ARTERIAL PRESSURE-FLOW RELATIONSHIPS IN HYPERTENSIVE DOGS - EFFECT OFCAROTID-SINUS BAROREFLEX

The effect of the carotid sinus baroreflex reflex on arterial pressure -flow relationships was studied in Goldblatt hypertensive and normoten sive dogs on cardiopulmonary bypass. Dogs were anesthetized with pento barbital sodium, vagotomized, and the carotid sinuses were isolated at controlled carotid sinus pressures (CSP). The mean arterial pressure- flow relationships were measured at different levels of CSP. The arter ial pressure-flow relationship was found to be linear except at extrem e levels of flow. The slopes derived from the linear regression of the pressure-flow relationships [total peripheral resistance (TPR)] were 1.466 +/- 0.111 and 0.786 +/- 0.13 mmHg.ml-1.min.kg at CSP of 50 and 2 00 mmHg in the normotensive group and 1.758 +/- 0.183 and 0.937 +/- 0. 114 mmHg.ml-1.min.kg at CSP of 50 and 250 mmHg in the hypertensive gro up. The increases in slope measured when CSP was decreased from satura tion to threshold were 0.68 mmHg.ml-1.min.kg (187% increase) in the no rmotensive group and 0.82 mmHg.ml-1.min.kg (188% increase) in the hype rtensive group. Zero-flow arterial pressures at CSP of 50, 125, and 20 0 mmHg were found to be 23.1 +/- 2.9, 21.7 +/- 2.2, and 17.1 +/- 1.8 m mHg in the normotensive group and 28.4 +/- 2.2, 23.8 +/- 1.5, and 20.0 +/- 1.2 mmHg in the hypertensive group. A nonlinear model fit was fou nd to give a significantly better fit [coefficient of determination (r 2) = 0.932 linear, 0.956 nonlinear] of the arterial pressure-flow rela tionships. We conclude that, in experimental hypertension, carotid bar oreflex control of TPR is shifted to a higher operating point without any reduction in overall reflex gain.