Isoflurane and large coronary artery haemodynamics. A study in dogs.

In the dog, stepped increases in isoflurane concentration (up to 1.5 MAC) caused peripheral and coronary vasodilatation. In the presence of significant decreases in arterial pressure (-35%), contractility (-46%), cardiac output (-17%) and coronary perfusion pressure (-40%), coronary blood flow remained unchanged, while the effective coronary vascular resistance was halved. The coronary reserve, estimated by the hyperaemic response to short periods (10 s) of coronary occlusion was reduced by the stepped increases in isoflurane concentration. Linear relationships were observed between peak hyperaemic flow, volume repayment, repayment: deficit ratio and coronary perfusion pressure. The vasodilation induced by isoflurane was of such magnitude that, at 1.5 MAC, the repayment: deficit ratio was close to unity, indicating that the vasodilatory reserve was almost exhausted.