Rhythmic phrenic nerve activity and respiratory activity in spinal dogs

The possibility of respiratory activity in adult spinal dogs was reinvestigasted with emphasis placed on the contribution of the phrenic nerves and diaphragm. Under chloroform anesthesia, the spinal cord was transected at either the C1 or C2 level. After spinal transection and occlusion of the blood flow to the head, anesthesia was discontinued. In 6 dogs spinal rhythmic respiratory activity was induced by administration of doxapram HCl, 3-5 mg/kg i.m., while in 2 dogs such activity occurred spontaneously. The observed cyclic changes in intrapleural pressure correlated with unilateral phrenic neurogram. The bursts frequency of the phrenic nerve activity was altered by the artificial positive-pressure respiration synchronizing the phrenic activity with the respirator. This suggests that afferent reflexes can modulate this spinal, cyclic phrenic nerve activity. This study demonstrates that the phrenic nerve and the diaphragm play a major role in spinal respiratory activity.