Quantification of posture induced changes in wearable seismocardiogram signals for heart failure patients

Our goal is to characterize the effects of posture - supine, seated, and standing - on the seismocardiogram (SCG) signal for patients with heart failure (HF). Posture can (1) distort the SCG signal, for example due to altering the body's mechanical vibration response, and (2) affect a person's cardiovascular physiology, for example due to changes in venous return. This work focuses on characterizing the former, such that in future studies we can use the SCG to assess physiological changes in patients with HF at home. Our team has developed a circular patch (7 cm in diameter) which, when placed on the sternum, simultaneously measures the electrocardiogram (ECG) along with SCG signals in the dorso-ventral and head-to-foot directions. We recruited six HF patients thus far for this ongoing study. Each subject was asked to lie down in a supine position on a patient bed for 1 minute followed by 1 minute in each of the seated and standing postures. A novel algorithm was implemented to compare distortion in the shape of the SCG signals in the supine and seated postures as compared to the standing upright posture. The frequency domain analysis of the SCG signals revealed presence of high energy in bands greater than 8 Hz for supine and seated postures. Based on the findings of this paper, features can be derived to correct for posture related changes in the measured SCG signals for accurate assessment of patients with HF at home.