Cardioventilatory coupling: effects of IPPV

Cardioventilatory coupling (CVC) is the temporal coherence of respiratory a nd cardiac rhythms. We have suggested that this coherence is the result of triggering of inspiratory onset by a preceding cardiovascular afferent. One implication of this triggering hypothesis is that coupling should only exi st under conditions of spontaneous ventilation and not under conditions whe re the ventilatory period is fixed, as during intermittent positive pressur e ventilation (IPPV). This study compared the degree of CVC in 20 ASA I fem ale subjects, aged 21-50 yr, 10 of whom were breathing spontaneously and 10 were undergoing mechanical ventilation. Over 5-10 min, we recorded the tim ing of consecutive ECG R waves and inspiratory onsets. Coupling was demonst rated by examining these epochs for constant timing relationship between R waves and inspiration (RI intervals). Constancy of RI intervals was examine d graphically (RI plot) and quantitatively using the Shannon entropy of Ri interval distribution. We observed CVC in all spontaneously breathing subje cts but in none of those receiving IPPV. In spontaneously breathing subject s, temporal alignment with inspiratory onset was greatest for the heart bea t preceding inspiration. We conclude that although coupling has been shown to persist in the presence of electrical cardiac pacing, IPPV disrupts the coupling process, consistent with the view that in anaesthetized subjects, coupling is the triggering of inspiratory onset by a preceding heart beat a nd not the converse.