Noninvasive Brachial Artery Mechanics and Endothelial Function

Abstract

It has been recognized that endothelial dysfunction is an early indication of Arterial disease. Endothelial function can be noninvasively evaluated by Inducing a temporary increase in blood flow and then observing the degree of vasodilation response or flow-mediated dilation. Impaired flow mediated vasodilation is then an indication of impaired endothelium. Vascular ultrasound Imaging has been the typical approach to access vasodilation by flow-mediated dilation most often at the brachial artery. Together with other measures of cardiovascular risk, the flow-mediated dilation response provides a very early noninvasive screen for cardiovascular disease. The skill and equipment required for brachial artery ultrasound imaging have limited the use of flow-mediated dilation as a routine medical test. Moreover, it has been recognized that other vascular parameters such as vessel size and blood pressure may influence the test itself. We have introduced a potential solution to the routine measurement of flow-mediated dilation by Analyzing the response of a simple occlusive arm cuff to obtain the Brachial Artery diameter in a noninvasive way. The analysis for occlusive cuff Plethysmography was provided here in a calibrated manner. This approach is an alternative to ultrasound flow-mediated dilation testing. It requires no special operator skills and may be automated for precision. Two experimental evaluations of the proposed cuff method are provided. First, The cuff- based brachial diameters were compared to Ultrasound obtained diameters. Second, as a sensitivity test, the cuff-based dilation test was used to measure the dilation response of several subjects to blood sugar loading. For further evaluation, the cuff-based measurements were applied to a mechanical model of the brachial artery to reveal a standard error of estimate less than 5%. The results show that the cuff-based diameters compare well to those obtained via ultrasound imaging. Moreover, the cuff-based dilation testing showed the expected reduction in endothelial function response due to a blood sugar load. Additionally, cuff-based flow-mediated dilation testing provides measurements as a function of the subject blood pressure, which Ultrasound generally cannot.