Heart Rate Variability from Wearables: A Comparative Analysis Among Standard ECG, a Smart Shirt and a Wristband

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Wearable Technology

Background:

• Heart Rate Variability (HRV) is a key indicator of autonomic nervous system function.
• Wearable sensors offer convenient methods for continuous physiological monitoring.
• Accurate HRV assessment is crucial for various health and performance applications.

Purpose of the Study:

• To compare the accuracy of HRV derived from an ECG shirt and a PPG wristband against a reference ECG.
• To evaluate the reliability of online data acquisition from wearable devices.
• To assess the impact of body position on the accuracy of wearable-based HRV measurements.

Main Methods:

• Simultaneous data acquisition from a standard ECG, an ECG shirt, and a PPG wristband in 8 subjects.
• Recording signals during seated, standing, and controlled respiration phases.
• Analysis using time and frequency domain HRV parameters and Bland-Altman methods for beat-to-beat comparison.

Main Results:

• ECG shirt HRV parameters closely matched the reference ECG, outperforming the PPG wristband.
• PPG wristband inter-beat intervals (IBI) showed significant differences from ECG-derived HRV, particularly in the standing position.
• A high number of missing beats were observed with the wristband, suggesting potential design limitations.

Conclusions:

• ECG shirts offer a more reliable method for online HRV monitoring compared to PPG wristbands.
• Caution is recommended when interpreting online PPG-derived IBI due to observed inaccuracies.
• Improvements in wearable device design, such as sensor adhesion, are needed to enhance PPG signal quality and reduce measurement errors.