Alessandro Monti

Instantaneous parameter estimation in cardiovascular time series by harmonic and time-frequency analysis

Time-frequency distributions, such as smoothed pseudo Wigner-Ville distribution (SPWVD) and complex demodulation (CDM) provide useful time-varying spectral parameter estimators. However, each of these methods has limitations that a joint utilization could largely reduce, due to their interesting complementary features. The aim of this paper is to validate the joint SPWVD-CDM method on synthetic and real cardiovascular time series with normal and reduced variability such as in autonomic blockade or autonomic deficiency. We propose two indexes related to the noise present in the signal and to the dispersion of the power spectrum in order to validate instantaneous parameter estimation. In the low-frequency band, the interpretation of the instantaneous frequency and phase of cardiovascular time-series should be discarded in many real-life situations. Conversely, in the high frequency band, under paced breathing, the reliability of the instantaneous parameters is demonstrated even in conditions of reduced cardiovascular variability.

Altered baroreflex gain during voluntary breathing in chronic heart failure.

We assessed the behavior of the baroreflex (BR) gain in chronic heart failure (CHF) patients using the spectral analysis method during application of a forcing stimulus, i.e. respiration.

Cardiorespiratory system dynamics in chronic heart failure

With the complex demodulation (CDM) method, we assessed the instantaneous amplitude and frequency of cardiovascular (CV) and respiratory oscillations, and the instant phase (IP) between the CV and respiratory signals using respiration as a periodic forced stimulation. We hypothesised a possible lack of synchronisation between CV and respiratory signals under regular breathing at different frequencies.