The effects of flow heterogeneity on the measurement of capillary
exchange in the lung.
Caruthers, Sd, Tr Harris, Ka Overholser, Na Pou, and Re Parker.
Departments of Biomedical Engineering and Medicine, Vanderbilt
University, Nashville, TN, 37235
APStracts 2:0210A, 1995.
The effects of flow heterogeneity on the measurement of transcapillary
escape of small molecules for perfused, in situ sheep lungs were
evaluated. Lungs were studied at five flows (1.5 to 5.0 l/min)
ranging from Zone II to Zone III conditions. At each flow, multiple
indicator dilution curves were collected using 14C-labeled urea (U)
or butanediol (B) as the diffusing tracer, and radiolabeled 15[mu]m
microspheres were injected. The lungs were removed, dried, sectioned,
weighed, and counted for microsphere radioactivity. Flow
heterogeneity, expressed as relative dispersion, decreased with
increasing flow, from 0.838+/-0.179 (mn+/-sd, n=8) to 0.447+/-0.119
(n=6). We applied homogeneous flow models of capillary exchange to
compute PS (Permeability x Surface area) and a related parameter, D
S, for diffusing tracers. (D is effective diffusivity of capillary
exchange.) PS and D S increased to a maximum with increasing flow,
but the ratio between D SU and D SB remained constant. A new model
incorporating flow heterogeneity and recruitment (the variable
recruitment, VR, model) was used. The VR model described the effects
of flow on capillary recruitment, but incorporating heterogeneity
into the computation did not alter D S values from those computed
assuming homogeneous flow.
Received 15 November 1993; accepted in final form 9 May 1995.
APS Manuscript Number A1107-3.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.