Observation of Deformation Process of Elastic Tubes for Pulsatile Flows by Impinging Jet Flows and Its Application to Novel Measurement Method of Blood Pressure

Abstract

Recently, due to the spreading of COVID-19 infection, non-contact measurement of vital information has been required at hospitals. Conversely, as for the measurement of continuous blood pressure and its fluctuations, it has been more important to find a high risk of diseases earlier. Although most of them are obtained by a mechanical contact sensor based on principle of tonometry, the method cannot be applied to non-contact measurement. In this research, a novel method composed of a jet flow and a camera for measuring blood pressure without contact is proposed, and continuous blood pressure and its fluctuations can be detected by this method. In this paper, to develop this novel method, a blood arterial is simulated as an elastic tube, and the deformation process of the elastic tube is observed under pulsatile flow, and the relationship between the deformation process and blood pressure will be obtained. In the experiments, a silicone tube is used to simulate a blood vessel, and the fluid is circulated by a roller pump to create a pulsatile flow. The jet flow is targeted to the tube surface from a nozzle from 0 to 0.37 MPa, and internal pressure in the tube is measured by a pressure sensor. As a result, the displacement and the internal pressure of the tube increased rapidly when a jet flow of a certain pressure was targeted to the tube surface. In addition, it was confirmed that a gradient of cross-sectional area of the tube with the jet pressure reached to inflection point when the internal pressure increased rapidly. Therefore, there is a possibility that jet pressure applicable to blood pressure measurement can be estimated from the gradient change of the cross-sectional area.