Nonuniform expansion of constricted dog lungs.
Hubmayr, Rolf D., Mark J. Hill, and Theodore A. Wilson.
Thoracic Research Unit, Mayo Clinic and Foundation, Rochester, MN
55905; and Department of Aerospace Engineering and Mechanics,
University of Minnesota, Minneapolis, MN 55455
APStracts 2:0432A, 1995.
The parenchymal marker technique was used to measure regional tidal
volumes of samples of lung parenchyma in four open-chested supine
dogs. Radio-opaque markers that had been implanted in the lower lobe
were tracked by biplane videofluoroscopy during sinusoidal volume
oscillations at tidal volumes of 20% of total lung capacity and
frequencies of 1 to 40 breaths per minute both before and after
methacholine was administered by aerosol. The volumes of tetrahedra
with apices at four markers were computed, and sine waves were fit to
the data for volume vs. time for each tetrahedron. The ratio of mean
regional volume to mean airway pressure decreased by 10 - 45% after
exposure to methacholine. Dynamic lung elastance and resistance of
the constricted lungs were larger than control and both were
frequency-dependent. Regional elastance and resistance varied
considerably among tetrahedra, and these were also frequency
-dependent. The data were fit by a model in which tissue elastance was
uniform and nearly equal to elastance in the control state, but small
airway resistance was high and variable. We conclude that the lung
contracts under bronchoconstriction but that the increased dynamic
elastance and resistance of the constricted lung may be primarily the
result of nonuniform increased airway resistance at the level of the
terminal bronchioles.
Received 23 December 1994; accepted in final form 29 August 1995.
APS Manuscript Number A1305-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95