Effect of lung volume on in vivo contraction characteristics of the human diaphragm
We performed transcutaneous bilateral phrenic nerve stimulation at varying lung volumes between RV and TLC in 6 normal male volunteers. Peak twitch transdiaphragmatic pressure declined from a mean of 49.1 (SD: 9.1) cm H2O at RV to a mean of 19.6 cm H2O (SD: 5.97) at TLC. Twitch contraction time fell from a mean of 91.8 (SD: 11.3) at RV to a mean of 57.7 ms (SD: 7.4) at TLC. There was a good correlation between changes in contraction time and transdiaphragmatic pressure (r = 0.7). The fall in transdiaphragmatic pressure was almost all due to a fall in pleural pressure, with little change in gastric pressure between RV and TLC. At TLC the pleural pressure in response to phrenic nerve stimulation was −0.58 cm H2O. We conclude that as lung volume increases and the diaphragm shortens, it becomes less effective as a pressure. At a lung volume close to TLC the diaphragm ceases to act as an inspiratory muscle.
Key WordsLung volume contraction characteristics in vivo diaphragm phrenic nerve stimulation transcutaneous bilateral pleural pressure gastric pressure inspiratory muscle.
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- 1.AGOSTONI E., RAHN H.: Abdominal and thoracic pressures at different lung volumes. J. Appl. Physiol. 1960. 1087–1092.Google Scholar
- 3.BELLEMARE F., BIGLAND-RITCHIE B., Woods J.J.: Contractile properties of the human diaphragm in vivo. J. Appl. Physiol. (In Press).Google Scholar
- 8.EDWARDS R.H.T., FAULKNER J.A.; Lung biology in health and disease, In: The Thorax, Part A. Respiratory muscles: Structure and Function. New York, Structure and Function. 1986. Vol. 29, p. 297.Google Scholar
- 15.MARSHALL R.: Relationships between stimulus and work of breathing at different lung volumes. J. Appl. Physiol. 1962. 17: 917–921.Google Scholar
- 16.MILIC-EMILI J., TURNER J.M., GLAUSER E.M.: Improved technique for estimating pleural pressure from esophageal balloons. J. Appl. Physiol. 1964. 19: 207–211/Google Scholar
- 20.PETIT J.M., MILIC-EMILI J., DELHEZ L.: Role of the diaphragm in breathing in conscious man, an electromyography study. J. Appl. Physiol. 1964. 15: 1101–1106.Google Scholar
- 21.RACK P.M.H., WESTBURY D.R.: The effects of length and stimulus rate on tension in the isometric cat soleus muscle. J. Physiol. (London) 1969. 204: 443–460.Google Scholar