Joint symbolic dynamics as an effective approach to study the influence of respiratory phase on baroreflex function

This study sought to employ a novel approach based on joint symbolic dynamics (JSD) to study the influence of respiratory phase on baroreflex function. We recorded electrocardiograms (ECG), blood pressure and respiration in 10 (5 male/5 female) healthy experienced athletes. For our analysis, time series of R-R intervals and systolic blood pressure were extracted, and respiratory phases were obtained using the Hilbert transform. Based on the changes between successive values, each series was transformed into binary symbol vectors, and words of length `2´ were formed. From parallel analysis of the symbolic dynamics in the three time series, the relationship between respiratory phases and baroreflex function was quantified. We analysed baroreflex patterns via different word combinations for specific respiratory phases and observed that baroreflex patterns occurred at similar frequency during expiration, inspiration and phase transitions (25.0±14.4% vs. 33.4±19.5%, expiration-inspiration: 25.0±12.6% and inspiration-expiration: 22.1±17.4%, respectively). From this study, it appears that JSD provides a novel and efficient technique for the combined analysis of interactions between respiration, heart rate and blood pressure.