Diaphragm Pacing by Electrical Stimulation of the Phrenic Nerve

Abstract

Sophisticated techniques for electrical stimulation of excitable tissue to treat neuromuscular disorders rationally have been developed over the past 3 decades. A historical review shows that electricity has been applied to the phrenic nerves to activate the diaphragm for some 200 years. Of the contemporary methods for stimulating the phrenic nerve in cases of ventilatory insufficiency, the authors prefer stimulation of the phrenic nerve in the thorax using a platinum ribbon electrode placed behind the nerve and an attached subcutaneously implanted radiofrequency (RF) receiver inductively coupled to an external RF transmitter. Instructions are given for implanting the electrode-receiver assembly, emphasizing atraumatic handling of the phrenic nerve and strict aseptic techniques. Diaphragm pacing is conducted with low frequency electrical stimulation at a slow repetition (respiratory) rate to condition the diaphragm muscle against fatigue and maintain it fatigue-free. Candidates for diaphragm pacing are those with ventilatory insufficiency due to malfunction of the respiratory control center or interruption of the upper motor neurons of the phrenic nerve. In the Yale series, there were 77 patients treated by diaphragm pacing; 63 (82%) started before 1981 and thus were available for follow-up for at least 5 years; 33 (52%) were paced for 5 to 10 years, and 15 (24%) were paced for 10 to 16. Long term stimulation of the phrenic nerves to pace the diaphragm is an effective method of ventilatory support in selected cases.

Inspiratory Muscle Pacing in Spinal Cord Injury: Case Report and Clinical Commentary

“…The second intercostal space is the most commonly used surgical approach for thoracic placement (11,14). Electrodes are often placed on each phrenic nerve during a single procedure.…”

“…A thorough assessment of phrenic nerve function should be performed in all patients contemplating DP (14,17,21,26,27). Unfortunately, many patients with tetraplegia have sustained injury to the phrenic motoneurons in the spinal cord and/or phrenic rootlets.…”

“…If phrenic nerve function is absent or significantly reduced, DP should not be undertaken. Phrenic nerve function should be assessed both by measurements of phrenic nerve conduction times (38,39) and by fluoroscopic evaluation of diaphragm movement (14,34) during phrenic nerve stimulation.…”

“…Therefore, fluoroscopic examination of the diaphragm during electrical stimulation should also be performed. The diaphragm should descend at least 3 to 4 cm during stimulation as visualized fluoroscopically (14,34). In individuals with normal function, the diaphragm descends more than 5 cm.…”

“…They developed an implantable electrode/receiver system (6)(7)(8) that could be activated by radiofrequency waves generated by a power source external to the body. These investigators also accumulated a significant clinical experience that defined patient evaluation methods, surgical techniques, and safe parameters of stimulation that resulted in optimal diaphragm conditioning (9)(10)(11)(12)(13)(14)(15)(16)(17).…”