TRANSFER ENTROPY ESTIMATION SUPPLEMENTS TIME-DOMAIN BEAT-TO-BEAT BAROREFLEX SENSITIVITY INDEX UNDER POSTURAL STRESS

Abstract

Baroreflex mechanism plays a vital role in cardiovascular regulation by contributing in sympathetic-vagal imbalance triggered by baroreceptor reflex. This study estimates BRS (Baroreflex Sensitivity) index from beat-to-beat systolic blood pressure (SBP) and RR interval (RRi) series using time-domain windowed cross-correlation method. This index is supplemented by an information domain technique called Transfer Entropy (TE) is applied to decipher the directional coupling between SBP and RRi series. The study is performed on EUROBAVAR data. The results show that BRS index calculated is large (1.157±0.533) in supine position which supplemented by TE (SBP-RR) of (0.129±0.09) as compared to standing position for which BRS index is (0.866±0.472) and a TE (SBP-RR) of (0.04±0.03) for EUROBAVAR data with a p-value<0.05. Also, it is found that both the TE indices i.e. from SBP to RR and from RR to SBP show correlated results with the time domain BRS index in both supine and standing positions. Further, the cases with possible BRS failure are having very small values of BRS index, which are not assigned any value by prevalent methods. This shift is absent in BRS failure patients which is supplanted by TE (RR-SBP) sharing more information bits than TE (SBP-RR). Further, it is observed that patients having baroreflex impairment show reversal of information flow which is indicated by a larger TE (RRSBP) index as compare to TE (SBP-RR) index. Time domain BRS index lacks directional information which is provided by TE and hence this supplemental information gives better interpretation of BRS index especially in patients having suppressed baroreflex. Index Terms: Baroreflex sensitivity, Directional coupling, Cross-correlation, and Transfer entropy