Journal of Applied Physiology, Vol 55, Issue 3 731-735, Copyright © 1983 by American Physiological Society

ARTICLES

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

S. A. Esau, P. T. Bye and R. L. Pardy

The rate of relaxation of the diaphragm after stimulated (4 subjects) and voluntary (8 subjects) contractions was compared in normal young men. Stimulated contractions were induced by supramaximal unilateral 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 (tau) of the later exponential decline in Pdi was independent of Pdi. The mean +/- SE rate constant of relaxation (MRR/Pdi) was 0.0078 +/- 0.0002 ms-1 and the mean tau 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 sniffs were performed (in the range of residual volume to functional residual capacity + 1 liter) or by the relative contribution gastric pressure made to Pdi. After diaphragmatic fatigue was induced by inspiring against a high alinear resistance there was a decrease in relaxation rate. In the 1st min postfatigue MRR/Pdi decreased (0.0063 +/- 0.0003 ms-1; P less than 0.005) and tau increased (83 +/- 5 ms; P less than 0.005). Both values returned to prefatigue levels within 5 min of the end of the studies. We conclude that the sniff may prove to be clinically useful in the detection of diaphragmatic fatigue.

This article has been cited by other articles:

				ATS/ERS Statement on Respiratory Muscle Testing Am. J. Respir. Crit. Care Med., August 15, 2002; 166(4): 518 - 624. [Full Text] [PDF]

				D Kyroussis, L C Johnson, C-H Hamnegard, M I Polkey, and J Moxham Inspiratory muscle maximum relaxation rate measured from submaximal sniff nasal pressure in patients with severe COPD Thorax, March 1, 2002; 57(3): 254 - 257. [Abstract] [Full Text] [PDF]

				R. Chen, B. Kayser, S. Yan, and P. T. Macklem Twitch transdiaphragmatic pressure depends critically on thoracoabdominal configuration J Appl Physiol, January 1, 2000; 88(1): 54 - 60. [Abstract] [Full Text] [PDF]

				C. Coirault, D. Chemla, and Y. Lecarpentier Relaxation of diaphragm muscle J Appl Physiol, October 1, 1999; 87(4): 1243 - 1252. [Abstract] [Full Text] [PDF]

				Y. Lecarpentier, C. Coirault, O. Langeron, F. X. Blanc, S. Salmeron, P. Attal, B. Riou, and D. Chemla Impaired load dependence of diaphragm relaxation during congestive heart failure in the rabbit J Appl Physiol, October 1, 1999; 87(4): 1339 - 1345. [Abstract] [Full Text] [PDF]