Photoplethysmography and ultrasonic-measurement-integrated simulation to clarify the relation between two-dimensional unsteady blood flow field and forward and backward waves in a carotid artery.

Understanding the spatiotemporal change in hemodynamics is essential for the basic research of atherosclerosis. The objective of this study was to establish a methodology to clarify the relation between a two-dimensional (2D) unsteady blood flow field and forward and backward propagating waves in a carotid artery. This study utilized photoplethysmography (PPG) for blood pressure measurement and two-dimensional ultrasonic-measurement-integrated (2D-UMI) simulation for flow field analysis. The validity of the methodology was confirmed in an experiment for a carotid artery of a healthy volunteer. Synchronization between the pressure measurement and flow field analysis was achieved with an error of <10 ms. A 2D unsteady blood flow field in the carotid artery was characterized in relation to forward and backward waves. 2D-UMI simulation reproduced the flow field in which the wall shear stress takes a maximum at the time of the backward wave superiority in the systolic phase, whereas 2D ordinary simulation failed to reproduce this feature because of poor reproducibility of velocity distribution. In conclusion, the proposed methodology using PPG and 2D-UMI simulation was shown to be a potential tool to clarify the relation between 2D unsteady blood flow field and the forward and backward waves in a carotid artery.