Flow-mediated change in viscoelasticity of radial arterial wall measured by 22-MHz ultrasound

The endothelial dysfunction is considered to be an initial step of atherosclerosis. Moreover, 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 the regional endothelial function and mechanical property of the arterial wall. There is an ultrasound-based conventional technique to measure the change in inner diameter of the brachial artery caused by flow-mediated dilation (FMD) after release of avascularization. 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. For this measurement, the minute change in thickness (strain) of the radial artery was measured using the ultrasonic phased tracking method, together with the waveform of blood pressure (stress) which was continuously measured at the radial artery. From in vivo experiments, it was found the slope of the stress-strain hysteresis loop decreased due to FMD and the area, which depends on the ratio of elastic modulus and loss modulus (depends on viscosity), increased. These results show a potential of the proposed method for thorough analysis of the transient change in viscoelasticity due to FMD.