Correlation of rheoencephalography and laser Doppler flow: a rat study

Measuring brain electrical impedance (rheoencephalography) is a potential technique for noninvasive, continuous neuro-monitoring of cerebral blood flow autoregulation in humans. In the present rat study, we compared changes in cerebral blood flow autoregulation during CO₂ inhalation measured by rheoencephalography to changes measured by laser Doppler flowmetry, an invasive continuous monitoring modality. Our hypothesis was that both modalities would reflect cerebral blood flow autoregulation.

Male Sprague-Dawley rats (n=28; 28 control and 82 CO₂ challenges) were measured under anesthesia. The surgical preparation involved implantation of intracerebral REG electrodes and an LDF probe into the brain. Analog waveforms were stored in a computer.

CO₂ inhalation caused transient, simultaneous increases in the signals of both laser Doppler flow (171.99 ± 46.68 %) and rheoencephalography (329.88 ± 175.50%). These results showed a correlation between the two measured modalities; the area under the receiver operating characteristic curve was 0.8394.

The similar results obtained by measurements made with laser Doppler flowmetry and rheoencephalography indicate that rheo-encephalography, like laser Doppler flowmetry, reflects cerebral blood flow autoregulation. Rheoencephalography therefore shows potential for use as a continuous neuro-monitoring technique.