A diffusion wake model for tracer ultrastructure-permeability studies in microvessels. Fu, B. M., F. E. Curry, S. Weinbaum. Dept. of Mechanical Engineering, The City College of the City University of New York, New York, NY 10031, Dept. of Human Physiology, School of Medicine, University of California at Davis, Davis, CA 95616, Dept. of Mechanical Engineering, The City College of the City University of New York, New York, NY 10031, (212)-650-5202, (212)-650-8013 (Fax)
APStracts 2:0252H, 1995.
We developed a time dependent diffusion model for analyzing the concentration profiles of low molecular weight tracers in the interendothelial clefts of the capillary wall, which takes into account the three-dimensional, time dependent filling of the surrounding tissue space. The model provides a connecting link between two methods to investigate transvascular exchange: electron microscopic experiments to study the time dependent wake formed by low molecular weight tracers (such as lanthanum nitrate) on the tissue side of the junction strand discontinuities in the inter -endothelial cleft of frog mesentery capillaries (Adamson and Michel, Journal of Physiology (London) 466:303-327) and confocal microscope experiments to measure the spread of low molecular weight fluorescent tracers in the tissue space surrounding these microvessels (Adamson et al., Microcirculation 1(4): 251-265, 1994). We show that the interpretation of the presence of tracer as an all-or-none indication of a pathway across the junctional strand is likely to be incorrect for small solutes. Large pore pathways in which the local tracer flux densities are high reach a threshold concentration for detection and are likely to be detected after relatively short perfusion times whereas distributed small pore pathways may not be detected until the tissue concentrations surrounding the entire vessel approach threshold concentrations. The analysis using this approach supports the hypothesis advanced in Fu et al. (ASME Journal of Biomedical Engineering: 116:502-513) that the principal pathways for water and solutes &LT 1.0 nm diameter across the interendothelial cleft may be different and suggests new experiments to test this hypothesis. 

Received 12 January 1995; accepted in final form 31 May 1995.
APS Manuscript Number H32-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  6 July 1995.