Airway smooth muscle orientation in intraparenchymal airways.
Lei, M., H. Ghezzo, M. F. Chen, D. H. Eidelman.
Meakins-Christie Laboratories, Montreal Chest Institute Research
Centre, Royal Victoria and Montreal General Hospitals, McGill
University, Montreal, Quebec, Canada, H2X 2P2
APStracts 3:0415A, 1996.
Airway smooth muscle (ASM) shortening is the central event leading to
bronchoconstriction. The degree to which airway narrowing occurs as a
consequence of shortening is a function both of the mechanical
properties of the airway wall as well as of the orientation of the
muscle fibres. 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 in normal lungs
using a morphometric approach. We analysed 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 cm H2O for 48 hrs. The
fixed material was dissected along the airway tree to permit
isolation of generations 4 to 18 in the cats, 5 to 22 in. the human
specimen. Each airway generation was individually embedded in
paraffin. 5[mu]m thick serial sections were cut parallel to the
airway long axis and stained with haematoxylin-phloxine-saffron. Each
block yielded 3-5 sections containing ASM. To determine the ASM
angle, we measured the orientation of ASM nuclei relative to the
transverse axis of the airway (I) using a digitizing tablet and a
light microscope (X250) equipped with a drawing tube attachment.
Inspection of the sections revealed extensive ASM criss-crossing
without a homogeneous orientation. I was clustered between -20o and
+20o in all airway generations and did not vary much between
generations in any of the cats or in the human specimen. When I was
expressed without regard to sign the mean angle was 13.2o in the cats
and 13.1o in the human. This magnitude of obliquity is unlikely to
result in physiologically important changes in airway length during
bronchoconstriction.
Received 8 April 1996; accepted in final form 21 August 1996.
APS Manuscript Number A332-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996