Hypotensive mechanisms of pulmonary insufflation in dogs

¹ Department of Physiology, Baylor University College of Medicine, Houston, Texas

To differentiate between the mechanisms which have been proposed to account for the hypotensive effect of pulmonary insufflation, cyclic volume changes of the right ventricle were qualitatively monitored by means of a variable resistance strain gauge sutured to the right ventricular wall. Artificially created decreases in venous return as well as cardiac tamponade of a degree sufficient to produce hypotension for brief periods were found to decrease the volume of the right ventricle. Increased right ventricular outflow resistance, however, produced a marked increase in right ventricular volume. With brief periods of hypotensive levels of pulmonary insufflation, right ventricular volume was found to increase in the animal with a wide-open chest; the volume decreased with the chest closed. It is concluded that in the open-chest condition the hypotensive mechanism of pulmonary insufflation is an increase in pulmonary vascular resistance, whereas in the closed-chest condition decreased venous return, cardiac tamponade, or both are predominantly responsible for the hypotension.