Bilateral Carotid Sinus Control of Ventricular Performance in the Dog

Left and right carotid sinus pressures were independently varied while the left ventricular systolic pressure was recorded in an anesthetized canine preparation with an isolated, isovolumetric left heart. Intrasinus pressures were changed in steps of 50 mm Hg to produce either an increase or decrease in pressure from a mean level of 150 mm Hg. The response to eight combinations of increases and decreases in left- and right-sided pressures was examined. Blockade of the sympathetic impulses to the heart produced a loss of response of left ventricular systolic pressure when the intrasinus pressure was decreased from 150 to 100 mm Hg. Parasympathetic blockade produced a loss of response to an increase in pressure from 150 to 200 mm Hg. Left ventricular systolic pressure was more sensitive to a decrease in pressure from 150 to 100 mm Hg in the right sinus than in the left, but there was no difference in sensitivity between left and right sides when intrasinus pressure was raised from 150 to 200 mm Hg. The summation pattern of the response to simultaneous steps in left and right pressure was mutually facilitative for steps from 150 to 100 mm Hg and mutually inhibitory for steps from 150 to 200 mm Hg. The entire system was simulated with a hybrid computer model consisting of separate functional relations used to represent the baroreceptors, central nervous system, and left ventricle. Due to the baroreceptor characteristics and other nonlinearities, the simulation results suggest that a careful distinction should be drawn between transient and steady-state responses when assessing the relative role of each autonomic division in any baroreceptor reflex.