Quantification of Posture-Induced Changes in Bed-Based Ballistocardiogram

The ballistocardiogram (BCG), a measurement of cardiogenic whole body movements, is a technique that enables non-invasive cardiovascular monitoring. A main challenge of the BCG signal is that its morphology and amplitude are sensitive to the posture of the subject during the recording period. This work elucidates effects of posture on bed-based BCG recordings by (1) creating templates for standing BCG signals obtained from subjects in a prior study, and (2) quantifying the distance between these templates and BCG waveforms obtained in different body postures on the bed for a new set of subjects. The signal quality index (SQI), defined in previous work and corresponding to the inverse of the distance to the templates, was the highest for the supine posture and the lowest for the lateral postures. A previously-reported system identification approach to correct for distortions in the lateral, prone, and seated postures was further validated. The system identification algorithm significantly improved the signal quality and correlation to the reference morphology - the supine and standing BCG. This work has implications for robust signal processing that allows for accurate physiological interpretation of the BCG obtained in a variety of postures from a subject in bed.