Journal of Applied Physiology, Vol 60, Issue 5 1686-1691, Copyright © 1986 by American Physiological Society
Respiratory and postural changes in intercostal muscle length in supine dogs
M. Decramer, S. Kelly and A. De Troyer
In an attempt to assess the physiological function(s) of the external (E)
and internal interosseous (I) intercostal muscles, we measured the changes
in intercostal muscle length during spontaneous breathing, during passive
inflation, and during passive rotation of the trunk. Studies were performed
on 46 muscles from 16 supine anesthetized dogs, and changes in muscle
length were assessed by sonomicrometry. The changes were small during
spontaneous breathing, whether before or after bilateral phrenicotomy, and
the pattern was variable among animals and among interspaces. The E,
however, particularly in the lower interspaces, often lengthened with
inspiration, and the I, in particular in the upper interspaces, often
shortened with inspiration. Only occasionally did the E and I in one
interspace change in length in opposing directions. This was also true
during passive inflation, where both E and I usually shortened in the upper
interspaces and lengthened in the lower interspaces. By contrast, during
passive rotation of the trunk, the E and I systematically changed in length
in opposing directions, and either muscle could successively lengthen and
shorten a substantial amount depending on the side of rotation. These
results suggest that 1) the E and I in supine dogs do not behave as
antagonistic muscles during moderate respiratory efforts; and 2) they do
behave as antagonistic muscles during rotation of the trunk. A primary
function of these muscles as rotators of the trunk, unlike breathing, may
explain why two layers of intercostal muscles with different fiber
orientation exist between the ribs.
