Pyke KE, Green DJ, Weisbrod C, Best M, Dembo L, O'Driscoll G, Tschakovsky ME
Nitric oxide is not obligatory for radial artery flow-mediated dilation following release of 5 or 10 min distal occlusion. [JOURNAL ARTICLE]
Am J Physiol Heart Circ Physiol 2009 Oct 30.
This study investigated the NO dependence of radial artery (RA) flow-mediated dilation (FMD) in response to 3 different reactive hyperemia (RH) shear stimulus profiles. Ten healthy males underwent 3 RH trials 1) 5min occlusion (5 trial), 2) 10min occlusion (10 trial), and 3) 10min occlusion with cuff re-inflation at 30s (10-30 trial). Trials were performed during saline infusion and repeated during L-NMMA infusion into the brachial artery. RA blood flow velocity was measured with Doppler ultrasound and B-mode RA images were analyzed using automated edge detection software. Shear rate estimation of shear stress, was calculated as the blood flow velocity/vessel diameter. L-NMMA decreased baseline vascular conductance by 35%. L-NMMA infusion did not affect the peak shear rate stimulus (P=0.681) or the area under the curve (AUC) of shear rate to peak FMD (P=0.088). The AUC was significantly larger in the 10 trial vs. the 10-30 or 5 trial (P<0.001). Although %FMD (% change in diameter) in the 10 trial was larger than that in the 5 trial (P=0.035), there was no significant difference in %FMD between the saline and L-NMMA conditions in any trial: 5 trial: 5.62 +/-1.48% vs 5.63 +/-1.27%; 10 trial: 9.07 +/-1.16% vs 11.22 +/-2.21%; 10-30 trial: 6.52 +/-1.43% vs. 7.98 +/-1.51 for saline and L-NMMA, respectively (P=0.158). We conclude the following: 1) RH following 10min of occlusion results in an enhanced stimulus and %FMD compared to 5min of occlusion. 2) When the occlusion cuff is re-inflated 30s post release of a 10min occlusion it does not result in an enhanced %FMD compared to that which results from RH following 5min of occlusion. 3) The lack of effect of L-NMMA on FMD suggests that NO may not be obligatory for radial artery FMD in response to either 5 or 10 min of occlusion in healthy volunteers. Key words: nitric oxide, endothelium, shear stress, flow mediated dilation.
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