Studies in rheoencephalography (REG)

Abstract

This article presents an overview of rheoencephalography (REG) - electrical impedance measurements of the brain - and summarizes past and ongoing research to develop medical applications of REG for neuro-critical care and for primary prevention of stroke and cardiovascular disease. The availability of advanced electronics and computation has opened up the potential for use of REG technology as a noninvasive, continuous and inexpensive brain monitor for military and civilian applications. The clinical background information presented here introduces physiological and clinical environments where REG has potential for use in research and clinical settings. REG studies over the past three decades have involved in vitro and in vivo groups (animal and human), including more than 1500 measurements and related electronic and computational results and practical applications. In vitro studies helped researchers understand the flow/volume relationship between Doppler ultrasound and electrical impedance signals and supported development of REG data processing methods. In animal studies, REG was used to monitor the lower limit of cerebral blood flow (CBF) autoregulation (AR) using a newly developed algorithm. These animal studies also confirmed correlations between REG and measurements of carotid flow (CF) and intracranial pressure (ICP). Human studies confirmed the applicability of REG for detecting cerebrovascular alteration, demonstrating the usefulness of REG in the field of stroke/cardio-vascular disease prevention. In these studies, REG was compared to known stroke risk factors and to results obtained using carotid ultrasound measurements. An intelligent REG system (Cerberus) has been developed for primary stroke prevention. In these studies, the biologically relevant variables of the REG signal were pulse amplitude (minimum - maximum distance) and duration of the anacrotic (rising) portion of the REG pulse wave. The principal limitation of REG for clinical application is the lack of pathological and physiological correlations. The studies presented here have initiated such inquiries, but many clinical questions about the pathophysiological background of REG remain unanswered. These results demonstrate that REG development is a multidisciplinary subject with relevance for medicine (vascular neurology and neurosurgery intensive care); electronic engineering; mathematics, and computer science (data processing). It is hoped that information presented in this article will provide assistance to those involved in REG research, particularly in development and clinical applications.