A computer simulation of pulmonary perfusion in three
dimensions.
Glenny, Robb W., H. Thomas Robertson.
Division of Pulmonary and Critical Care Medicine, Department of
Medicine, University of Washington, Seattle
APStracts 2:0105A, 1995.
Pulmonary perfusion is spatially correlated with neighboring regions
of lung having similar magnitudes of flow and distant pieces
exhibiting negative correlation. While local correlation has been
noted in a wide variety of natural processes, negative correlation
has not and may be unique to organ blood flow. We investigate the
regional perfusion predicted by a three-dimensional branching
vascular model to determine if such a model can create negative
correlation of perfusion. The distribution of flows is modeled by a
dichotomously branching tree in which the fraction of flow from
parent to daughter branches is [gamma] and 1-[gamma] at each
bifurcation. The flow asymmetry parameter, [gamma], is randomly
chosen for each bifurcation from a normal distribution with a mean of
0.5 with a standard deviation of s. The branches branch along one of
three orthogonal directions to assure a space filling structure. This
model produces flow distributions similar to those observed in
experimental animals, with perfusion being positively correlated
locally and negatively correlated at distance. The model is refined
by incorporating an effect of gravity which redirects a fraction,
[delta], of the flow against gravity to the companion daughter branch
in the gravitational direction. A flow bias in the $QUOTdorsal$QUOT
direction is also introduced to account for differences in supine
-prone perfusion gradients. In its final form, this three-dimensional
branching model accounts for previously observed 1) spatial
correlation of regional perfusion with negative correlation over
distance, 2) isogravitational perfusion heterogeneity, 3) differences
in supine and prone perfusion gradients, 4) positive correlation of
flows between supine and prone postures, 5) relatively small
contributions of gravity to perfusion heterogeneity, and 6) fractal
distributions of flow. This three-dimensional branching vascular
model relates the function and structure of the pulmonary vascular
tree, offering an explanation for both heterogeneous and spatially
correlated regional flows.
Received 18 November 1994; accepted in final form 6 March 1995.
APS Manuscript Number A1183-3.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.