Electrophysiological evaluation of phrenic nerve function in candidates for diaphragm pacing.

The electrophyisological status of phrenic nerve function has been determined by an assessment of the conduction time and diaphragm muscle action potential in patients who were being evaluated as candidates for diaphragm pacing, or who were being studied for suspected phrenic nerve injury or disease. The conduction time and muscle action potential were evoked by transcutaneous phrenic nerve stimulation or by stimulation with a permanently implanted diaphragm pacemaker. In normal volunteers the conduction time was found to be 8.40 msec +/- 0.78 msec (SD). Transcutaenous phrenic nerve stimulation was successful in predicting phrenic nerve viability in 116 of 120 nerves studied. The four false negatives were due to technical difficulty in locating the nerves in obese or uncooperative subjects. In patients who were selected for implantation of a diaphragm pacemaker, a conduction time that was prolonged (10 to 14 msec) preoperatively did not preclude successful diaphragm pacing. Postoperatively, a prolonged (> 10 msec) conduction time was associated with severe systemic disease or local nerve injury caused by trauma or infection. The elucidation of phrenic nerve function by such electrophysiological studies serves as a valuable adjunct to the selection and management of patients undergoing diaphragm pacing.