Аннотация
The epithelial folding that occurs during bronchoconstriction requires
that the pressure on the muscle side of the folding membrane be greater
than that on the lumen side. The pressure required for a given level of
folding depends on the elastic properties of the tissue and on the
geometry of the folding. To quantify the elastic properties, uniaxial
tensile stiffness of the tracheal inner wall of nine sheep was measured
in two directions: parallel to the tracheal axis and circumferentially.
The tissue showed anisotropic behavior, being approximately three times
stiffer longitudinally than circumferentially. Histological examination
showed that collagen in the lamina propria was randomly arranged,
whereas there were straight elastin fibers aligned with the tracheal
axis. This observation could explain the observed elastic anisotropy.
Mechanical removal of the epithelium had no effect on tensile stiffness.
It was also found that the tissue was under tension in situ. When a
strip was excised, its length decreased by greater than or equal to
30\%. After allowing for the systematic errors inherent in this
experiment, the in situ circumferential tensile stiffness is estimated
to be greater than or equal to 20 kPa. If the equivalent tissue in the
bronchioles has the same tensile stiffness as that in the trachea, the
forces required to fold the membrane are significant at small
transbronchial pressure differences and increase in the presence of
membrane thickening such as that seen in asthma.
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