Correction of change in propagation time delay of pulse wave during flow-mediated dilation in ultrasonic measurement of arterial wall viscoelasticity

Abstract

It is considered that the endothelial dysfunction occurs in the initial step of atherosclerosis. Although assessments of the endothelial function and viscoelastic properties of the intima-media region are important for the diagnosis of early-stage atherosclerosis, regional viscoelasticity has not yet been measured in vivo. Our group has developed an ultrasonic method for measuring the transient change in viscoelasticity during flow-mediated dilation (FMD). However, in this method, the stress (blood pressure) and strain of the intima-media region of the radial artery are measured in different arms, and the change in pulse wave velocity (PWV) due to FMD has not yet been considered. In the present study, we measured blood pressure waveforms using two pressure sensors, which were placed along the same radial artery for the ultrasonic measurement, to obtain blood pressure waveforms and estimate the PWV between the two sensors. Using the measured PWV, the pulse wave propagation time from the pressure sensor to the position of the ultrasound probe was corrected, and viscoelasticity was estimated from the corrected stress-strain relationship. In the basic experiment, we applied the proposed method to a silicone tube phantom and evaluated the accuracy of the estimation of viscoelasticity by comparing the ultrasonic measurement to the results of the tensile test. In the in vivo measurements, the change in the propagation time delay of the pulse wave was also corrected using the two pressure sensors and the stress-strain relationship of the radial arterial wall was then obtained to estimate viscoelasticity. Furthermore, a decrease in elasticity owing to FMD after recirculation was clearly observed, and the unstable temporal variation in viscosity was significantly reduced. These results demonstrated the improvement in the accuracy of the measurement of viscoelasticity by the proposed method.

Blood flow simulation during flow‐mediated dilation

“…Sato et al. measured elasticity modulus of radial artery blood in FMD response, and reported that the elasticity modulus in healthy persons dropped by about 40% against rest state . On the other hand, Young's modulus—corresponding to blood elasticity modulus—estimated with measured data of a healthy person fed back to the model decreases by about 40% as compared to rest state (Figure f).…”

Accurate measurement of elasticity of the radial artery wall considering changes in cross-sectional shape of artery caused by pushing pressure applied by ultrasound probe

“…First, to examine the relationship between the circumferential stress s q and the position x on the arterial cross-section, s q at systole and diastole, and the incremental stress s D q from diastole to systole were obtained for various values of q from  0 to  180 using Eq. (26). Next, to examine the relationship between the circumferential stress s q and the vessel shape, s D q from diastole to systole was obtained for various aspect ratios / a b of the vessel shape from 1 to 3.…”

“…Sakai et al proposed a method for measuring the blood pressure waveform and the strain of the vessel wall at the same position by a correction determined from the delay between the pressure waveforms measured by two pressure sensors, where the ultrasound probe for the strain measurement was placed at the center of the two pressure sensors. 26,27) However, it was difficult to accurately determine the delay between the two pressure waveforms because it depends on the instantaneous pressure of the pressure waveforms.…”

Near Real-time Measurement of Myocardial Contraction and Relaxation Based on High-frame-rate Ultrasound with a Graphical Processing Unit System

“…For the diagnosis of arteriosclerosis, the roughness of the blood vessels has been estimated using a highly accurate method for imaging the surface of a vessel (7)- (9) . Techniques for measuring the elasticity of a blood vessel using echoes from the radial artery have been studied (10)- (12) . For the evaluation of cardiac function, methods for visualization of hemodynamics (13)- (15) and tissue Doppler methods (16)- (18) have been reported.…”