Microdialysis substance recovery

Since the first reports on microdialysis in living animals, there have been efforts to estimate true (absolute) extracellular concentrations of recovered substances (ZetterstrOm et al., 1983 Tossman et al., 1986). Microdialysis sampling, however, is a dynamic process, and because of a relatively high liquid flow and small membrane area, it does not lead to the complete equilibration of concentrations in the two compartments. Rather, under steady state conditions, only a fraction of any total concentration is recovered. This recovery is referred to as relative or concentration recovery, as opposed to the diffusion flux expressed as absolute or mass recovery. The dependence of recovery on the perfusion flow rate is illustrated in Figure 6.2. As seen, relative recovery will exponentially decrease with increasing flow as the samples become more... 

Figure 6.5 The function of in vitro recovery versus molecular weights of 42 tested substances. The CMA 10 microdialysis probe with 5 mm polycarbonate membrane (cut off 20,000 Da) was perfused with Ringer s solution at 2 /xL/min.

A number of variables, such as the perfusion flow rate, the membrane surface area and geometry, the MWCO of the membrane, the diffusion characteristics of the collected analyte, the composition of the perfusion medium, and the temperature, influence recovery parameters. When the microdialysis is carried out in vivo, the recovery can also be affected by some tissue properties, including tissue tortuosity, the extracellular space volume, the tissue blood fluid and the tissue metabolism of the substance. 

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