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Elastic properties of the bronchial mucosa: epithelial unfolding and stretch in response to airway inflation

Physiology, School of Biomedical, Biomolecular, and Chemical Sciences, University of Western Australia, Perth, Australia

Submitted 28 April 2005 ; accepted in final form 10 July 2005

The bronchial mucosa contributes to elastic properties of the airway wall and may influence the degree of airway expansion during lung inflation. In the deflated lung, folds in the epithelium and associated basement membrane progressively unfold on inflation. Whether the epithelium and basement membrane also distend on lung inflation at physiological pressures is uncertain. We assessed mucosal distensibility from strain-stress curves in mucosal strips and related this to epithelial length and folding. Mucosal strips were prepared from pig bronchi and cycled stepwise from a strain of 0 (their in situ length at 0 transmural pressure) to a strain of 0.5 (50% increase in length). Mucosal stress and epithelial length in situ were calculated from morphometric data in bronchial segments fixed at 5 and 25 cmH₂O luminal pressure. Mucosal strips showed nonlinear strain-stress properties, but regions at high and low stress were close to linear. Stresses calculated in bronchial segments at 5 and 25 cmH₂O fell in the low-stress region of the strain-stress curve. The epithelium of mucosal strips was deeply folded at low strains (0–0.15), which in bronchial segments equated to 10 cmH₂O transmural pressure. Morphometric measurements in mucosal strips at greater strains (0.3–0.4) indicated that epithelial length increased by 10%. Measurements in bronchial segments indicated that epithelial length increased 25% between 5 and 25 cmH₂O. Our findings suggest that, at airway pressures <10 cmH₂O, airway expansion is due primarily to epithelial unfolding but at higher pressures the epithelium also distends.

mucosal folds; epithelium; airway mechanics

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