Accelerometer body sensor network improves systolic time interval assessment with wearable ballistocardiography

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Wearable Technology

Background:

• Systolic time intervals (STI) offer non-invasive cardiac function assessment, crucial for long-term cardiovascular disease monitoring.
• Ballistocardiography (BCG) measures cardiac vibrations, with wearable accelerometers presenting interpretation challenges compared to traditional scales.
• Accurate prediction of pre-ejection period (PEP) from wearable BCG is vital for advancing remote cardiac diagnostics.

Purpose of the Study:

• To investigate if a body sensor network of four accelerometers enhances beat-by-beat PEP prediction compared to individual sensors.
• To evaluate the effectiveness of combining signals from wrist, arm, sternum, and head accelerometers for PEP estimation.
• To compare different signal processing techniques for wearable BCG data.

Main Methods:

• A pilot study involving four subjects was conducted.
• Linear models were used to correlate R-J and R-I intervals from four wearable BCG sensors with PEP measured via impedance cardiography.
• Data were collected during isometric lower-body exercise, with 5-minute recordings analyzed.

Main Results:

• Double integration reduced the root mean square (RMS) error in PEP estimation from wearable BCG sensors.
• PEP estimates derived from R-I intervals exhibited a smaller standard deviation than those from R-J intervals.
• Combining R-J and R-I measurements from all four sensors yielded the best results: average correlation (r^2) of 0.96 ± 0.01 and lowest average RMS error of 2.5 ± 0.8 ms via 5×2-fold cross-validation.

Conclusions:

• A body sensor network utilizing multiple accelerometers significantly improves PEP prediction accuracy.
• Wearable BCG, when processed effectively, is a viable method for beat-by-beat PEP estimation.
• This approach holds promise for enhanced non-invasive, long-term monitoring of cardiac function in patients with cardiovascular disease.