Browsing by Author "Milutinovic-Smiljanic, Sanja (23971105900)"

Copula is a (cumulative) distribution function with a density that visualizes the dependency structure of two or more time series. Frank's copula is well suited for systolic blood pressure (SBP) and pulse interval (PI) signal pairs, but the copula analyses are restricted to the probabilistic domain. A new, single-dimensional, time series that reflects the fluctuations of the signal dependency level can be obtained by mapping the signal coupling strength at a beat-by-beat basis. Such a transformation requires a probability density estimation. This paper compares several methods of density estimation to produce a time series that correspond to the dependency fluctuation of SBP and PI time series. As an illustrative example, vasopressin selective V1a and V2 receptor antagonists were employed to modulate simultaneously multiple physiological functions. © 2020 IEEE.

Copula is a (cumulative) distribution function with a density that visualizes the dependency structure of two or more time series. Frank's copula is well suited for systolic blood pressure (SBP) and pulse interval (PI) signal pairs, but the copula analyses are restricted to the probabilistic domain. A new, single-dimensional, time series that reflects the fluctuations of the signal dependency level can be obtained by mapping the signal coupling strength at a beat-by-beat basis. Such a transformation requires a probability density estimation. This paper compares several methods of density estimation to produce a time series that correspond to the dependency fluctuation of SBP and PI time series. As an illustrative example, vasopressin selective V1a and V2 receptor antagonists were employed to modulate simultaneously multiple physiological functions. © 2020 IEEE.

Objectives: Copula is a tool for measuring linear and non-linear interactions between two or more time series. The aim of this paper is to prove that a copula approach can accurately capture and visualize the spatial and temporal fluctuations in dependency structures of cardiovascular signals, and to outline the application possibilities. Methods: The method for measuring the level of interaction between systolic blood pressure and the corresponding pulse interval is validated statistically and pharmacologically. The time series are recorded from the freely moving male Wistar rats equipped with radio-telemetry device for blood pressure recording, before and after administration of autonomic blockers scopolamine, atenolol, prazosin and hexamethonium. Implicit (Gaussian and t) and explicit (Clayton, Frank and Gumbel) copulas were calculated and compared to the conventional bivariate methods (Kendal, Pearson, Spearman and classical correlation). Further statistical validation was done using artificially generated surrogate data. A window sliding procedure for dynamic monitoring the signals’ coupling strength is implemented. Results: Under the baseline physiological conditions, SBP-PI dependency is significant for time lags 0 s–4 s. Hexamethonium completely abolished the dependency, scopolamine abolished it for time lags 0 s–2 s, atenolol first slightly increased, than for lags greater than 2 s decreased the dependency and prazosin had no effect. Isospectral and isodistributional surrogate data tests confirm that copulas successfully notify the absence of dependency as well. Conclusion: Copula approach accurately captures the temporal fluctuations in dependency structures of SBP and PI, simultaneously enabling a visualization of dependency levels within the particular signal zones. An analysis showed that copulas are more sensitive than the conventional statistical measures, with Frank copula exhibiting the best characterization of SBP and PI dependency. © 2018 The Authors

Objectives: Copula is a tool for measuring linear and non-linear interactions between two or more time series. The aim of this paper is to prove that a copula approach can accurately capture and visualize the spatial and temporal fluctuations in dependency structures of cardiovascular signals, and to outline the application possibilities. Methods: The method for measuring the level of interaction between systolic blood pressure and the corresponding pulse interval is validated statistically and pharmacologically. The time series are recorded from the freely moving male Wistar rats equipped with radio-telemetry device for blood pressure recording, before and after administration of autonomic blockers scopolamine, atenolol, prazosin and hexamethonium. Implicit (Gaussian and t) and explicit (Clayton, Frank and Gumbel) copulas were calculated and compared to the conventional bivariate methods (Kendal, Pearson, Spearman and classical correlation). Further statistical validation was done using artificially generated surrogate data. A window sliding procedure for dynamic monitoring the signals’ coupling strength is implemented. Results: Under the baseline physiological conditions, SBP-PI dependency is significant for time lags 0 s–4 s. Hexamethonium completely abolished the dependency, scopolamine abolished it for time lags 0 s–2 s, atenolol first slightly increased, than for lags greater than 2 s decreased the dependency and prazosin had no effect. Isospectral and isodistributional surrogate data tests confirm that copulas successfully notify the absence of dependency as well. Conclusion: Copula approach accurately captures the temporal fluctuations in dependency structures of SBP and PI, simultaneously enabling a visualization of dependency levels within the particular signal zones. An analysis showed that copulas are more sensitive than the conventional statistical measures, with Frank copula exhibiting the best characterization of SBP and PI dependency. © 2018 The Authors

The baroreceptor reflex (BRR) bears the important part in short term blood pressure (BP) control. Joint order pattern analysis is proposed to assess the complex nature of BP and pulse interval (PI) dynamic. The BP and PI signals were acquired from conscious radiotelemetred Wistar male rats with intact BRR loop and pharmacologically opened BRR loop at different levels using blockade of β-adrenergic, α-adrenergic and Mcholinergic receptors. The study revealed increase in complexity of relationship between BP and PI due to opening of BRR loop, as measured by permutation entropy and probability density function of transcriptions translating BP variations into PI responses. Synchronization measure significantly decreases in open BRR loop changing from 0.22 towards the values characteristic for random and independent data (0.02). It follows that BRR buffers random BP and PI changes and increases their synchronization.

The baroreceptor reflex (BRR) bears the important part in short term blood pressure (BP) control. Joint order pattern analysis is proposed to assess the complex nature of BP and pulse interval (PI) dynamic. The BP and PI signals were acquired from conscious radiotelemetred Wistar male rats with intact BRR loop and pharmacologically opened BRR loop at different levels using blockade of β-adrenergic, α-adrenergic and Mcholinergic receptors. The study revealed increase in complexity of relationship between BP and PI due to opening of BRR loop, as measured by permutation entropy and probability density function of transcriptions translating BP variations into PI responses. Synchronization measure significantly decreases in open BRR loop changing from 0.22 towards the values characteristic for random and independent data (0.02). It follows that BRR buffers random BP and PI changes and increases their synchronization.

The aim of the study was to examine alteration and possible application of fractal dimension, angular second moment, and correlation for quantification of structural changes in acutely inflamed tissue. Acute inflammation was induced by injection of turpentine oil into the right and left hind limb muscles of mice, whereas control animals received intramuscular saline injection. After 12 h, animals were anesthetised and treated muscles collected. The tissue was stained by hematoxylin and eosin, digital micrographs produced, enabling determination of fractal dimension of the cells, angular second moment and correlation of studied tissue. Histopathological analysis showed presence of inflammatory infiltrate and tissue damage in inflammatory group, whereas tissue structure in control group was preserved, devoid of inflammatory infiltrate. Fractal dimension of the cells, angular second moment and correlation of treated tissue in inflammatory group decreased in comparison to the control group. In this study, we were first to observe and report that fractal dimension of the cells, angular second moment, and correlation were reduced in acutely inflamed tissue, indicating loss of overall complexity of the cells in the tissue, the tissue uniformity and structure regularity. Fractal dimension, angular second moment and correlation could be useful methods for quantification of structural changes in acute inflammation. Lay Description: The aim of this study was to examine alteration, and possible application of mathematical parameters fractal dimension, angular second moment, and correlation for quantification of structural changes in acutely-inflamed tissue. An acute inflammation was induced by injection of turpentine oil into mice muscles, whereas control group received intramuscular injection of saline. After 12 h animals were anesthetized, and treated muscles were collected. The tissue was stained, and photos of the tissue were made. Mathematical parameters, namely fractal dimension, angular second moment, and correlation of the tissue photo, were determined by computer program. Standard histopathological analysis showed that inflammatory infiltrate and tissue damage were present in inflammatory group, whereas tissue structure in control group was preserved, and without inflammatory infiltrate. Fractal dimension of the cells, angular second moment and correlation of the treated tissue in inflammatory group decreased, when compared to control group. In this study we reported, for the first time, that fractal dimension of the cells, angular second moment, and correlation had decreased in acutely-inflamed tissue, indicating loss of overall complexity of cells in tissue, tissue uniformity, and structure regularity. Fractal dimension, angular second moment, and correlation could be useful methods for quantification of structural changes in acute inflammation. © 2016 Royal Microscopical Society.