Reflex changes in heart rate and ventilation induced by central blood pressure changes

Abstract

To determine the existence and assess the importance of reflex mechanoreceptor areas other than carotid and aortic baroreceptor sites in dogs, balloon and monitoring catheters were placed in the pulmonary artery proximal to the bifurcation, in the inferior vena cava, and in the thoracic aorta above the diaphragm. Inflation of these balloons made it possible to produce a variety of pressure distribution patterns in the circulation. Pressures were recorded from the bifurcation of the pulmonary artery, right and left atria, aortic arch, and intrathoracic esophagus to obtain evidence for the existence of blood pressure reflexes originating above the diaphragm. The results contain quantitative evidence for the following reflexes in dogs anesthetized with chloralose, and breathing normally with closed chest: 1) the Bainbridge "effect;" 2) the well-known barostatic reflexes, except that respiration rate was found to be independent of arterial pressure; 3) a previously unreported reflex: when the pulmonary artery pressure is lowered (the right atrial and aortic pressures being maintained constant) there results an immediate increase in respiration rate and depth without a concomitant change in heart rate.