[Rat heat structural and functional characteristics and gas exchange parameters after experimental myocardial infarction].

Rat heart structural and functional changes and gas exchange parameters were investigated in six months after experimental myocardial infarction. Left ventricular end-systolic and end-diastolic dimensions in rats with chronic heart failure were 78 and 30% higher than in control respectively. Left ventricle cavity volume in systole and diastole were 5 and 2 times increased respectively. Left ventricular cavity stretching was accompanied by thinning of the interventricular septum. Left ventricular structural changes leads to its functional deterioration. Left ventricular contraction fraction was reduced by 60%, and the ejection fraction--by 52% in comparison with control. Gas exchange investigation revealed that in six month after myocardial infarction oxygen consumption of operated rats was increased by 30% and production of carbon dioxide by more than 40%. Respiratory quotient, which reflects the nature of oxidized substrates, in rats with myocardial infarction was amounted to 0.85, indicating significant increase in the contribution of carbohydrates as an energy substrate for myocardial metabolism.

[The tissue oxygen partial pressure in organs of hens in the second half of embryogenesis and in the first days after hatching].

The aim of the study was measure the development chick tissue partial pressure of oxygen (pO2) in the brain cerebral hemispheres, liver, M. pectoralis, M. gastrocnemius, and to estimate the correlation of this index with our previously measured values (laser-Doppler flowmetry) volume blood flow (BF) in these organs. We studied 10-, 15-, and 19-day embryos and 4-day chickens thatwere anesthetized with urethane. pO2 measurements were made in thesurface layers of organs by the membrane amperometric Clark-type O2-electrode with a diameter of about 50 microm of the cathode placed in the center of the sensor with an outer diameter of 3.4 mm. Disclosed noticeable distinction of both the organ tissue pO2 values, and the dynamics of their changes duringthe study period. The most important of them: (1) the lowest pO2 (and BF) is observed in the brain and particularly in the liver of 10-day embryos; (2) in the subsequent period of embryogenesis pO2 in the brain increases 1.9 times (rising and BF) in M. pectoralis it falls by 1.7 times and in the liver.and in M. gastrocnemius changes little wherein the BF in both liver and muscles is not changed, (3) after hatching pO2 in the liver and M. petoralis fold increased (also increasing and BF), and in the brain and M. gastrocnemius, despite the increase BF (greater in the niuscle) did not significant change. In the analysis ofthedata are considered two possible mechanisms of change of tissue pO2 in the developing organs of chickens, one is due to the peculiarities of intracardiac blood flows; and the other is related to thesingularity of the oxyhemoglobin dissociation in the blood capillary bed of organ, determined by the specifics of its oxidative metabolism.

[Changes of gas exchange parameters and of functional-biochemical properties of erythrocytes in dynamics of experimental anemia in rats].

In experiments on Wistar male rats, on a specially constructed computer installation, O2 consumption by the animals in comparison with changes of hematological, biochemical, and rheological blood properties is studied after anemization--acute bloodletting (12-15% of the total blood mass). An increase of the O2 consumption by the organism and tissues by 18-28% has been revealed for the first 7 days after the bloodletting, in spite of a pronounced decrease of hematocrit, and of the amount of erythrocytes and hemoglobin in peripheral blood by 20-25% of the initial level. There was a 5-10-fold increase of the content of immature erythrocyte forms--reticulocytes and a progressive rise of cell acidic resistance, which is characteristic of young erythrocyte forms. An increase of O2 consumption at a decrease of the blood oxygen capacity (a low hemoglobin level) seems to be due to the more efficient transport and yield of O2 to tissues. At the 3rd 7th day after the bloodletting, activity of Na,K-ATPase has been shown to increase by 60% and 20%, respectively. Analysis of the erythrocyte rheological properties has shown that the maximal firmness of aggregates (Uq) and the aggregation rate (1/T) decrease progressively beginning from 3 days after the bloodletting; index of deformability (I(max)) turned out to be elevated by 7-11%, probably due to an increase of the cell membrane elasticity. The conclusion is made that changes of erythrocyte rheological properties are interconnected with changes of the Na,K-ATPase activity and are directed to optimization of blood circulation in large vessels and the capillary network.

[Mathematical model of fluid transport in the convoluted portion of the proximal kidney tubules and surrounding capillaries]. / Matematicheskaia model' transporta zhidkosti v izvitoi chasti proksimal'nogo kanal'tsa pochek i okruzhaiushchikh kapilliarakh.

Simulating transport of fluid and ions among proximal tubule, interstice and capillaries the mechanism of fluid transport in the kidney was studied. A mathematical model as a system of differential equations was processed with a numerical method by a digital computer. The results showed that 96% of fluid from the proximal convolution into interstice were reabsorbed because of the difference of osmotic pressures caused by HCO3-, ions and 4% -- at the expense of oncotic pressure gradient. Fluid transport from interstice into capillaries is realized by the higher oncotic pressure caused by proteins as a result of previous plasma filtration in the nephron glomerulus.

[A mathematical model of O2 transport by erythrocytes in capillaries]. / Matematicheskaia model' transporta O2 éritrotsitom v kapilliare.

A model of diffusive O2 transport in erythrocyte and surrounding plasma is suggested which allows for the calculation of pO2 distribution in a 3-dimensional capillary region. The dynamic of O2 diffusion inside and outside erythrocyte and reaction kinetics of red blood cell are considered. The finite differential method is used to obtain a pO2 profiles as a solution of the differential equations. Resulting pO2 profiles exhibit large peri-oxyhemoglobin and small plasma pO2 gradients. Such O2 transport peculiarity in capillary creates optimal conditions for tissue O2 supply.

[Active and passive properties of carotid arteries]. / Aktivnye i passivnye svoistva sonnykh arterii

A mathematical model of carotid arteries is constructed from the known experimental data. Passive properties of the vascular wall are characterized by an alternating module of elasticity, the active ones by the specific power of muscle contraction. Its maximum value (0,023 n/m-3) is shown to be reached with intravascular pressure 190 mm Hg. The dependence of inner radius on the power of muscle contraction is studied at different values of intravascular pressure. It is shown that theactive properties of carotid arteries are essentially determined by their passive properties and depend on the stretching of the vessel wall.

[Dynamics of O2 and CO2 tensions in the brain (mathematical modeling)]. / Dinamika napriazhenii O2 i CO2 v mozge (matematicheskoe modelirovanie)

The mathematical model for description of the circulation and gas exchange dynamics in the brain is suggested. The model is based on a cell of two compact parallel capillary network with a brain tissue within. The equation system describing the model was calculated on a computer. The simulation showed that steady state pO2 in the cell during blood flow changes from 0.5 mm/sec to 0.25 or 1 mm/sec is reached within 2--5 sec. The dynamics of pCO2 is more inert. It was shown that the main factor in the dynamics of pO2 in the brain is the velocity of blood flow in capillaries. The dynamic pattern of pCO2 depends on haemodynamical condition, the structure of capillary network and physical properties of CO2.

[Dynamics of oxygen transport in erythrocytes]. / Dinamika transporta kisloroda v éritrotsite.

Distribution dynamics of oxygen tension throughout the erythrocyte volume was calculated by means of a mathematical model describing the dynamics of oxygen transport in the erythrocyte, its shape, diffusion resistance of hemoglobin solution. The pattern of the dissociation curve of oxyhemoglobin being taken into account. The model is presented as a system of differential equations in partial derivatives. Its solution was performed on an electron computer by a net method. Sharp jumps of pO2 inside the erythrocyte at its fast movements in the media with different partial pressure of O2 were shown. A quantitative relationship was found between the rate of physico-chemical reactions of oxygen binding and yield by hemoglobin and the level of hemoglobin saturation with oxygen.

[Mathematical model of the dynamics of transport of inert gases in the microcirculatory system]. / Matematicheskoe modelirovanie dinamiki transporta inertnykh gazov v sisteme mikrotsirkuliatsii.

A mathematical model imitating transport of inert gases in the system of microcirculation under increased pressures was constructed. It has been shown that saturation of microareas nucleus of the brain cortex of average dimensions proceeds in about 90 sec. Effect of the blood flow velocity, gases tension in arterial blood and density of the capillary net on the dynamics of mass transfer of gases in a tissue was investigated.

[Formation of gas bubbles in biological tissues in decompression (a mathematical model)]. / Formirovanie gazovykh puzyrei v biologicheskikh tkaniakh pri dekompressii (matematicheskoe modelirovanie).

A mathematical model simulating transport of gases between a bubble resulted from decompression and tissue around is presented. With the help of the model the influence of gas mixture and density of the bubble forming centres upon the growth rate was studied. An important part of CO2 in the bubble forming was found out. The bubbles with He have been shown to grow faster than those with N2. At a 5-10-fold decrease of the outer pressure during 1-2 seconds the bubbles can reach sizes which violate hemodynamics in the system of microcirculation.

[Mechanisms of O2 transport in the microcirculatory system]. / Mekhanizmy transporta O2 v sisteme mikrotsirkuliatsii.

The O2 transport in erythrocytes was shown to depend mostly on the form of erythrocyte, concentration of hemoglobin and its interaction with O2. The O2 transport in microvessels and capillaries depends on distribution of erythrocytes over the blood flow and their velocity, whereas intensity of O2 consumption and architectonics of capillary net determine the velocity and amount of O2 supply in tissues. Study of intricate processes of the O2 transport in microcirculation is only possible when using modern physical-chemical and mathematical techniques revealing the complicated interactions among the parameters under study.

[Dynamic oxygen tension in the brain of rats under acute hypobaric hypoxia]. / Dinamika napriazheniia kisloroda v mozge krys v usloviiakh ostroi gipobaricheskoi gipoksii.

In unanesthetized rats at the "altitudes" of 4000 m (1st group) and 8000 m (2nd group), within 1.5 hrs the 1st group developed a 17-30% drop in the PO2 in 43% of cases, no changes occurred in 14% of cases, and in 43% the PO2 increased by 145-205%. In the 2nd group, the PO2 was decreased by 44-87%, on the average. The PO2 changes in the brain cortex under hypoxic conditions seems to have a phasic character as expressed by alternation of increased and decreased levels of the PO2 depending on the degree of hypoxia and induced, apparently, by systemic and local responses compensating for the lack of oxygen in the air.

[Dynamics of pO2 changes in brain tissue during physiologic variations in capillary blood flow rate]. / Dinamika izmenenii pO2 v tkaniakh mozga pri fiziologicheskikh kolebaniiakh skorosti krovotoka v kapilliarakh.

The effect of the rate of the blood flow on pO2 dynamics in capillaries, nerve cells, and surrounding tissue was analyzed on the mathematical model. A two-fold variation in the blood flow rate through capillaries from the average level of 500 micro/sec induced equal changes of pO2 of about 12 torr. A two-fold change in the intensity of oxygen consumption by a cell from the level of 400 microliter O2/g.min shifted the average pO2 in the cell body and surrounding tissue approximately by 2 times and 1.2--1.3 times, resp. Under all these conditions, when the rate of blood flow or the oxygen consumption by a cell changed sharply, a new stable state of pO2 was reached in 2--3 sec. The data obtained suggest that the rates of blood flow in cerebral capillaries are determined by physiological changes in oxygen demand by nerve cells and glia. The diffusion as a mechanism of oxygen transport in the brain, seems both to supply nerve cells with a sufficient amount of O2 under stationary conditions and induce rapid changes in the rate of O2 transport in response to changes in demand for it.

[Dynamics of brain oxygen saturation under increased pressure]. / Dinamika nasyshcheniia mozga kislorodom pri povyshennom davlenii.

A mathematical model of the O2 transport within the brain aided to calculate the transitional processes of O2 tension in stepwise increase of the O2 amount in arterial blood as well as in alterations of the main physiological and morphological factors determining the O2 content and its changes in the organs and tissues under these conditions. The mathematical model took into consideration the actual data of mass-transfer in the microcirculation system and was described in the form of differential equations which had been solved by a digital computer with the aid of nets technique. The change of the pO2 mean level within the space of the modelled construction and under the conditions of the stepwise alterations of the above factors, was shown to be actualized during a period of time longer by order than in normoxia. Parameters of the transitional processes of saturation of the brain tissue with oxygen were shown to depend on the O2 content in arterial blood, on the blood flow velocity in capillaries and their density.

[Effect of systemic hematocrit on blood supply in microvessels of the cerebral cortex]. / Vliianie sistemnogo gematokrita na krovotok v mikrososudakh kory golovnogo mozga krysy.

The rat systemic hematocrit was increased by 44-54% by means of substitution of 2 ml of the rat own blood with the same volume of washed erythrocytes. Cine-TV technique revealed that the linear velocity of blood flow decreased by 20% immediately after the erythrocytes administration in most vessels under study. Changes of the blood flow were different in some microvessels: in 89% of cases the velocity decreased by 100-1600 mu/sec; no changes occurred in 5% of cases; and in 6% of cases the velocity increased by 100-500 mu/sec. The above changes were followed by a drop of arterial pressure (118 and 107 mm Hg, resp.). Within 5 min after increase of the systemic hematocrit, the blood flow was practically restored followed by an increase in the arterial pressure even over initial values. The data obtained suggest that the systemic hematocrit plays a certain part in changes of the blood flow in microvessels, being not, however, a major factor.

[The rate of blood flow in the cerebral microvessels of rats with an elevated blood leukocyte count]. / Skorost' krotoka v mikrososudakh golovnogo mozga krys pri uvelichennom soderzhanii leikotsitov v krovi.

The effect of additional administration of leucocytes into the vascular bed upon average velocities of the blood flow in the brain cortex microvessels with the erythrocyte flow diameter 5-15 mu, was studied by means of cine-TV-technique in rats. The 25-55% increase of the leucocytes concentration did not change the average blood flow velocity in the vascular net equal to 1186 +/- 306.8 and 1152 +/- 280.0 mu, resp., neither did it change arterial pressure equal to 113 +/- 10 mm Hg. The leucocyte load, however, decelerated the blood flow velocity by 100-600 mu/sec in 45% of the vessels, accelerated it by 100-400 mu/sec in 36% and did not affect it in 19%. The data obtained suggest that the leucocyte load did not affect the resistance against blood flow in resistive vessels which control the blood flow in microvascular bed, but it led to a redistribution of the blood flow in the brain microcirculation system.

[Theoretical basis for the method of calculating blood-flow volume velocity from hydrogen clearance curves]. / Teoreticheskoe obosnovanie metoda rascheta ob'emnoi skorosti krovotoka po klirensnym krivym vodoroda.

Two models: a hemodynamic one where the was out velocity is determined by means of the blood flow intensity alone, and a microcirculation one taking into consideration diffusion processes in tissue as well as architectonics of the vascular bed, gave ground for calculation of interrelationship between the time constant of the clearance curve and the local blood flow velocity. The data obtained showed the necessity of amendment depending on the time constant of the clearance curve when using the hemodynamic model.

[Rate of blood flow in the microvessels of the brain of the rat with spontaneous arterial hypertension]. / Skorost' krovotoka v mikrososudakh mozga krys so spontannoi arterial'noi gipertenziei.

In normal and hypertensive rats, hematological indices were studied as well as the linear blood flow velocity in the microvessels with diameter 6-12 mu. Both groups of animals were shown to develop obvious oscillations of the blood velocity coinciding neither with heart beats nor with respiratory movements. In rats with spontaneous arterial hypertension, the mean velocity was 844 mu/sec and the amplitude of blood flow oscillations was 175 mu/sec which was higher by 35% and 33.5% resp. than in control animals. The erythrocyte concentration, hematocrit value and the amount of hemoglobin were higher by 11, 26 and 20% resp. in hypertensive animals. The revealed differences of the blood flow in hypertensive rats are due to the increased blood pressure, specific architectonics of the vascular bed and to changes of the blood rheological features.

[Blood flow dynamics in adjacent microvessels of the brain in hypertensive rats]. / Dinamika krovotoka v blizkoraspolozhennykh mikrososudakh mozga gipertenzivnykh krys.

Significant alterations in the blood flow velocity, its amplitude and oscillations were found in cerebral cortex's microvessels of 5-12 mu diameter in normotensive and spontaneously hypertensive rats. Associated alterations of the blood flow shifted by a few seconds, were found in adjacent vessels. These alterations seem to be due to hemodynamic readjustments in proximal parts of the vascular net. The absence of these alterations in adjacent vessels suggests no significant redistribution of the blood flow in resting in cerebral cortex's microvessels.

[Assessment of the regulatory resources of the pial and intracerebral arteries by using mathematical modeling]. / Otsenka reguliatornykh vozmozhnostei pial'nykh i vnutrimozgovykh arterii s pomoshch'iu matematicheskogo modelirovaniia

A mathematical model for estimation of regulatory abilities of pial and intracerebral arteries was used for studying the pressure - radius relationships for arteries of various calibres in passive and active states. In passive state the arteries were found to be characterized by high elasticity and low tensile force. The radius of the artery depends mainly on the smooth muscle contractile force. The data obtained suggest that the wall structure of small pial and intracerebral arteries well correspond to their function: the control of the adequate and rapid cerebral blood flow.