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J Appl Physiol 85: 2284-2290, 1998;
8750-7587/98 $5.00
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Vol. 85, Issue 6, 2284-2290, December 1998

Mechanical advantage of the canine diaphragm

Theodore A. Wilson1, Aladin M. Boriek2, and Joseph R. Rodarte2

1 Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota 55455; and 2 Baylor College of Medicine, Houston, Texas 77030

The mechanical advantage (µ) of a respiratory muscle is defined as the respiratory pressure generated per unit muscle mass and per unit active stress. The value of µ can be obtained by measuring the change in the length of the muscle during inflation of the passive lung and chest wall. We report values of µ for the muscles of the canine diaphragm that were obtained by measuring the lengths of the muscles during a passive quasistatic vital capacity maneuver. Radiopaque markers were attached along six muscle bundles of the costal and two muscle bundles of the crural left hemidiaphragms of four bred-for-research beagle dogs. The three-dimensional locations of the markers were obtained from biplane video-fluoroscopic images taken at four volumes during a passive relaxation maneuver from total lung capacity to functional residual capacity in the prone and supine postures. Muscle lengths were determined as a function of lung volume, and from these data, values of µ were obtained. Values of µ are fairly uniform around the ventral midcostal and crural diaphragm but significantly lower at the dorsal end of the costal diaphragm. The average values of µ are -0.35 ± 0.18 and -0.27 ± 0.16 cmH2O · g-1 · kg-1 · cm-2 in the prone and supine dog, respectively. These values are 1.5-2 times larger than the largest values of µ of the intercostal muscles in the supine dog. From these data we estimate that during spontaneous breathing the diaphragm contributes ~40% of inspiratory pressure in the prone posture and ~30% in the supine posture. Passive shortening, and hence µ, in the upper one-third of inspiratory capacity is less than one-half of that at lower lung volume. The lower µ is attributed primarily to a lower abdominal compliance at high lung volume.

respiratory muscles; mechanics; chest wall


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