An increase in world population along with a significant aging portion is forcing rapid rises in healthcare costs. The healthcare system is going through a transformation in which continuous monitoring of inhabitants is possible even without hospitalization. The advancement of sensing technologies, embedded systems, wireless communication technologies, nano technologies, and miniaturization makes it possible to develop smart systems to monitor activities of human beings continuously. Wearable sensors detect abnormal and/or unforeseen situations by monitoring physiological parameters along with other symptoms. Therefore, necessary help can be provided in times of dire need. This paper reviews the latest reported systems on activity monitoring of humans based on wearable sensors and issues to be addressed to tackle the challenges.

Wearable Sensors for Human Activity Monitoring: A Review

Photoplethysmography and its application in clinical physiological measurement

Photoplethysmography (PPG) technology has been used to develop small, wearable, pulse rate sensors. These devices, consisting of infrared light-emitting diodes (LEDs) and photodetectors, offer a simple, reliable, low-cost means of monitoring the pulse rate noninvasively. Recent advances in optical technology have facilitated the use of high-intensity green LEDs for PPG, increasing the adoption of this measurement technique. In this review, we briefly present the history of PPG and recent developments in wearable pulse rate sensors with green LEDs. The application of wearable pulse rate monitors is discussed.

Wearable Photoplethysmographic Sensors—Past and Present

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

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Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice.

Wearable Health Devices (WHDs) are increasingly helping people to better monitor their health status both at an activity/fitness level for self-health tracking and at a medical level providing more data to clinicians with a potential for earlier diagnostic and guidance of treatment. The technology revolution in the miniaturization of electronic devices is enabling to design more reliable and adaptable wearables, contributing for a world-wide change in the health monitoring approach. In this paper we review important aspects in the WHDs area, listing the state-of-the-art of wearable vital signs sensing technologies plus their system architectures and specifications. A focus on vital signs acquired by WHDs is made: first a discussion about the most important vital signs for health assessment using WHDs is presented and then for each vital sign a description is made concerning its origin and effect on heath, monitoring needs, acquisition methods and WHDs and recent scientific developments on the area (electrocardiogram, heart rate, blood pressure, respiration rate, blood oxygen saturation, blood glucose, skin perspiration, capnography, body temperature, motion evaluation, cardiac implantable devices and ambient parameters). A general WHDs system architecture is presented based on the state-of-the-art. After a global review of WHDs, we zoom in into cardiovascular WHDs, analysing commercial devices and their applicability versus quality, extending this subject to smart t-shirts for medical purposes. Furthermore we present a resumed evolution of these devices based on the prototypes developed along the years. Finally we discuss likely market trends and future challenges for the emerging WHDs area.

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Wearable Health Devices-Vital Sign Monitoring, Systems and Technologies.

Performance evaluation of green photoplethysmography

This study examined position dependency in photoplethysmography (PPG). For transmitted-light PPG, a sensor is usually attached on a fingertip and transmitted light is monitored. Although simple to use, a fingertip sensor and transmitted-light PPG cannot monitor vital signs during exercise and daily activities because the sensor attachment becomes disturbed. Reflected-light PPG can be applied to any part of the body. However, differences in cutaneous blood supply to different regions have been reported, and the accuracy of measurements can vary among neighboring sites. This position dependency can cause the pulse count to fail and necessitate sensor reattachment. The light source can also affect the characteristics of reflected-light PPG. To investigate position dependency in PPG, we compared the reflected light signals obtained from green and infrared PPG sensors at different sites. Eight young healthy subjects were recruited to participate in the study. Green and infrared PPG signals were collected simultaneously from three sites on the left arm of each participant. The correlations among adjoining green PPG signals were higher than those among adjoining infrared signals. Furthermore, the difference in the pulse interval was smaller among adjoining green PPG signals than among infrared signals. These results suggest that green-light PPG has less position dependency and thus may be more suitable for monitoring the pulse rate during daily activities.

Position Dependency in Photoplethysmographic sensor -Comparison of adjoining PPG signals in Light Sources and Measurement Sites-

PROBLEM TO BE SOLVED: To more accurately measure a pulse wave.SOLUTION: A pulse wave measurement device includes: a plurality of bandpass filters (24a and 24b) for dividing each of a plurality of signals into a plurality of frequency bands; a correlation coefficient computation part (28) for computing a correlation coefficient indicating a correlation between the plurality of signals that pass through the bandpass filters for each of the plurality of frequency bands; and a waveform synthesis part (30) for weighting each signal that passes through the plurality of bandpass filters according to the correlation coefficient, and synthesizing waveforms of each signal.SELECTED DRAWING: Figure 1

Yuka Maeda

Papers

Performance evaluation of green photoplethysmography

Position Dependency in Photoplethysmographic sensor -Comparison of adjoining PPG signals in Light Sources and Measurement Sites-

Pulse wave measurement device and pulse wave measurement method

Comparison of Measurement Sites and Light Sources in Photoplethysmography during Walking

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