engleski

Evaluation of perfusion method for measuring the cerebrospinal fluid formation rate

Introduction: The aim of the study was to evaluate whether the cerebrospinal fluid (CSF) formation rate (Vf) calculated according to the equation of Heisey et al. corresponded to the CSF actually produced. Two experimental approaches were used: one involved a plastic cylinder and the other used cats before and after sacrifice with anesthetic overdose. In the plastic cylinder, CSF formation was simulated by the infusion of mock CSF at a rate 40.0 µ L/min. If the Heisey method were accurate, the Vf should be the same (40.0 µ L/min). In sacrificed cats, there was obviously no Vf (0 µ L/min), so according to the Heisey method Vf should not have been detected. Material and Methods: Ventriculocisternal perfusion was performed (92.4 µ L/min) with an indicator substance (dextran blue) dissolved in mock CSF (1 mg/mL) using the method of Heisey et al. A needle was introduced into the left lateral ventricle until free communication with the CSF was obtained. The needle was connected to a perfusion pump via polyethylene tubing and the perfusion solution was infused at a desired rate. From a second needle, which punctured the cisterna magna, 20-min samples of the perfusate were collected into glass tubes. The perfusion was allowed to proceed for 60 min and to stabilize prior to collecting the first sample. The animals were sacrificed by an anesthetic overdose and the samples were collected at 20-min intervals after 30 min of perfusion under the same conditions as in anesthetized cats. Perfusion in the plastic cylinder was performed in a 2-mL plastic syringe. Two plastic cannulas (O.D. 1.2 mm) connected with perfusion pumps were introduced from the back of the syringe. The simulation of the CSF secretion was performed (40.0 µ L/min ; mock CSF) through the upper cannula by the first pump, and the plastic cylinder was perfused (dextran blue dissolved in mock CSF ; 1 mg/mL ; 250.0 µ L/min) through the lower cannula by the second pump. The specimens were collected through the cannula connected to the front syringe orifice. All connections on the syringe were hermetically closed. The CSF Vf was calculated by the equation derived from Heisey et al.: Vf = Vi (Ci - Co)/Co, where Vi is the inflow perfusate rate, Ci is the concentration of the indicator substance in the inflow perfusate, and Co is the concentration of the indicator substance in the outflow perfusate. Results: During the experiments in the plastic chamber, the calculated CSF formation (46.2 µ L/min) presented statistically higher values (p<0.0001) than those produced experimentally (Vf= 40.0 µ L/min). In the 90-minute experiments performed on dead cats, the calculated CSF formation obtained by the 92.4 µ L/min perfusion was 3.2 µ L/min. Conclusion: It seems that the perfusion method may not be suitable to calculate the CSF Vf using the equation of Heisey et al., because: (a) the calculated Vf showed that CSF continued to form even in dead animals ; and (b) the calculated Vf in plastic cylinder was different from the mock CSF infusion rate ("the rate of artificial secretion of CSF").

evaluation ; perfusion method ; CSF formation rate

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