Improved ensemble average approach for systolic blood pressure estimation

Abstract

There are many existing wearable devices which are meant to measure blood pressure and heart rate using the Electrocardiogram (ECG) and Photoplethysmogram (PPG), and can be worn on the wrist or finger. However, the future trend of wearable devices is moving towards head-mounted devices. Pulse wave transit time (PWTT) is used as a non-invasive and cuffless method for blood pressure estimation. Therefore, a question needs to be asked if Systolic Blood Pressure (SBP) can be measured or estimated from ECG and PPG recordings from the head. In this study, ECG signals from the head were first extracted by using improved ensemble averaging approach to compute for the PWTThead with reference to the Photoplethysmogram (PPG) signals from the earlobe. The chest ECG signals (lead II) and fingertip Photoplethysmogram (PPG) signals were simultaneously recorded with the head recordings and earlobe PPG to be used as reference signals to measure the PWTTchest from the chest and to verify the performance of the PWTThead measured from the head. The results obtained were analyzed by using regression plots, Bland-Altman plots and hypothesis test. The mean error ±SD (standard deviation) based on PWTThead for the 7 different recorded positions were from -90° Finger position, Sit Rest position, Stand Rest position, 45° head position, Supine position, 45° finger position and 90° head position. The mean error ±SD for -90° Finger position (2.6364 ± 2.5406 mmHg) and Sit Rest position (2.8182 ± 2.6007 mmHg) were within the ANSI.AAMI SP10:2002 standards for noninvasive blood pressure accuracy (±5[mmHg] mean error, 8[mmHg] standard deviations). Overall, this research has contributed a new ensemble based approach to estimate SBP from the head by extracting head ECG using earlobe PPG.