Journal of Applied Physiology, Vol 70, Issue 3 1059-1067, Copyright © 1991 by American Physiological Society
Dynamic behavior of excised dog rib cage: dependence on muscle
Y. Kikuchi, D. Stamenovic and S. H. Loring
Respiratory Biology Program, Harvard School of Public Health, Boston, Massachusetts 02115.
To assess the contribution of the rib cage to chest wall elastance and
hysteresis, we measured force-displacement behavior of the isolated canine
rib cage during sinusoidal forcing of the sternum in the midsagittal plane
at low frequencies (0.02-2.0 Hz). Elastance of the rib cage was nearly
invariant with frequency of forcing from 0.02 to 1.0 Hz and decreased with
increasing amplitude. Hysteresis, the width of the force-displacement loop
at middisplacement (zero displacement), was nearly constant with frequency
below 1.0 Hz and increased with increasing amplitude of forcing. Removal of
muscle reduced elastance and hysteresis of the rib cage substantially. The
data suggest that the excised dog rib cage shows dynamic behavior similar
to that of the intact human rib cage and chest wall and that respiratory
muscle is responsible for a major part of the behavior of the passive chest
wall. We also calculated the major and minor stiffnesses in the sagittal
plane, which differed by a factor of 3-11, and their directions lay close
to the dorsoventral and cephalocaudal axes, respectively. Removal of muscle
reduced the stiffnesses but did not change their directions. Thus, although
respiratory muscles impede motion in the sagittal plane, they do not alter
its pattern.
