Between 1913 and 1926, C. F. Hoover of Cleveland published a number of interesting articles on the mechanics of respiration in which he emphasized the diagnostic significance of the movements of the costal margins. According to this author, the intercostal muscles and the diaphragm have antagonistic actions. The intercostals enlarge the transverse and anteroposterior diameter of the lower part of the thorax in inspiration, and tend to draw the costal margins away from the median line and to widen the subcostal angle, while the contraction of the diaphragm increases the longitudinal diameter of the chest, and at the same time tends to draw the costal margins toward the median line, thus narrowing the angle between them. The extent and direction of the marginal motion are thus the result of the antagonistic forces exerted by the intercostal muscles and the diaphragm.
Hoover further claimed, however, that when the arch of the
BRAY HA, WILSON JL. THE EXCURSION OF THE COSTAL MARGINS IN HEALTH AND IN DISEASE. Arch Intern Med (Chic). 1929;43(2):187–195. doi:https://doi.org/10.1001/archinte.1929.00130250043004
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