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Search Results: 1 - 10 of 42 matches for " ?stemihan Tengiz "
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World Hypertension Congress 2013
stemihan Tengiz
Anadolu Kardiyoloji Dergisi , 2013,
The influence of α-adducin gene polymorphism on response of blood pressure to exercise in patients with hypertension
Emin Alio?lu,Ertu?rul Ercan,stemihan Tengiz,U?ur ?nsel Türk
Anadolu Kardiyoloji Dergisi , 2010,
Abstract: Objective: Clinical studies have indicated that an excessive response of blood pressure (BP) to exercise predicts risk of cardiovascular mortality. Although the mechanism responsible for the excessive BP response to exercise has not been revealed, there are some plausible mechanisms linking with underlying structural abnormalities in the cardiovascular system. Carriers of the Trp460 allele of the α-adducin Gly460Trp polymorphism have an increased risk of hypertension. The aim of the present study was to examine the influence of α-adducin gene polymorphism on response of BP to exercise in patients with hypertension. Methods: The cross-sectional observational study consisted of 49 hypertensive patients (29 women and 20 men; mean age, 53.1±8.8 years). All participants underwent a multistage exercise treadmill test according to the Bruce protocol. Arterial BPs were compared at rest, peak exercise and end of the recovery phase. Patients were classified according to their α-adducin gene polymorphisms; Gly460Gly homozygotes - Group 1 (n=28) and Trp460Trp homozygotes and Gly460Trp heterozygotes - Group 2 (n=21). Statistical analysis was performed using Chi-square, unpaired t, Mann-Whitney U and ANCOVA tests.Results: Mean exercise duration and mean exercise capacity in metabolic equivalents were not different between Group 1 and 2. The major finding of the study was that systolic BP responses at peak exercise and recovery period (3. min) were significantly higher (p=0.036) in hypertensive patients carrying at least one Trp460 allele of the α-adducin gene. Conclusion: Our results suggest that genetic variants that alter renal function and/or vasoreactivity are logical candidates to explain some of the individual variability in the BP response to exercise.
Echo-processing mechanisms in bottlenose dolphins
Tengiz Zorikov
Quantitative Biology , 2013,
Abstract: The mechanisms of echo-processing were investigated in our experiments, conducted on bottlenose dolphins. Hierarchically organized system of independent dimensions, describing echoes in animals perception, was revealed. The rules of discrimination and recognition of echoes in dolphins were established.
A Heuristic Solution of the Identifiability Problem of the Age-Period-Cohort Analysis of Cancer Occurrence: Lung Cancer Example
Tengiz Mdzinarishvili, Simon Sherman
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034362
Abstract: Background The Age–Period–Cohort (APC) analysis is aimed at estimating the following effects on disease incidence: (i) the age of the subject at the time of disease diagnosis; (ii) the time period, when the disease occurred; and (iii) the date of birth of the subject. These effects can help in evaluating the biological events leading to the disease, in estimating the influence of distinct risk factors on disease occurrence, and in the development of new strategies for disease prevention and treatment. Methodology/Principal Findings We developed a novel approach for estimating the APC effects on disease incidence rates in the frame of the Log-Linear Age-Period-Cohort (LLAPC) model. Since the APC effects are linearly interdependent and cannot be uniquely estimated, solving this identifiability problem requires setting four redundant parameters within a set of unknown parameters. By setting three parameters (one of the time-period and the birth-cohort effects and the corresponding age effect) to zero, we reduced this problem to the problem of determining one redundant parameter and, used as such, the effect of the time-period adjacent to the anchored time period. By varying this identification parameter, a family of estimates of the APC effects can be obtained. Using a heuristic assumption that the differences between the adjacent birth-cohort effects are small, we developed a numerical method for determining the optimal value of the identification parameter, by which a unique set of all APC effects is determined and the identifiability problem is solved. Conclusions/Significance We tested this approach while estimating the APC effects on lung cancer occurrence in white men and women using the SEER data, collected during 1975–2004. We showed that the LLAPC models with the corresponding unique sets of the APC effects estimated by the proposed approach fit very well with the observational data.
Basic Equations and Computing Procedures for Frailty Modeling of Carcinogenesis: Application to Pancreatic Cancer Data
Tengiz Mdzinarishvili and Simon Sherman
Cancer Informatics , 2012, DOI: 10.4137/CIN.S8063
Abstract: Modeling of cancer hazards at age t deals with a dichotomous population, a small part of which (the fraction at risk) will get cancer, while the other part will not. Therefore, we conditioned the hazard function, h(t), the probability density function (pdf), f(t), and the survival function, S(t), on frailty α in individuals. Assuming α has the Bernoulli distribution, we obtained equations relating the unconditional (population level) hazard function, hU(t), cumulative hazard function, HU(t), and overall cumulative hazard, H0, with the h(t), f(t), and S(t) for individuals from the fraction at risk. Computing procedures for estimating h(t), f(t), and S(t) were developed and used to fit the pancreatic cancer data collected by SEER9 registries from 1975 through 2004 with the Weibull pdf suggested by the Armitage-Doll model. The parameters of the obtained excellent fit suggest that age of pancreatic cancer presentation has a time shift about 17 years and five mutations are needed for pancreatic cells to become malignant.
Weibull-like Model of Cancer Development in Aging
Tengiz Mdzinarishvili,Simon Sherman
Cancer Informatics , 2010,
Abstract: Mathematical modeling of cancer development is aimed at assessing the risk factors leading to cancer. Aging is a common risk factor for all adult cancers. The risk of getting cancer in aging is presented by a hazard function that can be estimated from the observed incidence rates collected in cancer registries. Recent analyses of the SEER database show that the cancer hazard function initially increases with the age, and then it turns over and falls at the end of the lifetime. Such behavior of the hazard function is poorly modeled by the exponential or compound exponential-linear functions mainly utilized for the modeling. In this work, for mathematical modeling of cancer hazards, we proposed to use the Weibull-like function, derived from the Armitage-Doll multistage concept of carcinogenesis and an assumption that number of clones at age t developed from mutated cells follows the Poisson distribution. This function is characterized by three parameters, two of which (r and λ) are the conventional parameters of the Weibull probability distribution function, and an additional parameter (C0) that adjusts the model to the observational data. Biological meanings of these parameters are: r—the number of stages in carcinogenesis, λ—an average number of clones developed from the mutated cells during the first year of carcinogenesis, and C0—a data adjustment parameter that characterizes a fraction of the age-specific population that will get this cancer in their lifetime. To test the validity of the proposed model, the nonlinear regression analysis was performed for the lung cancer (LC) data, collected in the SEER 9 database for white men and women during 1975–2004. Obtained results suggest that: (i) modeling can be improved by the use of another parameter A- the age at the beginning of carcinogenesis; and (ii) in white men and women, the processes of LC carcinogenesis vary by A and C0, while the corresponding values of r and λ are nearly the same. Overall, the proposed Weibull-like model provides an excellent fit of the estimates of the LC hazard function in aging. It is expected that the Weibull-like model can be applicable to fit estimates of hazard functions of other adult cancers as well.
Basic Equations and Computing Procedures for Frailty Modeling of Carcinogenesis: Application to Pancreatic Cancer Data
Tengiz Mdzinarishvili,Simon Sherman
Cancer Informatics , 2013,
Heuristic Modeling of Carcinogenesis for the Population with Dichotomous Susceptibility to Cancer: A Pancreatic Cancer Example
Tengiz Mdzinarishvili, Simon Sherman
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100087
Abstract: At present, carcinogenic models imply that all individuals in a population are susceptible to cancer. These models either ignore a fall of the cancer incidence rate at old ages, or use some poorly identifiable parameters for its accounting. In this work, a new heuristic model is proposed. The model assumes that, in a population, only a small fraction (pool) of individuals is susceptible to cancer and decomposes the problem of the carcinogenic modeling on two sequentially solvable problems: (i) determination of the age-specific hazard rate in individuals susceptible to cancer (individual hazard rate) from the observed hazard rate in the population (population hazard rate); and (ii) modelling of the individual hazard rate by a chosen “up” of the theoretical hazard function describing cancer occurrence in individuals in time (age). The model considers carcinogenesis as a failure of individuals susceptible to cancer to resist cancer occurrence in aging and uses, as the theoretical hazard function, the three-parameter Weibull hazard function, often utilized in a failure analysis. The parameters of this function, providing the best fit of the modeled and observed individual hazard rates (determined from the population hazard rates), are the outcomes of the modeling. The model was applied to the pancreatic cancer data. It was shown that, in the populations stratified by gender, race and the geographic area of living, the modeled and observed population hazard rates of pancreatic cancer occurrence have similar turnovers at old ages. The sizes of the pools of individuals susceptible to this cancer: (i) depend on gender, race and the geographic area of living; (ii) proportionally influence the corresponding population hazard rates; and (iii) do not influence the individual hazard rates. The model should be further tested using data on other types of cancer and for the populations stratified by different categorical variables.
The Problem of the Double Time-Ordered Operator Product Calculation in the Nonequilibrium Quantum Field Theory
Tengiz M. Bibilashvili
Physics , 1994,
Abstract: It is shown that calculation of the operator's groups product with the independent time ordering procedure in each one is important for some problems in the nonequilibrium quantum field theory at finite temperature. This problem is solved in terms of path integrals by means of time-integration contour transformation. A role of thermal ghosts for this problem is also discussed.
Real-time quantum field theory at finite temperature in an inhomogeneous media
Tengiz M. Bibilashvili
Physics , 1995, DOI: 10.1142/S0217732396000564
Abstract: The method of the real time perturbative calculations of nonequilibrium averages is generalised to the case of varying chemical potential. Calculations are performed in the frame of Zubarev's nonequilibrium density matrix approach. In this approach perturbations of temperature and other thermodynamical parameters are taken into account explicitly including nonlinear terms. It differs from the Schwinger-Keldysh approach through the choice of more general initial conditions for the density matrix.
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