Journal of Applied Physiology, Vol 56, Issue 5 1320-1324, Copyright © 1984 by American Physiological Society
Salutary effect of fall in abdominal pressure during diaphragm paralysis
S. Kelly, W. A. Zin, M. Decramer and A. De Troyer
To examine the mechanical effects of the fall in abdominal pressure (Pab)
that occurs during inspiration in diaphragmatic paralysis, we studied lung
inflation and rib cage expansion before and after the abdomen was opened in
nine spontaneously breathing dogs with bilateral phrenicotomy . We measured
Pab, tidal volume, and parasternal electromyographic (EMG) activity during
quiet breathing and CO2-induced hyperpnea. In six dogs, we also measured
changes in anteroposterior and transverse rib cage diameters, the resting
length of the parasternal intercostal muscles, and the amount of shortening
of these muscles during inspiration. Opening the abdomen caused a marked
reduction in the fall in Pab during inspiration and invariably resulted in
a decrease in tidal volume (mean decrease, 13%), which contrasted with
marked increases in inspiratory rib cage expansion and in the amount of
parasternal intercostal shortening. The procedure, however, did not affect
the resting length or inspiratory EMG activity of the parasternals . These
findings indicate that although the fall in Pab, which occurs during
inspiration in diaphragmatic paralysis, causes paradoxical inward
displacement of the ventral abdominal wall, it has a salutary effect on
tidal volume. This phenomenon is probably due to the fact that the
diaphragm is part of the abdominal wall.
