How Google plans to use ANC earbuds for heart-rate monitoring
Google has unveiled its research into audioplethysmography (APG), a method that can incorporate heart rate monitoring features into active noise-canceling headphones/earbuds "with a simple software update." The tech giant considers the ear canal an optimal location for health monitoring, as the deep ear artery is part of a complex network of smaller blood vessels that extensively spread throughout the auditory canal. This groundbreaking approach has the potential to convert any ANC headphones into intelligent sensing devices without any additional hardware.
Understanding concept of audioplethysmography
Under Google's APG approach, a low-intensity ultrasound probing signal is transmitted via an ANC headphone's speakers, producing echoes picked up by built-in feedback microphones. The minuscule skin displacement in the ear canal and heartbeat vibrations modulate these ultrasound echoes. Google designed a model to convert this feedback into a heart rate measurement and heart rate variability (HRV) reading. The technique remains effective even when music is playing and earbud seals are poor, although it can be affected by body movement.
Multi-tone approach to obtain precise frequency
To mitigate the influence of body movement, Google has developed a multi-tone approach that acts as a calibration tool to identify the most suitable frequency for measuring heart rate and obtaining high-quality pulse waveforms. The company conducted two sets of experiments with 153 participants. "Our results demonstrate that APG achieves consistently accurate heart rate (3.21% median error across participants in all activity scenarios) and heart rate variability (2.7% median error in inter-beat interval) measurements," said Google.
APG has edge over traditional sensors
In contrast to existing heart rate monitors, APG is not influenced by skin tones, ear canal size, or less-than-ideal earbud seal conditions. Google asserted this technique is superior to integrating traditional photoplethysmogram (PPG) and electrocardiogram (ECG) sensors and microcontrollers into headphones and earbuds. APG integration would not lead to increased cost, weight, power usage, acoustic design complexity, and form factor challenges. It will offer new insights into biomedical and mobile research and open up new opportunities for affordable health monitoring.
