Contactless Vital Signs Monitoring

Contactless Vital Signs Monitoring 150 150 IEEE Pulse
Author(s): Paul H. King

Edited by Wenjin Wang and Xuyu Wang, Academic Press, 2021, ISBN: 9780128222812, xix + 341 pages, $190

This reviewer has had an interest in noncontact monitoring of patients, especially of newborns having a possibility of apneic episodes. This text appeared to be relevant from the title and related advertising material. This text consists of 14 chapters: an introductory chapter, seven chapters dealing with camera-based monitoring, and six chapters that cover wireless sensor-based monitoring. The text was edited by two editors and is the product of some 30 contributors. An overview, by chapter, follows.

Chapter 1, “Human physiology and contactless vital signs monitoring using camera and wireless signals,” briefly gives an overview of the remainder of the text. It lists and discusses first camera-based monitored vital signs, such as those related to the cardiac and respiratory systems, then lists those that can be detected using radar and related technologies. Mention is also made of related items, such as sleep posture and fall monitoring.

Part I of the text, titled “Camera-based vital signs monitoring,” begins with Chapter 2, “Physiological origin of camera-based PPG imaging.” This chapter covers the history of photoplethysmography, specifically through (transmission) pulse oximetry, followed by a discussion of the potential use of green light (reflectance) oximetry using a series of green light illumination and a camera system. Chapter 3, titled “Model-based camera-PPG pulse-rate monitoring in fitness,” gives an overview of a camera-based red/blue/green/near-infrared system that allows a reasonable heart rate estimation (within 5 bpm) of pulse rate in an exercising subject by visualizing a skin patch, such as someone’s cheek during treadmill exercise. Two appendixes elaborate on the mathematics involved. Chapter 4, “Camera-based respiration monitoring,” discusses the use of camera-based motion and color tracking (plethysmography) to estimate respiration data during magnetic resonance imaging. Of possible interest to the readers, the use of a low-resolution (752 × 480 8-bit image camera) led to poor-quality data. Chapter 5, “Camera-based blood oxygen measurement,” overviews the use of white light (diode) camera-based measurements to visualize skin and tissue patches responses to cyanosis, occlusions, and reperfusions. Chapter 6, “Camera-based blood pressure monitoring,” discusses potential uses of camera-based photoplethysmography combined with ballistocardiograph data to estimate blood pressure fluctuations in what appears to be a good review of the state of the art. Chapter 7, “Clinical applications for imaging photoplethysmography,” gives an overview of parameters often monitored in clinical situations, then suggests areas that might, because of the noncontacting nature of photoplethysmography, be augmented by the technique. Chapter 8, “Applications of camera-based physiological measurement beyond health care,” suggests that camera-based techniques might also be of value in such endeavors as telehealth evaluations, driver stress measurement, non-contact burn patient measurements, etc.

Part II of the text is titled “Wireless sensor-based vital signs monitoring” and begins with Chapter 9, “Radar-based vital signs monitoring,” which begins by reiterating the “contactless” nature of the method (as in the entire text), then briefly discussing Doppler versus continuous-wave radar monitoring. Applications discussed are whole body tracking and respiratory (chest wall) tracking to enable tumor motion cancellation during MRI scanning, for example. Chapter 10, “Received power-based vital signs monitoring,” reviews experimental setups designed to track respiration rate and pulse rate from a subject and details some of the equipment used and accuracy of results obtained. Chapter 11, “WiFi CSI-based vital signs monitoring,” reviews the use of Wi-Fi signals to detect respiration signals from one or more individuals. Chapter 12, “RFID-based vital signs monitoring,” details the methodology of using multiple “commercial off-the-shelf” RFID tags to track patient respiration. Chapter 13, “Acoustic-based vital signs monitoring,” details the use of an “active sonar” system where a returned high frequency sound aimed at a subject’s chest is sensed by a smartphone and analyzed for respiration rate. Lastly, Chapter 14, “RF and camera-based vital signs monitoring applications,” briefly reviews some of pros and cons of the topics covered in prior chapters, but also suggests the possibility of emotion detection using a combination of techniques.

In this reviewer’s opinion, this text does a reasonable overview of the material implied by its title, Contactless Vital Signs Monitoring. The text will likely be useful to electrical and BME students interested in the field as it relates to undergraduate instrumentation courses, and to graduate students interested in the development of patient monitoring systems. The text could use a more detailed listing of available equipment for the topics covered, as well as a cost of equipment discussion. One item missing from the text, however, is any discussion of the use of terahertz signal generation and uses, current and potential.

FYI: As of this writing (mid-October), Amazon has announced the (probably December) availability of their “Halo Rise” radar-based sleep classification device aimed at helping customers track and improve their sleep. The technology implied here appears to have been covered in the above text.

—Reviewed by Paul H. King Vanderbilt University