Changes in rate of relaxation of sniffs with diaphragmatic fatigue in humans

of the diaphragm after stimulated (4 subjects) and voluntary (8 subjects) contractions was compared in normal young men. Stimulated contractions were induced by supramaximal unilat-eral phrenic nerve stimulation and voluntary contractions by short, sharp sniffs of varying tensions against an occluded airway. The rate of relaxation of the diaphragm was calculated from the rate of decline of transdiaphragmatic pressure (Pdi). In both conditions the maximum relaxation rate (MRR) was proportional to the peak transdiaphragmatic pressure (Pdi), whereas the time constant (7) of the later exponential decline in Pdi was independent of Pdi. The mean t SE rate constant of relaxation (MRR/Pdi) was 0.0078 $- 0.0002 ms-l and the mean 7 was 57 & 3.8 ms for stimulated contractions. The rate of relaxation after sniffs was not different, and it was not affected by either the lung volume at which occluded sniff