Structural model of thorax and abdomen for respiratory mechanics

AbstractThis paper describes a structural model of the human rib cage and abdomen that incorporates many geometrical and functional features important to the understanding of respiratory mechanics. The rib cage, diaphragm, abdominal wall and lungs are characterized by nonlinear stress-strain characteristics that depend on muscle activity. The positions, volumes, forces and pressures for each set of initial conditions are found by determining mechanical equilibrium. Many such determinations allow predictions for large displacements. The model predicts passive respiratory system behavior and the action of individual respiratory muscles that are qualitatively consistent with physiological data. Respiratory mechanics includes both pulmonary mechanics and mechanics of the chest wall by which we mean the mechanics of the thorax, the abdomen and the diaphragm. The geometrical complexity of the chest wall and its associated muscles of respiration makes rigorous analysis of the mechanics of the respiratory system difficult. This paper describes a structural model of the respiratory system with two degrees of freedom of motion that has been useful for understanding the actions of respiratory muscles. The model was initially developed to test the hypothesis of Goldman and Mead[1] that the diaphragm, contracting by itself, can expand the abdomen and rib cage in the same way as passive inflation of the respiratory system. The model's predictions suggest that coordinated activity of rib cage musculature and diaphragm are required to expand the respiratory system in this way