Spatiotemporal pattern of the extracranial component of the rheoencephalographic signal

Characteristics of Rheoencephalography and some Associated Factors on Menopausal Women

The significant drop in estrogen levels during menopause increases the cardiovascular risks, one of which is cerebrovascular atherosclerosis. Research on rheoencephalography (REG) parameters for the early diagnosis of cerebrovascular atherosclerotic lesions is of great interest to scientists because of its ease of implementation, low cost, and non-invasiveness. The objectives of study are to evaluate the vascular tone, cerebral circulation flow in each hemisphere of the brain of menopausal women, and some associated factors through waveform characteristics and parameters in REG. A controlled cross-sectional descriptive study was conducted on a group of patients including 80 menopausal women and a control group of 46 menstruating women. All patients were measured REG in the frontal-occipital leads by VasoScreen 5000 impedance REG meter. In menopausal women, the percentage of sharp waves, the percentage of clear side waves, and the average REG were all lower than in the control group (p<0.01). The mean conduction time and mean slope ratio was lower than the control group (p<0.001). The mean peak time was higher than the control group (p<0.01). The mean elasticity index (alpha/T) was higher than the control group (p<0.001). Menopausal women have increased vascular tone, the highest in the group of women 50-60 years old, menopause <5 years, having a habit of eating red meat; and decreased blood flow intensity, the highest in the group of women <50 years old. However, the difference was statistically significant only in the left hemisphere (p<0.05). Vascular hypertonia in menopausal women with central obesity was higher than in the non-obese group in both hemispheres (p<0.05). In conclusion, menopausal women had atherosclerosis in both hemispheres of the brain, which was clearly shown in the rate of increased vascular tone. Central obesity may increase the risk of vascular hypertonia 3.75 times in the right and 5.44 times in the left hemisphere.

Study on the Cerebral Blood Flow Regulatory Features of Acupuncture at Acupoints of the Governor Vessel

Background: Many studies to clarify the influences of acupuncture at different acupoints of various meridians on cerebral blood flow (CBF) were conducted in the past. However, the influences of acupuncture at the points of the Governor Vessel on CBF have not yet been studied tangibly. Objective: The purpose of this study was to investigate the influences of acupuncture at individual acupoints of the Governor Vessel on cerebral hemodynamic indices. Materials and Methods: Two hundred and seventy-nine patients with chronic cerebral circulation insufficiency (CCCI) were observed, using a cerebrovascular disease diagnosis system (CVD 3000, KCC, Pyongyang, Democratic People's Republic of Korea). Various hemodynamic indices-such as vascular compliance, hemodynamic resistance, and blood flow quantity-were compared before and after acupuncture at individual acupoints of the Governor Vessel. Results: The influences of the points of Governor Vessel on CBF were different from each other, and systemic specificity of the Governor Vessel did not emerge. The largest number of indices showed significant changes when GV 16 was punctured, and the effects of GV 16, GV 20, and GV 14 on the head and the neck were relatively better than those of the points on the trunk. Conclusions: The points on the head and the neck of the Governor Vessel improve CBF biphasic regulation relatively better than the points on the trunk.

To what extent is the bipolar rheoencephalographic signal contaminated by scalp blood flow? A clinical study to quantify its extra and non-extracranial components

Background

Impedance plethysmography applied to the head by using a pair of electrodes attached to the scalp surface is known as bipolar Rheoencephalography or REG I and was originally proposed to measure changes in cerebral blood volume related to the heartbeat. REG I was soon discarded in favor of other REG configurations, since most of the signal was shown to be heavily contaminated by the extracranial blood flow. The main goal of this study was to identify and compare the part of the REG I signal caused by scalp blood flow with that originating from non-extracranial sources.

Methods

A clinical study involving thirty-six healthy volunteers was designed for this purpose. REG I was first registered in each subject under normal conditions. A pneumatic cuff was then placed around the head and was inflated to arrest the scalp blood flow and a second REG I was recorded. Finally, a third REG I was taken immediately after cuff deflation.

Results

The REG I signal is attenuated, but not extinguished, during cuff inflation in a wide subject-dependent range ratio from 0.12 to 0.68 (0.37 ± 0.15). The residual REG I signal has a waveform that is markedly different from that obtained before cuff inflation, which supports the hypothesis of the intracranial origin of the residual REG I signal. Additionally, an increase of 22% in REG I amplitude was observed when the head cuff was deflated.

Conclusions

Waveform differences between extra and non-extracranial components are significant and these differences could be used in a method to distinguish one from the other. However, a significant part of the REG I signal is caused by a non-extracranial source and, therefore, it should not be used as a footprint of the extracranial blood flow.

An extended model of intracranial latency facilitates non-invasive detection of cerebrovascular changes

A method has been recently developed to reduce the confounding factors of extracranial origins on the intracranial latency (the time interval between the electrocardiogram QRS component and the initial inflection of the resulting pulse). Although, the proposed model was shown to portray a better characterization of cerebral vasculature, the parameters of the model and their physiological interpretations have not been fully explored. The present work improves the physiological understanding of these parameters, refines the model and extends its ability to monitor real-time changes in overall cerebrovascular resistance. We show that the slope of the linear model which relates the latency of arterial blood pressure to that of the cerebral blood flow velocity, could be a measure of resistance, and that the intercept is a function of slope and pre-ejection period. A dataset of cerebral blood flow velocity and arterial blood pressure signals from 18 normal subjects at rest was used to validate the derived parameters of the model. Also, the results of further data processing verified our hypothesis that the slope of the model would significantly increase during a period of CO₂ rebreathing, due to dilation of the vessels and reduction of cerebrovascular resistance (p ≤ 0.02). Finally as the slope of the proposed model is shown to be highly correlated with other conventional measures of cerebrovascular resistance, (resistance area product and critical closing pressure), we conclude that the derived slope metric is a measure of overall cerebrovascular resistance and therefore could be useful in guiding the non-invasive cerebrovascular management of patients.

Extraction of the intracranial component from the rheoencephalographic signal: a new approach

The well-known inherent artifact on the rheoencephalogram (REG) caused by the pulsatility of the scalp blood flow left the REG out of the clinical practice. In fact, depending on the selected electrode arrangement, the measurement of the brain impedance changes time-locked with the heartbeat can be completely buried on that of the scalp. In this work, a novel mathematical method based on the physiological differences between the brain and scalp perfusions is proposed to extract the intracranial information from REG. This method is experimentally applied to REG signals recorded at five electrode positions and results are compared with those derived from our previous theoretical works. Intracranial components extracted from the REG signals are consistent with the stated hypothesis and reproduce the unexpected results obtained with our theoretical models. Although further studies would be needed, the evidences found in this work suggest that the method proposed in this work extracts the intracranial information from the REG signal.