Quantifying Redundant/Synergistic Interactions between Cardiorespiratory Reflexes and Cardiac Control Mechanisms During Light-to-Moderate Bicycle Exercise

Alberto Porta1, Beatrice Cairo1, Vlasta Bari2, Emanuele Vaini2, Beatrice De Maria3, Mara Malacarne4, Massimo Pagani4, Daniela Lucini4
1Department of Biomedical Sciences for Health, University of Milan, 2Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 3IRCCS Istituti Clinici Scientifici Maugeri, 4Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, University of Milan


Cardiorespiratory reflexes, comprising Hering-Breuer reflex, Bainbridge reflex and central modulation of cardiac vagal motoneuron activity and responsiveness, contribute to the regulation of heart period (HP) along with a myriad of additional mechanisms (e.g. baroreflex). The quantification of the redundant/synergistic interactions between cardiorespiratory reflexes and cardiac control mechanisms might be helpful to characterize cardiac regulation complexity. The aim is to quantify the net balance between synergy and redundancy of cardiorespiratory reflexes and cardiac regulation mechanisms during a protocol known to alter cardiorespiratory coupling via a graded sympathetic activation (i.e. incremental light-to-moderate bicycle exercise). We acquired electrocardiogram and respiration (RESP) via a thoracic belt at 300 Hz in 16 healthy humans (age: 22-58 yrs, 6 males). Signals were recorded at rest in recumbent position on bicycle ergometer (REST), during electronically braked exercise at 10%, 20% and 30% of the individual maximum load, and recovery (RC). HP was measured on beat-to-beat basis and RESP was sampled at the first R-wave peak defining the onset of the ith HP. The net balance between synergy and redundancy between cardiorespiratory reflexes and cardiac control mechanisms was quantified via a bivariate linear regression method based on the predictive information decomposition approach taking HP as the target series and exploiting the past of HP and RESP to characterize the cardiac control and cardiopulmonary reflexes respectively. Sequences of 250 HP and RESP consecutive values were analyzed in each session. The progressive decrease of HP mean and variance with the load and their recovery during RC assured the relevance of the sympathetic activation and vagal withdrawal. The balance between synergy and redundancy was close to 0 at REST (i.e. 0.01±0.11) and this balanced situation was maintained irrespective of the load. Despite vagal withdrawal, complex interactions between cardiorespiratory reflexes and cardiac control mechanisms were preserved during dynamical exercise.