2.4. Assessment of brachial artery endothelial function
To evaluate the endothelial function of the brachial artery noninvasively, flow-mediated endothelium-dependent vasodilation was assessed by measuring the brachial artery diameter at baseline and during reactive hyperemia. All patient fasted for at least 8 h and avoided consuming caffeine or smoking cigarettes for 12 h prior to their vascular examination. All vasoactive medications were withheld 8 hours before the scan. Each patient were rested in a supine position for 30 min and remained in a quiet, air-conditioned room, with its temperature kept between 20 and 22 ◦C. All studies were performed using an ultrasound system (Philips EPIQ 7C, Philips Healthcare, Andover, MA, USA) with a broadband linear array transducer with a 3-12 MHz range (Philips L12-3). The brachial artery was viewed longitudinally 5 cm above antecubital fossa and FMD was assessed according to the existing guidelines(10).
When the clearest image of the anterior and posterior intimal interfaces between the lumen and vessel wall was obtained, baseline diameter measurements were taken at the end of the diastole (timed by the peak of R wave on electrocardiogram) for ≥ 3 times. Before starting measurement, cuff was fitted distally to the brachial artery. After baseline measurement, the cuff was inflated to at least 50 mm Hg above systolic pressure to occlude arterial inflow for 5 minutes. The longitudinal image or artery was scanned continuously from 30 s before to 90 seconds after cuff deflation and the maximal diameter of the artery was defined during reactive hyperemia. The basal diameter was defined as the average of all measures collected before inflation, and FMD was calculated as the percentage change in peak vessel diameter from the baseline value following cuff deflation: peak diameter−baseline diameter) / baseline diameter. In present study, according to the results of previous studies, FMD value under 10.0% was accepted as endothelial dysfunction (11,12).