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The regularity and interrelation of respiratory and cardiac rhythms at rest and during exercise.

One of the hypotheses to account for the increase in the drive to ventilation in exercise mediated by the peripheral chemoreceptors is that there is an improved linkage between breathing rate and lung to carotid body circulation time, such that peaks of arterial carbon dioxide arrive during a subsequent inspiration thereby stimulating ventilation. This study was designed to examine the mechanisms which may underlie the improved linkage. Auto- and cross-correlations of breathing and heart rhythms in volunteers at rest and during exercise showed an increased regularity of the rhythms but not entrainment between the rhythms. Although the increased regularity of the cardiac rhythm should promote a decrease in the variability of the lung to carotid body circulation time, the lack of entrainment shows that if there is an improved linkage of breathing and lung to carotid body circulation time, it is not by a coupling of heart rhythm to breathing rhythm.