Model of functional restriction in chronic obstructive pulmonary disease, transplantation, and lung reduction surgery

Mechanical interactions between lung and chest wall are important determina nts of respiratory function. When chest wall expansion during maximal inhal ation generates insufficiently negative pleural pressures, the lungs remain functionally underinflated; this may be termed functional restriction. To explore mechanisms and effects of functional restriction in patients with e mphysema, and to predict effects of single lung transplantation and lung vo lume reduction surgery (LVRS), we used a computational model based on stand ard physiology and measurements from individual patients. The model's lungs , separated by a compliant mediastinum, exhibit flow limitation according t o the equal pressure point approach of Mead and coworkers. Pulmonary elasti c recoil pressure is characterized by an exponential equation modified to r eflect airway closure. Simulated respiratory maneuvers can be specified by variations in flow or pressure at the airway opening or in respiratory musc le activation. Model simulations successfully mimic recordings from individ ual patients. Input parameter values may then be altered to predict effects of surgical interventions in these same patients. The model simulations sh ow the following. Single lung transplantation in emphysema can cause functi onal restriction of the normal transplanted lungs, and larger transplanted lungs may perform less well than smaller ones. LVRS improves lung and chest wall function in emphysema, but not in normal states. Surgical reduction o f the native emphysematous lung after single lung transplantation can reduc e functional restriction of the transplant and thereby improve its function .