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How do Phonak Audéo Fit hearing aids track heart rate?

Heart rate tracking
The Sensor Receiver and Sensor cShell attached to the Audéo Fit hearing aids track the wearer’s heart rate using photoplethysmography (PPG), a technique in which light emitting diodes (LEDs) shine light into the skin, and an optical sensor detects how much light is reflected back. When the volume of blood in the blood vessels is high, more light is absorbed and therefore the intensity of the light that is reflected back is lower. The rate at which the intensity of the reflected light changes from high to low indicates how quickly the blood vessel volume is changing from low to high, allowing the number of beats per minute (i.e., heart rate) to be calculated and displayed.