Biomedical subjects
Publications and source records attributed to G B Vaĭnshteĭn.
In patients with partial craniospinal blocks, the impedance responses to certain functional tests were by 20-30% less obvious. Osteopathic procedures normalised the impedance fluctuations. The data obtained suggest that the CSF dynamics plays an important role in genesis and changes of the head impedance.
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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 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.
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.
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.
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.
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.
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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.
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 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.
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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.
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.
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 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.