The Effects of Halothane on Arterial Pressure. Preganglionic Sympathetic Activity and Barostatic Reflexes

The effects of halothane on arterial pressure and preganglionic sympathetic activity and the responses of these to stimulation of the aortic depressor nerve were studied in cats. When the end-expired concentration of halothane was 1.15 per cent, sympathetic activity was reduced only slightly, whereas blood pressure was markedly depressed. The magnitude of the sympathetic response to baroreceptor nerve stimulation was unaffected at this concentration, although the response of arterial pressure was reduced. Even when the end-expired concentration was 1.65 per cent, when baroreceptor nerve stimulation produced hardly any change in arterial pressure, the sympathetic nervous response was relatively little affected. The authors conclude, therefore, that halothane produces only slight depression in sympathetic activity and docs not extinguish barostatic reflexes, and that the cardiovascular depression produced is largely, although not entirely, due to an action peripheral to the central nervous system.