Enabling Cardiac Monitoring using In-ear Ballistocardiogram on COTS Wireless Earbuds

TL;DR

TWSCardio leverages existing IMU sensors in true wireless stereo earbuds to accurately monitor cardiac signals through in-ear ballistocardiogram, enabling practical, real-time cardiac health monitoring without extra hardware.

Contribution

It introduces a novel system that repurposes TWS earbuds' IMU sensors for cardiac monitoring, including a signal enhancement and reconstruction framework for accurate, real-time in-ear BCG and SCG signals.

Findings

Accurately reconstructs cardiac signals in real-time

Resilient to motion artifacts and missing data

Supports diverse cardiac monitoring applications

Abstract

The human ear offers a unique opportunity for cardiac monitoring due to its physiological and practical advantages. However, existing earable solutions require additional hardware and complex processing, posing challenges for commercial True Wireless Stereo (TWS) earbuds which are limited by their form factor and resources. In this paper, we propose TWSCardio, a novel system that repurposes the IMU sensors in TWS earbuds for cardiac monitoring. Our key finding is that these sensors can capture in-ear ballistocardiogram (BCG) signals. TWSCardio reuses the unstable Bluetooth channel to stream the IMU data to a smartphone for BCG processing. It incorporates a signal enhancement framework to address issues related to missing data and low sampling rate, while mitigating motion artifacts by fusing multi-axis information. Furthermore, it employs a region-focused signal reconstruction method to translate the multi-axis in-ear BCG signals into fine-grained seismocardiogram (SCG) signals. We have implemented TWSCardio as an efficient real-time app. Our experiments on 100 subjects verify that TWSCardio can accurately reconstruct cardiac signals while showing resilience to motion artifacts, missing data, and low sampling rates. Our case studies further demonstrate that TWSCardio can support diverse cardiac monitoring applications.