Journal of Applied Physiology, Vol 58, Issue 6 1788-1801, Copyright © 1985 by American Physiological Society
Forced expiration and HeO2 response in canine peripheral airway obstruction
C. Jadue, H. Greville, J. J. Coalson and S. N. Mink
We examined the effect of peripheral airway obstruction on parameters of
maximum expiratory flow (Vmax) in a canine model of bronchiolitis
obliterans (B). B was produced by the repeated intrabronchial instillations
of a 1% nitric acid solution in seven dogs (group B). In seven control dogs
(group C), a normal saline solution was used. During forced vital capacity
deflation, Vmax on air, the relative increase in Vmax on 80% He-20% O2
(delta Vmax), and airway sites of flow limitation "choke points" (CP) were
determined at multiple lung volumes (VL). The findings were interpreted in
terms of the wave-speed theory of flow limitation. Wave-speed parameters
were identified with a pressure-measuring device positioned in the airway.
Compared with the findings for group C, Vmax decreased substantially at the
lower VL (less than 50% vital capacity) in group B, whereas there were no
changes in delta Vmax at any VL. CP were identified in central airways in
both groups but were slightly more upstream in group B. Our analysis
indicated that the reduction in Vmax in group B was due to an increase in
upstream frictional pressure losses (Pfr) that caused a relative reduction
in the pressure head, so that choking occurred in slightly upstream
airways. delta Vmax did not change in group B because with CP identified in
central airways, Pfr were density dependent, and significant differences in
head loss on the two gas mixtures did not occur. Choking therefore occurred
with similar wave-speed variables on the two gas mixtures, and delta Vmax
was maintained.
