Fundamental Investigation on Contactless and Continuous Blood Pressure Measurement by Impinging Jet Flow and Imaging Photoplethysmography

Due to the recent COVID-19 infection spreading, contactless measurement of vital information has been required at hospitals. On the other hand, as for measurement of continuous blood pressure (BP) 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, we have proposed a novel method by ejecting jet flow and a camera for measuring BP without contact, which can detect continuous BP and its fluctuations. However, it has not been confirmed yet whether the continuous measurement of blood pressure is possible or not in our previous investigations. In this study, to develop this contactless and continuous BP measurement system that uses the deformation of blood vessels, effects of the jet timing and pulse duration on the behaviour of the pulsating elastic tube are investigated. In the experiments, a silicon tube is used to simulate a blood vessel, and the fluid is circulated as a pulsatile flow. The jet flow is ejected from a nozzle to the tube surface, and internal pressure is measured by a pressure sensor. From comparing the internal pressure with displacement of elastic tube surface, it was concluded that 1) it is possible to control jet pressure that does not affect the internal pressure in the tube, 2) it was suggested that the averaged displacement by impinging jet flow follows the averaged internal pressure in the tube at the same time, and 3) internal pressure measurement by short duration time of jet pulses can be applied to continuous BP measurement.