Diaphragmatic fatigue in normoxia and hyperoxia

742, 1985.-Diaphragmatic fatigue was induced in six normal young men inspiring against a variable alinear resistance. Breathing pattern was rigidly controlled (tidal volume 0.75 liter, 12 breaths min-‘). Fatigue was defined as an inability to continue to generate a target transdiaphragmatic pressure (Pdi = 0.65- 0.84 Pdi,,,). Diaphragmatic electromyogram (EMG, esophageal electrode) and perceived effort (PE, open-ended scale) were recorded. Subjects were tested on an identical resistance inspiring air or 100 % 02 in random order on different days. They were unaware of the gas mixture inspired. Mean endurance time (tli,) t SE for air was 4.1 t 1.4 min and for O2 was 8.6 t 2.7 min (P < 0.005). The increased tlim in O2 was associated with a delay in onset of EMG changes heralding diaphragmatic fatigue and a decrease in PE at any time during the study compared with the level of PE in air. Arterial O