The Journal of surgical research
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An experimental study was performed to determine the main site of fatigue associated with diaphragm pacing. Using 24 mature mongrel dogs, weighing 7.5 to 12.7 kg, direct phrenic nerve pacing was conducted from the right cervical area at three different respiration rates, 37 (Group 1, n = 6), 25 (Group 2, n = 6) and 12 (Group 3, n = 6) times per minute, under fixed stimulation conditions (pulse duration, 200 microseconds; frequency, 25 Hz; pulse train repetition time, 1.2 sec). Diaphragm fatigue was defined as the reduction in transdiaphragmatic pressure (Pdi) to less than or equal to 60% of the initial value. ⋯ Following administration of aminophylline, Pdi showed a significant (P less than 0.05) increase over time in all groups: 19.8 +/- 13.5% at 5 min, 23.0 +/- 13.5% at 15 min, and 16.2 +/- 14.9% at 30 min for Group 1; 23.6 +/- 11.6% at 5 min, 27.3 +/- 15.5% at 15 min, and 19.0 +/- 16.1% at 30 min for Group 2; and 29.9 +/- 21.1% at 5 min, 29.5 +/- 18.6% at 15 min, 22.3 +/- 13.8% at 30 min, and 15.5 +/- 13.4% at 45 min for Group 3. In contrast, administration of aminophylline caused no significant changes in Edi. Based upon the finding that aminophylline was significantly effective at the time of diaphragm fatigue, it is concluded that fatigue of the muscle itself constitutes one of the contributing factors for the fatigue phenomenon associated with diaphragm pacing.