Pulmonary hemodynamics during positive-pressure breathing

¹ Departments of Pediatrics, Physiology, and Medicine, School of Medicine, University of California; and Respiration Laboratory, Veterans Administration Hospital, Los Angeles, California

The effects of positive-pressure breathing on pulmonary blood flow in the intact anesthetized dog were measured and compared with pulmonary hemodynamics during spontaneous breathing. Using fluoroscopically placed cardiac catheters, pulmonary arterial and venous pressures were measured. Transmural pressures were determined by subtraction of intrapleural pressures, using a differential transducer. Cardiac outputs were determined by the dye-dilution technique, using cardiogreen. Cardiac output fell significantly with positive-pressure breathing, compared with the value during spontaneous respiration. Pulmonary vascular resistance did not differ with the two types of respiration. Although absolute pulmonary arterial and venous pressures rose, as expected, with pressure breathing, their transmural pressures did not change. These studies indicate that there is no primary change in pulmonary hemodynamics with positive-pressure breathing. Decreased cardiac output results from the decreased venous return which is related to the increased intrathoracic pressure during positive-pressure breathing.