A Power-Efficient Sensing Approach for Pulse Wave Palpation-Based Heart Rate Measurement.

Gabriel Bravo,Ernesto Sifuentes,Francisco J Enríquez,Erwin A Martínez,Jesús M Silva,Salvador A Noriega

doi:10.3390/s21227549

Gabriel Bravo, Ernesto Sifuentes + Show 4 more

Open Access

https://doi.org/10.3390/s21227549

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Abstract

Heart rate (HR) is an essential indicator of health in the human body. It measures the number of times per minute that the heart contracts or beats. An irregular heartbeat can signify a severe health condition, so monitoring heart rate periodically can help prevent heart complications. This paper presents a novel wearable sensing approach for remote HR measurement by a compact resistance-to-microcontroller interface circuit. A heartbeat’s signal can be detected by a Force Sensing Resistor (FSR) attached to the body near large arteries (such as the carotid or radial), which expand their area each time the heart expels blood to the body. Depending on how the sensor interfaces with the subject, the FSR changes its electrical resistance every time a pulse is detected. By placing the FSR in a direct interface circuit, those resistance variations can be measured directly by a microcontroller without using either analog processing stages or an analog-to-digital converter. In this kind of interface, the self-heating of the sensor is avoided, since the FSR does not require any voltage or bias current. The proposed system has a sampling rate of 50 Sa/s, and an effective resolution of 10 bits (200 mΩ), enough for obtaining well-shaped cardiac signals and heart rate estimations in real time by the microcontroller. With this approach, the implementation of wearable systems in health monitoring applications is more feasible.

Highlights

Health monitoring parameters measured by noninvasive sensing methods have been the object of study over the past decades [1]
The integration of the Internet of Things (IoT) into healthcare has led to intelligent applications such as remote healthcare and intelligent healthcare monitoring systems
Force Sensing Resistor (FSR) are based on piezoresistive sensing technology, which has the advantage of providing an observable resistance change induced by minimal stresses

Summary

Introduction

Health monitoring parameters (such as heart and respiration rate) measured by noninvasive sensing methods have been the object of study over the past decades [1]. Electromechanical Film (EMFi) and piezoelectric sensors were used; nowadays, Force-Sensing Resistors (FSRs) are preferred because of the simplicity of the interface circuits used to convert the resistance changes into output voltage or current [3]. A simplified circuit to interface resistive sensors has been proposed and widely analyzed [18–21] This circuit connects the sensors directly to a microcontroller (MCU) without using an analog signal conditioning path or ADC. In this topology, called Direct Interfaced Circuit (DIC), the MCU excites the resistive sensor to obtain a time-modulated signal digitized by a timer embedded into the MCU. HR can be estimated in real time by a simple algorithm implemented in the MCU without any additional digital signal processing With this sensing approach, wearable systems for ubiquitous health telemonitoring are more feasible. The heartbeat’s signal could be transmitted via Wi-Fi to a secured cloud server where any Wi-Fi device could access the report server with proper credential authentication

Direct Interface Circuit

Materials and Method

Conclusions