Effects of halothane on carotid occlusion in rabbits.

Effects of halothane on the carotid sinus baroreflex control of circulation were studied in chronically instrumented rabbits. The carotid sinus baroreflex was evaluated by the hemodynamic responses to bilateral carotid occlusion (BCO). Either 0.5 or 1.0 MAC of halothane inhalation did not alter mean arterial pressure (MAP) or total peripheral resistance (TPR), but significantly increased heart rate (HR). Carotid occlusion produced a significant increase in MAP and HR, and both responses were attenuated dose-dependently by halothane. Halothane depressed the reflex gain of arterial pressure from 3.5 +/- 0.3 at conscious state to 1.3 +/- 0.2 at 1.0 MAC halothane. Response of cardiac output (CO) to BCO was attenuated significantly only at 1.0 MAC compared with those responses at conscious state and at 0.5 MAC. Response of TPR was attenuated at both 0.5 and 1.0 MAC halothane as compared with at conscious state but no significant difference existed between the two concentrations of halothane. These data suggested that halothane could attenuate the carotid occlusion responses to various degrees in the involved effector components. 0.5 MAC halothane attenuated MAP response to BCO predominantly by attenuating reflex peripheral vasoconstriction. The reduced CO response was mainly responsible for further attenuation of MAP response at 1.0 MAC halothane.