Cardioventilatory coupling: effects of IPPV

Abstract

Cardioventilatory coupling (CVC) is the temporal coherence of respiratory and 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 exist under conditions of spontaneous ventilation and not under conditions where the ventilatory period is fixed, as during intermittent positive pressure ventilation (IPPV). This study compared the degree of CVC in 20 ASA I female subjects, aged 21-50 yr, 10 of whom were breathing spontaneously and 10 were undergoing mechanical ventilation. Over 5-10 min, we recorded the timing of consecutive ECG R waves and inspiratory onsets. Coupling was demonstrated by examining these epochs for constant timing relationship between R waves and inspiration (RI intervals). Constancy of RI intervals was examined graphically (RI plot) and quantitatively using the Shannon entropy of RI interval distribution. We observed CVC in all spontaneously breathing subjects but in none of those receiving IPPV. In spontaneously breathing subjects, temporal alignment with inspiratory onset was greatest for the heart beat 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 and not the converse.

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

“…There was no correlation between the degree of RSA and the degree or pattern of coupling observed. The magnitude of RSA observed in this study was less than we have observed in humans at similar anaesthetic depths [17].…”

“…Coupling has been observed in the presence of a fixed heart rate (during cardiac pacing) [13], with a fixed rate artificial pulsatile circulation [3] and with a heart rate which is not governed by efferent vagal activity (during atrial fibrillation [18]). Coupling is not seen with a fixed respiratory frequency (during mechanical ventilation [17]). During pattern II coupling we have described quantal changes in ventilatory period that approximate to a multiple of the heart period.…”

“…We therefore believe that cardioventilatory coupling is the triggering of inspiratory onset by a cardiovascular afferent associated with the preceding heart beat [8,9,10,13,17,18]. Although no single pathway for this interaction has been identified, a number of cardiovascular afferent pathways with end terminals in and around areas associated with ventilatory control have been identified in the rat and cat [14,21].…”

Cardioventilatory Coupling in Resting Human Subjects

“…During anaesthesia, the RI _1 interval is the most consistent R wave-inspiratory timing relationship during cardioventilatory coupling (Galletly & Larsen, 1997b;Larsen et al 1999b). This is one reason why we believe it is generally the heart beat immediately preceding inspiration that triggers inspiratory onset.…”

“…During coupling inspiratory onset occurs at a fixed interval after an ECG R wave. This interval we have termed the 'coupling interval', which is approximately 0.5 s in human subjects, and we believe represents the temporal delay associated with a cardiac-related event 'triggering' the onset of inspiration via an unidentified afferent pathway Larsen et al 1999b). The coupling process is distinct from the more widely known respiratory modulation of cardiovascular and autonomic efferent activity (Gilbey et al 1984;Schafer et al 1998).…”