Lung tissue distortion in response to methacholine in rats: effect
of lung volume.
Dolhnikoff, M., M. Dallaire, M. S. Ludwig.
Meakins-Christie Laboratories, Royal Victoria Hospital, McGill
University, Montreal, Quebec, Canada
APStracts 2:0174A, 1995.
We have previously shown that, after induced constriction, there is
substantial distortion of the parenchymal tissues. In this study we
investigated whether differences in parenchymal morphology occurred
when the lung was constricted at different lung volumes (VL). We
measured tracheal pressure (Ptr) in open-chested, mechanically
-ventilated (Vt=8 ml/kg, f=1Hz) rats under control conditions and
after aerosol administration of methacholine (256 mg/ml), at
different positive end-expiratory pressures (PEEP = 7,5 and 3 cmH2O).
We calculated lung resistance (RL) by fitting the equation of motion
to changes in Ptr. The lungs were frozen with liquid nitrogen at PEEP
= 3,5 or 7 cmH2O and processed via freeze substitution. Airway
constriction was assessed by measuring the ratio of the airway lumen
(Ai) to the ideally relaxed area (Ai*), alveolar size by measuring
the mean linear intercept between alveolar walls (Lm), and tissue
distortion by measuring the standard deviation of the number of
intercepts (SDI) in the 40 fields sampled per lung. The increase in
RL was largest at PEEP = 3 cmH2O. Whereas Ai/Ai* and Lm increased at
higher PEEP, SDI did not change. These results indicate that, at
higher VL, airway constriction was reduced and alveolar size was
increased; the degree of tissue distortion was not affected. As
airway constriction was less marked at higher VL, these data suggest
that parenchymal distortion after induced constriction was not
attributable to airway narrowing and/or closure.
Received 19 July 1994; accepted in final form 5 April 1995.
APS Manuscript Number A729-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 2 May 1995.