Functional role and structural characteristics of the scalene
muscle: an accessory inspiratory muscle in the hamster.
Fournier, Mario, and Michael I. Lewis.
Division of Pulmonary/Critical Care Medicine, Department of
Medicine, The CSMC Burns & Allen Research Institute, UCLA School
of Medicine, Los Angeles, California 90048
APStracts 3:0386A, 1996.
While the scalene muscle (SCA) is a primary inspiratory muscle in man,
its respiratory function in other species is less clear. The
electromyographic (EMG) activity of the SCA was studied during
resting ventilation (eupnea) in both the awake and anesthetized
hamster, and following a variety of respiratory challenges in the
anesthetized animal. The EMG activities of the medial SCA and the
costal diaphragm were compared. The medial SCA, the major component
of the SCA, originates from cervical transverse processes 2 to 5 and
inserts primarily onto rib 4, with a small segment onto rib 3. In
both the anesthetized and awake animal, the SCA was always silent
during quiet breathing. With CO2-stimulated hyperpnea, the SCA was
always recruited during inspiration in phase with the diaphragm.
Active recruitment of the SCA was also observed following resistive
loading and total airway occlusion. Following ipsilateral
phrenicotomy, the SCA was persistently recruited during eupnea. The
specificity of the EMG signals was tested both by excluding cross
-contamination from other rib cage muscles and by selective
denervation studies. Muscle spindles were identified in the medial
SCA histochemically, suggesting that the respiratory activity of the
SCA can also be modulated by changes in muscle length and/or load.
These results indicates that the SCA functions as an accessory
inspiratory muscle in the hamster and may play an important role in
conditions of chronic load.
Received 18 September 1995; accepted in final form 6 August 1996.
APS Manuscript Number A1012-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996