[Biomechanical properties of the human cranium: aging aspects].

Biomechanical properties of the human skull affect its dynamic tensility (pliability, compliance) by changes of intracranial volume and pressure (deltaV/deltaP). The goal of this study is to substantiate a possibility of noninvasive and dynamic evaluation of cranial compliance. The transcranial dopplerogram of middle cerebral artery and hemispheric bioimpedance were synchronously recorded, which represent information about pulsative changes of intracranial pressure and volume, respectively. The parameters were recorded at rest and during adequate hemo- and liquorodynamic tests in different age groups--20-30, 40-50, and 70-85 years. As compared with the young group, a decrease of the cranial compliance in the intermediate age group was revealed due to an observed increase if rigidity of skull bones and ligaments, which indicates a decrease of stability of the intracranial circulatory system. However, in the group of 70-85 years the compliance rose again due to an enlargement of intracranial liquor spaces and facilitation of liquor circulation inside the intracranial cavity; this can be suggested to be a compensatory mechanism for supporting the adequate brain circulatory-metabolic state.

[Frequency analysis of arterial pulse transmission in the cranial cavity]. / Chastotnyi analiz peredachi arterial'noi pul'satsii v polosti cherepa

The changes of intracranial and arterial pulse shape under functional loads (hypervolemia and intracranial hypertension) were compared. The logarithmic amplitude-frequency characteristics were found and used for the synthesis of equivalent electrical circuit of arterial pressure pulses transmission on cerebrospinal fluid (CSF) in the cranial cavity. The model obtained points to the necessity of taking into account the induction which was not performed in the earlier models of the CSF-system. It is found that the attenuation factor permitted to estimate the stability of the intracranial circulation system to input influences under different functional conditions.

[Changes in intracranial impedance during cerebral dehydration]. / Izmeneniia vnutricherepnogo impedansa pri degidratsii mozga.

The intracranial impedance (34 kHz, AC) decreased by 20--40% during i. v. infusion of hypertonic mannitol and urea solutions (1.5 g/kg) and 1 hr later owing to osmotic dehydration of the brain tissue in cats. The specific resistance of the blood also diminished by 20--30% which contributed significantly to increasing of cerebral impedance oscillations. These findings make impedance methods unreliable for evaluation of cerebral circulation during dehydration therapy.

[Mechanisms of the change in blood electrical conductivity on the administration of dehydrating substances]. / Mekhanizmy izmeneniia élektroprovodimosti krovi pri vvedenii degidratiruiushchikh veshchestv.

After i.v. infusion with 20% mannitol or 30% urea (1.5 g/kg) for 30 min, the specific electrical resistance (100 kHz, AC) of the whole blood decreased by 20-30% in anesthetized cats, although the plasma electroconductivity remained unchanged. Hematocrit, owing to osmotic hypervolemia, was significantly decreased thus causing a drop in the whole blood electrical resistance according to Maxwell's equation.

[Dynamics of central venous, arterial, and cerebrospinal fluid pressures following polyethyleneglycol administration]. / Dinamika tsentral'nogo venzonogo, arterial'nogo i likvornogo davleniia pri vvedenii poliétilenglikolia.

The polyethylenglycol -- 400 (PEG) in dose 6 ml/kg at the rate of 0.2 ml/kg/min was i. v. administered to 12 anesthetized cats. The increase of osmolarity in the blood serum caused the hypervolemia, increase of arterial (by 20-30 mm Hg) and systemic venous (by 80-100 mm H2O) pressures, but in 30 min after the end of PEG infusion the hemodynamics returned to the initial levels due to increased diuresis, whereas the cistern CSF pressure decreased as a result of dehydration of the brain. This decrease was counteracted by the high venous and arterial pressures, but, after normalizing of hemodynamics the CSF pressure was decreased by 90-100 mm H2O as against initial level.

[Intracranial hemodynamics in arterial hypertension (the renal model)]. / Vnutricherepnaia gemodinamika pri arterial'noi gipertenzii (renal'naia model').

The changes of intracranial hemodynamics were studied at the early stage of vasorenal arterial hypertension in 7 rabbits. During first 4-5 weeks of the hypertension development, the AP increased to 170 mm Hg which was followed by a drop in the blood flow by 15% in the cortex and by 19% in white matter. The blood flow increment in response to inhalation of CO2 lowered from initial 120% to 106% in the cortex and from 126% to 109% in white matter. The data on the brain tissue impedance suggested an absence of the hyperhydration of extracellular space. A mathematical model of the development of cerebral hemodynamic shift was suggested for this form of arterial hypertension, and the hypothesis was formed that vasoconstrictor response of the brain resistive vessels decreased cerebral blood flow thus preventing th shift of the Starling equilibrium and the fluid outflow from the vascular bed.

[The informational significance of the pulse waves of an intracerebral rheoencephalogram]. / Informatsionnoe znachenie pul'sovykh voln vnutrimozgovoi reoéntsefalogrammy.

The evidence obtained on the pulse waves of intracerebral rheoencephalogram in rabbits and cats, suggests active responses of cortical vessels to the loads altering the correlation of the CSF and blood pulse volumes in the process of formation of these waves. The intracerebral rheoencephalogram seems to be able to reflect the changes of both the vascular tone and the brain tissue hydration.

[The role of the perivascular spaces in shaping the pulse waves of the intracerebral rheoencephalogram]. / O roli perivaskuliarnykh prostranstv v formirovanii pul'sovykh voln vnutrimozgovoi reoéntsefalogrammy.

The intracerebral rheoencephalogram's pulse waves were recorded in rabbits and cats with indwelling electrodes. The waves' amplitude and form were rather diverse and they were inverted in 25% cases: the systolic peak was directed to an increase in the impedance. The dynamics of the waves reflect complex hemoliquorodynamic interrelations in perivascular space.

[The effect of a calcium channel blockade on the reactivity of the cerebral vessels in rabbits]. / Vliianie blokady kal'tsievykh kanalov na reaktivnost' sosudov golovnogo mozga krolikov.

The changes of cerebrovascular reactivity (CVR) under influence of calcium antagonist nimodipine (0.01 and 0.06 mg/kg i.v.) and verapamil (0.6 and 1.0 mg/kg i.v.) were investigated in chronic experiments in 12 rabbits. Platinum electrodes were implanted into cortex, thalamus and hypothalamus, and cerebral blood flow was measured in these zones by H2-clearance method. CVR was evaluated as a ratio: cerebral blood flow after 7% CO2 inhalation to initial level. This ratio, or reactivity coefficient (RC), in normal conditions is 1.49-1.59. Nimodipine in dose 0.01 mg/kg resulted in significant decrease (by 15-20%) of RC only in cortex. In dose 0.06 mg/kg this decreased RC was about 20-30% in cortex and in hypothalamus, but in thalamus the changes of RC were insignificant. Verapamil in dose 0.6 mg/kg resulted in different changes of RC: increase in cortex, decrease in thalamus, but in hypothalamus no changes. In dose 1.0 mg/kg RC was decreased in cortex by 15-20%, in other zones were no changes.

[Dynamics of the cerebral blood flow and reactivity of the cerebral vessels after bilateral occlusion of the carotid arteries]. / Dinamika mozgovogo krovotoka i reaktivnosti tserebral'nykh sosudov posle dvukhstoronnei okkliuzii sonnykh arterii.

A model of cerebral ischemia was implemented by means of bilateral occlusion of carotid arteries in rabbits. A reduction of the blood flow was observed during first 3 days after the occlusion in the cortex and white matter, followed by a slow restoration up to 80 per cent of initial level. The responses of the blood flow to CO2 were reduced and often inverted during the 1st week, had a phasic character and returned to near normal by the 14th day. The responsiveness of vessels to CO2 and head-down tilt were sharply reduced and inverted during the 1st week and did not return to normal. Simultaneous recording of the blood flow parameters and of the responsiveness of cerebral vessels provides a better insight into the dynamics of postischemic restoration of functional state of various parts of the brain vascular system.

[Ways to optimize the cerebral circulation during extreme actions on the brain]. / Puti optimizatsii mozgovogo krovoobrashcheniia pri ékstremal'nykh vozdeistviiakh na golovnoi mozg.

The effect of mildronate (25 mg/kg, i.v.) administration during 14 days on the restoration of cerebral blood flow and vascular reactivity after local lesions and ischemia, was studied in rabbits. The effect involved an improvement of restorative processes due to a faster normalizing of reactivity of cerebral vessels. The latter seems to be more important for optimization of cerebral blood flow after extreme effects than the absolute level of the cerebral blood flow.

[Functioning of the cerebral circulatory system in rabbits during hyperthermia]. / Funktsionirovanie sistemy mozgovogo krovoobrashcheniia krolikov pri gipertermii.

In chronic experiments on rabbits, the effect of hyperthermia growing up to 41 degrees C upon the cerebral circulation system, was studied. Cortical blood flow decreased by 20-25% due to hypercapnia and constriction of arterioles whereas the blood flow in the thalamus and hypothalamus either remained the same as initial one or increased insignificantly. The reactivity of cerebral vessels in CO2 inhalation and orthostatic load decreased along with the rise of body temperature. The signs of lesion of the hemato-encephalic barrier and an increase of the water content by 3-4% in the cortex and white matter were revealed in hyperthermia. The impedance data corroborated extracellular character of cerebral oedema. Comparative study of vasodilators euphylline, cavinton and flunaresine has revealed that the calcium blocking agent flunaresine provides the best restoration of the cerebral blood flow level and the reactivity of cerebral vessels in hyperthermia.

[Relation of the level of blood flow and reactivity of cerebral vessels to the functional state of brain tissue]. / O vzaimosviazi urovnia krovotoka i reaktivnosti mozgovykh sosudov s funktsional'nym sostoianiem tkani mozga.

The local cerebral blood flow (LCBF) and cerebrovascular reactivity to CO2 inhalation test were studied in rabbits after experimental local brain lesions. A decrease of the LCBF and cerebrovascular reactivity was observed in the grey and white matter surrounding the traumatic focus at the distance of about 15 mm, being minimal on the 3rd-5th days followed by normalizing by the 10th-14th days after lesions. The cerebrovascular reactivity was found to be a valuable prognostic parameter to assess the functional restoration of the brain.

[Relationship between the intracranial pressure, intracranial blood volume and total cerebral blood flow]. / O vzaimosviazi vnutricherepnogo davleniia, krovenapolneniia polosti cherepa i summarnogo mozgovogo krovotoka.

Studies in cats and in neurosurgical patients reveal that intraskull pressure, blood volume and total brain blood flow depend on the same factors, to a different extent though. This is determined by structural--functional organization of the intraskull circulation system, the analysis of which revealed a scheme of functional interrelationships among volumes and pressures of fluid media in the closed skull space. The features of interrelationships are not rigid and can have their own specifics in concrete situations.

[Informativeness of indices of reactions of cerebral vessels to adequate stimuli]. / Ob informativnosti pokazatelei reaktsii mozgovykh sosudov na adekvatnye vozdeistviia.

The functional stability of cerebral circulation involves its ability to resist against external influences and is based on the cerebral vessels reactivity. Objective methods for evaluation of this reactivity are proposed using standard and specific functional loads. The indices of intracranial and systemic hemodynamics were recorded in experimental animals, healthy humans and patients with head injuries during postoperative period. The dynamics of cerebral vessel reactivity was found to depend on the body functional state.

[The effect on the cerebral microcirculation of in vivo stains used in biomicroscopy]. / Vliianie na mikrotsirkuliatsiiu mozga nekotorykh prizhiznennykh krasitelei, ispol'zuemykh pri biomikroskopii.

Vasoactive properties of semi-colloidal acid stains of the Evan blue and tripane blue, were revealed in rabbits and rats. The microphoto-technique revealed a dose-depending vasodilating effect of the stains. The response of the arteries had sometimes a biphasic character: constriction--dilation. I. v. administration of the stains induced a dose-dependent significant reduction of local blood flow in the cortex, subcortical white substance and other parts of the brain, of total cerebral blood flow in the venous sinus; a drop of systemic arterial pressure in normo- and hypertensive animals; a change in cerebral bioelectrical activity with increasing theta-waves, appearance of spikes and polyspikes in the EEG. Acting upon the formation of vascular tonus, these stains can interfere with the mechanisms of regulation of cerebral blood flow.

[Cerebral blood flow and cerebrovascular reactivity in the early postnatal ontogeny of rats]. / Mozgovoi krovotok i tserebrovaskuliarnaia reaktivnost' v rannem postnatal'nom ontogeneze krys.

The development of cortical cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) were studied in Wistar rats during early postnatal ontogenesis, in groups aged 2-5, 6-8, 9-11, 12-15, 16-18 and 19-25 days. CBF was measured polarographically using inhaled hydrogen clearance method, with platinum electrodes inserted into parietal cortex. At the mentioned age periods, CBF and its percentage of adult level averaged as 38 (21%), 81 (45%), 142 (78%), 85 (47%), 110 (61%), and 118 (65%) ml/100 g/min, respectively. Hence, during the early postnatal ontogenesis CBF increased gradually, however, it did not reach the adult level up to the end of the first month. CBF peak at 9-11 days period is suggested as a result of sharp rise of the brain vessels growth. CVR was assessed as the percentage of CBF increase after standardized 5% CO2 inhalation test. At the above age periods, CVR was found to bi 26, 33, 36, 41, 44 and 31% respectively, and was similar to adult rat CVR of 36%. The conclusion was drawn that regulatory mechanisms of adequate responses of brain vasculature to chemical metabolic factors are well developed already at the very beginning of postnatal life.