On mathematical models of microdialysis: geometry, steady-state models, recovery and probe radius

Commonly used methods for microdialysis recovery measurement are reviewed a nd the zero flow and no net flux methods are suggested as the most robust i n practice. Six different mathematical models of microdialysis assumptions are investigated and compared for varying dialysis probe radius. One transm itter (dopamine), three metabolites (DOPAC, HVA and 5HIAA) and two drugs (c affeine and theophylline) were studied. Histology and functional response t o a drug were measured. Deficiencies were demonstrated for several of the m odels, the one: best explaining experimental data includes both passive dif fusion and active tissue regulation in a cylindrical symmetric geometry. Th e recovery decreased with decreasing probe radius but smaller probes caused less tissue injury. It Is concluded that a mathematical model of microdial ysis must include diffusional and physiological processes in order to accur ately account for experimentally observed phenomena. The experiments also d emonstrated that, for small brain nuclei, the size of the nucleus may influ ence the recovery. (C) 2000 Elsevier Science B.V. All rights reserved.