Contact pressure-guided wearable dual-channel bioimpedance device for continuous hemodynamic monitoring

Abstract

Wearable devices for continuous monitoring of arterial pulse waves have the potential to improve the diagnosis, prognosis, and management of cardiovascular diseases. These pulse wave signals are often affected by the contact pressure between the wearable device and the skin, limiting the accuracy and reliability of hemodynamic parameter quantification. Here, we report a continuous hemodynamic monitoring device that enables the simultaneous recording of dual-channel bioimpedance and quantification of pulse wave velocity (PWV) used to calculate blood pressure (BP). Our investigations demonstrate the effect of contact pressure on bioimpedance and PWV. The pulsatile bioimpedance magnitude reached its maximum when the contact pressure approximated the mean arterial pressure of the subject. We employed PWV to continuously quantify BP while maintaining comfortable contact pressure for prolonged wear. The mean absolute error and standard deviation of the error compared to the reference value were determined to be 0.1 ± 3.3 mmHg for systolic BP, 1.3 ± 3.7 mmHg for diastolic BP, and -0.4 ± 3.0 mmHg for mean arterial pressure when measurements were conducted in the lying down position. This research demonstrates the potential of wearable dual-bioimpedance sensors with contact pressure guidance for reliable and continuous hemodynamic monitoring.

Keywords: contact pressure; cuffless blood pressure; hemodynamic monitoring; pulse wave velocity; wearable bioimpedance sensors.

Figure 1.

Design of contact pressure-guided continuous BP monitoring device. (a) Schematic illustration of 2-channel bioimpedance measurements along a radial artery from the wrist. Examples of the pulse transit time (PTT) calculation from (b) 2-channel bioimpedance signals and (c) derived first-time derivative of the bioimpedance. (d) Illustration of the arterial blood volume change with increasing contact pressure, quantifiable by the pressure sensor. (e) Optical image of the wearable device with two pressure sensors quantifying the contact pressure in real time. (f) Optical images of add-on electrodes from different views. (g) Optical images of a printed circuit board with six gold-plated copper pads before and after placing add-on electrodes.

Figure 2.

Bioimpedance measurements with varying current injection frequencies. (a) Ch. 1 and (b) Ch. 2 bioimpedance signals obtained with varying current injection frequencies, and corresponding (c) Ch. 1 and (d) Ch. 2 derived dZ/dt.

Figure 3.

Effect of contact pressure on bioZ signals and dZ/dt. (a) Ch. 1 and (b) Ch. 2 bioimpedance signals obtained at varying contact pressures, and corresponding (c) Ch. 1 and (d) Ch. 2 derived dZ/dt.

Figure 4.

Effect of contact pressure on pulse wave velocity (PWV). (a) Ch. 1 and (b) Ch. 2 bioimpedance signals obtained with a contact pressure of 4.9 kPa, and corresponding (c) Ch. 1 and (d) Ch. 2 derived dZ/dt. The PWV values quantified at different contact pressures while (e) sitting and (f) lying down.

Figure 5.

Bioimpedance changes induced by leg lifting exercises. (a) Ch. 1 and (b) Ch. 2 bioimpedance signals obtained during vertical leg lifts exercise (E) and rest (R) while lying down, and corresponding (c) Ch. 1 and (d) Ch. 2 derived dZ/dt.

Figure 6.

PWV and BP changes induced by leg lifting exercises. (a) PWV, (b) diastolic blood pressure (DBP), (c) systolic blood pressure (SBP), and (d) mean arterial pressure (MAP) changes during vertical leg lifts exercise (E) and rest (R) while lying down.

Figure 7.

Continuous BP quantification using PWV. Linear correlations between (a) DBP and PWV, (b) SBP and PWV, and (c) MAP and PWV. Comparison between (d) reference DBP and bioimpedance quantified DBP, (e) reference SBP and bioimpedance quantified SBP, and (f) reference MAP and bioimpedance quantified MAP. Error estimation of continuously quantified (g) DBP, (h) SBP, and (i) MAP.