Model Based Estimates of Gain between Systolic Blood Pressure and Heart-Rate Obtained from Only Inspiratory or Expiratory Periods

Many physiological mechanisms influence in the heart rate variability (HRV), such as the baroreflex response due the compensatory increase in blood pressure, as well as the breathing cycle (with an increase of heart-rate during inspiration). Model-based methods have thus been proposed to unravel this intricate interaction between heart-rate and blood pressure modulated by the baroreflex and breathing cycle. The complex interaction between systolic blood pressure (SAP) , heart-rate variability (HRV) and breathing can be studied through closed loop linear models. In previous work it has been suggested that the baroreflex (the change in heart-rate in response to a change in SAP) differs between the inspiratory and expiratory periods. We investigated this on 25 healthy volunteers breathing spontaneously, through a causal closed loop model with distinct estimates for the inspiratory and expiratory periods, using an estimator for gapped data. The results showed no significant difference in baroreceptor gain between the inspiratory and expiratory phases, but there was a significant difference in high frequency (0.15-0.5 Hz) in the gain HRV-> SAP. The proposed method provides a convenient means for system identification with a switched-type non-linearity, with wide applicability in biomedical signals.