Effect of lung inflation in vivo on airways with smooth muscle tone
or edema
Brown, ]obert H., Wayne Mitzner, Yonca Bulut, Elizabeth M. Wagner.
Department of Anesthesiology and Critical Care Medicine, Department
of Radiology, Department of Environmental Health Sciences/Division of
Physiology, Department of Medicine, Division of Pulmonary and
Critical Care Medicine
APStracts 3:0482A, 1996.
Fibrous attachments to the airway wall and a subpleural surrounding
pressure can create an external load against which airway smooth
muscle must contract. A decrease in this load has been proposed as a
possible cause of increased airway narrowing in asthmatics. To study
the interaction between the airways and the surrounding lung
parenchyma, we investigated the effect of lung inflation on relaxed
airways, airways contracted with methacholine, and airways made
edematous by infusing bradykinin into the bronchial artery.
Measurements were made in anesthetized sheep using high resolution
computed tomography (HRCT) to visualize changes in individual
airways. During methacholine infusion airway area was decreased, but
increased minimally with increases in transpulmonary pressure.
Bradykinin infusion caused a 50% increase in airway wall area and a
small decrease in airway lumenal area. In contrast to airways
contracted with methacholine, the lumenal area after bradykinin
increased substantially with increases in transpulmonary pressure,
reaching 99% of the relaxed area at TLC. Thus, airway edema by itself
did not prevent full distension of the airway at lung volumes
approaching TLC. Therefore, we speculate that, if a deep inspiration
fails to relieve airway narrowing in vivo, this must be a
manifestation of airway smooth muscle contraction and not airway wall
edema.
Received 26 March 1996; accepted in final form 9 October 1996.
APS Manuscript Number A298-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996