Ventilatory effects on left atrium and pulmonary vascular resistance

¹ Public Health Research Institute for Chronic Disease, State University of New York at Buffalo, New York

Pulmonary vascular resistance was studied in thoracotomized dogs enclosed in a respirator. The lung was inflated by respirator pressure, the trachea being open to the atmosphere. Blood flow through the lung was held constant. "Intrapleural" and left atrial pressures fell equally during inspiration; the pulmonary arterial pressure fell to a lesser extent. Calculated resistance increased during the midinspiratory phase and became maximal at end-inspiration and early expiration. Negative-pressure lung inflation had only small effects on resistance at minimal negative respirator pressures; resistance increased markedly as "intrapleural" pressure became progressively more negative. Resistance returned to control values at each end-expiration, regardless of the previous degree of negative-pressure inflation. Resistance increased in isolated lungs under constant flow perfusion when pulmonary venous and "intrapleural" pressures oscillated together; resistance fell when pulmonary venous pressure was held constant with respect to atmospheric pressure. The results suggest that previous disagreements on pulmonary vascular resistance may have been due to failure to evaluate the effect of "intrapleural" pressure on left atrial pressure. The increased resistance during negative-pressure inflation may result from a negative transmural pressure in the collapsible vessels of the lung.