Changes in relaxation rate with diaphragmatic fatigue in humans

J Appl Physiol Respir Environ Exerc Physiol. 1983 May;54(5):1353-60. doi: 10.1152/jappl.1983.54.5.1353.


Maximum relaxation rate (MRR) and the time constant of relaxation (tau) of transdiaphragmatic pressure (Pdi) was measured in four male subjects and compared with the high-to-low frequency ratio (H/L) of the diaphragmatic electromyogram (EMG) as a predictor of diaphragmatic fatigue. Pdi and inspiratory time-to-total breath duration ratios (TI/TT) were varied, and TT and tidal volume were held constant; inspiratory resistances were used to increase Pdi. Studies were performed at various tension-time indices (TTdi = Pdi/Pdimax X TI/TT). Base-line MRR/Pdi was 0.0100 +/- 0.0004 (SE) ms-1, and baseline tau was 53.2 +/- 3.2 ms. At TTdi greater than 0.20, MRR and H/L decreased and tau increased, with maximum changes at the highest TTdi. At TTdi less than 0.20, there was no change in H/L, MRR, or tau. The time course of changes in H/L correlated with those of MRR and tau under fatiguing conditions. In this experimental setting, change in relaxation rate was as useful a predictor of diaphragmatic fatigue as fall in H/L of the diaphragmatic EMG.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Diaphragm / physiology*
  • Electromyography
  • Humans
  • Inspiratory Capacity
  • Male
  • Muscle Contraction*
  • Muscle Relaxation*
  • Pressure
  • Respiration*
  • Tidal Volume