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Determination of Brain Interstitial Concentrations by Microdialysis
Author(s) -
Benveniste Helene,
Hansen Anker Jon,
Ottosen Niels Saabye
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb07252.x
Subject(s) - microdialysis , interstitial fluid , tortuosity , diffusion , interstitial space , chemistry , extracellular fluid , dialysis , chromatography , membrane , saline , extracellular , porosity , pathology , thermodynamics , anesthesia , surgery , biochemistry , organic chemistry , medicine , physics
Microdialysis is an extensively used technique for the study of solutes in brain interstitial space. The method is based on collection of substances by diffusion across a dialysis membrane positioned in the brain. The outflow concentration reflects the interstitial concentration of the substance of interest, but the relationship between these two entities is at present unclear. So far, most evaluations have been based solely on calibrations in saline. This procedure is misleading, because the ease by which molecules in saline diffuse into the probe is different from that of tissue. We describe here a mathematical analysis of mass transport into the dialysis probe in tissue based on diffusion equations in complex media. The main finding is that diffusion characteristics of a given substance have to be included in the formula. These include the tortuosity factor (λ) and the extracellular volume fraction (α). We have substantiated this by studies in a welldefined complex medium (red blood cell suspensions) as well as in brain. We conclude that the traditional calculation procedure results in interstitial concentrations that are too low by a factor of λ 2 /α for a given compound.