A square signal wave method for measurement of brain extra- and intracellular water content.

Brain tissue electrical impedance is a commonly used method to evaluate the dynamics of brain edema. We have found the square wave impedance method simpler and more cost-effective than the currently used sine wave impedance method. This square wave method avoids the necessity for expensive frequency control and amplitude-phase measuring devices as well as simplifying on-line data processing. In our experiments the electrical impulse was generated by a pulse generator of Macintosh data acquisition system. The signal (I = 11 muA, t = 2-20 ms) was delivered every 2-3 s external electrodes of a tetrapolar system through a specially designed isolation-calibration device. This electrode system was inserted into the cerebral cortex of experimental animals (rat). The cerebral cortex was found to have linear electrical properties in the 5-30 muA range. Our impedance measurement system was tested in calibration trials, and showed system reliability and accuracy. The system was also tested in pilot experiments, in vivo, in a rat brain osmotic edema model.

Off-line methods for detection and correction of EEG artefacts of various origin.

Conventional methods for the correction of the effects of blinking and eyeball movement artefacts in the EEG have been considered. The limitations of present methods are reviewed. Considering the brain as a volume conductor, the ways of revealing the ocular movement artefacts in the frontal EEG leads have been suggested. On the basis of the proposed criteria an optimal method of artefact correction in the frontal EEG leads have been developed. General principles in the developing the program for the correction of artefacts of different origin are set forth.

[Mechanical properties of the brain during the development of postischemic edema]. / Mekhanicheskie svoistva golovnogo mozga v protsesse razvitiia postishemicheskogo oteka.

The mechanical properties of the brain during the development of postischemic edema in rabbits were studied in vivo by an original method. The effect of the circulatory factors was removed during the study. The experiments showed that ischemia reduces the pliancy of the brain, this is indicative of compensatory processes in its tissue which limit the entry of water into it from the blood. Before the development of marked edema, however, pliancy diminishes which is conducive to advancement of edema. The last circumstance, just as the increase of hysteresis, is evidence that the brain becomes "poor" from the standpoint of the development of edema. The brain consistency index may be an objective in vivo criterion of the degree of water accumulation in it.

[Effect of systemic arterial and venous pressures on blood volume in the cerebral vessels]. / Vliianie sistemnogo arterial'nogo i venoznogo davleniia na ob"em krovi v sosudakh golovnogo mozga.

In rabbit chest-head preparation with largely exposed brain, the cerebral volume (CV) and the cerebral blood volume (CBV) were continuously recorded number conditions of controlled alterations of the systemic arterial and venous pressures (SAP and SVP resp.). The obtained relationships were linear and described by the equations as follows: delta CV = 0.0028 SAP; delta CBV = 0.0013 SAP; delta CV = 0.028 SVP; delta CBV = 0.013 SVP; they show the effect of the SVP changes to be nearly ten times greater than that of the SAP. Half of the increase in CV was caused by the CBV increase and the other half - by tissue hydration under particular conditions of the experiments. The data obtained bear on the effects of the systemic circulation on brain oedema development.

[Venous pressure in the brain, its relationship to systemic venous pressure and to the development of cerebral edema]. / Venoznoe davlenie v mozge, ego sviaz' s sistemnym venoznym davleniem i s razvitiem oteka golovnogo mozga.

Studies on rabbits have shown that cerebral venous pressure (continuosly recorded in the sagittal venous sinus) is linearly dependent on the systemic venous pressure measured from the cranial vena cava. On the other hand, the changes in the brain volume are also linearly dependent on the systemic and hence the cerebral venous pressure. In the preedematous brain, the slope of the curve considerably rose due to the increased pliancy of its tissue. When brain edema developed the slope fo the curve became appreciably less as compared to the normal brain. This is evident of the increased rigidity of edematous brain tissue.

[Reaction of the pre-edematous brain to an increase in venous pressure]. / Reaktsiia predotechnogo mozga na povyshenie venoznogo davleniia.

Changes in the volume of the open brain were recorded in rabbit experiments ("chest-head" preparation) in a series of tests with controlled increase in general venous pressure by approximately 13 mm Hg. At the beginning of the experiments the changei in the volume of the open brain and general venous pressure occurred parallely to each other, but later, when the brain became preedematous, hysteresis was detected on the curves of their dependence. Hysteresis increased gradually during the experiment, indicating that impedement of blood drainage from the venous system of the brain and/or resorption of fluid from its tissue had begun to the development of stable edema. It is assumed that the predematous condition of the brain is caused by changes either in the mechanical properties of its tissue or in its osmolarity.

[Transcapillary water filtration in the presence of an increase in intravascular pressure as a factor in the development of brain edema]. / Transkapilliarnaia fil'tratsiia vody pri povyshenii vnutrisosudistogo davleniia kak faktor razvitiia oteka golovnogo mozga.

The concentration of K+ and Na+ ions in the extracellular fluid of the parietal cortex of the brain was studied in experiments on rabbits ("chest-head" preparation) by means of selective electrodes during a controlled increase in general venous pressure by approximately 13 mm Hg. A decrease in the concentration of Na+ ions and mild changes in the concentration of K+ ions indicated that the extracellular fluid was diluted due to filtration of water from the blood vessels. In the normal brain this process was reversible, while in a pre-edematous condition the excess filtration of water led ultimately to the development of edema of the brain with the corresponding changes in the function of the plasma membranes and changes in the concentration of K+ and Na+ ions in the extracellular fluid.