Flow-mediated change in viscoelasticity of radial artery noninvasively measured by 22-MHz ultrasound

The endothelial dysfunction is considered to be an initial step of atherosclerosis. Additionally, it was reported that the smooth muscle, which constructs the media of the artery, changes its characteristics due to early-stage atherosclerosis. Therefore, it is essential to develop a method for assessing endothelial function and mechanical property of arterial wall. There is a technique to measure the transient change in diameter of the brachial artery caused by flow-mediated dilation (FMD) after release of avascularization. For more sensitive and regional evaluation, we developed a method to measure the change in elasticity of the radial artery due to FMD. In this study, the transient change in the mechanical property of the arterial wall was further revealed by measuring the stress-strain relationship during each heartbeat. The minute change in thickness (strain) of the radial arterial wall during a cardiac cycle was measured using the phased tracking method. At the same time, the waveform of blood pressure at the radial artery was continuously measured with a sphygmometer. Transient change due to FMD in the stressstrain relationship during a cardiac cycle was obtained from the measured strain and blood pressure to show instantaneous viscoelasticity. From the stress-strain relationship, we estimated the viscoelasticity by using least-squire method. In this study, the repeated in vivo measurement for 10 minutes shows the deviation of this method. The temporal decrease of static elasticity after recirculation due to FMD is much larger than maximum difference from the mean. These results show a potential of the proposed method for thorough analysis of the transient change of viscoelasticity due to FMD.