Time-variant closed-loop interaction between HR and ABP variability signals during syncope

The mutual interactions existing between Heart Rate (HR) and Arterial Blood Pressure (ABP) variability signals are investigated by means of a bivariate, time-variant model. The linear, parametric, closed-loop model, chosen to describe the relationships between HR and ABP spontaneous variability, is updated recursively according to the dynamic variations in the signals. In this way a beat-to-beat description of the interaction of the two signals and a beat-to-beat extraction of the relevant spectral and cross-spectral parameters are obtained. Furthermore, as a result of proper modelisation, a non-invasive measurement of the α-baroceptive gain is extracted, on a beat-to-beat basis. The quantification of these parameter is obtained through an automatic spectral decomposition technique for ARMA model. The parameters achieved from the proposed model are used to investigate episodes of vasovagal syncope. In particular we are interested in a quantitative assessment of the changes of the Autonomic Nervous System (ANS) behavior in the epoch preceding the episode and in the evaluation of ANS role in association with the vasovagal event.