HALOTHANE AND THE RESPONSES OF THE HEART TO AUTONOMIC NERVE STIMULATION

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Abstract
The effect of halothane on the responses to stimulation of the efferent autonomic nerves to the heart was determined in dogs lightly anaesthetized with chloralose. In the absence of nerve stimulation halothane (inspired concentration 0.8%) led to significant falls in heart rate and blood pressure and in the maximum rate of change of left ventricular pressure measured at a constant paced heart rate. The slowing of the heart produced by vagal stimulation was not altered by halothane. The increases in heart rate produced by stimulating the right and left ansae subclaviae were not affected by halothane. Using LV dP/dt max at a constant heart rate as an index of the inotropic state of the heart, halothane shifted to the right the response curve resulting from stimulation of the left ansa; this shift could be accounted for by a fall in blood pressure produced by halothane. It was concluded that halothane in this concentration did not produce changes in the cardiovascular system by altering the responsiveness of the heart to the acetylcholine and noradrenaline released at the local nerve endings.

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