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J Appl Physiol 79: 1449-1460, 1995;
8750-7587/95 $5.00
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Journal of Applied Physiology, Vol 79, Issue 5 1449-1460, Copyright © 1995 by American Physiological Society

ARTICLES

Effects of flow heterogeneity on the measurement of capillary exchange in the lung

S. D. Caruthers, T. R. Harris, K. A. Overholser, N. A. Pou and R. E. Parker
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA.

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 (1.5-5.0 l/min) ranging from zone 1 to zone 3 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-microns 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 (mean +/- SD, n = 8) to 0.447 +/- 0.119 (n = 6). We applied homogeneous flow models of capillary exchange to compute permeability-surface area product (PS) and a related parameter, D1/2S, for diffusing tracers. (D is effective diffusivity of capillary exchange.) PS and D1/2S increased to a maximum with increasing flow, but the ratio of D1/2SU to D1/2SB remained constant. A new model incorporating flow heterogeneity and recruitment (the variable recruitment model) was used. The variable recruitment model described the effects of flow on capillary recruitment, but incorporating heterogeneity into the computation did not alter D1/2S values from those computed assuming homogeneous flow.


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S. D. Caruthers, C. B. Paschal, N. A. Pou, R. J. Roselli, and T. R. Harris
Regional measurements of pulmonary edema by using magnetic resonance imaging
J Appl Physiol, June 1, 1998; 84(6): 2143 - 2153.
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