Cardiac output and total peripheral resistance in carotid sinus reflex.

SCHMIDT,ROBERT M., MAMORU KUMADA, AND KIICHI SAGAWA. Cardiac output and total peripheral resistance in carotid sinus reflex. Am. J. Physiol. 221(Z) : 480-487. 197 1 .-The sensitivity of the carotid sinus baroreceptor reflex to step change in sinus pressure was studied in anesthetized dogs, with emphasis on the relative contributions of cardiac output (CO) and total peripheral resistance (TPR) in bringing about a lowering of mean arterial pressure (MAP). Changes in MAP, CO, and TPR were determined after successive 25-mm Hg step increases in intrasinus pressure (ISP) from 50 to 200 mm Hg. Arterial pressure fell significantly with each step from 75 to 175 mm Hg ISP; CO showed a slight but consistent reduction throughout this range of sinus pressure. However, TPR was sensitive to altered sinus pressure only between 100 and 150 mm Hg ISP. In this latter range, where the greatest blood pressure reduction occurred, a reciprocal relationship between AC0 and ATPR was evident in individual dogs. Vagotomy influenced the magnitude of all three response variables. Step increase in carotid sinus pressure brought about a fall in MAP through either AC0 or ATPR, or both. The magnitude of arterial pressure change appeared to be influenced by the aortic baroreceptor reflex, but it did not seem to influence the effector mechanisms through which that change was brought about.