Instrument for the noninvasive evaluation of human arterial endothelial function via measurement of changes in the transit time of an artificial pulse

Impairment of arterial endothelial function is an early event in atherosclerosis and correlates with the major risk factors for cardiovascular disease. The most widely used noninvasive measure of endothelial function involves the brachial artery (BA) diameter measurement using ultrasound imaging before and after several minutes of blood flow occlusion. The change in arterial diameter is a measure of flow-mediated vasorelaxation (FMVR). The high variability of results and high cost of instrumentation render this technique unsuitable for routine clinical use. We present an instrument we call the "relaxoscope" that is designed to overcome many obstacles that confine noninvasive assessment of FMVR to research settings. The relaxoscope induces an artificial pulse at the superficial radial artery via a linear actuator. An ultrasonic Doppler stethoscope detects this pulse 10-20 cm proximal to the point of pulse induction. The delay between pulse application and detection provides the pulse transit time (PTT). By measuring PTT before and after 5 minutes of BA occlusion and ensuing reactive hyperemia, FMVR may be measured based on the changes in PTT caused by changes in vessel caliber, smooth muscle tone and wall thickness. We compare the results obtained using the relaxoscope with M-mode BA diameter measurements in human subjects.