Journal of Applied Physiology, Vol 53, Issue 2 496-504, Copyright © 1982 by American Physiological Society
Effect of gaseous interaction between lung units on the expired concentration of nitrogen
W. Nixon and A. I. Pack
There is debate over the mechanisms that produce the alveolar slope, with
theories relating to both series and parallel inhomogeneity being proposed.
We use a mathematical model of pulmonary gas transport, which incorporates
both series and parallel effects, to investigate the relevance of each in
the production of this alveolar slope. Interaction between lung units is
specifically studied by simulating mixing at both proximal- and
distal-branch points in the bronchial tree. During expiration mixing of the
gas from inhomogeneous parallel lung units leads to concentration gradients
within each unit. The resultant effect on the concentration of the expirate
depends on the position in the bronchial tree at which this mixing takes
place; proximal interaction alters the initial phase of the expired
concentration profile, whereas distal interaction changes the magnitude of
the alveolar slope. The net effect of distal interaction is to produce a
greater alveolar slope for gases with low molecular diffusivity. These
effects are present even in the absence of asynchronous emptying of lung
units but may be enhanced by it. These results help to clarify
controversies about the mechanisms underlying production of the alveolar
slope.
