Biomedical subjects
Publications and source records attributed to B I Tkachenko.
In increase of pre- and postcapillary resistance due to hypothermia, hypoxia induced no considerable shifts in back-ground values of the organ hemodynamics in the cat small intestine preparations constantly perfused with own blood.
The velocity of transcapillary shift of fluid in the heart, the resistance against blood flow in the heart arterial and venous vessels, the capillary filtration coefficient were assessed in the cat isolated heart perfused with a donor--cat blood. The capillary hydrostatic pressure, at 0 and 10 mm Hg venous pressure in the heart, was 5.1 +/- 1.2 and 16.3 +/- 2.8 mm Hg, resp. Infusion of noradrenaline lowered the capillary hydrostatic pressure. The average capillary filtration coefficient was 0.22 +/- 0.03 ml/min/100 g/mm Hg in the heart and did not depend on the venous pressure. Noradrenaline increased the coefficient.
In regimen of the constant blood flow perfusion of skeletal muscles and intestine, hypoxia reduced precapillary resistance and increased the capillary filtration coefficient in both organs whereas postcapillary resistance and capillary pressure were reduced in the intestine and increased in the muscle. Hypothermia increased precapillary resistance in the intestine rather than in the muscle whereas the changes of the capillary filtration coefficient were contrary in both organs; postcapillary resistance and capillary pressure had a tendency to increase in the muscle whereas an increase in these parameters was quite evident in the intestine. Combined effect of hypoxia and hypothermia involved a decrease in precapillary resistance and distensibility of venous vessels, an increase in capillary filtration coefficient in both vascular regions, an increase in postcapillary resistance and in capillary pressure in the intestine, and their decrease in the muscle. In hypothermia (about 30 degrees C), the hypoxic stimulus induced insignificant shifts in all the parameters under study in both organs.
The effect of the ventrolateral medulla electrical stimulation of various intensity on resistance, capacitance and exchange functions was studied in the vascular bed of the small intestine. Brain activation with superliminal current applied to a point 2 mm rostral-wise of the middle of the twelfth cranial nerve rootlets has been shown to produce the strongest effect on the precapillary resistance of the vascular bed, whereas brain stimulation in a point 2 mm caudal-wise of this level produces a much stronger effect on the postcapillary small intestine resistance.
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Experiments in cats with the constant blood volume perfusion of the small intestine vessels revealed constrictor responses of arterial, venous and lymphatic vessels to electrical stimulation of sympathetic nerves, the responses being most obvious at the 8, 10 and 10-20 Hz frequency of stimulation. Activation of sympathetic nerves augmented the pre- and postcapillary resistance of the vessels, the resistance being the greatest at 8 and 10 Hz. Stretching ability of venous vessels decreased. The capillary hydrostatic pressure increased, its shift being maximal at 10 Hz. The capillary filtration coefficient increased, the increment being maximal at 1 Hz. The lymph production and outflow enhanced. The motor activity of the intestine was suppressed. Analysis of the conjugated shifts in macro- and microhemodynamic parameters as well as in lymph flow revealed a transcapillary transition of intravascular fluid into the extravascular space due to the increase in the capillary hydrostatic pressure followed with a resorption into the roots of the intestine lymphatic system.
In perfused with constant flow isolated cat hindlimbs, i.a. infusion of 0.1-1.0 micrograms.min-1.kg-1 histamine and bradykinin caused a dilatation of arteries and veins and an increase of the capillary filtration coefficient. Histamine elevated capillary hydrostatic pressure and dilated lymphatic ducts with no alteration in the lymph formation process in the hindlimb. Bradykinin decreased capillary hydrostatic pressure and activated formation of lymph. The elevation of transcapillary fluid movement under the effect of bradykinin seems to be the result of a disturbance in colloid osmotic (oncotic) pressures on both sides of the capillary wall.
In acute experiments on cats, effects of occlusion of common carotid arteries, stimulation of afferent fibers of the brachial plexus, application of acetylcholine to reflexogenous zones of peritoneum and mesentery of the small intestine on macro- and microcirculation of the isolated small intestine perfused under constant flow, were studied. Under effects of occlusion and afferent stimulation, arteries and veins of the small intestine were constricted, whereas in stimulation of abdominal reflexogenous zones their reactions were different. All the reflexes induced augmentation of the capillary hydrostatic pressure, capillary filtration coefficient and post-capillary resistance, whereas decreasing the venous vessels distention.
In cats with implanted ultrasonic transducers, interrelationships between phasic oscillations of the blood flow in posterior v. cava due to the chest sucking function and changes of intrapleural pressure, were studied. Linear dependence of shifts of these parameters was only observed in an increased pressure and respective drop in venous blood flow. The dependence was absent in drop of the pressure and increase of venous blood flow. The ratio of the intrapleural pressure shift to magnitude of phasic changes of the blood flow in the posterior v. cava (the pumping coefficient) is suggested for estimation of effect of the chest sucking function upon the venous outflow and for relative estimation of rigidity of the vascular bed's venous portion.
A technique has been developed enabling to change the tone of venous vessels without affecting the effector structures of arteries and capillaries. The selective increase of the tone of muscle veins with noradrenaline augmented postcapillary resistance and capillary pressure, reduced the distensibility of veins and did not affect either precapillary resistance or the capillary filtration coefficient.
In cats with normal body temperature, hypoxia (10% O2 in nitrogen) induced depressor shifts of the arterial pressure due to a drop of the general peripheral resistance, whereas in cooling of the organism to +30 degrees C a slight increase of the arterial pressure occurred. Hypothermia was found to reduce the degree of increase in the venous return in response to a hypoxic stimulus.
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Acute experiments on cats using perfusion of the innervated calf muscle and small intestinal vessels with self blood at a constant blood flow rate have established decreased sensitivity of vessels (cooled to 30 degrees C) to hypoxic stimulus effect (inhalation of 10% O2 in N2). The essence of the phenomenon consists in considerably smaller deviations of pre- and postcapillary resistance, capillary filtration coefficient, mean capillary pressure during simultaneous exposure to cold and hypoxia than during separate application of hypoxic or hypothermic stimuli. Organ distinctions in the degree and direction of changes in vascular resistance and metabolism have been observed.
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Acute experiments in cats revealed by means of volumometry of extracorporeal blood flow that the exchange surface of the microcirculation bed in working skeletal muscles increased irrespective of whether they were perfused under constant pressure or in constant blood flow. Capillary hydrostatic pressure depended on the perfusion mode: it decreased in conditions of stabilized blood expenditure through muscles, and increased in constant pressure perfusion. An increase of the capillary filtration coefficient is considered from the standpoint of dilatory effect of metabolites on precapillary sphincters. Changes of pre-and postcapillary resistance take part in shifts of fluid movement in the muscle during contraction.
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Rise of body temperature to 41.0-41.2 degrees C led to an increase of the integral, pre- and postcapillary resistance in the vascular bed of the cat small intestine and skeletal muscles. The increase of the resistance function in veins led to an increase of the mean capillary hydrostatic pressure. The above shifts enhanced with increasing of the hyperthermia. The latter was found to reduce distensibility of veins and the capillary filtration coefficient (CFC) in the small intestine vascular bed but to increase the CFC in skeletal muscles. The role of the small intestine and skeletal muscles venous vessels in the shifts of the filtration-absorption ration and the capacitance function in hyperthermia is discussed.