Interactions between lung stretch and PaCO2 in modulating ventilatory activity in dogs.

The effects of changes in airway pressure (Paw) and arterial PCO2 (PaCO2) on ventilatory activity were studied in anesthetized thoracotomized dogs in which both lungs were ventilated separately. Pulmonary artery occlusion on one side and contralateral vagotomy allowed the reflex effects on ventilation of changes in Paw and PaCO2 to be elicited independently of each other. Ventilatory activity was assessed from integrated efferent phrenic activity, analyzed with respect to burst amplitude (Phr), burst frequency (f), and inspiratory TI) and expiratory duration (TE). While Phr increased linearly with PaCO2, it was independent of Paw. Both PaCO2 and Paw affected f in a complex nonadditive way; this response was entirely mediated by effects on TE, TI being unaffected by either stimulus. The analog of ventilation, estimated as Phr x f, increased linearly with PaCO2 and decreased linearly with Paw, but the effects of both stimuli appeared to be additive. It is concluded that the apparently simple effect of Paw and PaCO2 on ventilation results from more complex effects these stimuli exert on its components.