Flow-mediated brachial artery vasoactivity has been recently proposed as a noninvasive means for assessing endotheial function. This endothelial function is impaired in certain cardiovascular conditions, including essential hypertension.

The study population included 50 healthy subjects aged 22 to 62 years (mean±SD, 42±12 years), all normotensive, nondiabetic with cholesterol level <220 mg/dL and no family history of premature vascular disease. Normal subjects were classified according to age into those younger than and those older than 40 years. Using high-resolution ultrasound, brachial artery diameter and flow were measured at rest, during reactive hyperemia (with flow increase causing flow-mediated dilation [FMD], which depends on normal endothelial function), and after sublingual nitroglycerin, an endothelium-independent vasodilation. To better characterize this technique, this study was an attempt to assess the flow-mediated vasodilation in two separate protocols (as follows); (1) the stimulus response to various duration of occlusion (using 1 and 5 min), and (2) the stimulus response to various pressure of occlusion (using low and high pressure). In 28 patients (mean±SD, 52±7 years) with essential hypertension, this study was additionally evaluated endothelial function. The measurements have been compared with those of 14 healthy control subjects. In all subjects, the intima-media thickness (IMT) of the common carotid artery was also measured. This study sought to 1) determine whether endothelial dysfunction was presented in patients with essential hypertension, and 2) examine IMT in these patients.

1) Both in the younger and the older groups, the basal diameter and flow of the brachial artery were significantly increased in men than women. The values were 4.4±0.1 mm and 186±16 ml/min in men and 3.6±0.09 mm and 125±13 ml/min in women (p<0.001; p<0.01). In subjects younger than 40 years, flow-mediated dilation (FMD) and the difference in flow response were similar between men and women. But, in subjects older than 40 years, FMD was decreased in men than women (6.6±1.6 vs. 14.7±1.6%. p<0.01) and the difference in flow response was also decreased in men than women (217±24.3 vs. 314±40.5%, p<0.05). In younger and older groups, there were no significant change in the nitroglyserin response in either gender. 2) Fifteen normal subjects underwent sequential evaluation following 1 and 5 min of upper arm blood pressure cuff occlusion. There were substantial increase in brachial artery diameter and flow immediately after release of 1 and 5 min of occlusion. The FMD and the difference in flow response following release of occlusion between 5 min duration (11.5±1.9%, 253±36%) and 1 min duration (6.6±1.2%, 53±11%) were statistically significant (p<0.05; p<0.001). But, the percent change of diameter following release of occlusion between 5 and 1 min was not statistically significant (p<0.05). 3) Fourteen normal subjects was evaluated the effects of various pressure on endothelial cell function. Inflation pressure was maintained at 30 mm Hg higher than systolic pressure for 5 min and 200 mm Hg (70-90 mm Hg higher than systolic pressure) for 5 min in a random fashion, and then the cuff was suddenly deflated. The diameter and flow response following release of occlusion between high and low pressure were not statistical significance (p>0.05). 4) Flow-mediated dilatation was significantly lower in patients with essential hypertension than in normotensive control subjects (4.2±0.8 vs. 7.3±1.3 %, p<0.05). Intima-media thickness was significantly higher in patients with hypertension than in normotensive control subjects (0.82±0.04 vs. 0.64±0.04 mm, p<0.05). Nitroglycerin-mediated vasodilation (9.5±1.4 %) in patients with essential hypertension did not differ significantly from those in normotensive control subjects (10.0±2.6%, p>0.05).

The study demonstrated that 1) in men older than 40 years, flow-mediated, endothelium-dependent vasodilation of the brachial artery was declined, 2) longer brachial artery occlusion resulted in more vasodilation despite similar hyperemic responses, 3) using low (30 mm Hg higher than systolic pressure) and high (70-90 mm Hg higher than systolic pressure) pressure, each pressure of occlusion was similar hyperemic response, and 4) in patients with essential hypertension, flow-medeiated vasodilation was significantly impaired and IMT was increased than in normotensive control subjects.