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.
Highlights
Several BP monitoring devices have been proposed, based on Pulse Arrival Time (PAT), Pulse Transit Time (PTT) and Pulse Wave Velocity (PWV)
The proposed method in this study investigates continuous BP estimation based on PTT measurements for the first time using on-body radar sensors on the chest and PPG signals from the ear
By positioning the Continuous wave radar (CWR) sensor on the sternum and evaluating its signal, pre-ejection periods (PEP) is measured as the difference between the foot of CWR signal and ECG R-peak
Summary
Several BP monitoring devices have been proposed, based on Pulse Arrival Time (PAT), Pulse Transit Time (PTT) and Pulse Wave Velocity (PWV) These all use different devices and data analysis methods. The PEP is measured using pulsed doppler echocardiography (ECHO)[36] Another technique is to measure the time between the B-point of the impedance cardiogram (ICG) (aortic valve opening) and the start of the Q-wave of the ECG37. The accuracy of the two techniques ( with respect to detecting aortic valve opening) has been compared using ECHO over the ascending aorta with subjects in either a supine position, or lying with their head up at 60 degrees[36], showing that ECHO calculated a non-significantly lower PEP than ICG. When the CWR antenna is placed on the sternum, the foot of the CWR signal, compared to the ICG B-point, is validated to correspond to the opening of the aortic valve[38,39,40]
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