Flow-mediated dilation in human brachial artery after different circulatory occlusion conditions

Abstract

Betik, Andrew C., Victoria B. Luckham, and Richard L. Hughson. Flow-mediated dilation in human brachial artery after different circulatory occlusion conditions. Am J Physiol Heart Circ Physiol 286: H442-H448, 2004. First published August 28, 2003 10.1152/ ajpheart.00314.2003.-Different magnitudes and durations of postocclusion reactive hyperemia were achieved by occluding different volumes of tissue with and without ischemic exercise to test the hypotheses that flow-mediated dilation (FMD) of the brachial artery would depend on the increase in peak flow rate or shear stress and that the position of the occlusion cuff would affect the response. The brachial artery FMD response was observed by high-frequency ultrasound imaging with curve fitting to minimize the effects of random measurement error in eight healthy, young, nonsmoking men. Reactive hyperemia was graded by 5-min occlusion distal to the measurement site at the wrist and the forearm and proximal to the site in the upper arm. Flow was further increased by exercise during occlusion at the wrist and forearm positions. For the two wrist occlusion conditions, flow increased eightfold and FMD was only 1 to 2% (P Ͼ 0.05). After the forearm and upper arm occlusions, blood flow was almost identical but FMD after forearm occlusions was 3.4% (P Ͻ 0.05), whereas it was significantly greater (6.6%, P Ͻ 0.05) and more prolonged after proximal occlusion. Forearm occlusion plus exercise caused a greater and more prolonged increase in blood flow, yet FMD (7.0%) was qualitatively and quantitatively similar to that after proximal occlusion. Overall, the magnitude of FMD was significantly correlated with peak forearm blood flow (r ϭ 0.59, P Ͻ 0.001), peak shear rate (r ϭ 0.49, P Ͻ 0.002), and total 5-min reactive hyperemia (r ϭ 0.52, P Ͻ 0.001). The prolonged FMD after upper arm occlusion suggests that the mechanism for FMD differs with occlusion cuff position.hyperemia; endothelium; shear stress; ischemic exercise; blood flow THE MAGNITUDE OF FLOW-MEDIATED DILATION (FMD) of conduit arteries is a widely used test of endothelial function (7,8,11,29,31,32). Endothelial dysfunction is believed to be an early event in atherogenesis and has been shown to exist in patients with coronary artery disease and other cardiovascular risk factors (7,8,11,32). An increase in vascular shear stress with an increase in blood flow velocity and the subsequent release of nitric oxide (NO) has been identified as the probable mechanism for FMD (10,16,34).Between-laboratory comparisons of the magnitude of FMD are often difficult because of different experimental protocols that might examine different physiological aspects of FMD. Even in healthy volunteers, the range of reported FMD can be from a few percent to 22% (1,3,7,11,16,20,27). The magnitude of FMD appears to be related to many factors, including the method of measurement (e.g., echo wall tracking versus echo Doppler imaging), artery studied (brachial versus radial), site of occlusion (either proximal or distal to the measurement site), ...

Is endothelial function impaired in erectile dysfunction patients?

“…In a study evaluating the FMD in human brachial artery after different circulatory occlusion conditions revealed that the type of occlusion (proximal vs distal) had an effect on FMD. 28 These studies demonstrated that there are important betweenmethod differences in the FMD response of the brachial artery.…”

“…However, some limitations on the measurement of blood flow in human brachial artery have been reported. 14,[26][27][28][29] The magnitude of FMD appears to be related to many factors in addition to artery studied, including the method of measurement (e.g. echo wall tracking vs echo Doppler imaging), site of occlusion (either proximal or distal to the measurement site), duration of occlusion and presence or absence of exercise.…”

The origin of Korotkoff sounds and the accuracy of auscultatory blood pressure measurements

“…Learoyd and Taylor 25 give wall thickness ratio h/r of about 0.15 at low pressures < 50 mmHg, so that the wall thickness would be 0.225 mm or 0.022 cm. Betik et al 26 found in control subjects using ultrasound at normal arterial pressures brachial artery radii averaging 0.22 cm. Iwamoto et al 27 , using ultrasound in adult human subjects with normal blood pressure found brachial artery radius averaging 0.2 cm and wall thickness 0.03 cm.…”

Long-term hyperglycaemia impairs vascular smooth muscle cell function in women with type 1 diabetes mellitus

“…In addition, the subject squeezed a rubber ball in the left hand 20 times between the third and fourth minute of ischaemia in order to augment further post-occlusive hyperaemia. 17 After cuff deflation, velocity data were recorded at 10 and 120 seconds and frozen B-mode images in end-diastole at 45, 75, 105, 150 and 240 seconds. Following 10 minutes' rest, B-mode images were recorded before and five minutes after sublingual administration of 0.4 mg glyceryl trinitrate (GTN).…”