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

Some information domain metrics have been devised to quantify whether subsystems contribute to information carried by a target variable more or less than the sum of their separate contributions leading to synergistic or redundant behaviors respectively. We evaluated the net balance between synergy and redundancy of cardiac and cardiorespiratory controls from spontaneous variability of heart period (HP) and respiration (R). HP variability and R were recorded from 16 healthy subjects (22–58 yrs, 6 males) at rest (REST), during bicycle ergometer exercise at 10%, 20% and 30% of the maximum load and recovery. The net balance between synergy and redundancy was estimated via a linear regression approach along with HP mean, HP variance, HP power in the high frequency (HF, from 0.15 to 0.45 Hz) band (HFa
HP
) and squared HP-R coherence at HF [K
²
HP-R
(HF)]. HP mean, HP variance and HFa
HP
power significantly decreased during exercise and K
²
HP-R
(HF) tended to decline. The net balance between synergy and redundancy remained unvaried and was not correlated to traditional variability markers. Despite vagal withdrawal, complex cardiac and cardiorespiratory control interactions are preserved during exercise and indexes of synergy and redundancy might provide extra information that more traditional variability markers cannot capture.