An open-loop analysis of the aortic arch barostatic reflex.

ALLISON,JAMES L., KIICHX SAGAWA, AND MAMORU KUMADA. Ati open-loop analysis of the aortic arch barustatic reflex. Am. J. Physiol. 217(6): 1576-1584. 1969.-The effects of stepwise pressure variations in the isolated aortic arch on cardiac pumping and systemic vascular resistance were studied in anesthetized open-chest dogs. The systemic arterial bed, except the aortic arch and brachiocephalic area, was perfused by a constant-flow pump. The mean left atria1 pressure was maintained by an overflow mechanism, and the ventricle ejected blood into a compliance chamber via a short segment of ascending aorta. The outflow pressure load was also maintained constant by a servomechanism. Multistep elevation of the isolated aortic arch pressure (AAP) from 0 to 300 mm Hg produced an average reduction of 34?$ in systemic arterial perfusion pressure (SAP). Heart rate (HR) decreased by 30% while cardiac output (CO) decreased by 15 %. The average maximum static gain of the reflex on the systemic vascular resistance (ASAP)/(AAAP) was -0.5 1 and occurred at a mean AAP of 144 mm Hg. The average threshold AAP for vascular effect was 90 mm Hg, whereas the threshoId for the HR response was 125 mm Hg. The HR response was most marked at a mean AAP of 17 1 mm Hg, whereas the CO response was greatest at 178 mm Hg. Besides the nonlinear static gain, both the vascular and cardiac responses to the step inputs contained nonlinear transient components. It was concluded that the experimental results confirmed the conventional concept that the aortic arch baroreceptor reflex is in many ways similar to the carotid sinus reflex though there are some quantitative differences between the two.