Wearable Medical Devices

A wearable medical device can be defined as a device that is autonomous, that is noninvasive, and that performs a specific medical function such as monitoring or support over a prolonged period of time. The term ‘‘wearable’’ implies that the support environment is either the human body or a piece of clothing. Handheld and portable devices are therefore not strictly speaking wearable, but this distinction is not always clear as it also depends on the conditions of their use. Personal digital assistants (PDAs), for example, are handheld devices by design, but they have also been used as components of wearable personal medical monitoring systems. In a broader sense, commonly used medical equipment such as splints, bandages, eyeglasses, and contact lenses can be referred to as wearable medical devices, because they are wearable and provide a medical function. In this context, however, we deal with more sophisticated devices that integrate mechanical functions with microelectronics, computing capabilities, and in some cases, a degree of intelligence. The medical functions that are currently performed by such devices cover applications of medical monitoring, rehabilitation assistance, and long-term medical aid. Wearable monitoring devices assist in managing the treatment of chronic diseases such as heart diseases, asthma, and diabetes and the monitoring of vital signs such as heart rate, blood oxygen level, respiration, and body fat. They normally provide noninvasive sensing, local processing, user feedback, and communication capabilities. However, most of the current devices usually rely on user intervention to record data that are processed later offline. The most established wearable monitoring device is the heart holter monitor that records the cardiac activity of patients during normal activities, usually for a time period of 24 hours. Electrodes are placed on the patient’s chest and are attached to a small recording monitor that is worn by the patient and is battery operated. Patients are required to keep a diary of their activities used by their therapist along with a tape of the recordings. Any irregular heart activity can then be correlated with the patient’s activity at that time. The next generation of wearable monitoring devices goes beyond recording and aims to provide intelligent patient monitoring with real-time feedback, in the form of alerts and clinical decision support (1). Such devices collect, process, display, and often transmit information related to the user’s health condition, which involves the use of noninvasive electronic, mechanical, or biochemical sensors for monitoring physiological and kinesiological parameters, depending on the application. A processing unit deals with the incoming information and provides the necessary feedback. Devices with wireless connection capabilities can instantly send alerts to the health care provider, which provide ambulatory health monitoring within the health-care environment. Sleep apnea monitors are examples of medical monitoring and warning devices available at home or at the hospital (2). They monitor patients in periods of high risk, such as infants susceptible to sudden infant death syndrome. The infant wears a respiratory effort belt while sleeping, and an alert is provided to the parents or doctors when the breathing patterns cause reasons for concern. The miniaturization of wearable devices enables the provision of clinical monitoring beyond the hospital area, in the home or during outdoor daily activities. The evolving applications of multisignal monitoring, real-time monitoring, and the incorporation of varying degrees of intelligence improve their capabilities. Feedback and assessment is provided to the wearers in real time. Devices incorporating wireless data transmission capabilities can also immediately communicate with remote sources or destinations of information providing a telemedicine service. Products with such capabilities are already available, and they target the health market, researchers, health-conscious individuals, and athletes. Patients can constantly monitor several vital signs such as electrocardiography (ECG), respiration, skin temperature, pulse, blood pressure or blood oxygen saturation, body kinematics, as well as sensorial, emotional, and cognitive reactivity. The analysis of the received information provides feedback in the form of alerts or medical decision support directly to the patient and the medical supervisors. Devices intended for athletes measure parameters such as heart rate, pace, speed, and calorie burn, with the information constantly accessible during exercise. They also enable the long-term monitoring of progress and planning of workouts. It is important that these advancements provide an improved service to the users while minimizing the risk of becoming overwhelming. Wearable medical aid devices are designed to provide long-term assistance to patients with temporary or permanent disabilities. Conventional medical aid devices include contact lenses and hearing aids, both of which provide specific medical functions. More advanced systems include information processing capabilities such as speech recognition, contextual awareness enhancement, alerts, or feedback. Examples of such devices include a range of global positioning system (GPS)-based navigation devices designed for the visually impaired to assist in wayfinding, obstacle avoidance, and navigation (3). Wearable rehabilitation assistance devices can combine functions of monitoring and medical aid devices for patients in rehabilitation. A monitoring device may assist in rehabilitation through the prevention or diagnosis of potentially dangerous situations for patients in periods of high risk, such as after surgery or a heart attack. W