Journal of Applied Physiology, Vol 50, Issue 3 575-579, Copyright © 1981 by American Physiological Society
Inhalation patterns and predominant site of bronchoconstriction in healthy subjects
K. P. Strohl, C. F. O'Cain, R. H. Ingram Jr, M. A. Yanta, W. D. Kaplan and E. R. McFadden Jr
To determine the relationship between changes in density dependence of
maximal expiratory flow and changes in the predominant site of
bronchoconstriction, we altered the pattern of inhalation of a methacholine
aerosol to achieve deposition either centrally (by short choppy breaths) or
peripherally (by slow deep breaths). Partial expiratory flow volume curves
on air and on 80% helium-20% oxygen (HeO2) were recorded in six healthy
subjects before and after each pattern of methacholine inhalation. We
varied concentrations of methacholine and number of inhalations to achieve
equivalent degrees of bronchoconstriction as assessed by decreases in
maximal flow (Vmax) on air, which fell 27% from control values. Vmax on
HeO2 also fell after both inhalation patterns. Density dependence (Vmax on
HeO2 divided by Vmax on air) decreased following slow deep breaths of
bronchoconstrictor aerosol, and increased following short choppy breaths.
In three subjects, inhalation of radiolabeled methacholine aerosol
confirmed that the slow deep pattern was associated with a diffuse, more
peripheral deposition, whereas the short choppy pattern led to central
deposition. We conclude that changes in density dependence reflect the
predominant site of obstruction after acute methacholine aerosol challenge
in healthy subjects.
