Journal of Applied Physiology, Vol 73, Issue 6 2328-2332, Copyright © 1992 by American Physiological Society
Heterogeneous airway tone in asthmatic subjects
G. Julia-Serda, N. A. Molfino, K. R. Chapman, P. A. McClean, N. Zamel, A. S. Slutsky and V. Hoffstein
Department of Medicine, University of Toronto, Ontario, Canada.
We examined the effect of volume history on the dynamic relationship
between airways and lung parenchyma (relative hysteresis) in 20 asthmatic
subjects. The acoustic reflection technique was employed to evaluate
changes in airway cross-sectional areas during a slow continuous expiration
from total lung capacity to residual volume and inspiration back to total
lung capacity. Lung volume was measured continuously during this
quasi-static maneuver. We studied three anatomic airway segments: extra-
and intrathoracic tracheal and main bronchial segments. Plots of airway
area vs. lung volume were obtained for each segment to assess the relative
magnitude and direction of the airway and parenchymal hysteresis. We also
performed maximal expiratory flow-volume and partial expiratory flow-volume
curves and calculated the ratio of maximal to partial flow rates (M/P) at
30% of the vital capacity. We found that 10 subjects (group I) showed a
significant predominance of airway over parenchymal hysteresis (P <
0.005) at the extra- and intrathoracic tracheal and main bronchial
segments; these subjects had high M/P ratios [1.53 +/- 0.27 (SD)]. The
other 10 subjects (group II) showed similar airway and parenchymal
hysteresis for all three segments and significantly lower M/P ratios (1.16
+/- 0.20, P < 0.01). We conclude that the effect of volume history on
the relative hysteresis of airway and lung parenchyma and M/P ratio at 30%
of vital capacity in nonprovoked asthmatic subjects is variable. We suggest
that our findings may result from heterogeneous airway tone in asthmatic
subjects.
