Article,
Airway smooth muscle orientation in intraparenchymal airways
JOURNAL OF APPLIED PHYSIOLOGY, 82 (1): 70-77 (January 1997)
Abstract
Airway smooth muscle (ASM) shortening is the central event leading to
bronchoconstriction. The degree to which ah-way narrowing occurs as a
consequence of shortening is a function of both the mechanical
properties of the airway wall as well as the orientation of the muscle
fibers. Although the latter is theoretically important, it has not been
systematically measured to date. The purpose of this study was to
determine the angle of orientation of ASM (theta) in normal lungs by
using a morphometric approach. We analyzed the airway tree of the left
lower lobes of four cats and one human. All material was fixed with 10\%
buffered Formalin at a pressure of 25 cmH(2)O for 48 h. The fixed
material was dissected along the airway tree to permit isolation of
generations 4-18 in the cats and generations 5-22 in the human specimen.
Each airway generation was individually embedded in paraffin.
Five-micrometer-thick serial sections were cut parallel to the airway
long axis and stained with hematoxylin-phloxine-saffron. Each block
yielded three to five sections containing ASM. To determine theta, we
measured the orientation of ASM nuclei relative to the transverse axis
of the airway by using a digitizing tablet and a light microscope (X250)
equipped with a drawing tube attachment. Inspection of the sections
revealed extensive ASM crisscrossing without a homogeneous orientation.
The theta was clustered between -20 degrees and 20 degrees in all
ail-way generations and did not vary much between generations in any of
the cats or in the human specimen. When theta was expressed without
regard to sign, the mean values were 13.2 degrees in the cats and 13.1
degrees in the human. This magnitude of obliquity is not likely to
result in physiologically important changes in airway length during
bronchoconstriction.
