Serial phrenic nerve conduction studies in candidates for diaphragm pacing.

Serial phrenic nerve conduction studies in 3 patients with high cervical cord injuries have demonstrated a pattern of function that changes with time. Nerves may be responsive initially and may then become unresponsive only to have responses reappear at a later date. Before a final decision is made about phrenic nerve viability prior to diaphragm pacing, serial studies should be carried out for at least 6 weeks postinjury on initially responsive nerves, and for at least 2 years postinjury on nonresponsive nerves or those with a changing functional pattern.