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Dynamic mechanical response of airway mucosal membrane

University of British Columbia

Folding of the mucosal membrane of the airways during bronchoconstriction can provide an elastic load [Lambert 1991, 1994] which impedes the airway smooth muscle shortening. The mechanical properties of the membrane, both in tension and in compression, are needed to quantify this load. To measure the mechanical properties of the airway mucosal membrane in tension, a high accuracy stress-strain-time apparatus was designed and constructed. 40 New Zealand White female rabbits of ages between 2 and 35 months were studied for the mechanical response of the airway mucosal membrane. A pair of membrane strips (one in the circumferential, the other in the longitudinal direction of the airway) were dissected from each trachea and mounted in the apparatus. Static uniaxial tensile tests, sinusoidal oscillations and pulse tests were used to measure the steady-state stiffness as well as the frequency response of the membrane in tension. The results of the pulse tests were fitted to a Kelvin model, from which the elastic component, viscous component and the time constants were calculated. The tested strips were histologically processed after the mechanical experiments. The elastic fiber orientation in the airways was measured using a new geometrical approach. The volume fraction of the elastic fibers in the mucosal membrane was measured using the classical point counting technique. Statistically significant linear relationships were found between the Kelvin model parameters and the morphometrical measurements. In summary, the rabbit airway mucosal membrane is viscoelastic. Age (2-35 months) has no statistically significant effect on either the mechanical properties of the membrane or the morphometrically measured parameters of the elastic fibers. The membrane is stiffer in the longitudinal than in the circumferential direction of the airway. The volume fraction of the elastic fibers is linearly related to the steady-state stiffness of the membrane. The viscous component in the dynamic response is inversely related to the percentage of the fibers that have components in both circumferential and longitudinal directions (wavy fibers). The time constants are proportional to the percentage of the wavy fibers.

Thesis/Dissertation

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2009-04-17

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http://hdl.handle.net/2429/7333

Chemical and Biological Engineering

University of British Columbia

UBCV

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