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 contributionsleading to synergistic or redundant behaviors respectively. We evaluatedthe 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 wererecorded from16 healthy subjects (22–58 yrs, 6 males) at rest (REST), during bicycle ergometer exerciseat10%, 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 (HFaHP) and squared HP-R coherence at HF [K2HP-R(HF)]. HPmean, HP variance and HFaHPpower significantly decreasedduring exercise and K2HP-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 arepreservedduring exercise and indexes ofsynergy and redundancy might provideextra informationthat more traditional variability markerscannot capture.