Papers by Raimundas Lekas
Elektronika Ir Elektrotechnika, Mar 19, 2015
Journal of Molecular and Cellular Cardiology, Jul 1, 1991
Journal of Electrocardiology, 2007
Objectives: of the present study were to verify the topography of the intracardiac nerve subplexu... more Objectives: of the present study were to verify the topography of the intracardiac nerve subplexuses (INS) by using electrophysiological methods, its relations with sinoatrial (SA) node function and investigate the possibility of selective surgical SA node denervation. Design, Methods and Results: 32 mongrel dogs were used for electrophysiological studies. Nervus subplexuses destructions were performed by electrocoagulation or cryoablation in three zones located around the right superior vena cava: ventral, lateral and dorsal. The sinus rhythm, SA node function recovery time, atrioventricular (AV) node conductivity, the AV node and the atrial effective refractory period were measured. Eight experiments in each of the three zones were performed. The average changes of electrophysiological parameters before and after INS destruction have shown that the destruction of the ventral and lateral zones modifies the effects of sympathetic tone to SA node activity. The destruction of the dorsal zone modifies the effects of the vagus nerve to the SA node. Conclusions: The function of the SA and AV nodes can be modified by the destruction of the ventral, lateral and dorsal zones of the right atrium. It is necessary to point up that while performing interventions and radiofrequency ablations in the zones of nerve plexuses surgeons must be aware of possible changes in SA node's function because of the impairment of these nerve plexuses and, if possible, to avoid surgical manipulations in these zones.
PubMed, 2004
The aim of the study was to investigate the dynamics of experimental parasystole taking into cons... more The aim of the study was to investigate the dynamics of experimental parasystole taking into consideration the peculiarities of recurrent arrhythmias recorded in clinical settings. Material and methods: The experiments were conducted on isolated right atria of seven chinchilla rabbits. Parasystolic arrhythmias using periodical one-site electrostimulation were provoked in one atrium, where the sinus node was not affected, and in two atria with the spontaneous low value activity of pacemakers. The parasystolic arrhythmias by the dual-site periodical pacing were provoked in four atria, in which the spontaneous activity had disappeared, while the membrane potential of cardiomyocytes remained at the level of 70 to 80 mV. Results: The parasystolic arrhythmias of the shape of single extrapotentials were obtained in atria when the periods of excitation impulses were within the limits of 0.9-1.2 s, and the differences between these periods being relatively small (0.04-0.2 s). The increase of these differences resulted the various allorhythmias. In cases of single extrapotentials, the recurrence periods of arrhythmias reached 5.6-29 s; while in cases of allorhythmias they shortened to 2.4-4.8 s. Conclusion: The parasystoles in isolated atria of rabbits can be induced by two competitive excitation sources. They may manifest themselves through single extrapotentials or allorhythmias, whose form depends on the duration of the periods of excitation impulses, the difference between these durations, as well as on effective refractory periods of atrial cardiomyocytes. The determination and evaluation of the recurrence period of these arrhythmias can serve in any given clinical situation as a supplementary criterion.
![Research paper thumbnail of [Trace elements, cholesterol and ultrastructural alterations of aorta in hypodynamic stress]](https://a.academia-assets.com/images/blank-paper.jpg)
PubMed, 2003
Hypodynamic stress of 48-day duration was provoked by permanent and periodically recurrent interv... more Hypodynamic stress of 48-day duration was provoked by permanent and periodically recurrent intervention (the hypodynamics periodically exchanged to physically activity) for Chinchilla rabbits (weight 2.5-3.0 kg) (n=19) by placing them in metal hutches according to B. V. Fiodorow. Rabbits (n=10) of the control group which had no intervention were kept in vivarium conditions. The concentration of trace elements (Zn, Mn, Cu) in the blood plasma and thoracic aorta was assessed by atomic absorption spectrophotometer (Perkin-Elmer 503, USA). The level of cholesterol was determined by enzymatic analysis. Ultrathin sections of thoracic aorta were examined with electron microscope "Tesla BS-500" (Italy). After 48 days of permanent hypodynamic stress the concentration of Zn and Mn in blood plasma of rabbits was found to be significantly decreased while the cholesterol and Cu level was greater than before the stress. In case of permanent stress significant decrease also was found in the concentration of Cu and Mn in aorta in comparison with that in the case of periodically recurrent stress. The mentioned changes of the trace elements and cholesterol concentration in tissues of rabbits in case of permanent hypodynamic stress were accompanied by ultrastructural alterations in endothelium--desintegration of cells, and winding and fragmentation of internal elastic lamina, accumulation of lipids. In case of periodically recurrent hypodynamic stress of the some duration these changes were less expressed.
Medicina-lithuania, Jun 11, 2008
The aim of this study was to investigate antiradical activity of aqueous and ethanolic hawthorn f... more The aim of this study was to investigate antiradical activity of aqueous and ethanolic hawthorn fruit extracts, their flavonoids, and flavonoid combinations. Material and methods. Total amount of phenolic compounds and the constituents of flavonoids were determined using a high-performance liquid chromatography. The antioxidant activity of Crataegus monogyna extracts and flavonoids (chlorogenic acid, hyperoside, rutin, quercetin, vitexin-2O-rhamnoside, epicatechin, catechin, and procyanidin B 2) quantitatively was determined using the method of spectrophotometry (diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging assay and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid)(ABTS•+) radical cation decolorization assay). The level of tyrosine nitration inhibition was determined using a highperformance liquid chromatography. Results. Ethanolic hawthorn fruit extract contained 182±4 mg/100 mL phenolic compounds, i.e. threefold more, as compared to aqueous extract. The antioxidant activity according to DPPH• reduction in the ethanolic extracts was higher 2.3 times (P<0.05). The ABTS•+ technique showed that the effect of ethanolic extracts was by 2.5 times stronger than that of aqueous extracts. Tyrosine nitration inhibition test showed that the effect of ethanolic extracts was by 1.4 times stronger than that of aqueous extracts. The investigation of the antiradical activity of the active constituents in aqueous and ethanolic extracts revealed that epicatechin and catechin contribute to radical-scavenging properties more than other components. Procyanidin B 2 only insignificantly influenced the antiradical activity of the extracts. Conclusion. Both aqueous and ethanolic hawthorn extracts had antiradical activity, but ethanolic extract had stronger free radical-scavenging properties, compared to the aqueous extract. The antioxidant activity of the studied preparations was mostly conditioned by epicatechin and catechin. The individual constituents of both extracts had weaker free radical-scavenging properties than the combination of these substances did.
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Papers by Raimundas Lekas