Journal of Applied Physiology, Vol 61, Issue 6 2243-2251, Copyright © 1986 by American Physiological Society
Changes in flow-volume curve configuration with bronchoconstriction and bronchodilation
C. R. O'Donnell, R. G. Castile and J. Mead
Changes in the configuration of maximum expiratory flow-volume (MEFV)
curves following mild degrees of bronchodilation or bronchoconstriction
were studied in five normal and five asthmatic subjects. In a
volume-displacement plethysmograph, MEFV curves were performed before and
after inhalation of aerosolized isoproterenol (I) or histamine (H). Five
filtered MEFV curves were averaged, and slope ratio vs. volume (SR-V) plots
were obtained from averaged curves. Following I, maximal flows at 75% of
the vital capacity (VC) were decreased in asthmatics but not in normal
subjects. Flows at 50 and 25% of the VC increased in normal subjects and
asthmatics, whereas VC's were unchanged. In asthmatics, sudden large
decreases in flow (bumps) occurred at lower lung volumes following I. H
reduced flows over the entire VC, with greater reductions occurring in
asthmatics than in normals, particularly at low lung volumes. In
asthmatics, VC was slightly reduced, and bumps in MEFV curve configuration
occurred at higher lung volumes or were abolished entirely following H. A
reduction in the amount of configurational detail appreciable in MEFV
curves following histamine in asthmatics was best seen in SR-V plots.
Following H, SR's decreased regularly with decreasing lung volume in all
the asthmatics but in none of the normals. This was the single most
striking finding of this study. Mild I- and H-induced perturbations of
airway bronchomotor tone produced small but consistent changes in MEFV
curve configuration.(ABSTRACT TRUNCATED AT 250 WORDS)
