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 μm 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 Nω-nitro- -arginine ( -NNA, 2 μmol/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 μm; 15.4% ± 2.2%) than in large arterioles (≥110 μm; 4.2% ± 1.2%, p< 0.0001). -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 -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.