Information domain analysis of cardiovascular variability signals: evaluation of regularity, synchronisation and co-ordination

A unifying general approach to measure regularity, synchronisation and co-o rdination is proposed. This approach is based on conditional entropy and is specifically designed to deal with a small amount of data (a few hundred s amples). Quantitative and reliable indexes of regularity, synchronisation a nd co-ordination (ranging from 0 to 1) are derived in a domain (i.e. the in formation domain) different from time and frequency domains. The method is applied to evaluate regularity, synchronisation and co-ordination among car diovascular beat-to-beat variability signals during sympathetic activation induced by head-up tilt (T), during the perturbing action produced by contr olled respiration at 10, 15 and 20 breaths/min (CR10, CR15 and CR20), and a fter peripheral muscarinic blockade provoked by the administration of low a nd high doses of atropine (LD and HD). It is found that: (1) regularity of the RR interval series is around 0.209; (2) this increases during T, CR10 a nd HD; (3) the systolic arterial pressure (SAP) series is more regular (0.4 06) and its regularity is not affected by the specified experimental condit ions; (4) the muscle sympathetic (MS) series is a complex signal (0.093) an d ifs regularity is not influenced by HD and LD; (5) the RR interval and SA P series are significantly, though weakly, synchronised (0.093) and their c oupling increases during T, CR10 and CR15; (6) the RR interval and respirat ion are coupled (0.152) and their coupling increases during CR10; (7) SAP a nd respiration are significantly synchronised (0.108) and synchronisation i ncreases during CR10; (8) MS and respiration are uncoupled and become coupl ed (0.119) after HD; (9) the RR interval, SAP and respiration are significa ntly co-ordinated (0.118) and co-ordination increases during CR10 and CR 15 ; (10) during HD the co-ordination among SAP, MS and the respiratory signal is larger than that among the RR interval, SAP, MS and the respiratory sig nal, thus indicating that the RR interval contributes towards reducing co-o rdination.