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 N ω-nitro- l -arginine ( l -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 (