Dynamic collapse of the intra-mediastinal airway is the cause of decrease in FEV1.0: direct evidence by 4D-CT during maximum forced expiration

Abstract

The cause of decrease in FEV1.0 in chronic obstructive pulmonary diseases (COPD) has been believed due to the obstruction of peripheral small airways. However, direct evidences of the proposed mechanism have never been shown. We have proposed a hypothesis that overinflated lungs compressed the inra-mediastinal airway (IMA, intra-thoracic trachea, main bronchi, and right lobar bronchi) in COPD at the beginning of forced expiration and would let IMA collapse due to Bernoulli effect. We have verified the hypothesis by 4D-CT images during maximum forced expiration of five COPD patients and one normal volunteer. The IMA of all 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 at two seconds after were highly correlation to FEV1.0 (r2= 0.93).