Google’s tech can evolve any noise cancelling earbuds into heart rate monitors

Google has made headway into a technology that can give any and all true wireless earbuds you may already own, a significant upgrade. Potentially, with just a software update, wireless earbuds can integrate heart rate monitoring without any additional hardware requirement. Except that the earbuds, earphones or headphones in question must have active noise cancellation, since it’ll use a similar route as noise cancellation to work.

Google Research image.
Google Research image.

The research paper, titled ‘APG: Audioplethysmography for Cardiac Monitoring in Hearables’, details the experimental tech that uses a low intensity ultrasound probing signal routed via an ANC, or active noise cancellation, headphone’s microphone and speakers and subsequently receiving echoes via the on-board feedback microphones. This low intensity signal will bounce off the ear canal, and since each ANC earphone has a tiny microphone to detect ambient sounds, that’ll be used to hear back for how the skin surface responds to blood flow.

The more commonly used tech in fitness and health tracking wearables is Photoplethysmography (PPG), which uses light pulses to measure blood activity. In fact, most smartwatches, fitness bands, health tracking rings and other wearables rely on PPG to different degrees (alongside software and algorithms to make sense of these readings), to measure blood flow activity and thereby calculate the heart rate which is presented to you as a number – that is also why it is recommended to wear a smartwatch or fitness band without leaving a gap between the sensors on the watch and your skin.

With APG, a low-intensity ultrasound signal is bounced off the wearer’s ear canal and the microphone in the earphones or headphones that is used to detect ambient sound, is then used to listen back for skin surface perturbations as the blood pumps.

There are limitations to the APG tech, but fewer than alternatives which have held back the use of ear wearables to be used as health tracking tech too.

“We observed that, as the volume of ear canals slightly changes with blood vessel deformations, the heartbeats will modulate these ultrasound echoes,” say researchers, including Xiaoran Fan who is an Experimental Scientist at Google, Longfei Shangguan from the University of Pittsburg and Richard Howard from the Rutgers University.

Researchers suggest APG is resistant to variables such as skin tone, seat or fit of the wearable in the ear or canal size. The material used for the eartips (silicon and foam are popular ones that earphones come with) also doesn’t impact the readings. “We built mathematical models to analyze the underlying physics and propose a multi-tone APG signal processing pipeline to derive the heart rate and heart rate variability in both constrained and unconstrained settings,” they add.

Google’s researchers insist this works in the real world. The study, conducted over a period of 8 months and with 153 participants, returned heart rate readings with 3.21% median error in all scenarios, while heart rate variability reported 2.70% median error in interbeat interval, or IBI.

The expectation is this evolution from PPG tech will be able to detect and monitor cardiac activity even when a user may be listening to music on the headphones or earphones.

However, there are limitations, such as disturbed signal readings in noisy environments, but work is on using multiple frequencies and then using software to capture the readings from the one returning the most accurate signal.

There is potential, but it doesn’t mean Google will be able to get this out into the real world immediately. Or if at all, anytime in the near future. There is significant testing and refinement still being done, and in all likelihood, Google could embed this tech in their Pixel wireless earbuds products at some point down the line.

For other brands’ headphones and true wireless earphones, they’ll have to greenlight any integration in companion app software for those audio products. It’s certainly a long road ahead, but if successful, we could introduce a health tracking method that would be quite relevant for outdoor fitness routines.

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