Blood pressure measurement using piezoelectric effect by an ultrasonic probe

An ultrasonic method to measure the changes in radial arterial diameter and blood pressure in a noninvasive manner was proposed to estimate viscoelastic characteristics of the arterial wall to diagnose vascular endothelial dysfunction at an extremely early stage. In the present study, a measurement method of blood pressure using the piezoelectric effect of the ultrasonic probe was investigated. At first, blood pressure waveform measured by the piezoelectric element was discussed using piezoelectric constitutive equations. We confirmed that the blood pressure waveform can be obtained by integrating the waveform measured by the piezoelectric element. Then, a conventional ultrasonic probe was modified to measure a blood pressure waveform and the measurement is demonstrated. Changes in the radial diameter was also measured using an ultrasonic diagnosis equipment with a conventional linear ultrasonic probe. The measured voltage by the piezoelectric element was of the same order as the result estimated from the theoretical consideration with typical material constants of the piezoelectric element. The diameter expanded with an increase in blood pressure and then gradually returned due to the decrease in blood pressure with viscosity. From the relationship between the arterial diameter and blood pressure, the hysteresis characteristic of the artery wall during one heartbeat was confirmed.