Blood Pressure Estimation Using On-body Continuous Wave Radar and Photoplethysmogram in Various Posture and Exercise Conditions

Abstract

The pulse arrival time (PAT), pre-ejection period (PEP) and pulse transit time (PTT) are calculated using on-body continuous wave radar (CWR), Photoplethysmogram (PPG) and Electrocardiogram (ECG) sensors for wearable continuous systolic blood pressure (SBP) measurements. The CWR and PPG sensors are placed on the sternum and left earlobe respectively. This paper presents a signal processing method based on wavelet transform and adaptive filtering to remove noise from CWR signals. Experimental data are collected from 43 subjects in various static postures and 26 subjects doing 6 different exercise tasks. Two mathematical models are used to calculate SBPs from PTTs/PATs. For 38 subjects participating in posture tasks, the best cumulative error percentage (CEP) is 92.28% and for 21 subjects participating in exercise tasks, the best CEP is 82.61%. The results show the proposed method is promising in estimating SBP using PTT. Additionally, removing PEP from PAT leads to improving results by around 9%. The CWR sensors present a low-power, continuous and potentially wearable system with minimal body contact to monitor aortic valve mechanical activities directly. Results of this study, of wearable radar sensors, demonstrate the potential superiority of CWR-based PEP extraction for various medical monitoring applications, including BP measurement.

Clinical study of a chest‐based cuffless blood pressure monitoring system

“…The heart rate frequency (HRF) is extracted from each person's PPG signal, and its value is used to choose the cut-off frequencies of the filter as follows: To remove the remaining noise from the CWR signal, an algorithm is applied based on wavelet transform and adaptive filtering which has been explained in detail in a previous publication (Ebrahim et al, 2019). The algorithm is also useful to avoid the loss of timing information from the CWR signal caused by the displacement of the signal's foot.…”

“…The PAT 2 is chosen as the time difference between the ECG R-peak t p and the rising slope of the BImp/PPG signal t r , Equation (13). Besides, the PEP is calculated as the time difference between the ECG R-peak t p and the foot of the CWR signal t f , Equation 14, (Ebrahim et al, 2019).…”

“…The corresponding beat-to-beat PTTs are also derived from the ECG, CWR, BImp and PPG signals. Using predefined minimum and maximum thresholds (Ebrahim et al, 2019;Heydari et al, 2020)…”

“…The typical method used to calculate the PEP is by a pulsed Doppler echocardiography (ECHO) over the ascending aorta (Ebrahim et al., 2019). Another method is to calculate the time between the B‐point of the impedance cardiogram (ICG) and the Q‐wave of the ECG (Buxi, Dugar, Redouté, & Yuce, 2017).…”

Signal Separation Using a Mathematical Model of Physiological Signals for the Measurement of Heart Pulse Wave Propagation With Array Radar

“…Buxi et al [2]- [4] attached a 1-GHz continuous wave (CW) radar antenna to the neck/chest and also attached an impedance cardiography sensor on the waist/shoulders to measure the PTT from the time difference between the signals. Ebrahim et al [5], [6] attached a 900-MHz CW radar antenna to the chest, and also attached a photoelectric plethysmography (PPG) sensor to the ear; they measured the PTT from the rise time difference between the radar and PPG signals. Kuwahara et al [7] measured PTT and PWV from the peak time difference between the 2.4-GHz CW radar and a piezoelectric pulse wave sensor attached to the finger.…”