Phrenic nerve stimulation in patients with spinal cord injury.

Phrenic nerve pacing (PNP) is a clinically useful technique to restore inspiratory muscle function in patients with respiratory failure secondary to cervical spinal cord injury. In this review, patient evaluation, equipment, methods of implementation, clinical outcomes, and the complications and side effects of PNP are discussed. Despite considerable technical development, and clinical success, however, current PNP systems have significant limitations. Even in patients with intact phrenic nerve function, PNP is successful in achieving full-time support in approximately 50% of patients. Inadequate inspired volume generation may arise secondary to incomplete diaphragm activation, reversed recruitment order of motor units, fiber type conversion resulting in reduced force generating capacity and lack of coincident intercostal muscle activation. A novel method of pacing is under development which involves stimulating spinal cord tracts which synapse with the inspiratory motoneuron pools. This technique results in combined activation of the intercostal muscles and diaphragm in concert and holds promise to provide a more physiologic and effective method of PNP.