Technologies for Wearable and Portable Physiological Measurement Devices

Abstract

The study investigates technologies for portable and wearable physiological measurement devices. Physiological measurement is already an important field of research and is likely to become even more so in the future. An aging population in much of the industrialised world has led to increases in age- and lifestyle-related diseases. This increase places a greater burden on healthcare provision and healthcare costs for society a whole.

One way to offset this trend is developing and improving health monitoring applications. The benefits of such telemedicine and telemonitoring systems include earlier patient discharge from hospital since monitoring of recovery can be performed remotely via a data connection. Telemonitoring and alert applications also help the elderly to remain independent longer in the home environment and postpone the need for institutional care.

The study examines the technologies required in the implementation of portable and wearable physiological measurement devices. In such devices, as in all portable and mobile measurement devices, energy consumption is a critical design factor in ensuring the feasibility of the entire implementation. Here a novel method is presented for optimizing energy consumption caused by software running in a microcontroller or in a microprocessor. It has been shown that in low power 8-bit microcontrollers, savings of a few percent in energy consumption can be achieved by optimizing the software at the level of assembler instruction. The energy storage technologies utilized in current portable devices are investigated as well as methods for scavenging energy from external sources, such as the user or the environment.

A measurement device needs a communication link through which it can transfer the measurement results to a data terminal device such as a computer and a memory to store the results. An effective approach for a data link is to utilize wireless methods since wires readily impede the user during normal daily activity. The study presents the properties of the most common radio protocols utilized today. It also tests four different radio circuits and implements a radio link for a portable physiological measurement device with an ANT-protocol compliant radio. Various types of memory for measurement data storage are examined along with their suitability for the devices in question.

An important element in a physiological measurement device is an analogue front end that modifies the measured analogue signal to make it suitable for the analogue to digital converter. The signal can be modified in various ways such as filtering, amplification, and offset changes. The structure of the front-end block depends on the measurement signal and the interface of the analogue to digital converter. To understand the requirements of this front-end, some background is presented to the physiological signals that were measured with the devices implemented during the research. These signals include temperature, acceleration, body posture, bioimpedance, and electrocardiogram. When body-generated electrical signals are measured, an interface such as an electrode is needed between the body and the electronics. The properties and placement of such interfaces are also briefly discussed.

Several prototypes are implemented to demonstrate the practicability of portable and wearable physiological measurement devices. These include two smart clothing prototypes, one for measuring and adjusting the user’s thermal comfort and the other for measuring body impedance that can be used for determining water levels in the body. The study also describes the development of a device to measure the user’s electrocardiogram, dynamic changes in bioimpedance, and acceleration on three axes.