Hemodynamic and respiratory responses to carotid sinus pressure alteration in experimental hypertension

The purpose of this study was to determine whether baroreflex control of respiratory responses is diminished in hypertension. Ten dogs were made chronically hypertensive with use of a bilateral renal wrap technique. Eight sham-operated dogs served as normotensive controls. After the development of experimental hypertension, carotid baroreflex control of arterial pressure, heart rate, respiratory frequency, tidal volume, and ventilation was acutely assessed. Under pentobarbital anesthesia and with bilateral vagotomy, the carotid sinuses were isolated and perfused at controlled pressures. Before the carotid sinus region was manipulated, the mean arterial pressure was significantly higher (P < 0.005) in the hypertensive group (146.4 +/- 2.3 mmHg) than in the normotensive group (124.7 +/- 2.6 mmHg). The mean arterial pressures and heart rates measured at every level of carotid sinus pressure were significantly higher in the hypertensive group. Reflex gain of heart rate, but not mean arterial pressure, was significantly reduced in the hypertensive group. Respiratory frequency, tidal volume, and ventilatory responses to changes in carotid sinus pressure were significant and resulted in an approximately 40% reflex change in ventilation. These responses were not diminished in the hypertensive group. We conclude that respiratory baroreflex responses are preserved in experimental hypertension.