Faculty Publications
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Item Quantifying spatiotemporal complexity of cardiac dynamics using ordinal patterns(Institute of Electrical and Electronics Engineers Inc., 2015) Schlemmer, A.; Berg, S.; Shajahan, T.K.; Luther, S.; Parlitz, U.Analyzing the dynamics of complex excitation wave patterns in cardiac tissue plays a key role for understanding the origin of life-threatening arrhythmias and for devising novel approaches to control them. © 2015 IEEE.Item Structure of Protein Interaction Network Associated With Alzheimer’s Disease Using Graphlet Based Techniques(Springer Science and Business Media B.V., 2022) Khasim, A.; Subramanian, V.; Ajith, K.M.; Shajahan, T.K.The crucial step in analyzing a real-world network is to choose an acceptable network model. We try to select an appropriate network model for the protein-protein interaction (PPI) network of Alzheimer’s disease (AD) using Graphlet-based metrics. The Relative Graphlet Frequency (RGF) count in the AD-PPI network is similar to that of the corresponding Scale-Free network. However, based on Graphlet Degree Distribution (GDD), the AD-PPI network has a good match with Geometric random graphs. The graphlet correlation statistics of the AD network show that it has a core-periphery topology. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Dynamics of Chemical Excitation Waves Subjected to Subthreshold Electric Field in a Mathematical Model of the Belousov-Zhabotinsky Reaction(Springer Science and Business Media B.V., 2022) Sebastian, A.; Amrutha, S.V.; Punacha, S.; Shajahan, T.K.We present a numerical study of the dynamics of spiral waves in a weak external electric field, using the Oregonator model of the Belousov-Zhabotinky (BZ) reaction. Both free and pinned spiral waves are studied in two types of electric fields: unidirectional (DC) and Circularly Polarised Electric Field (CPEF). Both free spirals and pinned spiral waves rotate faster in the DC field. The CPEF can help a free spiral to be spatially confined. A pinned spiral period can be controlled by varying the period of the CPEF. Both DC and CPEF can unpin the pinned spiral wave, but the minimum electric field required to unpin is much less with CPEF compared to DC. Thus, CPEF is more energy efficient to unpin a pinned spiral wave. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Variations in the Scroll Ring Characteristics with the Excitability and the Size of the Pinning Obstacle in the BZ Reaction(Springer Science and Business Media B.V., 2022) Sibeesh, P.; Amrutha, S.V.; Shajahan, T.K.We report the experimental results of the effects of excitability on the wave characteristics of free rotating and pinned scroll rings in the Belousov-Zhabotinsky (BZ) reaction. The experiments show that the stability of the scroll ring depends on the excitability of the medium. At low excitability, the scroll ring becomes less stable and eventually breaks up. As we increase the excitability of the medium, the time period (T) and wavelength (λ ) of the excitation wave decrease while wave velocity (v) increases. Properties of both free and pinned scroll rings change in the same way. However, at a given excitability, both the λ and v of a pinned scroll ring increase with the size of the obstacle. For the range of parameters chosen in our experiments, the excitability changes brought by varying reactant concentrations have a higher impact on the scroll ring properties than those induced by the size of the pinning obstacle. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Image Acquisition and Electric Field Application in the Belousov-Zhabotinsky Reaction Using LabVIEW(Springer Science and Business Media Deutschland GmbH, 2024) Sibeesh, P.; Shajahan, T.K.This paper introduces LabVIEW-based software and hardware designed to simultaneously record and control chemical wave activity in the Belousov-Zhabotinsky (BZ) reaction. The chemical waves in the BZ reaction can be controlled by DC and polarized electrical stimuli. Our software can be used to study the interaction of DC or different types of polarized electric fields with chemical waves. The software allows the user to capture and save images for further analysis. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.Item Drift and Annihilation of a Counter-Rotating Spiral Pair in Belousov-Zhabotinsky Reaction Under a DC Electric Field(Springer Science and Business Media Deutschland GmbH, 2024) Mishra, P.R.; Sebastian, A.; Shajahan, T.K.We present a numerical study of the dynamics of the counter-rotating spiral pair in the presence of a DC electric field using the Oregonator model of the Belousov-Zhabotinky (BZ) reaction. The dynamics of the counter-rotating pair is investigated by changing the strength and direction of the electric field. The dynamics can change from meander to drift with increasing field strength. The drift velocity increases with the field strength, and its direction depends on the direction of the field. Finally, the spiral pair is annihilated when the applied field is above a threshold value. With further increase in field strength, the annihilation is followed by generation of a new counter-rotating pair oriented opposite to the initial pair. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.Item Scanning and resetting the phase of a pinned spiral wave using periodic far field pulses(Institute of Physics Publishing helen.craven@iop.org, 2016) Shajahan, T.K.; Berg, S.; Luther, S.; Krinski, V.; Bittihn, P.Spiral waves in cardiac tissue can pin to tissue heterogeneities and form stable pinned waves. These waves can be unpinned by electric stimuli applied close to the pinning center during the vulnerable window of the spiral. Using a phase transition curve (PTC), we quantify the response of a pinned wave in a cardiac monolayer to secondary excitations generated electric field pulses. The PTC can be used to construct a one-dimensional map that faithfully predicts the pinned wave's response to periodic field stimuli. Based on this 1D map, we predict that pacing at a frequency greater than the spiral frequency, over drive pacing, leads to phase locking of the spiral to the stimulus, which hinders unpinning. In contrast, under drive pacing can lead to scanning of the phase window of the spiral, which facilitates unpinning. The predicted mechanisms of phase scanning and phase locking are experimentally tested and confirmed in the same monolayers that were used to obtain the PTC. Our results have the potential to help choose optimal parameters for low energy antifibrillation pacing schemes. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.Item Mechanisms of vortices termination in the cardiac muscle(Royal Society, 2017) Hornung, D.; Biktashev, V.N.; Otani, N.F.; Shajahan, T.K.; Baig, T.; Berg, S.; Han, S.; Krinsky, V.I.; Luther, S.We propose a solution to a long-standing problem: how to terminate multiple vortices in the heart, when the locations of their cores and their critical time windows are unknown. We scan the phases of all pinned vortices in parallel with electric field pulses (E-pulses). We specify a condition on pacing parameters that guarantees termination of one vortex. For more than one vortex with significantly different frequencies, the success of scanning depends on chance, and all vortices are terminated with a success rate of less than one. We found that a similar mechanism terminates also a free (not pinned) vortex. A series of about 500 experiments with termination of ventricular fibrillation by E-pulses in pig isolated hearts is evidence that pinned vortices, hidden from direct observation, are significant in fibrillation. These results form a physical basis needed for the creation of new effective low energy defibrillation methods based on the termination of vortices underlying fibrillation. © 2017 The Authors.Item Spiral wave unpinning facilitated by wave emitting sites in cardiac monolayers(Royal Society Publishing, 2019) Punacha, S.; Berg, S.; Sebastian, A.; Krinski, V.I.; Luther, S.; Shajahan, T.K.Rotating spiral waves of electrical activity in the heart can anchor to unexcitable tissue (an obstacle) and become stable pinned waves. A pinned rotating wave can be unpinned either by a local electrical stimulus applied close to the spiral core, or by an electric field pulse that excites the core of a pinned wave independently of its localization. The wave will be unpinned only when the pulse is delivered inside a narrow time interval called the unpinning window (UW) of the spiral. In experiments with cardiac monolayers, we found that other obstacles situated near the pinning centre of the spiral can facilitate unpinning. In numerical simulations, we found increasing or decreasing of the UW depending on the location, orientation and distance between the pinning centre and an obstacle. Our study indicates that multiple obstacles could contribute to unpinning in experiments with intact hearts. © 2019 The Author(s) Published by the Royal Society. All rights reserved.Item Theory of unpinning of spiral waves using circularly polarized electric fields in mathematical models of excitable media(American Physical Society subs@aip.org;revtex@aps.org;prx@aps.org;prxtex@aps.org;help@aps.org;prb@aps.org, 2020) Punacha, S.; Naveena Kumara, A.N.; Shajahan, T.K.Spiral waves of excitation are common in many physical, chemical, and biological systems. In physiological systems like the heart, such waves can lead to cardiac arrhythmias and need to be eliminated. Spiral waves anchor to heterogeneities in the excitable medium, and to eliminate them they need to be unpinned first. Several groups focused on developing strategies to unpin such pinned waves using electric shocks, pulsed electric fields, and recently, circularly polarized electric fields (CPEF). It was shown that in many situations, CPEF is more efficient at unpinning the wave compared to other existing methods. Here, we study how the circularly polarized field acts on the pinned spiral waves and unpins it. We show that the termination always happens within the first rotation of the electric field. For a given obstacle size, there exists a threshold time period of the CPEF below which the spiral can always be terminated. Our analytical formulation accurately predicts this threshold and explains the absence of the traditional unpinning window with the CPEF. We hope our theoretical work will stimulate further experimental studies about CPEF and low energy methods to eliminate spiral waves. © 2020 American Physical Society.