| abstract |
An impedance monitor (100) is adapted for use in long-term monitoring of intracellular (neuronal) swelling in the brains (102) of mammals over periods of hours or days. The monitor has an electrically isolated current source (103), supplying a one microampere AC square waveform at 200 Hz. This current is passed through an outer pair of electrodes (104, 105) of a four-electrode arrangement having skin electrodes, extradural electrodes, or in some cases surface electrodes embedded in surgical retractors. Sensing electrode pairs (107, 108) may also detect EEG activity. Impedance changes are displayed graphically (109). Multiple electrode arrays may be used for localization of affected portions of the brain. Even trans-cranially measured impedances reflect intracellular oedema and are clinically useful indicators of treatment efficacy and outcome in cases of ischaemia, asphyxia, trauma, and the like. |