Single-Channel Bioimpedance Measurement for Wearable Continuous Blood Pressure Monitoring

Pulse transit time (PTT) sensing technology is rapidly evolving for cuffless continuous blood pressure (BP) monitoring. However, PTT-based BP methods must implement multidevices that could impede wearable applications. This work presents the study and development of a single-channel wrist-worn impedance plethysmography (IPG) system for wearable continuous BP measurement. IPG-based BP mathematical model with two-step calibration was derived for single physiological signal acquisition. The high-resolution IPG measurement was performed by optimized injection current frequency and electrode arrangement in response to obvious impedance difference between systolic BP (SBP) and diastolic BP (DBP) feature points in the IPG waveform, resulting in an impedance difference of 594
$\text{m}\Omega $
. The BP accuracy results within 30 subjects indicated that SBP estimation error was 2.01 ± 1.40 mmHg and 1.83 ± 1.29% in terms of mean absolute error (MAE) and mean absolute percentage error (MAPE), and 2.26 ± 1.43 mmHg and 4.96 ± 3.02% for DBP estimation. The novel system could potentially be implemented as a wearable cardiovascular monitoring device with two-in-one functions (continuous BP and heart rate monitoring) using a single physiological sensor in the future.