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Lending an ear to optical heart-rate measurement

Feature

By Christoph Kämmerer, Field Applications Engineer, Analog Devices  

Advancements in sensor technology have transformed how and where people diagnose their vital statistics and health. Portable, non-invasive measurement techniques allow fast and simple measurements to be performed on the go. But, although this type diagnostic technology has become very popular in the fitness industry, there were limits to its accuracy that were only recently overcome.

Fitness trackers measure heart rate and other vital statistics to help users set their exercise routines. These trackers often have built-in motion sensors to detect movement, distinguishable between walking, running and swimming, and also used as pedometers. For comfort and convenience, the measurements are typically made on the wrist, since sensors can be housed in accessories such as watches, jewelry and wrist straps.

However, the wrist is not optimal for measurement quality. Heart-rate detection is limited by motion artifacts and difficult because relatively high muscle mass limits access to arteries. In contrast, the ear is much more suitable for optical heart rate measurements. The earlobe is already used by medical experts for measuring blood oxygen levels. Nevertheless, up to now, it has not been fully exploited on a consumer level because ear-based measurement devices have limited space and require a large battery due to their very-high power consumption.

Now, since the introduction of highly-integrated, low-power devices, there are solutions appearing that overcome these problems; functioning vital sign measuring device can now be integrated into typical in-ear headphones. The improved responsivity opens up new applications and possibilities. One such system is described and evaluated in this article.

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