Determination of Brain Interstitial Concentrations by Microdialysis

Research output: Contribution to journalArticle


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 λ2/α for a given compound.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Mechanical Engineering


  • Interstitial space size, Tortuosity factor, Diffusion characteristics, Mass transport, Complex media, Diffusion equations, Brain interstitial space, Microdialysis
Original languageEnglish
Pages (from-to)1741-1750
JournalJournal of Neurochemistry
Issue number6
Publication statusPublished - 1989
Publication categoryResearch