Endothelium-derived nitric oxide enhances the effect of intraaortic balloon pumping on diastolic coronary flow.

BACKGROUND: High shear rate with pulsation is one of the major stimuli for the release of endothelium-derived nitric oxide leading to coronary arteriolar dilation. Intraaortic balloon pumping mechanically enhances shear rate and diastolic-to-systolic flow oscillation. We aimed to evaluate whether or not coronary blood flow augmentation during intraaortic balloon pumping is mediated by coronary arteriolar dilation through endothelium-derived nitric oxide release. METHODS: Using a charge-coupled device intravital videomicroscope, we observed epicardial coronary arterioles (40 to 220 microm in diameter) in anesthetized open-chest dogs (n = 10) during 2:1 mode of intraaortic balloon pumping. Endothelium-derived nitric oxide-mediated vasodilatory effects of intraaortic balloon pumping were evaluated by comparing end-diastolic arteriolar diameters between the coupled beats of on and off intraaortic balloon pumping before and after intracoronary endothelium-derived nitric oxide synthesis inhibition with Nomega-nitro-L-arginine (L-NNA, 2 micromol/min) administration. RESULTS: Intraaortic balloon pumping increased coronary arteriolar diameters and coronary blood flow by 11.4%+/-1.8% (p < 0.0001) and 33.4%+/-4.1% (p < 0.001), respectively. Vasodilation was greater in small arterioles (<110 microm; 15.4%+/-2.2%) than in large arterioles (> or =110 microm; 4.2%+/-1.2%, p < 0.0001). L-NNA attenuated the intraaortic balloon pumping-induced vasodilation and augmentation of coronary blood flow to 4.6%+/-1.0% (p < 0.001) and to 20.8%+/-2.1%, (p < 0.05), respectively. Attenuation of vasodilatory effect by L-NNA was observed mainly in small arterioles (from 15.4%+/-2.2% to 5.9%+/-1.2%). CONCLUSIONS: Intraaortic balloon pumping augmented coronary blood flow by dilating coronary arterioles in diastole, more significantly in small arterioles than in large arterioles. Endothelium-derived nitric oxide inhibition markedly attenuated these effects. We conclude that, in a canine model, endothelium-derived nitric oxide contributes to mechanical enhancement of the coronary blood flow with diastolic arteriolar vasodilation during intraaortic balloon pumping.