The Association among Transient Forearm Ischemia, Reactive Hyperemia, and Brachial Artery Vasodilation

Brachial artery flow-mediated dilation is a well established non-invasive measurement of endothelial function. This technique requires a transient forearm ischemia to generate hyperemia-induced vasodilation. Given that transient ischemia is the stimulus for reactive hyperemia, we can reasonably speculate that alteration in the magnitude of forearm ischemia may result in changes in hyperemia and vasodilation. Manipulation of the duration of forearm occlusion may be an effective approach to evoke distinct magnitudes of proportional ischemia. PURPOSE: To determine the impact of ischemia on hyperemia and subsequent vasodilation. It was hypothesized that greater increments in forearm ischemia would be associated with increases in hyperemia and vasodilation. METHODS: Five apparently healthy adults laid supine with their right arm extended out laterally. A near-infrared spectrometry (NIRS) scanner was placed at the mid-portion of the anterior forearm. An automatic cuff was placed around the forearm proximally from the NIRS scanner. The brachial artery was imaged longitudinally via ultrasound. Three different forearm ischemic conditions (250 mm Hg) were applied in a randomized order: a) 1 min of forearm occlusion (O1), b) 3 min of forearm occlusion (O3), and c) 5 min of forearm occlusion (O5). For each condition, baseline and post-occlusion brachial artery blood velocities and diameters were measured. Forearm oxygen tissue saturation (StO2) was measured at baseline and during the occlusion period. RESULTS: One-way ANOVA demonstrated distinct magnitudes of ischemia among forearm conditions (O1 = 11.61 ± 2.9%; O3 = 31.99 ± 6.3%; O5 = 45.80 ± 8.4% change in StO2; P<0.0001). When combining all three conditions, significant correlations were found between change in StO2 and peak blood velocity (r=0.513; P=0.05), peak blood velocity and change in brachial artery diameter (r=0.720; P=0.002), and changes in StO2 and brachial artery diameter (r=0.732; P=0.002). CONCLUSIONS: Greater increments in forearm ischemia are associated with increases in hyperemia and vasodilation. Further research is warranted to determine whether correcting FMD for magnitude of forearm ischemia generated is necessary for accurate assessment of endothelial function.