Ml. Itkis et al., A SQUARE SIGNAL WAVE METHOD FOR MEASUREMENT OF BRAIN EXTRACELLULAR AND INTRACELLULAR WATER-CONTENT, Acta neurochirurgica, 1994, pp. 574-576
Brain tissue electrical impedance is a commonly used method to evaluat
e the dynamics of brain edema. We have found the square wave impedance
method simpler and more cost-effective than the currently used sine w
ave impedance method. This square wave method avoids the necessity for
expensive frequency control and amplitude-phase measuring devices as
well as simplifying on-line data processing. In our experiments the el
ectrical impulse was generated by a pulse generator of Macintosh data
acquisition system. The signal (I = 11 muA, t = 2-20 ms) was delivered
every 2-3 s external electrodes of a tetrapolar system through a spec
ially designed isolation-calibration device. This electrode system was
inserted into the cerebral cortex of experimental animals (rat). The
cerebral cortex was found to have linear electrical properties in the
5-30 muA range. Our impedance measurement system was tested in calibra
tion trials, and showed system reliability and accuracy. The system wa
s also tested in pilot experiments, in vivo, in a rat brain osmotic ed
ema model.