Significance of the Crossed Phrenic Phenomenon

Abstract

In barbiturate-anesthetized animals with spinal hemisections at C1-C2, muscle action potentials were recorded simultaneously from each hemidiaphragm during various procedures designed to explain the appearance of increased crossed activity (ipsilateral to the hemisection) following interruption of the direct phrenic nerve (contralateral to the hemisection). Activity of the crossed hemidiaphragm was always less than that of the direct hemidiaphragm. Using activity on the direct side as an index of central respiratory discharge, activity on the crossed side was found to vary in a fashion parallel to that on the direct side during procedures which altered the intensity of the central respiratory discharge. Activity on the crossed side increased following interruption of the direct phrenic nerve during spontaneous uncontrolled ventilation. Qualitative and quantitative recordings revealed that such a change did not occur during controlled artificial ventilation. Central respiratory discharge increased following interruption of the direct phrenic nerve during spontaneous uncontrolled respiration. Such a change did not occur during controlled artificial ventilation. It is concluded that the amount of crossed respiratory activity is directly proportional to intensity of the central respiratory discharge and is entirely independent of the state of conduction in the direct phrenic nerve. The crossed phrenic phenomenon occurs only when exptl. conditions permit an augmentation of central respiratory discharge to take place as a secondary result of interruption of the direct phrenic nerve.