Journal of Applied Physiology, Vol 53, Issue 2 361-366, Copyright © 1982 by American Physiological Society
Regional distribution of ventilation at residual volume in induced bronchospasm
L. Delaunois, R. Boileau, J. Diodatti, J. Gauthier and R. R. Martin
The regional distribution of a bolus of gas inhaled at residual volume (RV)
is attributed to regional airway closure and is responsible for the phase
IV of the single-breath washout during the following deflation. As
bronchospasm increases the range of airway opening pressures through the
lung, the regional distribution of the bolus could change with effects on
the shape of the single-breath washout. We investigated the regional
distribution of boluses inhaled at RV and their single-breath washouts
during methacholine-induced bronchospasm in prone dogs. With increasing
total lung resistance (RL) we first observed in five out of eight animals a
preferential "redistribution" of the bolus to the upper caudal regions of
the lung, which could be partially attributed to the increased lung volume
at RV. When maximal RL was attained, the bolus was evenly distributed
through all regions of the lung in these animals with disappearance of
phase IV and increased slope of phase III, and a final decrease of tracer
concentration at low lung volumes was observed. We conclude from these data
that increased bronchomotor tone in dogs results in a less homogeneous
intraregional distribution of the bolus with increased slope of phase III
and in a more even interregional distribution leading to disappearance of
phase IV. In severe bronchospasm the downward slope at low lung volume
suggests intraregional closed lung units emptying through collateral
pathways into still open neighboring units.
