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J Appl Physiol 65: 649-656, 1988;
8750-7587/88 $5.00
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Journal of Applied Physiology, Vol 65, Issue 2 649-656, Copyright © 1988 by American Physiological Society

ARTICLES

Relationship among EMG and contractile responses of the diaphragm elicited by hypotension

S. N. Hussain, J. E. Marcotte, H. Burnet, P. Collett and C. Roussos
Department of Medicine, Royal Victoria Hospital, Montreal, Quebec, Canada.

In a canine model, we investigated the effects of severe hypotension on the indexes of diaphragmatic failure. We measured 1) the transdiaphragmatic pressure obtained in response to 20- and 100-Hz stimulation of phrenic nerves (Pdi20 and Pdi100), 2) the power spectrum of diaphragmatic electromyogram (EMG), 3) the ratio of integrated diaphragmatic EMG to Pdi (Edi/Pdi), and 4) the rate of relaxation of Pdi100 and Pdi20. Arterial blood pressure (Pa) was reduced to 40-50 mmHg by a balloon inflated in the inferior vena cava and was maintained at this level until Pdi100 declined to 75% of the control value (100% shock time, ST). A recovery period of 60 min at normal Pa was allowed. During hypotension, Pdi100 and Pdi20 declined only at 100% ST [95.0 +/- 13.0 (SE) min]; however, only Pdi100 recovered within 15 min. The power spectrum shifted to low frequencies early and progressively during shock period. Edi/Pdi rose significantly at 80 and 100% ST and recovered within 15 min. The relaxation rate of Pdi20 and Pdi100 increased significantly at 100% ST only. We conclude that 1) diaphragmatic contractility is depressed during severe hypotension, 2) changes in the power spectrum occurred first in the shock state, followed by alterations in Edi/Pdi, and subsequently both changes in the frequency-pressure curve and relaxation rate occurred last.


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J Appl Physiol, April 1, 2007; 102(4): 1556 - 1564.
[Abstract] [Full Text] [PDF]


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