Enhanced Rheoencephalograhy

Abstract

A close monitoring of the cerebrovascular parameters is essential in some neurological diseases to prevent secondary brain insults. Persistent rises in intracranial pressure caused by oedema, tumours, or haematomas may decrease the cerebral blood flow (CBF) to values below the minimum required for neuronal survival (Lang & Chesnut, 1994). As a method to evaluate CBF, Polzer and Schuhfried proposed in 1950 to apply the well-known impedance plethysmography techniques to the head, which was specifically referred to as Rheoencephalography (REG) (Polzer & Schuhfried, 1950). For this purpose, bipolar and tetrapolar electrode arrangements, named as REG I and REG II respectively, were used to measure the impedance changes of the head synchronized to the heartbeat. In REG I, a low-amplitude current is injected through two electrodes attached to the scalp, and the related electric potential difference is measured between these electrodes, whereas in REG II, a second pair of electrodes is used to measure the electric potential difference (Geddes & Baker, 1989). The latter technique reduces eventual artifacts caused by mechanical alterations in the electrode-skin interface of the current injection electrodes.