Browsing by Author "Özbek M."
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Item Rate-dependent effects of dofetilide on epicardial monophasic action potentials in isolated rabbit heart with atrial pacing(2002) Özbek M.; Gök Ş.Dofetilide (UK 68,798), a new antiarrhythmic agent, blocks potassium channels selectively and acts primarily by prolonging repolarization duration. The aim of this study was to investigate rate-dependent repolarization changes due to dofetilide in a fast beating in-vitro heart model. The study was designed using Langendorff perfusion of rabbit hearts at the drug concentrations of 1 nM, 3 nM and 10 nM. The electrophysiological evaluations were performed using the recording of epicardial monophasic action potentials. Atrial pacing was set at the cycle length (ms) of 300, 325, 350, 375 and 400 so that repolarization duration could be measured in different heart rates, The study also focused on the interventricular repolarization heterogeneity between the right and left epicardial regions. Dofetilide prolonged monophasic action potential duration at 90 % of repolarization on both sides of the epicardium in a concentration- and reverse-rate-dependent manner. However, the rate-dependent prolongation of action potential duration due to dofetilide was not accompanied by increased interventricular dispersion of repolarization. No proarrhythmia due to dofetilide was seen in our model. This may be explained by the rate-dependent stability in repolarization dispersion. Thus, the presented model indicated that dofetilide-induced prolongation of repolarization is not proarrhythmic in isolated fast beating hearts.Item Sensitively recorded breathing signals of rats and their nonlinear dynamics(2007) Zeren T.; Özbek M.; Ekerbiçer N.; Yalçin G.Ç.; Akdeniz K.G.Nonlinear dynamical properties of sensitively recorded breathing signals (SRBS), which include cardiac induced air flow pulsations so-called pneumocardiogram (PNCG) signals, are investigated, in this methodological study. For this purpose, we assessed the SRBS of laboratory rat. The nonlinear behaviors of SRBS were investigated by the reconstructing phase space, using the autocorrelation function and the false nearest neighbor method. The chaotic SRBS attractors were discussed from the point of view of the cardiopulmonary system. This method can be used to assess the heart performance and respiratory mechanics, and might be useful to design for the physiological studies of cardiorespiratory system in small laboratory animals. © 2007 Elsevier B.V. All rights reserved.Item A physical model of the thermodilution method: Influences of the variations of experimental setup on the accuracy of flow rate estimation(2011) Özbek M.; Özel H.F.; Ekerbiçer N.; Zeren T.The thermodilution method has been widely used to estimate cardiac output by injecting a cold solution into circulating blood. It is uncertain if radial heat transfer from the vascular/cardiac wall to circulating injectate can cause inaccurate results with this method. In this study, we have introduced a physical experimental model of the thermodilution method without recirculation of the cold solution. To test the accuracy of the thermodilution method, the experimental setup included an aluminum tube to allow radial heat transfer. Variations of the following parameters were conducted: (i) the real flow rate, (ii) the distance between injection point of cold solution and the temperature sensor, (iii) the volume of injectate, and (iv) the temperature of injectate. By following the above variations, we have calculated different correction factors eliminating the influence of radial heat transfer on the estimation of flow rate by the thermodilution method. The results indicate that changes in both injectate temperature and volume have no influence on the estimation of flow rates. The experimental variations, which can cause greater radial heat transfer, seem to be responsible for the result of the smaller estimation of the flow rate than the real value. These variations include (i) a decreased real flow rate and (ii) increased distances between the injection point of cold fluid and the thermosensor. Such an incorrect estimation could be eliminated by using correction factors. The correction factor seems to be a function of the area of the thermodilution curve, assuming no recirculation. © 2011 by Walter de Gruyter Berlin New York.Item Significance of using a nonlinear analysis technique, the lyapunov exponent, on the understanding of the dynamics of the cardiorespiratory system in rats(Turkiye Klinikleri Journal of Medical Sciences, 2016) Zeren T.; Özbek M.; Kutlu N.; Akilli M.Background/aim: Pneumocardiography (PNCG) is the recording method of cardiac-induced tracheal air flow and pressure pulsations in the respiratory airways. PNCG signals reflect both the lung and heart actions and could be accurately recorded in spontaneously breathing anesthetized rats. Nonlinear analysis methods, including the Lyapunov exponent, can be used to explain the biological dynamics of systems such as the cardiorespiratory system. Materials and methods: In this study, we recorded tracheal air flow signals, including PNCG signals, from 3 representative anesthetized rats and analyzed the nonlinear behavior of these complex signals using Lyapunov exponents. Results: Lyapunov exponents may also be used to determine the normal and pathological structure of biological systems. If the signals have at least one positive Lyapunov exponent, the signals reflect chaotic activity, as seen in PNCG signals in rats; the largest Lyapunov exponents of the signals of the healthy rats were greater than zero in this study. Conclusion: A method was proposed to determine the diagnostic and prognostic values of the cardiorespiratory system of rats using the arrangement of the PNCG and Lyapunov exponents, which may be monitored as vitality indicators. © TÜBITAK.Item Application of the nonlinear methods in pneumocardiogram signals(Springer, 2020) Yılmaz N.; Akıllı M.; Özbek M.; Zeren T.; Akdeniz K.G.In this work, the pneumocardiogram signals of nine rats were analysed by scale index, Boltzmann Gibbs entropy and maximum Lyapunov exponents. The scale index method, based on wavelet transform, was proposed for determining the degree of aperiodicity and chaos. It means that the scale index parameter is close to zero when the signal is periodic and has a value between zero and one when the signal is aperiodic. A new entropy calculation method by normalized inner scalogram was suggested very recently. In this work, we also used this method for the first time in an empirical data. We compared the both methods with maximum Lyapunov exponents and observed that using together the scale index and the entropy calculation method by normalized inner scalogram increases the reliability of the pneumocardiogram signal analysis. Thus, the analysis of the pneumocardiogram signals by those methods enables to compare periodical and/or nonlinear aspects for further understanding of dynamics of cardiorespiratory system. © 2020, Springer Nature B.V.Item Classical heart rate variability and nonlinear heart rate analysis in mice under Na-pentobarbital and ketamine/xylazine anesthesia(Turkiye Klinikleri, 2022) Kazdağli H.; Özel H.F.; Özbek M.; Alpay Ş.; Alenbey M.Background/aim: Anesthetics are often used in animal experiments to achieve immobilization and relieve pain. However, many anesthetics can alter the dynamics of cardiovascular systems. We aimed to compare the effects of two frequently used anesthetics agents on heart rate variability (HRV) parameters in mice. Materials and methods: This observational study was performed between May and June 2014 in 21 male BALB/c mice aged 16–20 weeks. The animals were divided into three groups: pentobarbital (P), (n = 7); pentobarbital+fentanyl (P+F), (n = 7); and ketamine+xylazine (K+X), (n = 7). Surface electrocardiography (ECG) electrodes were placed in lead II configuration. The tachogram of RR intervals was obtained after R waves were detected using the Pan-Tompkins real-time QRS recognition algorithm. Frequency-domain, time-domain, and nonlinear HRV analyses were performed. Results: The bradycardia effect was higher in the K+X group (p < 0.01). Time-domain indices were higher in group K+X compared to group P (p < 0.01) and group P+F (p < 0.001). Very low frequency (VLF) power was significantly lower in group K+X compared to group P and group P+F (p < 0.01). Low frequency (LF) power, low frequency/high frequency (LF/HF) ratio, and total power (TP) were higher in group K+X compared to group P (p < 0.01) and group P+F (p < 0.001). The detrended fluctuation analysis short-term parameter (DFAα1 ) was significantly higher in group K+X compared to group P+F (p < 0.05) and the long-term parameter (DFAα2 ) was lower in group K+X compared to group P (p < 0.05). Standard deviations SD1 and SD2 were higher in group K+X compared to group P (p < 0.001) and group P+F (p < 0.001), SD2/SD1 ratio was lower in group K+X compared to group P (p < 0.05) and group P+F (p < 0.05). Entropy measures did not differ between groups. Conclusion: HRV analyses, including nonlinear methods, indicated that a K+X combination reduces imbalance and disorder in the regulation of the autonomic nervous system (ANS) in comparison to both P and the P+F combination. © The Authors.Item Effects of Ketamine/Xylazine and Urethane Anesthesia on Compound Muscle Action Potential Latency of Gastrocnemius Muscle in Rats(Wolters Kluwer Medknow Publications, 2023) Mentese B.; Özel H.F.; Özbek M.; Kutlu N.Objective: Anesthetic agents, which are used in appropriate doses for the application of the experimental procedure in animals, relieve pain when applied in sufficient amounts as well as muscle relaxation. However, many anesthetics can alter the dynamics of neuromuscular systems. We aimed to compare the effects of two frequently used anesthetic agents on electromyographic parameters in rats. Materials and Methods: This study was performed on male Wistar albino rats aged 22-24 months. The animals were divided into two groups: urethane (1.5 gkg-1, i.p; n = 6) and ketamine+xylazine (K+X) (80 mg/kg, i.p; n = 6). Under general anesthesia, rats were electrically stimulated with bipolar hook electrodes from both legs, and compound muscle action potential (CMAP) was recorded from the needle electrode of the gastrocnemius muscle. Motor nerve action potential latency (MNAPL) was measured from the sciatic nerve of the rats. Results: The results of electrodiagnostic findings related to two different anesthetics in the animals were compared, and CMAP parameters were found to differ between the groups. MNAPL in both the right and left legs was significantly reduced in the urethane group compared to the K+X group (P < 0.05). Conclusion: Urethane anesthesia may be a better choice than K+X anesthesia to evaluate nerve and muscle functions in animal electromyography studies. © 2023 Neurological Sciences and Neurophysiology.Item The effects of mechanical ventilation on heart rate variability and complexity in mice(Hellenic Veterinary Medical Society, 2023) Kazdağli H.; Özel H.F.; Özbek M.In a variety of diseases, altered respiratory modulation is often as an early sign of autonomic dysfunction. Therefore, understanding and evaluating the effects of mechanical ventilation on the autonomic nervous system is vital. The effects of mechanical ventilation on autonomic balance have been assessed by heart rate variability (HRV) using frequency domain and non-linear analysis including fractal complexity and entropy analysis in anesthetized mice. BALB/c mice (n=48) were divided into two groups: Spontaneous breathing and mechanical ventilation. The electrocardiograms were recorded. Four different types of analysis were employed: i. frequency domain analysis, ii. Poincaré plots, iii. Detrended Fluctuation Analysis (DFA) and iv. Entropy analysis. An unpaired t-test was used for statistical analysis. In a ventilated group, very low frequency (VLF) and low frequency (LF) parameters were not changed, whereas the high frequency parameter was decreased compared to spontaneous breathing mice. DFAa1 was significantly increased due to mechanical ventilation but DFAa2 was unchanged. In Poincaré plots analysis, standard deviation 2 (SD2) / standard deviation 1 (SD1) ratio was increased, however, SD1 and SD2 were not significantly affected. Also, Approximate Entropy and Sample Entropy remained unchanged. HF parameter, DFAa1, and SD2/SD1 were affected by mechanical ventilation. Decreased HF and increased DFAa1, further support the notion that HRV is dominated by respiratory sinus arrhythmia at high frequencies, this may be due to decreased vagal tone caused by mechanical ventilation. This novel results of HRV analysis are important considering increased usage of HRV techniques day by day in animal models and other medical practices. © 2023 H Kazdağli, HF Ozel, MA Özbek. All Rights Reserved.Item Cardioprotective effects of H3 receptor activation could be double-sided: insights from isoproterenol-induced cardiac injury(Springer Science and Business Media Deutschland GmbH, 2025) Özel H.F.; Özbek M.; Özden M.T.; Vatansever H.S.Histamine H3 receptors (H3Rs) are known to modulate neurotransmitter release in the nervous system, but their role in cardiac injury remains unclear. The present study aimed to investigate the cardioprotective role of H3Rs in a mouse model of myocardial injury. Forty BALB/c male mice were divided into four groups: Control (SF), Isoproterenol (ISO), Imetit (IMT), and IMT + ISO. The IMT and IMT + ISO groups were pretreated orally with 10 mg/kg imetit-dihydrobromide(imetit) for 7 days. In the last 2 days, the ISO and IMT + ISO groups received a subcutaneous injection of 85 mg/kg isoproterenol to induce myocardial ischemia. Electrocardiogram (ECG) recordings were obtained, and heart tissues were analyzed histopathologically. The results demonstrated that the administration of imetit resulted in the prolongation of the PR interval in the IMT group. QRS and QT intervals were prolonged in the ISO group. The J-wave area in the ISO group was significantly larger than in the other groups. Histopathological analyses revealed the presence of small vacuoles, inflammatory cell infiltration, and collagen aggregates in cardiomyocytes in the ISO group. No significant cellular changes were observed in the IMT group, in contrast. The IMT + ISO group exhibited fewer ischemic findings than the ISO group. Immunohistochemical analyses revealed positive H3R immunoreactivity in all groups. Imetit pretreatment increased the immunoreactivity of H3Rs in both the IMT and IMT + ISO groups. The findings of this study suggest that H3Rs may be present on the postsynaptic side in cardiac myocytes, in addition to adrenergic presynaptic nerve endings. Furthermore, imetit has been found to significantly reduce the effects of myocardial ischemia by activating H3Rs. The better characterization of the postsynaptic role of H3Rs offers potential for the development of new therapeutic strategies. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.