Hearable Heartbeats: Recording the Heart Rate from the Ear

Area of Science:

• Biomedical Engineering
• Physiological Monitoring
• Wearable Technology

Background:

• Longitudinal physiological measurements offer a more complete health assessment than single readings.
• Cardiovascular signals synchronized to heartbeat have been detected in the ear using body-coupled microphones (BCM).
• This suggests potential for estimating heart rate (HR) non-invasively via ear-based BCM.

Purpose of the Study:

• To investigate the feasibility of extracting time-varying heart rates (HR) using body-coupled microphones (BCM) placed in the ears.
• To assess the accuracy and reliability of BCM-based HR estimation compared to electrocardiography (ECG).

Main Methods:

• 10 subjects were recorded for 5 minutes with BCMs in each ear.
• Heart rate (HR) was estimated using the PYIN pitch detection algorithm, with hyperparameters optimized via grid search.
• BCM-derived HR estimates were compared against ECG recordings for detection rate, error distribution, and root mean square error (RMSE).

Main Results:

• In 9 out of 19 ears, the RMSE for HR estimation was below 4 beats per minute (BPM).
• However, 4 out of 10 subjects showed both low detection rates and high RMSE, indicating significant inter-individual variability.
• The error distributions suggested that BCM-based HR estimation is unbiased.

Conclusions:

• Heart rate estimation using body-coupled microphones in the ear is feasible.
• Considerable inter-ear variability exists in detection rates and HR error, likely due to signal representation and algorithm performance.
• Ear-level sensing, enhanced with BCM-based cardiovascular monitoring, holds promise for future health applications.