A comparative study on pulsatile intracerebral impedance and rheoencephalography

Abstract

Intracerebral pulsatile impedance was compared with the bipolar rheoencephalogram (REG) and extracranial subcutaneous tissue impedance. The investigations were carried out in man during stereotaxic surgery or through implanted steel wire electrodes. The following observations were made. 1. 1. The timing of the intracerebral impedance wave varied slightly in different parts of the brain, but it differed clearly from that of the REG wave: its descending phase started later than that of the REG and lasted almost twice as long. REG and extracranial impedance waves resembled each other in timing. 2. 2. The percentage amplitude of the intracerebral impedance wave was 20–50 times as large as that of the REG and extracranial impedance. 3. 3. The intracerebral base line impedance normally oscillated with a frequency of 2–3/min, while the base line impedance in REG and extracranial impedance was very constant. 4. 4. Intracranial hypertension was associated with a delayed, paradoxical, intracerebral impedance wave, whereas the REG and extracerebral impedance were normal in the same patients. All these findings constitute strong evidence that REG does not reflect intracerebral impedance and circulation.