Influence of alternate sources of blood flow on the reactive hyperemia response in aorta-coronary saphenous vein bypass grafts in man

Reactive hyperemia responses (RHR) of various magnitudes were obtained after release of a brief occlusion in six of 10 coronary bypass grafts. All of the vein grafts responded to an injection of sodium nitroprusside (50 microgram) directly into the open graft with an increase in blood flow that was always greater than the flow recorded after release of the occlusion. This response indicates that there were no flow-limiting stenoses and that the distal vascular beds were responsive to vasodilator stimuli. RHR's, expressed as percent repayment of calculated flow debt, were correlated significantly (r = 0.96, p less than 0.01) with the magnitude of the decrease in vein graft pressure measured during occlusion of the graft. It is suggested that the decrease in pressure is related to the amount of blood flow from alternate sources to the vascular bed during occlusion of the graft, and that this collateral flow is an important determinant of the magnitude of RHR in bypass grafts.