Measurement of arterial viscoelastic properties using a foil-type pressure sensor and a photoplethysmography

This paper proposes a noninvasive method for estimating the dynamic characteristics of arterial walls using pulse waves measured in various parts of the body by a foil-type pressure sensor (FPS) and a photoplethysmography. The FPS not only has high sensitivity and flexibility but also features the ability to continuously measure the alternating-current component of pulse waves, and was employed to measure pulse waves based on the tonometry approach. Then a method of estimating changes in arterial viscoelastic indices was proposed based on the measured pulse waves and photoplethysmograms. First, in order to measure amplitude variation of the blood pressure wave shape accurately, we examined suitable mechanical forces externally applied to the FPS, and found that values of 5 - 25 [N] yielded the best performance. Next, in order to verify the time characteristics of the pulse waves, the brachial-ankle Pulse Wave Velocity (baPWV) was measured and found that baPWVs measured by the FPS and the noninvasive vascular screening device are quite similar. We then estimated the arterial viscoelastic indices of a radial artery and a dorsal pedis artery when mechanical pain stimuli were applied to the subjects. The results suggested the estimated indices could be used to quantitatively assess vascular response caused by sympathicotonia. We thus concluded the proposed method enabled noninvasive measurement of pulse waves and estimation of viscoelastic indices.