A noninvasive, continuous brain monitoring method: rheoencephalography (REG)

This paper deals with the sustainability under anoxic conditions of human beings, both when healthy, and diseased. As our attention is focused these days on the environment, sustainability, and green energy, a similar effort is being made in neuromonitoring to switch from invasive to noninvasive monitoring methods. Keys to these changes are computerization and shrinking size of electronic hardware. Computerization is going on in all areas of biomedical engineering, both in research and in clinical fields of medicine. In neurology, brain imaging is the most characteristic change in recent decades. These modalities of imaging (MRI, CT, PET scan, etc.) are predominantly utilized for localizing brain pathology. Brain imaging offers great spatial resolution, but poor time resolution. Therefore, for continuous monitoring, neurocritical care departments require an additional tool with good time resolution. There are invasive and noninvasive neuromonitoring methods. The standard method to monitor intracranial pressure (ICP) is an invasive method. Computerization allows for calculating the cerebral blood flow autoregulation (CBF AR) index (pressure reactivity index - PRx) from ICP and systemic arterial pressure (SAP) in real time, continuously, but invasively. The new development, discussed in this paper, is to calculate this index noninvasively by using rheoencephalography (REG), called REGx. We present the road to this invention and summarize multifold REG related results, such as using REG for primary stroke prevention screening, comparison incidence of arteriosclerotic risk factors, various studies by using CBF manipulations, and correlations with other neuromonitoring methods, and validation with in vitro and in vivo methods. REG by using different algorithms allow for real time calculation of autoregulated blood flow. This paper presents results of validation of CBF algorithms as an effective, noninvasive method. The author’s intent is to supply sufficient physiological background information. This review covers the author’s research efforts over several decades; it pertains multiple studies and has an updated addition to human sustainability by considering that Covid-19 is increasing stroke and cardiovascular disease (CVD) morbidity and mortality.