The rate of rise of intraventricular pressure as an index of myocardial contractility in conscious and anaesthetised ponies.

Measurements of the rate of rise of left ventricular blood pressure (dP/dt) have been made in conscious and anaesthetised ponies. Concurrent measurements of heart rate, mean arterial pressure and left ventricular pressure were also made in order to assess their relationship to values of dP/dt. Thiopentone-halothane and thiopentone-ether anaesthesia reduced the maximal rate of rise of intraventricular pressure (dP/dt max) from conscious control levels. After correcting for variations in the loading conditions of the ventricle, the depressant effect of halothane was still apparent, but the action of ether was not. It was concluded that the negative inotropic effect of halothane in the pony was greater than that of ether, possibly because a compensatory sympathoadrenal stimulation occurred during ether but not during halothane anaesthesia.