Wearable Blood Pressure Monitoring using Bioimpedance and Pulse Transit Time Methods

Abstract

Noninvasive, cuffless, and continuous blood pressure (BP) monitoring is essential to prevent and control hypertension. A well-known existing method for this measurement is pulse transit time (PTT). However, it is bulky and inconvenient by contemporary standards. To find a more sensitive method to be used in a BP measurement device, this study studied electrical bioimpedance measurement as a potential indicator for BP determination. First, only one electrical bioimpedance channel is used to estimation BP. The experiment was evaluated on eight healthy subjects with the ambulatory BP monitor on the upper arm as a reference. The results demonstrated the potential of the proposed method by the correlation of estimated systolic (SBP) and diastolic (DBP) BP against the reference at 0.84 ± 0.05 and 0.83 ± 0.05, respectively. The proposed system also tracked the DBP well with a root-mean-squared-error (RMSE) of 7.5 ± 1.35 mmHg. Second, electrical bioimpedance method is combined with PTT method to estimated blood pressure more accurate. The IPG sensor, then, was performed at the wrist while photoplethysmography (PPG) sensor was located at index finger in measuring PTT. With cuff BP reference at the upper arm, the proposed model was validated on 15 subjects and compared to the most cited conventional PTT models to evaluate the efficacy. The proposed model correlated with BP fairly well with the group average correlation coefficients was 0.88 ± 0.07 for SBP and 0.88 ± 0.06 for DBP. In comparison with the other PTT methods, PTT-IPG-based BP estimation achieved lower RMSE of 8.47 ± 0.91 mmHg for SBP and 5.02 ± 0.73 mmHg for DBP. We conclude that using bioimpedance and PTT methods is a promising approach toward a ubiquitous cuffless BP device.