Ballistocardiogram amplitude modulation induced by respiration: a wavelet approach

Ballistocardiography is recognized as a reliable method for non-invasive assessment of cardiovascular functions. In this work, a wavelet approach was used on the y-axis ballistocardiogram (BCG) to evaluate the respiratory sinus arrhythmia (RSA) phenomenon using a new parameter: the ballistocardiogram amplitude modulation induced by respiration (BAMR). Eamax, local maximum energy of BCGy, was quantified for each cardiac cycle. Then a time series of Eamax was created and analyzed using continuous wavelet transform to provide BAMR values. The ECG was used to compute the RSA amplitude as reference. Data were collected on four subjects participating to an imposed controlled breathing protocol with four different breathing sequences. RSA amplitudes and BAMR present significant changes (p < 0.05) for low breathing rate (0.10 Hz) compared to high breathing rate (0.25 Hz) and a within-subject correlation was observed. This study suggests that BAMR could be used as a relevant alternative to RSA amplitude for HRV investigation.