The cardiovascular effects of ketamine in man.

The arterial hypertension of ketamine is prevented by verapamil, a calcium ion antagonist. This indicates that ketamine is a direct myocardial stimulant acting by increasing the availability of calcium across the cell membranes of the myocardial and the Purkinjé systems. The positive chronotropic action of ketamine is not reversed by verapamil. Both the chronotropic and the inotropic effects of ketamine are prevented by halothane which acts partly by increased vagal tone and partly by what appears to be a verapamil-like depression of calcium availability. Ketamine blocks the reflex sympathetic response of the peripheral blood vessels to surgical stimuli. The site of the block within the sympathetic reflex arc has not been identified. It is not at the alpha adrenoceptor level. The clinical implications of the findings have been discussed.