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

2025-01-12

AI Summary

Existing ear-worn cardiac monitoring systems suffer from poor portability and high integration complexity. This paper presents the first demonstration of repurposing the built-in inertial measurement unit (IMU) in commercial true wireless stereo (TWS) earbuds to acquire intracranial ballistocardiogram (BCG) signals—without requiring additional hardware. We propose a fine-grained BCG-to-seismocardiogram (SCG) reconstruction framework that jointly employs multi-axis signal fusion for denoising and physiological-region-focused feature extraction. Integrated with Bluetooth low-latency streaming and motion-artifact suppression, the system achieves robust performance across 100 subjects: it maintains high-fidelity reconstruction of cardiac mechanical signals under motion interference, packet loss, and low sampling rates (≤50 Hz). The approach enables clinical-grade monitoring of heart rate variability (HRV) and phonocardiographic timing parameters. This work establishes a lightweight, highly reliable paradigm for wearable cardiac health assessment.

Technology Category

• Intelligent Robots: State Estimation
• Machine Learning: Hardware-aware ML
• Computer Vision: Motion & Tracking

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Sustainability and carbon-aware systems for Web, mobile, and WoT
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

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.

Problem

• Heart health monitoring
• Portable devices
• Wireless earbuds integration

Innovation

• TWSCardio
• Wireless Earbuds
• Seismo-Cardiogram