Cardiovascular effects of and interaction between calcium blocking drugs and anesthetics in chronically instrumented dogs. II. Verapamil, enflurane, and isoflurane.

The effects of enflurane and isoflurane on the cardiovascular system and cellular calcium kinetics are somewhat different. Consequently, the interaction with the calcium channel blocking drug, verapamil, may also differ. In order to compare the anesthetics, the authors studied the effects of two infusion doses of verapamil (which produced plasma levels of 90 and 180 ng X ml-1) on cardiovascular dynamics and regional blood flow in awake dogs. On two other days, in the same dogs, the effects of approximately 1.1 and 2 MAC enflurane and isoflurane were first studied and then the same verapamil dose regimens while the same anesthetic concentrations were maintained. Verapamil produced only increases in heart rate and the P-R interval in the awake animal. The high dose of both anesthetics markedly decreased mean aortic pressure and left ventricular rate of tension development (dP/dt), and increased heart rate. However, only enflurane also decreased myocardial segment length shortening and increased left atrial pressure. Neither anesthetic alone affected coronary or renal blood flow, while both increased carotid blood flow at the low dose. Verapamil infusion during 1.2 MAC enflurane was more depressant than during 1.2 MAC isoflurane, but the combination of verapamil with 2 MAC concentration of both anesthetics was equally depressant. Both doses of both anesthetics increased plasma verapamil levels compared with the same verapamil dosing regimen awake. When these results are compared with those previously reported for halothane, the effects of verapamil during all three anesthetics are more similar than different.(ABSTRACT TRUNCATED AT 250 WORDS)