Changes in arterial function and structure are thought to precede measurable atherosclerosis and may be the earliest markers for disease potential. Among the most promising are measures of vascular stiffness and endothelial function.
Endothelial Function (EF) is assessed by measuring vessel relaxation in response to a shear stress. Active vessel relaxation or dilation is measured by high-resolution ultrasound, with the medial-adventitial interfaces as the basis of the measurement.
A blood pressure cuff is placed below the antecubital fossa on the right arm. Using high resolution B-mode ultrasound the participant is connected to a EKG monitor while the sonographer locates a 1 cm segment of the brachial artery above the antecubital fossa maximizing the intima, media and advential interfaces. Using the Brachial Analysis System, BAS, (MIA, University of Iowa), digitized images of the brachial artery are captured on the R wave for 20 seconds. The arm cuff is then inflated 50 mmHg above the systolic pressure for 4 minutes and then deflated. Immediately after deflation, images are digitized on the R wave for 3 minutes. (Images at or within 30 msec of the peak R wave are just prior to mechanical systole and thus at “end diastole”.) One centimeter of the media-adventitial interfaces are marked and measured pre- and post stress. The measures of interest are the maximum dilatation, the percent change from baseline and the time to peak.