TY - JOUR
T1 - Mechanical action of the internal intercostal muscles in dogs
AU - DiMarco, A. F.
AU - Supinski, G. S.
AU - Simhai, B.
AU - Romaniuk, J. R.
PY - 1993
Y1 - 1993
N2 - The pattern of electrical activation and muscle length changes of the internal intercostal (II) muscles (9th or 10th interspace) of the lower rib cage were evaluated in supine anesthetized dogs. Studies were performed during resting breathing and expiratory threshold loading. Results were compared with simultaneous measurements of the better-studied triangularis sterni muscle (4th interspace). In general, both muscles lengthened with passive inflation and shortened with passive deflation. During resting breathing, both the II and TS muscles were electrically active and shortened below resting length, 7.7 ± 1.6% (SE) and 5.3 ± 1.7%, respectively. With the addition of positive end-expiratory pressure, the degree of electrical activation and muscle shortening increased progressively for both muscles, although to a somewhat greater extent for II muscles. Isolated denervation of the II muscles eliminated their shortening during resting breathing and often resulted in muscle lengthening, indicating that II muscle shortening was secondary to its own activation. Expiration was associated with lateral inward movement of the lower rib cage below its relaxation position. This motion was not significantly affected by abdominal muscle section but was markedly reduced by bilateral II denervation (7th-11th spaces). Our results indicate that the II muscles of the lower rib cage 1) are electrically active and shorten below resting length during resting breathing, 2) respond to positive end-expiratory pressure by increasing their level of activation and degree of shortening, and 3) are primarily responsible for inward lateral motion of the lower rib cage below its relaxation position during expiration.
AB - The pattern of electrical activation and muscle length changes of the internal intercostal (II) muscles (9th or 10th interspace) of the lower rib cage were evaluated in supine anesthetized dogs. Studies were performed during resting breathing and expiratory threshold loading. Results were compared with simultaneous measurements of the better-studied triangularis sterni muscle (4th interspace). In general, both muscles lengthened with passive inflation and shortened with passive deflation. During resting breathing, both the II and TS muscles were electrically active and shortened below resting length, 7.7 ± 1.6% (SE) and 5.3 ± 1.7%, respectively. With the addition of positive end-expiratory pressure, the degree of electrical activation and muscle shortening increased progressively for both muscles, although to a somewhat greater extent for II muscles. Isolated denervation of the II muscles eliminated their shortening during resting breathing and often resulted in muscle lengthening, indicating that II muscle shortening was secondary to its own activation. Expiration was associated with lateral inward movement of the lower rib cage below its relaxation position. This motion was not significantly affected by abdominal muscle section but was markedly reduced by bilateral II denervation (7th-11th spaces). Our results indicate that the II muscles of the lower rib cage 1) are electrically active and shorten below resting length during resting breathing, 2) respond to positive end-expiratory pressure by increasing their level of activation and degree of shortening, and 3) are primarily responsible for inward lateral motion of the lower rib cage below its relaxation position during expiration.
KW - expiratory muscles
KW - positive end-expiratory pressure
KW - rib cage motion
KW - triangularis sterni muscles
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U2 - 10.1152/jappl.1993.75.6.2360
DO - 10.1152/jappl.1993.75.6.2360
M3 - Article
C2 - 8125851
AN - SCOPUS:0027750847
SN - 8750-7587
VL - 75
SP - 2360
EP - 2367
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 6
ER -