Discriminant parameters representing cerebral cortical function during anoxic anoxia investigations.

In order to quantify the effect of specific drugs on the cerebral cortex an "in vivo" model has been developed for the induction and the observation of anoxic anoxia. Rabbits are used as test animals. Sensors for the assessment of local parameters are chronically implanted: ECoG electrodes are applied; pO2 electrodes are inserted into the cortical tissue. The derived somatosensory evoked potentials are used for evaluating the cerebral cortical function. Animals are cannulated with a tracheal tube, curarized and artificially ventilated. Anoxic anoxia, controlled by a special purpose microprocessor system, may then be induced and repeated in a reproducible way. During the experiments local (pO2, ECoG, SEP) as well as general parameters (ECG, heart rate, systemic blood pressure, rectal temperature) are recorded and stored on analog magnetic tape as well as digitized with the microprocessor system. The cortical pO2 is measured with a polarographic method, the SEP's are obtained on-line by time coherent averaging and the ECoG states (e.g. epilepsy during anoxia) are derived by using band-pass filters and rms detectors. Off-line the signals (pO2, heart rate, mean systemic blood pressure, temperature) are standardized and represented together with parameters derived from ECoG and SEP. SEP-waveform parameters indicating intensity (norm) and similarity with a reference SEP signal (correlation value) are used. The measuring and processing method is still being optimized; special attention is being paid towards the quality of the calculated SEP's which are to be used for the quantification of the cortical function during reference, anoxia and recovery period. As such, in order to improve the signal-to-noise ratio of the SEP's and, consequently, of the derived parameters, ECoG signals are digitized off-line and subjected to a preprocessing, implying filtering and spectral analysis procedures.