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Flow dependent changes in the effective surface area of microdialysis probes
G M Alexander1, J R Grothusen, R J Schwartzman
1Department of Neurology, Jefferson Medical College, Philadelphia, PA 19107.
Life Sciences
|January 1, 1988
Summary
Microdialysis probe efficiency was measured in vitro and in vivo using tritiated water (THO). Probe efficiency decreases with flow rate, with in vivo efficiency being lower than in vitro efficiency except at very low flow rates.
Area of Science:
- Neuroscience
- Pharmacology
- Biomedical Engineering
Background:
- Microdialysis is a technique used to measure the concentration of substances in the brain extracellular fluid.
- Accurate quantification requires knowledge of the microdialysis probe's relative efficiency.
Purpose of the Study:
- To determine the relative efficiencies of microdialysis probes in vitro and in vivo.
- To establish a method for calculating the effective surface area of microdialysis probes.
Main Methods:
- Relative efficiencies were determined using tritiated water (THO) in anesthetized rats.
- Microdialysis probes were inserted into the caudoputamen, and samples were collected at varying flow rates (0.2–10.0 ul/min).
- In vitro efficiency was calculated as dialysate THO concentration/solution THO concentration; in vivo efficiency as brain dialysate THO concentration/plasma THO concentration.
Main Results:
- Both in vitro and in vivo relative efficiencies for THO decreased as flow rates increased.
- In vivo and in vitro efficiencies differed, except at flow rates below 0.25 ul/min.
- The surface of effective exchange (Se) was introduced as the fraction of maximum in vitro efficiency attained in vivo.
Conclusions:
- The study provides a method to compute the effective surface area of microdialysis probes at any flow rate.
- This effective surface area can be used as a correction factor for accurate in vivo measurements.
- Understanding probe efficiency is crucial for accurate neurochemical measurements using microdialysis.