Neckband-Based Continuous Blood Pressure Monitoring Device With Offset-Tolerant ROIC

Abstract

This study presents a wearable neckband device for continuous cuffless blood pressure (BP) monitoring, where reliable neck-based BP measurement is achieved by utilizing the electrocardiogram (ECG) and impedance plethysmogram (IPG). Optimal composition and position of sensing electrodes around the neck were decided with consideration for physiological characteristics of the human body, and the core parameter of IPG magnitude was experimentally selected to improve the BP estimation accuracy. For its small-featured noises-tolerant detection capability, a customized readout integrated circuit (ROIC) was developed, which includes two kinds of analog front-ends (AFEs) for biopotential and bio-impedance. Both AFEs are proposed to include an attenuator-assisted hybrid DC-servo loop (DSL) structure, achieving precise pulse transit time (PTT) calculation by lowering the high-pass filtering cutoff frequency and also stable signal acquisition by widening the offset-cancellation range. Real-time PTT monitoring and BP estimation are wirelessly conducted, and its continuous operation time with 350-mAh battery capacity is longer than 5 hours. Efficacy of the proposed neckband BP device was evaluated for 8 healthy subjects under the physical stress condition, where the mean correlation coefficient and the standard deviation were achieved as 0.8508 and 4.17mmHg respectively.INDEX TERMS Neckband device, pulse transit time, continuous blood pressure monitoring, impedance plethysmogram, readout integrated circuit.

Emerging sensing and modeling technologies for wearable and cuffless blood pressure monitoring

“…Electrodes for ECG can also be used for bioimpedance monitoring, such as IPG monitoring 44 . IPG, also known as bioimpedance plethysmography (BPG) 45 , can provide useful features for BP calculation algorithms 46 , 47 .…”

“…For instance, impedance cardiogram (ICG), a special IPG waveform that measures the thoracic electrical bioimpedance, is often used to calculate the pre-ejection period. In bioimpedance monitoring, two pairs of electrodes are required: one for AC current injection (some methods use a short current pulse 47 ) and the other for voltage difference sensing 44 . In IPG, the electrode placement is flexible; that is, the electrode pairs need not cross the heart as ECG electrodes do.…”

“…In IPG, the electrode placement is flexible; that is, the electrode pairs need not cross the heart as ECG electrodes do. For example, IPG electrodes can be placed on the neck 44 , wrist 48 , 49 , arm 7 , leg 50 , feet 51 , or on multiple body sites 45 .…”

“…Noise reduction is an indispensable component for wearable cuffless BP monitoring systems. The most broadly used denoising tool is filter, which has been typically applied to suppress the noise of a certain frequency range in TAG 75 , ECG 40 , 78 , 79 , IPG 7 , 44 , 49 , PPG 13 , 75 , ultrasound 76 , 80 , and BCG 72 , 81 signals. While filtering can serve as a universal tool for almost all types of sensing modalities, there have also been signal-specific denoise methods developed to improve the noise removal efficiency and accuracy.…”

“…It is worth noting that BP can also be estimated using IPG-ECG 51 , IPG-PPG 49 , 97 , IPG-IPG 8 (including IPG + ICG 45 ) combinations, or even single-channel IPG 48 . Several studies have evaluated the performance of PTT-based BP estimates using IPG + ECG and PPG + ECG and reported that the former is superior to the latter in a manner 7 , 44 .…”