To assess cerebral energy processes by the parameters of SCP, you need to enter some reference point and determine the measure that will be used to quantify the measured values. This is necessary because the goal of measuring SCP is not the phenomenon itself, but what is behind it – an assessment of the CRR and energy processes in the brain. The situation is complicated by the fact that at the present time there is no scale for translating measured SCP values into the energy exchange indicators scale, therefore using the SCP you can only get a relative measure of changes in cerebral energy processes.
At any age, there is a certain intensity of cerebral energy exchange, which provides the necessary level of adaptation in the norm. Therefore, to determine the age-related characteristics of AMR, which correspond to the normal level of energy metabolism at rest, it is necessary to register AMR in healthy people of the same age and gender who are in conditions of calm wakefulness. Naturally, different people will get slightly different values of SCP, but the average values of SCP and their standard error, measured in a fairly large sample, will give such a reference value. A similar principle underlies the definition of many indicators used in medicine (blood pressure, temperature, etc.).
An age-dependent normative scale for healthy people converts SCP values in brain regions into criteria for assessing energy metabolism in these departments, which are characterized as a normal level, moderately increased or decreased, significantly increased or decreased.
The reference distribution of quantitative SCP values for each region is divided into intervals equal to the standard deviation, and the arithmetic mean value is taken as a reference point. It is known that in the case of a normal distribution, approximately 67% of the entire set of measurements taken are in the range of values that differ from the average by one standard deviation and 95% of the measurements are in the range that differs from the average by two standard deviations. The resulting scale corresponds to five- and one-percent statistical significance levels accepted in biology in assessing the differences between the distributions of random variables. This scale is a non-linear probability measure with a step value equal to the standard deviation. In accordance with this scale, the level of energy metabolism is considered normal if the SCP value does not differ from the average by more than one standard deviation; moderately increased or decreased – if the level of constant potentials is in the range from one to two mean square deviations from the average; significantly increased or decreased – if the SCP deviates from the mean by more than two mean square deviations. An age-dependent normative scale is the basis for the diagnosis of changes in the energy metabolism of the brain according to SCP.
SCP are recorded in a state of calm wakefulness and with functional tests. Various stress tests (hyperventilation, dosed physical activity, solving psychological problems, etc.), as well as physiotherapeutic and pharmacological effects, can serve as such samples. Functional tests allow you to assess the energy reserves of the brain, its ability to carry the load. It is clear that in case of sufficiency of energy resources, the total energy consumption should not change significantly. When the load exceeds the adaptive capacity of the body, a dual reaction is possible: an increase or decrease in energy metabolism. The first reaction is characteristic of the initial stages of stress associated with activation, the second – for the last stage – exhaustion. Under the influence of the load, changes in the sign of the interhemispheric gradient of the SCP are possible. As will be described in detail below, during stress, the right hemisphere is often activated, which leads to a change in the distribution of normalized SCP.
Change in AMR under the influence of physiotherapeutic procedures and pharmacological drugs allows us to evaluate the effectiveness of therapeutic effects. SCP at rest and under the influence of functional tests gives a complete picture of the current energy state of the human brain and its reaction to both stress tests and other types of influences.
Thus, when registering SCP, principles are applied that are largely common to various electrophysiological methods (EEG, VP), while the analysis and interpretation of the data obtained is close to that adopted in visual methods for assessing energy metabolism (PET, NMR spectroscopy and other).
The methodology for recording and analyzing SCP should satisfy the principles adopted in modern electrophysiology, which allow taking into account and, if possible, eliminating artifacts of physical and biological origin.
Recording is performed using DC amplifiers with a large input impedance and non-polarizable electrodes. The most important sources of artifacts of physical origin are electrode potentials; therefore, the interelectrode potential difference should be measured and eliminated when registering SCP. Skin potentials are a biological source of artifacts. To reduce artifacts of skin origin, the relationship between skin potentials and skin resistance is used. Reducing skin resistance to 5 kOhm and continuous monitoring of its stability during the recording process can significantly reduce the effect of skin potentials, in particular the skin-galvanic reaction on the recorded SCP.
The magnitude of SCP between the head and arm depends on the pH difference flowing from the brain and peripheral blood, which in turn is associated with differences in the intensity and energy exchange of the brain and tissues of the hand . To assess cerebral
energy processes according to SCP parameters, an age-dependent normative scale was developed, which was based on SCP data in healthy subjects of different ages. Using this scale, depending on how much the SCP is reduced or increased compared to the reference one, one can judge changes in the CRR and the intensity of brain energy metabolism in a particular person. Assessment of SCP includes a mathematical analysis of this indicator in comparison with the normative characteristics contained in the database, as well as mapping the distribution of SCP on the surface of the head in comparison with the standard.
The specialized hardware and software complex “Neuroenergometer”, developed in accordance with the stated principles, allows you to record SCP with control of artifacts of physical and biological origin, perform mapping, as well as mathematical analysis of SCP. The complex consists of a five-channel DC biopotential amplifier with an analog-to-digital converter, as well as software for recording, analysis, graphical representation and storage of recorded brain SCP values and processing results .