Electrophysiological methods earlier than others began to be used to indirectly determine the intensity of energy metabolism. We will name two methods that are related to energy metabolism. This is a polarographic method by which the oxygen tension in the brain tissue is determined. In addition, the determination of hydrogen tension in the brain is used to assess LMC. But since the method is invasive, its application is limited by the scope of neurosurgical operations, mainly associated with the implantation of long-term intracerebral electrodes.
The second method, rheoencephallography (REG), is quite widespread. The REG is based on recording a changing value of electrical resistance when high-frequency currents are passed through the head. Changes in electrical resistance depend on the blood supply to the cerebral vessels and the speed of blood flow, which makes it possible to assess the state of blood supply to the brain. REG is used both normally, for example, in assessing age-related changes in cerebral blood flow, and in all major types of cerebral and vascular pathologies. In terms of informativeness, REG is inferior to the method for determining LMK, since information on cerebral blood flow in the case of registration of REG is little related to specific brain structures, but in many cases of integral assessment of the dynamics of blood supply, the use of REG is useful.
In recent decades, methods have been developed to visualize certain biochemical processes in the brain and to study cerebral energy metabolism. PET, SPECT, functional MRI and the isotope clearance method make it possible to obtain an image of the brain using computer technology and map the content of certain substances involved in energy metabolism in its structures, as well as local blood flow in its various structures. All these methods require expensive equipment, most of them involve the introduction of radioactive substances into the body, which limits their use.
Rheoencephalography reflects the state of blood supply in the systems of the carotid and vertebral arteries, but does not allow mapping of local blood flow in specific brain structures. The polarographic method for determining local cerebral blood flow is applied provided electrodes are inserted directly into the brain.