Modeling the kinematics of the canine midcostal diaphragm

The hypotheses that the chest wall insertion (CW) is displaced laterally du ring inspiration and that this displacement is essential in maintaining mus cle curvature of the costal diaphragmatic muscle fibers were tested. With t he use of data from three dogs, caudal, lateral, and ventral displacements of CW during both quiet, spontaneous inspiration and during inspiratory eff orts against an occluded airway were observed and recorded. We have develop ed a kinematic model of the diaphragm that incorporates these displacements . This model describes the motions of the muscle fibers and central tendon; the displacements of the midplane, muscle-tendon junction (MTJ), CW, and c enter of the muscle fiber-central tendon arcs are modeled as functions of m uscle fiber length. In the model, the center of the fiber arcs and MTJ both move caudally parallel to the midplane during inspiration, whereas CW move s both caudally and laterally. The observed lateral displacement of CW and the observed caudal displacement of MTJ, as functions of muscle fiber lengt h, both approximate well the theoretical displacements that would be necess ary to maintain curvature of the fiber arcs. In confirming our hypotheses, we have found that lateral displacement of CW is a mechanism by which chang es in the shape of the costal diaphragm, as described by its curvature, are limited.