Three-Dimensional Axisymmetric Computational Modeling of Diaphragm Motion, Shape, and Stress Distribution During the Respiratory Cycle

The diaphragm is the primary muscle responsible for respiration. A computational study was conducted to investigate diaphragm motion and stress development during breathing. A three-dimensional axisymmetric model of the diaphragm was developed using physiologically realistic geometry and material properties obtained from experimental measurements of diaphragmatic muscle. The model incorporates both transdiaphragmatic pressure and a diaphragm muscle activation parameter to simulate the mechanical response of the diaphragm throughout an entire respiratory cycle. In addition, a simplified cylindrical thoracic cavity model containing a fixed volume of air was coupled to the diaphragm to examine the relationship between diaphragm activation, cavity volume change, and internal air pressure. The governing equilibrium equations were solved to predict diaphragm deformation and the resulting stress distributions during inspiration and exhalation. The simulations show that mechanical stress is not uniformly distributed throughout the diaphragm and varies considerably during the breathing cycle. The overall shape and curvature of the diaphragm muscle fibers undergo relatively small changes during normal breathing despite significant internal stress variations. The cylindrical model predicts that diaphragm activation increases thoracic volume and decreases internal air pressure, reproducing the fundamental mechanics of inspiration. These results demonstrate the complex relationship between diaphragm shape, muscle activation, transdiaphragmatic pressure, cavity pressure, and stress distribution.