Google has revealed its research on audioplethysmography (APG), an innovation that enables the addition of heart rate sensing capabilities to active noise canceling (ANC) headphones and earbuds through a straightforward software upgrade.
According to Google, the ear canal is an optimal site for health sensing due to the intricate network of smaller vessels derived from the deep ear artery that extensively permeate the auditory canal.
The APG technique involves transmitting a low-intensity ultrasound probing signal through the speakers of ANC headphones. This signal prompts echoes that are received via onboard feedback microphones. Google observes that minute ear canal skin displacement and heartbeat vibrations modulate these ultrasound echoes.
Google’s model processes this feedback to provide a heart rate reading and measure heart rate variability (HRV), even while music is playing and with imperfect earbud seals. However, the method is susceptible to body motion. To counter this, Google employs a multi-tone approach as a calibration tool to identify the most suitable frequency for accurate pulse waveform measurement.
Through two sets of studies involving 153 individuals, Google found that APG delivers consistently precise heart rate (3.21% median error across participants in all activity scenarios) and HRV (2.70% median error in inter-beat interval) measurements. Unlike existing HR sensors, APG is not influenced by skin tones, ear canal size, or sub-optimal seal conditions, thus overcoming significant obstacles associated with incorporating traditional photoplethysmograms (PPG) and electrocardiograms (ECG) sensors, along with a microcontroller, into headphones or earbuds.
Google emphasizes that APG can easily transform any true wireless stereo (TWS) ANC headphones into smart sensing devices via a simple software upgrade, performing robustly across various user activities. The sensing carrier signal remains inaudible and unaffected by music playback. Importantly, APG signifies a significant advancement in biomedical and mobile research, unlocking new possibilities for affordable health sensing.
It’s worth noting that APG is the result of collaboration across various Google teams, including Google Health, product, UX, and legal teams. As a result, its integration into Pixel Buds is not guaranteed at this stage.