Document Detail

Effects of inspiratory flow on diaphragmatic motor output in normal subjects.
MedLine Citation:
PMID:  10926629     Owner:  NLM     Status:  MEDLINE    
Increasing inspiratory flow (V) has been shown to shorten neural inspiratory time (TI(n)) in normal subjects breathing on a mechanical ventilator, but the effect of V on respiratory motor output before inspiratory termination has not previously been studied in humans. While breathing spontaneously on a mechanical ventilator, eight normal subjects were intermittently exposed to 200-ms-duration positive pressure pulses of different amplitudes at the onset of inspiration. Based on the increase in V above control breaths (DeltaV), trials were grouped into small, medium, and large groups (mean DeltaV: 0.51, 1.11, and 1.65 l/s, respectively). We measured TI(n), transdiaphragmatic pressure (Pdi), and electrical activity (electromyogram) of the diaphragm (EMGdi). Transient increases in V caused shortening of TI(n) from 1.34 to 1.10 (not significant), 1.55 to 1.11 (P < 0.005), and 1.58 to 1.17 s (P < 0. 005) in the small, medium, and large DeltaV groups, respectively. EMGdi measured at end TI(n) of the pulse breaths was 131 (P < 0.05), 142, and 155% (P < 0.05) of the EMGdi of the control breaths at an identical time point in the small, medium, and large trials, respectively. The latency of the excitation was 126 +/- 42 (SD) ms, consistent with a reflex effect. Increasing V had two countervailing effects on Pdi: 1) a depressant mechanical effect due primarily to the force-length (11.2 cmH(2)O/l) relation of the diaphragm, and 2) an increase in diaphragm activation. For the eight subjects, mean peak Pdi did not change significantly, but there was significant intersubject variability, reflecting variability in the strength of the excitation reflex. We conclude that increasing inspiratory V causes a graded facilitation of EMGdi, which serves to counteract the negative effect of the force-length relation on Pdi.
S Corne; K Webster; M Younes
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  89     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2000 Aug 
Date Detail:
Created Date:  2000-09-15     Completed Date:  2000-09-15     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  481-92     Citation Subset:  IM    
Section of Respiratory Medicine, Department of Medicine, University of Manitoba, Winnipeg, Canada.
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MeSH Terms
Air Pressure
Diaphragm / physiology*
Muscle Contraction / physiology
Pulmonary Ventilation / physiology*
Respiration, Artificial
Comment In:
J Appl Physiol (1985). 2001 May;90(5):2014-5   [PMID:  11386232 ]

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