title: Respiratory effects of the scalene and sternomastoid muscles in humans.
abstract: Previous studies have shown that in normal humans the change in airway opening pressure (DeltaPao) produced by all the parasternal and external intercostal muscles during a maximal contraction is approximately -18 cmH(2)O. This value is substantially less negative than DeltaPao values recorded during maximal static inspiratory efforts in subjects with complete diaphragmatic paralysis. In the present study, therefore, the respiratory effects of the two prominent inspiratory muscles of the neck, the sternomastoids and the scalenes, were evaluated by application of the Maxwell reciprocity theorem. Seven healthy subjects were placed in a computed tomographic scanner to determine the fractional changes in muscle length during inflation from functional residual capacity to total lung capacity and the masses of the muscles. Inflation induced greater shortening of the scalenes than the sternomastoids in every subject. The inspiratory mechanical advantage of the scalenes thus averaged (mean +/- SE) 3.4 +/- 0.4%/l, whereas that of the sternomastoids was 2.0 +/- 0.3%/l (P < 0.001). However, sternomastoid muscle mass was much larger than scalene muscle mass. As a result, DeltaPao generated by a maximal contraction of either muscle would be 3-4 cmH(2)O, which is about the same as DeltaPao generated by the parasternal intercostals in all interspaces.
authors.affiliation: Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine, and Chest Service and Department of Radiology, Erasme University Hospital, 1070 Brussels, Belgium.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Legrand
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Schneider
authors.forename: Pierre-Alain
authors.initials: PA
authors.lastname: Gevenois
authors.forename: Andre
authors.initials: A
authors.lastname: De Troyer
mesh_terms: D000328:Adult; D005260:Female; D005652:Functional Residual Capacity; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009334:Neck Muscles / Q000000981:diagnostic imaging / Q000502:physiology*; D012016:Reference Values; D015656:Respiratory Mechanics; D012143:Respiratory Physiological Phenomena; D014057:Tomography, X-Ray Computed; D014109:Total Lung Capacity