Cardioventilatory coupling in atrial fibrillation.

Cardioventilatory coupling is an entrainment phenomena, distinct from respiratory sinus arrhythmia, whereby heart and breathing rhythms show temporal coherence. Coupling is commonly observed during rest, sleep and anaesthesia. Five graphical methods, each with different underlying mechanistic assumptions, have been suggested for studying this entrainment relationship: (a) time relationship between inspiration and a preceding heart beat, (b) time relationship between inspiration and a following heart beat, (c) phase of the cardiac cycle at which inspiration occurs, (d) phases of the ventilatory cycle at which heart beats occur and (e) 'relative phases' over multiple ventilatory cycles at which heart beats occur. In eight elderly human subjects with atrial fibrillation, breathing spontaneously during general anaesthesia, we recorded heart period and ventilatory time series and compared each of the graphical methods used for demonstration of coupling. We observed cardioventilatory coupling in seven of eight subjects. In each of these seven subjects, coupling was best described, both qualitatively and quantitatively, in terms of the relationship between inspiration and a preceding heart beat. The variation of the interval between inspiration and a preceding heart beat was less than for any other phase or time relationship. These data support a model of cardioventilatory coupling in which a heart beat triggers the onset of inspiration, rather than modulation of cardiac timing by ventilation or a phase relationship between the two systems.