Kinematics and mechanics of midcostal diaphragm of dog

Radiopaque markers were attached to the peritoneal surface of three neighboring muscle bundles in the midcostal diaphragm of four dogs, and the locations of the markers were tracked by biplanar video fluoroscopy during quiet spontaneous breathing and during inspiratory efforts against an occluded airway at three lung volumes from functional residual capacity to total lung capacity in both the prone and supine postures. Length and curvature of the muscle bundles were determined from the data on marker location. Muscle lengths for the inspiratory states, as a fraction of length at functional residual capacity, ranged from 0.89 +/- 0.04 at end inspiration during spontaneous breathing down to 0.68 +/- 0.07 during inspiratory efforts at total lung capacity. The muscle bundles were found to have the shape of circular arcs, with the three bundles forming a section of a right circular cylinder. With increasing lung volume and diaphragm displacement, the circular arcs rotate around the line of insertion on the chest wall, the arcs shorten, but the radius of curvature remains nearly constant. Maximal transdiaphragmatic pressure was calculated from muscle curvature and maximal tension-length data from the literature. The calculated maximal transdiaphragmatic pressure-length curve agrees well with the data of Road et al. (J. Appl. Physiol. 60: 63-67, 1986).