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      Rheoencephalography: A non-invasive method for neuromonitoring

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          Abstract

          In neurocritical care, the gold standard method is intracranial pressure (ICP) monitoring for the patient's lifesaving. Since it is an invasive method, it is desirable to use an alternative, noninvasive technique. The computerized real-time invasive cerebral blood flow (CBF) autoregulation (AR) monitoring calculates the status of CBF AR, called the pressure reactivity index (PRx). Studies documented that the electrical impedance of the head (Rheoencephalography – REG) can detect the status of CBF AR (REGx) and ICP noninvasively. We aimed to test REG to reflect ICP and CBF AR.

          For nineteen healthy subjects we recorded bipolar bifrontal and bitemporal REG derivations and arm bioimpedance pulses with a 200 Hz sampling rate. The challenges were a 30-second breath-holding and head-down-tilt (HDT – Trendelenburg) position. Data were stored and processed offline. REG pulse wave morphology and REGx were calculated.

          The most relevant finding was the significant morphological change of the REG pulse waveform (2 nd peak increase) during the HDT position. Breath-holding caused REG amplitude increase, but it was not significant. REGx in male and female group averages have similar trends during HDT by indicating the active status of CBF AR.

          The morphological change of REG pulse wave during HDT position was identical to ICP waveform change during increased ICP, reflecting decreased intracranial compliance. A correlation study between ICP and REG was initiated in neurocritical care patients. The noninvasive REG monitoring would also be useful in space research as well as in military medicine during the transport of wounded service members as well as for fighter pilots to indicate the loss of CBF and consciousness.

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          Most cited references80

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          Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

          Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO 2 )]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO 2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.
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            Cerebral blood flow and oxygen consumption in man.

            N A LASSEN (1959)
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              Continuous assessment of the cerebral vasomotor reactivity in head injury.

              Cerebrovascular vasomotor reactivity reflects changes in smooth muscle tone in the arterial wall in response to changes in transmural pressure or the concentration of carbon dioxide in blood. We investigated whether slow waves in arterial blood pressure (ABP) and intracranial pressure (ICP) may be used to derive an index that reflects the reactivity of vessels to changes in ABP. A method for the continuous monitoring of the association between slow spontaneous waves in ICP and arterial pressure was adopted in a group of 82 patients with head injuries. ABP, ICP, and transcranial doppler blood flow velocity in the middle cerebral artery was recorded daily (20- to 120-min time periods). A Pressure-Reactivity Index (PRx) was calculated as a moving correlation coefficient between 40 consecutive samples of values for ICP and ABP averaged for a period of 5 seconds. A moving correlation coefficient (Mean Index) between spontaneous fluctuations of mean flow velocity and cerebral perfusion pressure, which was previously reported to describe cerebral blood flow autoregulation, was also calculated. A positive PRx correlated with high ICP (r = 0.366; P < 0.001), low admission Glasgow Coma Scale score (r = 0.29; P < 0.01), and poor outcome at 6 months after injury (r = 0.48; P < 0.00001). During the first 2 days after injury, PRx was positive (P < 0.05), although only in patients with unfavorable outcomes. The correlation between PRx and Mean index (r = 0.63) was highly significant (P < 0.000001). Computer analysis of slow waves in ABP and ICP is able to provide a continuous index of cerebrovascular reactivity to changes in arterial pressure, which is of prognostic significance.
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                Author and article information

                Contributors
                Journal
                J Electr Bioimpedance
                J Electr Bioimpedance
                joeb
                joeb
                Journal of Electrical Bioimpedance
                Sciendo
                1891-5469
                13 March 2024
                January 2024
                : 15
                : 1
                : 10-25
                Affiliations
                [1 ]University of Szeged, Faculty of General Medicine, Department of Aviation and Space Medicine. Kecskemet, Hungary; Hungarian Defence Forces Medical Center, Aeromedical, Military Medical Screening and Healthcare Instituter; Kecskemet, Hungary
                [2 ]John von Neumann University , Kecskemet, Hungary
                [3 ]Uniformed Services University of the Health Sciences , Bethesda, MD, USA
                Author notes
                [#]

                In memoriam Gusztav Merenyi [ 1]

                Article
                joeb-2024-0003
                10.2478/joeb-2024-0003
                10936697
                38482467
                11495695-bda0-462a-b24e-dd7dbd89e2c1
                © 2024 Sandor Szabo et al., published by Sciendo

                This work is licensed under the Creative Commons Attribution 4.0 International License.

                History
                : 7 December 2023
                Page count
                Pages: 16
                Categories
                Article

                intracranial pressure,pulse wave morphology,rheoencephalography,cerebral blood flow,autoregulation,breath-holding,head-down-tilt position,noninvasive

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