Journal of Applied Physiology, Vol 66, Issue 3 1414-1420, Copyright © 1989 by American Physiological Society
Passive shortening of canine parasternal intercostals during breathing
A. De Troyer and G. A. Farkas
Thoracic Diseases Research Unit, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905.
We have previously demonstrated that the shortening of the canine
parasternal intercostals during inspiration results primarily from the
muscles' own activation (J. Appl. Physiol. 64: 1546-1553, 1988). In the
present studies, we have tested the hypothesis that other inspiratory rib
cage muscles may contribute to the parasternal inspiratory shortening.
Eight supine, spontaneously breathing dogs were studied. Changes in length
of the third or fourth right parasternal intercostal were measured during
quiet breathing and during single-breath airway occlusion first with the
animal intact, then after selective denervation of the muscle, and finally
after bilateral phrenicotomy. Denervating the parasternal virtually
eliminated the muscle shortening during quiet inspiration and caused the
muscle to lengthen during occluded breaths. After phrenicotomy, however,
the parasternal, while being denervated, shortened again a significant
amount during both quiet inspiration and occluded breaths. These data thus
confirm that a component of the parasternal inspiratory shortening is not
active and results from the action of other inspiratory rib cage muscles.
Additional studies in four animals demonstrated that the scalene and
serratus muscles do not play any role in this phenomenon; it must therefore
result from the action of intrinsic rib cage muscles.
