mechanics. Caption reads: "FIGURE 3.—Schematic showing of pathologic physiology of flail chest. A. Inspiratory phase. Chest wall collapses inward (a), forcing air out of bronchus of involved lung into trachea and bronchus to uninvolved lung and causing shift of mediastinum to uninvolved side (b). B. Expiratory phase. Chest wall balloons outward (a) so that air expelled from lung on uninvolved side (b) enters lung on involved side and mediastinum shifts toward involved side (a). This is a very inefficient form of respiration, and the patient will die of hypoxia and exhaustion if it occurs in an extreme phase and is not relieved."