THE EFFECTS OF MEDETOMIDINE ON CARDIAC CONTRACTILITY IN AUTONOMICALLY BLOCKED DOGS

The effects of medetomidine on load-dependent and relatively load-independent indices of left ventricular contractility and hemodynamics were studied in 8 chloralose-anesthetized, autonomic-blocked dogs. Left ventricular contractility was assessed by the maximum rate of increase in pressure (dP/dt(max)), the slope of the end-systolic pressure volume relationship (Ees), preload recruitable stroke work (PRSW). and dP/dt(max)-end-diastolic volume relation (SdPV), Dogs received 5 or 10 mu g/kg of medetomidine IV. The dP/dt(max) decreased significantly 30 minutes after both doses of medetomidine. The Ees did not change. Both SdPV and PRSW increased 5 minutes after both doses of medetomidine. Mean arterial pressure, left-ventricular end-diastolic and end-systolic pressures, peripheral vascular resistance and effective arterial elastance increased 5 minutes after both doses of medetomidine. Stroke volume, cardiac output, and stroke work decreased 5 minutes after medetomidine administration. End-diastolic volume did not change. End-systolic volume increased but the difference was not significant. Our study suggests that medetomidine increases inotropy and vascular resistance in autonomic-blocked dogs and that both ventricular and vascular responses to pharmacological manipulation must be considered for a complete assessment of the inotropic effects of a drug. (C)Copyright 1995 by The American College of Veterinary Surgeons