Journal of Applied Physiology, Vol 69, Issue 4 1323-1329, Copyright © 1990 by American Physiological Society
Distribution of airway narrowing during hyperpnea-induced bronchoconstriction in guinea pigs
D. W. Ray, S. Eappen, C. Hernandez, M. Jackson, L. E. Alger, A. R. Leff and J. Solway
Department of Medicine, University of Chicago, Illinois 60637.
Increasing minute ventilation of dry gas shifts the principal burden of
respiratory heat and water losses from more proximal airway to airways
farther into the lung. If these local thermal transfers determine the local
stimulus for bronchoconstriction, then increasing minute ventilation of dry
gas might also extend the zone of airway narrowing farther into the lung
during hyperpnea-induced bronchoconstriction (HIB). We tested this
hypothesis by comparing tantalum bronchograms in tracheostomized guinea
pigs before and during bronchoconstriction induced by dry gas hyperpnea,
intravenous methacholine, and intravenous capsaicin. In eight animals
subjected to 5 min of dry gas isocapnic hyperpnea [tidal volume (VT) = 2-5
ml, 150 breaths/min], there was little change in the diameter of the
trachea or the main stem bronchi up to 0.75 cm past the main carina (zone
1). In contrast, bronchi from 0.75 to 1.50 cm past the main carina (zone 2)
narrowed progressively at all minute ventilations greater than or equal to
300 ml/min (VT = 2 ml). More distal bronchi (1.50-3.10 cm past the main
carina; zone 3) did not narrow significantly until minute ventilation was
raised to 450 ml/min (VT = 3 ml). The estimated VT during hyperpnea needed
to elicit a 50% reduction in airway diameter was significantly higher in
zone 3 bronchi [4.3 +/- 0.8 (SD) ml] than in zone 2 bronchi (3.5 +/- 1.1
ml, P less than 0.012).(ABSTRACT TRUNCATED AT 250 WORDS)
