Journal of Applied Physiology, Vol 70, Issue 2 539-547, Copyright © 1991 by American Physiological Society
Chest wall motion during epidural anesthesia in dogs
D. O. Warner, J. F. Brichant, E. L. Ritman and K. Rehder
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905.
To determine the relative contribution of rib cage and abdominal muscles to
expiratory muscle activity during quiet breathing, we used lumbar epidural
anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to
paralyze the abdominal muscles while leaving rib cage muscle motor function
substantially intact. A high-speed X-ray scanner (Dynamic Spatial
Reconstructor) provided three-dimensional images of the thorax. The
contribution of expiratory muscle activity to tidal breathing was assessed
by a comparison of chest wall configuration during relaxed apnea with that
at end expiration. We found that expiratory muscle activity was responsible
for approximately half of the changes in thoracic volume during
inspiration. Paralysis of the abdominal muscles had little effect on the
pattern of breathing, including the contribution of expiratory muscle
activity to tidal breathing, in most dogs. We conclude that, although there
is consistent phasic expiratory electrical activity in both the rib cage
and the abdominal muscles of pentobarbital-anesthetized dogs lying supine,
the muscles of the rib cage are mechanically the most important expiratory
muscles during quiet breathing.
