Journal of Applied Physiology, Vol 66, Issue 2 870-875, Copyright © 1989 by American Physiological Society
Diaphragm length adjustments with body position changes in the awake dog
J. W. Fitting, P. A. Easton, R. Arnoux, A. Guerraty and A. Grassino
Hopital Notre-Dame, Universite de Montreal, Quebec, Canada.
Sonomicrometry was used to measure end-expiratory length and tidal
shortening of the costal and crural diaphragm in awake chronically
instrumented dogs in the right lateral decubitus, standing, and sitting
postures. End-expiratory length did not change significantly in standing
but fell by 11.5% for the costal and by 14.4% for the crural segment in
sitting, when compared with decubitus position. Tidal shortening of both
segments did not change significantly in the three postures. From decubitus
to sitting, diaphragmatic electromyogram (EMG) activity increased only in
some dogs, not significantly for the group. The inspiratory swing of
abdominal pressure was always positive in decubitus and negative in
standing and sitting. In the latter two postures, abdominal pressure
increased gradually during expiration and fell in inspiration, suggesting a
phasic expiratory contraction of abdominal muscles. We conclude that
diaphragmatic tidal shortening is maintained in the different postures
assumed by the awake dog during resting breathing. It seems that the main
compensatory mechanism for changes in diaphragmatic operational length is a
phasic expiratory contraction of the abdominal muscles rather than an
increase in diaphragmatic EMG activity.
