Novel interpretations of respiratory impedance in COPD based on computational fluid dynamics

Although it has been conventionally believed that negative frequency dependence of respiratory resistance and deep decline of respiratory reactance during expiratory phase in COPD are due to ventilation inhomogeneity caused by small airway obstructions, there have been neither experimental theoretical evidence. We have recently confirmed that the airflow limitation site in COPD is the intra-mediastinal airway (intra-thoracic trachea, main bronchi, and right lobar bronchi) whose membranous part is displaced inward during expiration by the use of 4D-CT (see our another presentation) . Therefore, we have hypothesized they are also due to the might occur in the membranous part of the intra-thoracic trachea in emphysema by FOT, because it may be easily flip-flopped. In order to validate this hypothesis theoretically, we constructed an oscillated 4D lung model with tracheal deformation and reproduced the respiratory impedance by the use of computational fluid dynamics.