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.
Highlights
Blood pressure (BP) is a primary vital sign in clinical assessments to clarify cardiovascular conditions, and it is a kind of dynamic physiological index which is closely affected by physical and mental states or activities
The pulse morphology of photoplethysmogram (PPG) has been used to estimate the BP. It extracts correlation parameters such as amplitude [2] and steepness [3] from the PPG, and it provides the BP estimation based on its empirical correlation relationship that is obtained from a lot of experiments in advance
Phase shift occurs on the bio-impedance waveform in the deactivated attenuator condition which causes the incorrect impedance plethysmogram (IPG) peak position, and it was eliminated by activating the attenuator which enables to find an accurate pulse transit time (PTT)
Summary
Blood pressure (BP) is a primary vital sign in clinical assessments to clarify cardiovascular conditions, and it is a kind of dynamic physiological index which is closely affected by physical and mental states or activities. The pulse morphology of photoplethysmogram (PPG) has been used to estimate the BP It extracts correlation parameters such as amplitude [2] and steepness [3] from the PPG, and it provides the BP estimation based on its empirical correlation relationship that is obtained from a lot of experiments in advance. This method is convenient to measure it by utilizing only single PPG device, but there is a difficulty in continuous feature extraction because it is critically vulnerable to noises and motion artifacts. It has been adopted to portable devices such as wrist band, but it is sensitive to misaligned sensing position and body movement, giving long-lasting uncomfortable pressures on the artery [4]
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