Changes of circulatory-metabolic indices and skull biomechanics with brain activity during aging.

The cerebral blood flow values used in experimental and clinical investigations as the informative criteria for brain blood supply are often misleading. The correlation between the cerebral blood supply and brain function is not proven in all cases. An increase of brain activity is known to be accompanied by a rise of blood flow in activated regions, while a decreased activity results in a decreased blood flow. This demonstrates the close correlation between the brain blood supply and its activity. Such a correlation had not been noted in the age-dependent decrease of cerebral blood flow, suggesting the existence of special age-related mechanisms that develop with age to maintain brain metabolism. The biomechanical properties are of special significance as predicted in the early 20th century. Only recently were they validated by the simultaneous recording of Transcranial Dopplerogram and Rheoencephalogram with in-depth analysis focused on single cardiac cycles. Functioning of the intracranial blood and cerebrospinal fluid dynamics was integrated with a special physiological test "Prognosis-2" to measure brain cognitive function. Correlation was demonstrated with the circulatory-metabolic state of brain activity, especially in people with changing cognitive function. The data supports a conceptual model of adequate circulatory-metabolic supply of brain activity, showing the functional unity, which follows from integration of the mentioned systems.

[Age-related characteristics of relationships between brain blood flow, liquor dynamics and biomechanical properties of human cranium].

The peculiarities of relationships between changes of cerebral blood flow, intracranial liquor dynamics and skull biomechanics in humans were studied in an age aspect. For this aim, a non-invasive method was proposed based on concomitant registration of rheoencephalogram and transcranial dopplerogram and evaluation of relationships between intracranial volume and pulse pressure changes (P-V index). The data obtained were analyzed by pattern-phase computer processing and compared with the blood flow parameters. The investigation was carried out on healthy volunteers of 18-25, 40-50 and 65-75 years of age. It was shown that circulatory-metabolic supplying of human brain was supported by such factors as volume brain blood flow, intracranial liquor dynamics in cooperation with skull biomechanics. The cerebral blood flow decrease at aging could be compensated by increase of the reserve-compensatory abilities of the system of cranial-spinal liquor dynamics.

Blood flow dynamics in different layers of the somatosensory region of the cerebral cortex on the rat during mechanical stimulation of the vibrissae.

The present work reports studies of the quantitative spatial and temporal characteristics of changes in local blood flow in different layers of the somatosensory cortex of rats during adequate mechanical stimulation of the vibrissae. Studies were performed using 34 Wistar rats. Skull trepanning was performed under urethane (1 g/kg) anesthesia. Television-guided microscopy was used to introduce a set of three platinum electrodes (100 microns in diameter, with tip diameters of 30-40 microns) into the somatosensory cortex projection zone of the vibrissae. The first and third electrodes were positioned in cortical layers I-III and IV-VI and the central electrode was used to generate hydrogen within the tissue. Electrode positions were confirmed histologically after experiments. Animals were placed on artificial ventilation and one or all vibrissae were stimulated at a frequency of 3 Hz for 60 sec, with interstimulus intervals of 3 min. Changes in the local blood flow were measured during stimulation and for 1 min afterwards, using the hydrogen clearance method, and brain tissue impedance was also measured. There was a small (up to 5-7%) reduction in blood flow in the first seconds of stimulation, which was followed 15-25 sec later by an increase and subsequent return to initial when stimulation stopped. The increases in blood flow during stimulation of all vibrissae were by 24.2 +/- 6.7% (n = 36) in layers IV-VI and 24.5 +/- 5.6% (n = 34) in layers I-III; increases in response to stimulation of single vibrissae were by 19.4 +/- 7.4% (n = 28) and 17.8 +/- 6.4% (n = 28) respectively. The dynamics of impedance changes corresponded to those of blood flow changes. Thus, heterogeneity was found in changes of local brain blood flow in different layers of the somatosensory cortex during increases in cortical functional activity.

[Dynamics of local cerebral blood flow in different somatosensory cortical layers during whisker stimulation in rats]. / Dinamika krovotoka v razlichnykh sloiakh somatosensornoi oblasti kory golovnogo mozga u krys pri mekhanicheskoi stimuliatsii vibriss.

Whisker stimulation in rats was found to increase the local cerebral blood flow (lCBF), its SD and to damp slow oscillations. It was established that lCBF drops slightly within a few seconds after the stimulus onset. The data obtained suggest that lCBF evoked sensory stimulation changes are distinctly localized in different layers of the somatosensory cortex.

[A comparison of the measurements of local cerebral blood flow by hydrogen clearance with hydrogen inhalation and by its electrochemical generation in brain tissue]. / Sopostavlenie izmerenii lokal'nogo mozgovogo krovotoka vodorodnym klirensom s ingaliatsiei vodoroda i s ego élektrokhimicheskoi generatsiei v tkani mozga.

The goal of the present investigation was to compare data received by modifications of H2-clearance method with inhalation (H2-Inh) and electrochemical generation in brain tissue (H2-Gen) of H2 from the same recording electrodes in acute experiments (urethane 1g/kgip) with Wistar rats (n = 39). Block of three or four Pt electrochemically sharpened electrodes to tip diameters of 20-40 mu, 0.3-0.5 mm apart and 0.8-1.0 mm in length were inserted through the dura into sensorimotor cortex. One electrode was used for H2 generation (DC current 3-5 microA) and the others for PH2 recordings by polarographical method. Durations of H2 inhalation and H2 electrochemical generation were 3 or 10s with similar amplitudes of PH2. Data was recorded with a MacLab analog-digital system and Macintosh 11si computer. Recordings of resting LCBF were made with H2-Gen and H2-Inh the beginning of the experiment and after 40-60 min. LCBF was stimulated with inhalation of 7.5% CO2 for 60s. In 6 preparations LCBF was measured 10-20 min. after occlusions of two branches of the middle cerebral artery. After experiments the brain was perfused with India ink and cut in frozen sections for morphological analyses. The mean values of resting LCBF measured by H2-Inh was 1.67 +/- 0.54 ml/g/min. (+/- SD, N = 149), and by H2-Gen 3.17 +/- 0.91 (N = 147). The diffusional component was estimated as 1.2-2.5 (equivalent units, ml/g/min.) in dead cortex. The ratio of clearances in H2-Gen to H2-Inh varied in different experiments from 1.0 up to 4.0.(ABSTRACT TRUNCATED AT 250 WORDS)

The involvement of cerebrovascular reactivity in pathogenesis of space motion sickness.

The aim of the presented work is to investigate the mechanisms of involvement of cerebral circulation in pathogenesis of space motion sickness. In experiments on chronic rabbits the 2-hours rocking and antiorthostasis served as a model of influences of the zero-gravity conditions intracranial hemo- and liquorodynamics. Cerebravascular reactivity was evaluated as a response of cerebral blood flow and intracerebral rheoencephalography to functional loads (photostimulation, CO2-inhalation, Stookey test). Shifts of water balance in the brain tissue has been assessed by means of three-frequency brain electrical impedance. Rocking plus aniorthostatis resulted in decrease of the cerebrovascular reactivity and hyperhydration. The data obtained show a significant decrease of compensatory abilities of the cerebrovascular system under the zero-gravity conditions.

Investigation of human cerebral circulation in spaceflight conditions.

The effective control of the main physiological systems during spaceflight and investigation of the mechanisms involved is a difficult problem, but the success of manned space missions greatly depends on the solution of these problems. In this respect, the cerebral circulation system is of particular importance for control and research. The large amount of experimental evidence concerning the functional peculiarities of the cerebral circulation system gives us every reason to suggest that this part of the circulatory system could be readily affected by spaceflight dynamic factor-accelerations and weightlessness.