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Monitor respiration with non-contact sensor

Posted: 19 Aug 2015     Print Version  Bookmark and Share

Keywords:sensors  ultra-wideband  XeThru  spirometer 

Respiration rate is an important vital sign that can provide insight into a person's general state of health and quality of sleep. Breathing rate and breathing patterns are also considered good indicators of underlying medical conditions. While current technologies in today's market promise accurate and dependable monitoring, the majority are less than ideal—either they are not accurate and require continual adjustment or are uncomfortable for subjects to use.

This article explores the various established methods for measuring and analysing respiration to understand their limitations when applied to the requirements for daily health care and fitness tracking. Overcoming these challenges is not easy but ultra-wideband (UWB) impulse radar can serve as the basis of sensors such as Novelda's XeThru—enabling sensors to achieve an effective range up to 2.8m and capable of 'seeing through' obstacles, such as clothing, while also being low cost and easy to use.

Respiration monitoring for healthcare
Breathing rate is the number of breaths a person takes per minute, and is best measured when a person is at rest. The rate may increase with fever, illness, and with other medical conditions. The most common method for measuring breathing rate is by physical assessment, observing a person's chest and counting the number of breaths during one minute. Depth of breathing can be determined with a spirometer, a device that measures lung function based on the volume of air breathed in and out. In its simplest form doctors use a spirometer to detect conditions like asthma. Breathing rate on its own provides limited information, but breathing patterns—measuring rate, amplitude and other characteristics—provide far more valuable information, which can be used for medical diagnostics as well as the evaluation of sleep quality.

Most of the respiration monitoring technologies that exist today are invasive and require the subject to be connected to the measuring equipment. This is certainly true for the spirometer described above but even the simple electromechanical measurement of breathing rate will typically require an elastic strap to be tightened around the subject's chest. Alternative acoustic techniques require a device to be connected to a subject's neck, while capacitive techniques require a special mattress or sensing unit to be installed in the bed or on a subject's body. These methods are mainly used in professional monitoring situations and provide accurate breathing pattern data. However, a fundamental challenge still remains, which is the physical connection of a sensor to the body, causing stress to the monitored subject. Any associated discomfort will in turn affect the subject's breathing and potentially invalidate the data.

Consumer respiration monitoring
Until recently, even simple respiration tests have been confined to the doctor's office; more extensive monitoring has been the preserve of clinics and hospitals and then only for patients referred after preliminary diagnosis of a medical condition. The advent of smartphones and similar high-tech gadgetry, including devices such as heart rate and blood-sugar monitors, coupled with individuals who have become much more conscious of and concerned about their health and well-being has raised expectations of what should be possible away from a medical environment. Consequently the market has been flooded with healthcare and fitness monitoring devices introduced to provide consumers with the means to track their physical activity and manage their personal health. These products use technology similar to their medically qualified counterparts, while further refinements of medical designs address a trend towards providing complete health assessments by monitoring sleep quality and breathing patterns while at rest.

With an appreciation of the limitations of current solutions, and understanding that consumers expect health and fitness products to be comfortable, safe and easy to use, it is clear that a truly unobtrusive respiration/sleep monitor needs to meet some pretty demanding design criteria. It should be able to accurately measure and record breathing from a distance and its placement shouldn't be critical as long as the person is within a reasonable detection zone (figure 1). The person's orientation within that zone shouldn't matter and the monitor should operate reliably despite reasonable obstructions e.g. through a duvet.

Figure 1: Sample of a child's respiration recording, which clearly shows that remote monitoring needs to be able to detect a chest movement of just a few millimeters.

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