BED-Vol. 53, 2002 Advances in Bioengineering

The efficiency of sampling or dclivering solutes (analytes) by ill I'il'o microdialysis is influenced by the diffusive permeabilities of the probe and the tissue in which the probe is implanted. In tissue, processes removing the analyte from the extracellular space are as,mportant as diffusion in determining permeability. In addition to diffusion, analyte permeation through these media may be augmented or diminished by bulk fluid movement (transmembrane and interstitial convection). Within the perfusate, the dominant process is axial convection. Both diffusive and convective determinants of probe efficiency may be influenced by probe geometry (Figure I; longitudinal cross-sectional view). The main geometric parameters are the probe membrane length and radii, but inner cannula geometry can also be an appreciable factor. Figure 1. Schematic diagram of longitudinal cross-sectional view of microdialysis probe, indicating symbols for geometric parameters & constant perfusate flow rate, Qd The objective of this study is to generalize the mathematical description of microdialysis. The treatment extends in several ways previous mathematical models (Bungay et al. [I]; Morrison et al. [2]; 'vlorrison et al. [3]; Wallgren et al. [4]). [n addition to removing some.mplifications and approximations and adding convective transport,,ne revised theory is applicable to low-molecular-weight lipophilic, a