Cardiopulmonary baroreflexes: effects of staircase, ramp, and square-wave stimulation

Anesthetized dogs were pump perfused in a system that held systemic arterial pressure constant. Pulmonary arterial beds were pressurized, and the induced transient falls of systemic vascular resistance (SVR) were measured. An approximately linear relationship between percent fall of SVR and pulmonary artery pressure was obtained. Left atria and pulmonary venous beds were pressurized using square-pulse, staircase, and ramp wave forms, and changes in SVR were measured. The effect of varying the interval between stimuli was appraised. An approximately linear relationship was obtained for responses to square-wave left atrial forcing pressure (Pla). With staircase forcing, the change of SVR per unit change of Pla depended upon prestimulus Pla. With ramp forcing, responses increased approximately linearly with respect to the logarithm of the rate of pressure rise. Responses to square-wave stimulation varied directly with respect to the interstimulus interval. This study shows that left atrial-pulmonary vein baroreflexes are capable of producing substantial short-term falls of SVR, and that the response depends upon stimulus pressure, rate of pressure change, base-line pressure, and pressure history.