UBC Theses and Dissertations
Mechanical properties of tracheal cartilage Rains, Jeffrey K.
Large airways collapse has been implicated as one of the causes of maximal expiratory flow limitation. Since cartilage plays an important role in maintaining the form of these airways, an understanding of the mechanical properties of the cartilage is necessary for a better understanding of the mechanisms which limit maximal expiratory flow. This work establishes a technique whereby the tensile stiffness of human tracheal cartilage can be determined using uniaxial equilibrium tensile tests. A technique was developed in which standard shaped specimens were cut from tracheal cartilage rings and tested in a specially designed tensile tester in order to determine the stress-strain relationship of the specimen. The stress-strain relationship of the cartilage test specimens was found to be linear up to approximately 10 % strain. However, irreversible disruption of the cartilage matrix occurred at strains greater than 10 %. The tensile stiffness of the tracheal cartilage fell in the range 1-20 MPa and was found to decrease with increasing depth from the outer surface of the tissue. This layer-wise variation in tensile stiffness reflected the orientation of the collagen fibrils in the tissue. An age-related increase in the tensile stiffness of tracheal cartilage was found. This age-related change in tensile stiffness may reflect an increase in collagen cross-linking in specimens from older individuals. A possible bias of the test method toward the measurement of the mechanical properties of the collagen fibrils, as opposed the combined effects of the collagen and proteoglycans, was suspected. However, to the extent that equilibrium tensile testing reflects the ability of tracheal cartilage to bend in response to alterations in transmural pressure, these results suggest that age-related changes in large airway cartilage stiffness are not the cause of the age-related decrease in maximal expiratory flow.
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