial and venous pressures and blood flow on the mechanical behavior of the lungs. The left atrial pressure and the pulmonary blood flow were varied independently. In one set of experiments, volume-pressure curves were obtained during stepwise inflation and deflation of the lung over a wide range of volume starting from the passively collapsed state. In another group, pulmonary compliance and flow-resistance were studied during continuous cycling of the lungs in the normal tidal range of lung volume. Nembutal@ (25 to 45 mg. per Kg. body weight, intravenously). The chest was opened by splitting the sternum, and the chest wall was retracted to minimize crowding of the intrathoracic viscera during inflation of the lungs. The right ventricle was replaced by a pump without interruption of the circulation as in an experimental preparation previously described (12). Systemic venous blood was diverted into a reservoir from which it was pumped into either the main pulmonary artery or into the two pulmonary artery branches separately.When both pulmonary arteries were cannulated, the blood flow in the lung to be studied was varied by changing distribution of flow. In addition, pulmonary flow could be varied by changing pump output. Left atrial pressure was varied by mechanically altering the systemic arterial resistance (constriction of the ascending aorta, inflation of balloon in ascending aorta, systemic A-V shunt). Sometimes additional adjustment of left atrial pressure was obtained with an overflow system between the left atrium and the venous reservoir. In this way changes could be made in pulmonary flow or left atrial pressure independent of each other.Pulmonary blood flows were measured with rotameters. Pressures in the pulmonary arteries distal to the respective cannulae, in the left atrium, and in the femoral or carotid arteries were measured with electromanometers. These values were recorded on a direct-writing Sanborn oscillograph.Two methods were used to measure the mechanical characteristics of the lung.

Effect of Cyclooxygenase and Lipoxygenase Products on Pulmonary Function in Group B Streptococcal Sepsis

“…However, the magnitude of increase in h a w in the present study was less than those cited above (22,23,26), making it unlikely that changes in vascular pressure measured in our study alone resulted in alterations in lung function. One difference between the present study and those cited previously that may influence the magnitude of the changes in vascular pressure and lung function is the presence of pulmonary pathology in our subjects.…”

“…Investigators have described alterations in lung compliance with increases in pulmonary blood volume secondafy to an increase in left atrial pressure alone or with elevated Ppa (22)(23)(24)(25)(26). The resulting pulmonary vascular engorgement has been shown to produce a 20 to 40% decrease in lung compliance in laboratory animals with normal lungs when left atrial pressure is increased to 10-25 mm Hg (23).…”

“…One difference between the present study and those cited previously that may influence the magnitude of the changes in vascular pressure and lung function is the presence of pulmonary pathology in our subjects. Previous work (22)(23)(24)(25)(26) evaluating the relationship between vascular pressure changes and lung function were performed using animals with normal lungs.…”

Pulmonary vascular distensibility and lung compliance as modified by dextran infusion and subsequent atropine injection in normal subjects.

“…Acute changes of left heart and pul-monary venous pressures-besides producing the passive effects on PVR, distribution of blood flow, and lung mechanics that have been well documented in animal studies (45,48,56,62,71,(73)(74)(75)(76)-thus appear associated with active phenomena that increase the stiffness of the pulmonary vasculature and the lung as a whole.…”

Effect of Pulmonary Blood Flow upon Lung Mechanics*

“…Compliance is decreased in acute hemorrhagic shock when pulmonary blood flow is lowered (4). Borst et al., however, showed in a perfused canine lung preparation that compliance did not change over a wide range of blood flow (5). In patients with pulmonary overcirculation due to long standing intracardiac left-right shunts, 1625 lung compliance is decreased (6).…”