A chest-based continuous cuffless blood pressure method: Estimation and evaluation using multiple body sensors

Blood pressure (BP) is a critical vital sign in health, measured millions of times per day worldwide. Current BP measurement requires cumbersome tools, is painful and can be inconvenient. Non-invasive cuffless BP measurement based on pulse arrival time (PAT) techniques allow an alternative way of monitoring BP in healthcare settings with refined wearability and user-friendly features. PAT extraction requires at least two measurements, one as a time reference and another to obtain time delay; there are several approaches to calculate the PAT from various sensors placed on the body. Commonly used signals are electrocardiography (ECG) and photoplethysmography (PPG), which can be recorded from a patients body using more than two separate sensors attachment set-ups. In this work, cuffless BP calculation based on five different PAT readings using Bio-impedance (BImp) at the shoulder as an alternative to PPG, has been investigated. Sensor placement is on the patients chest; which hides them beneath the patient's clothes making them more suitable for ambulatory monitoring systems. Technology performance was assessed using different postures, exercises and Glyceryl Trinitrate (GTN) spray doses; which provided stable, rising and falling BPs for evaluation. Data were collected from 41 participants who were sitting, standing and supine. Twenty-four of 41 participants undertook experiments including a handgrip task (isometric exercise), three periods of cycling on an exercise bike with light, moderate and heavy resistance settings and an observed rest period at the end. The remaining 17 of 41 subjects received GTN spray for predefined times with variable recovery periods afterwards. Different methods of PAT extraction from BImp data were compared for accuracy. Comparisons were made between PAT readings alone and PAT combined with Heart Rate and the combination model performed better when calculating BP. Simultaneously, data were collected using PPG-based PATs compared to BImp-based PATs. BImp-based PATs proved 3% more accurate than PPG-based PATs, demonstrating the potential superiority of BImp-based BP calculations.