Recovery of PdiTwitch following the induction of diaphragm fatigue in normal subjects

Low frequency diaphragm fatigue (LFF) may play a major role in the pathogenesis of ventilatory failure; however, recovery from LFF is not well studied. We measured transdiaphragmatic twitch pressure (Pdi(T)) at FRC (using a reduction of Pdi(T) as an index of LFF) and maximum transdiaphragmatic pressure (Pdi(max)) before and after the induction of diaphragm fatigue in seven normal subjects, age 31 +/- 3 yr (mean +/- SD). Fatigue was induced by breathing through an inspiratory resistive load. Pdi(T) produced by bilateral transcutaneous supramaximal electrophrenic stimulation was measured at baseline, 15, 30 min, 1, 2, 3, 4 h, and then 1 to 3 times between hour 20-25 post-fatigue. Pdi(max) estimated by twitch occlusion was measured at baseline, 30 min, 2-3, and 20-25 h post-fatigue. Pre-fatigue values (mean +/- SE) were: Pdi(T) 23.6 +/- 2.5 cm H2O. The mean +/- SD time to fatigue was 25.3 +/- 12.3 min. Post-fatigue Pdi(T) was reduced to 50%, and by 3 h was 72% of the initial value; 100% by 25 h. Pdi(max) was reduced to 75% post-fatigue, but recovered to 87% by 3 h, and 100% by 25 h. We concluded that recovery of Pdi(T) and Pdi(max) in normal subjects starts to occur within the first few hours following diaphragm fatigue, and is complete by 25 h.