Technical aspects of evaluating brachial artery vasodilatation using high-frequency ultrasound.

Flow-mediated brachial artery vasoactivity has been recently proposed as a noninvasive means for assessing endothelial function. To better characterize this technique, we measured brachial artery diameter and flow using 7.5-MHz ultrasound following 1, 3, and 5 min of upper arm blood pressure cuff occlusion in 19 normal volunteers and 13 patients with coronary artery disease (CAD). Although similar flow increases were observed with each protocol, statistically significant vasodilatation (12.6 +/- 5.7%) was observed in the normals only after 5 min of occlusion. With the use of this protocol, postocclusion blood flow increased 528 +/- 271 and 481 +/- 247% in the normals and CAD patients, respectively (P = NS). More vasodilatation was observed in the normals compared with the CAD patients (11.3 +/- 5.4 vs. 1.6 +/- 5.2%, P < 0.001). Interestingly, vasodilatation persisted for 20 min despite return of blood flow to baseline in 2 min. With the use of lower arm occlusion, arterial diameter was found to decrease 4.4 +/- 3.9% in response to a 85 +/- 7% decrease in flow. We conclude that 1) longer brachial artery occlusion results in more vasodilatation despite similar hyperemic responses, 2) vasodilatation persists substantially beyond hyperemia, and 3) CAD patients have impaired flow-mediated vasodilatation using this noninvasive technique.