The Effects of Halothane on the Interactions Between Myocardial Contractility, Aortic Impedance, and Left Ventricular Performance;iv: Haemodynamic Responses to Vagus Nerve Stimulation

Abstract

The effects of electrical stimulation of the vagus nerves have been studied in anaesthetized dogs, before and after bilateral interruption of the cardiac sympathetic nerves. During constant heart rates, maintained by right atrial pacing, vagus nerve stimulation caused small but significant reductions of myocardial contractility, but these were minor compared with the effects of other negative interventions such as halothane anaesthesia and coronary artery ligation. When atrial pacing was withdrawn during vagus nerve stimulation, the ensuing bradycardia was associated with further marked reduction of myocardial contractility and in cardiac output. Vagus nerve stimulation depressed left atrial systole and left ventricular filling, and this might be expected to have greater effect in the halothane depressed heart than in the undepressed heart of a conscious animal. Halothane decreased the spontaneous heart rate of sympathectomized and vagotomized dogs, probably by a direct effect on the sino-atrial pacemaker. It is unlikely that increased vagal activity during halothane anaesthesia could significantly depress myocardial contractility, but these many mechanisms may contribute to the overall impairment of left ventricular performance at slow heart rates.

E.C.G. Changes During Halothane and Enflurane Anaesthesia for E.N.T. Surgery in Children

“…Suxamethonium given after Althesin did not prolong QT. Thiopentone depresses activity in all excitable tissues and increases the plasma concentration of catecholamines (Goodman and Gilman, 1975). Takki and others (1972) could not find an increase in the catecholamines in association with intubation after thiopentone plus suxamethonium.…”

“…These results with halothane are in agreement with those of Alexander (1971), Alexander, Bekheit and Fletcher (1972), Alexander (1974) and Saarnivaara and Kentala (1977), who found junctional rhythm in 33-51% of adults during oral surgery. Halothane has a tendency to cause junctional rhythm (Johnstone, 1956) because it reduces the firing rate of the sino-atrial pacemaker (Flacke and Alper, 1962;Hauswirth and Schaer, 1967;Gersh and Prys-Roberts, 1972). Junctional rhythm occurred during enflurane anaesthesia as often as during halothane anaesthesia.…”