Evaluation of electrical parameters for diaphragm pacing: An experimental study

A study of electrical parameters for pacing of the diaphragm in dogs was undertaken to determine which level of current, stimulation waveform, electrode design, impulse frequency, and pulse train repetition rate caused least fatigue of the diaphragm muscle. Stimulation of the phrenic nerve at a current level causing maximal tidal volume resulted in greater fatigue than stimulation at a somewhat lesser current level. A bidirectional waveform was less fatiguing than a unidirectional waveform, but the difference was not striking. Whether the electrode was monopolar or bipolar was not a factor, although recovery from fatigue was slightly faster and more complete after cessation of stimulation with the former. A marked differences in the development of fatigue occurred with the use of different stimulation frequencies. A high-frequency, narrow pulse interval (33 Hz; 30 msec PI) caused rapid and marked fatigue, a higher-frequency, wider pulse interval (25 Hz; 40 msec PI) somewhat less fatigue, while a stimulation frequency similar to the discharge of motor neurons to slow-contracting muscle (11 Hz; 90 msec PI) no fatigue, indeed, with continued stimulation, an improvement in tidal volume. There also appeared to be less fatigue with a pulse train repetition rate (rate of inspiration) of 10 per minute rather than 20. The results of these experiments are of importance in planning an effective pacing program for clinical use. It may be particularly helpful in the designing of stimulators for patients who require artificial ventilatory support but who are unable to be maintained on the available electrical apparatus for clinical application.