Cardioventilatory coupling in atrial fibrillation

Cardioventilatory coupling is an entrainment phenomena, distinct from respi ratory 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 assump tions, 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 t he cardiac cycle at which inspiration occurs, (d) phases of the ventilatory cycle at which heart beats occur and (e) 'relative phases' over multiple v entilatory cycles at which heart beats occur. In eight elderly human subjec ts with atrial fibrillation, breathing spontaneously during general anaesth esia, we recorded heart period and ventilatory time series and compared eac h of the graphical methods used for demonstration of coupling. We observed cardioventilatory coupling in seven of eight subjects. In each of these sev en subjects, coupling was best described, both qualitatively and quantitati vely, in terms of the relationship between inspiration and a preceding hear t beat. The variation of the interval between inspiration and a preceding h eart beat was less than for any other phase or time relationship. These dat a support a model of cardioventilatory coupling in which a heart beat trigg ers the onset of inspiration, rather than modulation of cardiac timing by v entilation or a phase relationship between the two systems.