LONG-TERM INTRAMUSCULAR ELECTRICAL ACTIVATION OF THE PHRENIC-NERVE - EFFICACY AS A VENTILATORY PROSTHESIS

The efficacy of a system for long-term intramuscular activation of the phrenic nerve as a ventilatory prosthesis was evaluated in seven dogs ; (The safety and reliability of this system is addressed in a compani on paper.) Five dogs underwent chronic bilateral intramuscular diaphra gm stimulation (IDS) for 61 to 183 days at stimulus parameters selecte d to evoke at least 120% of the animal's basal ventilation. Two dogs m aintained as controls did not undergo chronic stimulation. The ability of IDS to provide long term ventilation without diaphragm fatigue was evaluated in terms of the ventilatory capacity of IDS, the effects of chronic IDS on diaphragm contractile properties, acid the phrenic ner ve recruitment properties of chronic IDS electrodes. Hemidiaphragms wi th electrodes placed within 2 cm of the phrenic nerve trunk could be c ompletely activated by 25 mA pulses having a 100 mu s pulse width. The tidal volume evoked by IDS in this study was 167% (+/-48 s.d.) of tha t required for full-time basal ventilation without diaphragm fatigue. Evoked tidal volume increased after 8 to 9 weeks of chronic IDS for st imulus pulse intervals longer than 50 mS. Electrode recruitment proper ties were stable for both active and passive implanted electrodes, We conclude from these studies that with properly placed electrodes IDS i s capable of providing reliable full-time ventilatory support without fatiguing the diaphragm.