Abstract
It has recently been shown that the acinus can have a reduced efficiency
due to a ``screening effect'' governed by the ratio of oxygen
diffusivity to membrane permeability, the gas flow velocity, as well as
the size and configuration of the acinus. We present here a top to
bottom calculation of the functioning of a machine acinus at exercise
that takes this screening effect into account It shows that, given the
geometry and the breathing dynamics of real acini, respiration can be
correlated to a single equivalent parameter that we call the integrative
permeability. In particular we find that both (V) over dot(O2,max) and
PA(O2) depend on this permeability in a non-linear manner. Numerical
solutions of dynamic convection-diffusion equations indicate that only a
narrow range of permeability values is compatible with the experimental
measurements of PA(O2) and (V) over dot(O2,max). These permeability
values are significantly smaller than those found in the literature. In
a second step, we present a new type of evaluation of the diffusive
permeability, yielding values compatible with the top to bottom
approach, but smaller than the usual morphometric value. (C) 2012
Elsevier B.V. All rights reserved.
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