Recovery of respiratory function and autonomic diaphragm movement following unilateral recurrent laryngeal nerve to phrenic nerve anastomosis in rabbits

OBJECTIVE Respiratory dysfunction is the leading cause of mortality following upper cervical spinal cord injury (SCI). The authors’ previous study suggested that vagus nerve (VN) and phrenic nerve (PN) anastomosis could partially improve respiratory function in rabbits that had been subjected to PN transection. As a branch of the VN and a motor fiber–dominated nerve, the recurrent laryngeal nerve (RLN) seems a better choice to anastomose with the PN for respiratory function restoration after upper cervical SCI. This study was designed to determine whether RLN-PN anastomosis could restore the respiratory function after upper cervical SCI in rabbits. METHODS Twelve male New Zealand rabbits were randomly divided into 3 groups: 1) sham group (no injury), 2) transection group (right RLN and PN were transected), and 3) bridge group (transected right RLN and PN were immediately anastomosed). Spontaneous discharges of the RLN and PN were compared using a bio-signal collection system. RLN and PN cross sections were stained for acetylcholinesterase (AChE), and the numbers of motor fibers were compared. Three months after the initial surgical procedures, the movement of the diaphragm was assessed using a digital subtraction angiography (DSA) system, and discharges from the right diaphragm muscle were recorded. Toluidine blue staining, electron microscopy, and staining for AChE were used to assess whether motor fibers from the RLN regenerated into the PN, and sections of diaphragm were examined after AChE staining to assess the motor endplates. RESULTS Both the RLN and PN exhibited highly rhythmic discharges, synchronized with respiration, and most fibers in the RLN and PN were found to be motor fibers. Numerous myelinated fibers were observed in anastomosed PN using toluidine blue staining and electron microscopy. Staining for AChE showed that those regenerated fibers had typical characteristics of motor fibers, and motor endplates with typical morphological characteristics were observed in the diaphragm. Reestablished rhythmic contraction of the hemidiaphragm was directly observed using the DSA system, and rhythmic spontaneous discharge was recorded from the reinnervated hemidiaphragm using the bio-signal collection system. CONCLUSIONS Motor fibers from the RLN could regenerate into the PN after end-to-end anastomosis and reinnervate the denervated hemidiaphragm in rabbits. Those regenerated motor fibers restored rhythmic and autonomic movement of the paralyzed diaphragm. These results suggest that the RLN is an optimal donor nerve to anastomose with the PN in order to reestablish the autonomic movement of paralyzed diaphragms after high-level SCI.