Dependence of phrenic motoneurone output on the oscillatory component of arterial blood gas composition.

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Abstract
The hypothesis that respiratory oscillations of arterial blood gas composition influence ventilation was examined. Phrenic motoneuron output recorded in the C[cervical]5 root of the left phrenic nerve and the respiratory oscillations of arterial pH in the right common carotid artery were measured in vagotomized, anesthetized dogs paralyzed and artificially ventilated. The effect of a tidal volume change for 1 or 2 breaths on phrenic motoneuron output was measured with the inspiratory pump set at a constant frequency similar to, and in phase with, the animal''s own respiratory frequency. A reduction of tidal volume to 0 or an increase by 30% led to a corresponding change of mean carotid artery pH level. The changes of carotid artery pH resulted in a change of phrenic motoneuron output, predominantly of expiratory time (Te) but to a lesser extent of inspiratory time (Ti) and also peak amplitude of integrated phrenic motoneuron output (Phr). Carotid bifurcation denervation blocked this response. The inspiratory pump movement onset was triggered by the phrenic motoneuron output onset. When a time delay was interposed between them, the phase relationship between respiratory oscillations of arterial pH and phrenic motoneuron output altered. The dominant effect was to alter Te; smaller and less consistent changes of Phr and Ti were observed. When the inspiratory pump was maintained at a constant frequency but independent of and slightly different from the animal''s own respiratory frequency (as judged by phrenic motoneuron output), the phase relationship between phrenic motoneuron output and the respiratory oscillations of pH changed breath by breath over a sequence of 100-200 breaths, without change of the mean arterial blood gas composition level. Te varied by up to 30% about its mean value depending on the phase relationship. Ti and Phr were also dependent on the phase relationship but varied to a lesser extent. Phrenic motoneuron output was dependent partially on its relationship to the respiratory oscillations of arterial blood gas composition. Information concerning a transient ventilatory disturbance was stored in the arterial blood in the form of an altered pattern of the respiratory oscillations of blood gas composition; this in turn changed breathing by an effect on the carotid bodies.