Biomedical subjects

R R Aliev

Publications and source records attributed to R R Aliev.

11 recordsLinked to original sources

PubMed2005

[Pattern of excitation in isolated heart of hibernator ground squirrel Citellus undulatus].

Aim of our study was to measure conduction velocity and pattern of excitation during hypothermia in hearts of ground squirrels Citellus undulatus, known to be most resilient hibernators. We imaged electrical conduction in intact isolated hearts of summer active and winter hibernating ground squirrels at temperatures varying from +37 degrees C to +3 degrees C. Electrical activity was mapped using CCD camera (500 frames/sec) and voltage-sensitive dye di-4-ANEPPS during normal sinus rhythm and ventricular pacing. No spontaneous tachyarrhythmia was observed in all hearts at any temperature. Hearts were able to maintain spontaneous sinus rhythm and normal pattern of epicardial excitation throughout the whole range of studied temperatures. Despite responsiveness to pacing in all hearts ventricular conduction velocity was significantly reduced (about 10-fold) at low temperatures +3 degrees C. Our data provides the first direct demonstration that isolated heart of the summer active and winter hibernating ground squirrel Citellus undulatus is able to maintain normal excitation pattern in a range of temperatures from +37 degrees C to +3 degrees C.

Animals↗

PubMed2001

Patchy environment as a factor of complex plankton dynamics.

We study the role of the diffusive interaction in plankton dynamics in a patchy environment. We use a minimal reaction-diffusion model of the nutrient-plankton-fish food chain to simulate the diffusive interaction between fish-populated and fish-free habitats. We show that such interaction can give rise to spatiotemporal plankton patterns. The plankton dynamics depend on the fish predation rate and can exhibit both regular and chaotic behavior. We show that limit cycle and chaotic attractor coexist in the system. The entire basin of attraction of the limit cycles is found to be riddled with "holes" leading to the competitive chaotic attractors. The chaotic dynamics is typical of a wide range of the fish predation rates.

Animals↗

PubMed2001

Experimental and theoretical analysis of phase singularity dynamics in cardiac tissue.

INTRODUCTION: Quantitative analysis of complex self-excitatory wave patterns, such as cardiac fibrillation and other high-order reentry, requires the development of new tools for identifying and tracking the most important features of the activation, such as phase singularities. METHODS AND RESULTS: Image processing operations can be used to detect the phase singularity at the tip of a spiral wave. The phase space behavior of a spatiotemporal sequence of data may be reconstructed using time-series analysis. The phase singularities then are localized efficiently by computing the topologic charge density as the curl of the spatial phase gradient. We analyzed the singularity interaction dynamics of both experimentally observed and numerically simulated instances of quatrefoil reentry and found that the singularity behavior in the experimental preparations can be classified into three categories on the basis of how their separation changes with time. CONCLUSION: Topologic charge densities can be calculated easily and efficiently to reveal phase singularity behavior. However, the differences between theoretical and experimental observations of singularity separation distances indicate the need for more sophisticated numerical models.

Action Potentials↗

PubMed2000

A simple nonlinear model of electrical activity in the intestine.

We have simulated electrical activity of the intestine in a computer model that describes the coupled layers of longitudinal muscle (LM) and interstitial cells of Cajal (ICC). The model suggests that pacemaker activity is due to the ICC layer, while the pulse propagation involves the LM layer that is in the excitatory state. The model describes well the experimentally observed phenomena: frequency change along the intestine, synchronization along short distances and desynchronization for long distances, and the decrease of propagation distance and propagation time along the intestine. We have observed the occurrence of phase interruptions or breaks, which are responsible for the limited values of propagation distance and time.

Biological Clocks↗

PubMed1996

Modeling of heart excitation patterns caused by a local inhomogeneity.

We simulate wave propagation in the whole heart containing a local inhomogeneity whose properties mimic some properties of cardiac tissue during the acute phase of infarction. The dynamics of cardiac tissue is described by a FitzHugh-Nagumo (FHN) model. We show that two or several short-period stimulations of the heart lead to the development of a three-dimensional vortex ring, which is a temporal source of high frequency waves. The vortex ring is located near the boundary of the infarction and induces wave patterns which appear as several focal wave sources on the epicard and endocard. We have traced the filament of the vortex and show its dynamics. Continuous stimulation of the heart at high frequency resulted in the Wenckebach effect.

Electric Stimulation↗

PubMed1996