DYNAMIC EFFECTS OF CAROTID-SINUS BAROREFLEX ON VENTRICULOARTERIAL COUPLING STUDIED IN ANESTHETIZED DOGS

We evaluated dynamic effects of the carotid sinus baroreflex on ventriculoarterial coupling. In seven anesthetized, vagotomized dogs, we bilaterally isolated carotid sinuses and randomly changed carotid sinus pressure while measuring aortic pressure, aortic flow, and left ventricular pressure. Estimating left ventricular end-systolic elastance (E(es)) and effective arterial elastance (E(a)) on a beat-to-beat basis, we determined transfer functions from the carotid sinus pressure to E(es) (H(Ees)) and from the carotid sinus pressure to E(a) (H(Ea)) over the frequency range spanning 0.002 - 0.25 Hz. Both H(Ees) and H(Ea) exhibited characteristics of a second-order low-pass filter. The gains of H(Ees) and H(Ea) were 0.085 +/- 0.065 (mean +/- SD) and 0.081 +/- 0.049 mm Hg/ml/mm Hg, respectively. There were no significant differences in natural frequencies (0.039 +/- 0.013 versus 0.039 +/- 0.007 Hz) or damping ratios (0.65 +/- 0.11 versus 0.64 +/- 0.24). The results indicated that the carotid sinus baroreflex dynamically altered E(es) and E(a) to the same extent in the process of stabilizing arterial pressure. Because the arterial system extracts maximal external work from a given heart when E(a) equals E(es), the carotid sinus baroreflex appeared to be designed to regulate the ventricular and arterial properties to optimize the energy transmission from the left ventricle to the arterial system in anesthetized, vagotomized dogs.