Electrical techniques for stimulation of the phrenic nerve to pace the diaphragm: inductive coupling and battery powered total implant in asynchronous and demand modes.

A review of the electrical design of a rf inductively coupled phrenic nerve stimulator for the diaphragm developed in our laboratories will be discussed. Modifications of the original circuit are based on long-term laboratory and clinical studies. A total implant battery powered stimulator was designed exclusively for animal studies to evaluate the effects of several stimulating parameters on diaphragm fatigue and neuromuscular structure. On the basis of these studies the optimum current level, stimulus frequency, respiratory rate, electrode configuration, and waveform were selected for clinical use to pace the diaphragm. A multiprogrammable dual output stimulator responsive to interrogation has been constructed and used in the experimental laboratory in anticipation of clinical application. There was an insignificant difference between the effect on neural structure or diaphragm function of stimulation with pulse width modulated constant voltage or with amplitude-modulated constant current. Demand pacing: maintenance of normal PACO2 by monitoring ET PACO2 with feedback to the diaphragm pacemaker to adjust the pacing rate has been successful in the experimental animal.