Cardioventilatory coupling in the anaesthetised rabbit, rat and guinea-pig

Cardioventilatory coupling is a temporal coherence of respiratory and cardiac rhythms, seen in humans at rest, and during sleep and anaesthesia. In this study we compared the cardioventilatory coupling of anaesthetised rabbits, rats and guinea-pigs. Breathing two successive anaesthetic concentrations (1 or 2% isoflurane) we compared the effect of anaesthetic depth and species on (1) heart rate, (2) heart rate variability, (3) ventilatory rate (f), (4) ventilatory variability, (5) ratio HR/f, (6) degree of coupling (Shannon entropy of the distribution of intervals between inspiration and the preceding electrocardiographic R wave - the RI interval) and (7) coupling pattern, classified into four sub-patterns (I-IV) based upon inspection of the RI interval time series. Rabbits exhibited significantly less ventilatory variability and coupling than rats or guinea-pigs. The sub-pattern of coupling also differed between the three species. Rabbits showed coupling only when HR and f were close to integer ratios whereas other species coupled at non-integer ratios. Ventilatory variability in the rat and guinea-pig differed according to the pattern of coupling observed. Of the three species studied, the rat and guinea-pig demonstrated coupling most similar to that of anaesthetised human subjects. Anaesthetic concentration did not influence the pattern or degree of coupling.