Abstract
Functional disorder of the pulmonary emphysema has been believed due to dynamic compression of small airways. However, its direct evidences have never been shown. We hypnotized that overinflated lungs compressed the intra-mediastinal airway (IMA, intra-thoracic trachea, main bronchi, and right lobar bronchi) in emphysema at the beginning of forced expiration and would let IMA collapse due to fluid dynamical effect. We evaluated the morphological change of IMA during maximum forced expiration by 4D-CT, and investigated its relationship to the value of FEV_<1.0>. Five emphysema patients and a normal subject underwent 4D-CT by multi-detector row CT during maximum forced expiration over six seconds at supine posture. Voxel size was 0.7 mm x 0.7 mm x 1.0 mm with the range of 16 cm, and time interval was 0.5 sec. Volumes of intra-thoracic trachea and bilateral main bronchi are measured for each frame. The IMA of all emphysema patients were extremely narrowed just after the beginning of forced expiration and slightly recovered later. The membranous part of IMA was invaginated inside. There was no apparent shape change in the normal subject. The relative volume after two seconds was highly correlated to FEV_<1.0>. These 4D-CT images have revealed that low values of FEV_<1.0> in emphysema patients are caused by dynamic collapse of IMA. Pneumodynamics should be urgently reconstructed based on dynamic imaging.
