Browsing by Author "Bajić, Dragana (56186463400)"

Digital signal processing is a tool that is used not only in classic engineering but also in a range of multidisciplinary applications. To understand the benefits that a particular signal processing method offers, the researchers must be aware of the theory underlying the method, as well as the limitations thereof. © 2018 by Taylor & Francis Group, LLC.

Digital signal processing is a tool that is used not only in classic engineering but also in a range of multidisciplinary applications. To understand the benefits that a particular signal processing method offers, the researchers must be aware of the theory underlying the method, as well as the limitations thereof. © 2018 by Taylor & Francis Group, LLC.

This study investigates blood pressure (BP) and heart rate (HR) short-term variability and spontaneous baroreflex functioning in adult borderline hypertensive rats and normotensive control animals kept on normal-salt diet. Arterial pulse pressure was recorded by radio telemetry. Systolic BP, diastolic BP and HR variabilities and baroreflex were assessed by spectral analysis and the sequence method, respectively. In all experimental conditions (baseline and stress), borderline hypertensive rats exhibited higher BP, increased baroreflex sensitivity and resetting, relative to control animals. Acute shaker stress (single exposure to 200 cycles min-1 shaking platform) increased BP in both strains, while chronic shaker stress (3-day exposure to shaking platform) increased systolic BP in borderline hypertensive rats alone. Low- and high-frequency HR variability increased only in control animals in response to acute and chronic shaker (single exposure to restrainer) stress. Acute restraint stress increased BP, HR, low- and high-frequency variability of BP and HR in both strains to a greater extent than acute shaker stress. Only normotensive rats exhibited a reduced ratio of low- to high-frequency HR variability, pointing to domination of vagal cardiac control. In borderline hypertensive rats, but not in control animals, chronic restraint stress (9-day exposure to restrainer) increased low- and high-frequency BP and HR variability and their ratio, indicating a shift towards sympathetic cardiovascular control. It is concluded that maintenance of BP in borderline hypertensive rats in basal conditions and during stress is associated with enhanced baroreflex sensitivity and resetting. Imbalance in sympathovagal control was evident only during exposure of borderline hypertensive rats to stressors. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.

This study investigates blood pressure (BP) and heart rate (HR) short-term variability and spontaneous baroreflex functioning in adult borderline hypertensive rats and normotensive control animals kept on normal-salt diet. Arterial pulse pressure was recorded by radio telemetry. Systolic BP, diastolic BP and HR variabilities and baroreflex were assessed by spectral analysis and the sequence method, respectively. In all experimental conditions (baseline and stress), borderline hypertensive rats exhibited higher BP, increased baroreflex sensitivity and resetting, relative to control animals. Acute shaker stress (single exposure to 200 cycles min-1 shaking platform) increased BP in both strains, while chronic shaker stress (3-day exposure to shaking platform) increased systolic BP in borderline hypertensive rats alone. Low- and high-frequency HR variability increased only in control animals in response to acute and chronic shaker (single exposure to restrainer) stress. Acute restraint stress increased BP, HR, low- and high-frequency variability of BP and HR in both strains to a greater extent than acute shaker stress. Only normotensive rats exhibited a reduced ratio of low- to high-frequency HR variability, pointing to domination of vagal cardiac control. In borderline hypertensive rats, but not in control animals, chronic restraint stress (9-day exposure to restrainer) increased low- and high-frequency BP and HR variability and their ratio, indicating a shift towards sympathetic cardiovascular control. It is concluded that maintenance of BP in borderline hypertensive rats in basal conditions and during stress is associated with enhanced baroreflex sensitivity and resetting. Imbalance in sympathovagal control was evident only during exposure of borderline hypertensive rats to stressors. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.

The arterial baroreceptor reflex (BRR) is a key neurogenic control mechanism of the arterial blood pressure (BP) that acts as a negative feedback corrector. It counteracts BP deviations from a reference set point by modulating heart rate (HR) and peripheral resistance. The BRR is crucial for maintaining BP during postural challenge, including active standing and passive upright tilt (Eckberg 2008). By contrast, the BRR is suppressed during exercise and stress to allow simultaneous increase of BP and HR required for ‘fight and 200flight’ response (Raven et al. 2005; Bajic et al. 2010). Remodeling of the autonomic nervous system (ANS) control of the cardiovascular system, and of the baroreceptor function, occurs in cardiovascular diseases (La Rovere et al. 2008). Permanent resetting of the BRR characterizes primary hypertension, while reduction of BRR sensitivity (BRS) has been found to predict bad outcomes (Di Rienzo et al. 2009). Deregulation of BP in neurologic disorders associated with ANS dysfunction (dysautonomia) is due to impairment of BRR function. © 2018 by Taylor & Francis Group, LLC.

The arterial baroreceptor reflex (BRR) is a key neurogenic control mechanism of the arterial blood pressure (BP) that acts as a negative feedback corrector. It counteracts BP deviations from a reference set point by modulating heart rate (HR) and peripheral resistance. The BRR is crucial for maintaining BP during postural challenge, including active standing and passive upright tilt (Eckberg 2008). By contrast, the BRR is suppressed during exercise and stress to allow simultaneous increase of BP and HR required for ‘fight and 200flight’ response (Raven et al. 2005; Bajic et al. 2010). Remodeling of the autonomic nervous system (ANS) control of the cardiovascular system, and of the baroreceptor function, occurs in cardiovascular diseases (La Rovere et al. 2008). Permanent resetting of the BRR characterizes primary hypertension, while reduction of BRR sensitivity (BRS) has been found to predict bad outcomes (Di Rienzo et al. 2009). Deregulation of BP in neurologic disorders associated with ANS dysfunction (dysautonomia) is due to impairment of BRR function. © 2018 by Taylor & Francis Group, LLC.

Sudden death is a major health problem all over the world. The most common causes of sudden death are cardiac but there are also other causes such as neurological conditions (stroke, epileptic attacks and brain trauma), drugs, catecholamine toxicity, etc. A common feature of all these diverse pathologies underlying sudden death is the imbalance of the autonomic nervous system control of the cardiovascular system. This paper reviews different pathologies underlying sudden death with emphasis on the autonomic nervous system contribution, possibilities of early diagnosis and prognosis of sudden death using various clinical markers including autonomic markers (heart rate variability and baroreflex sensitivity), present possibilities of management and promising prevention by electrical neuromodulation. © The European Society of Cardiology 2017.

Copula density is a function that quantifies the level of dependency between two, or more, related time series, and also visualizes their (non)linear dependency structures. This paper aims to analyze and compare different methods for copula density estimation: local (naïve) estimation, kernel estimation, K nearest neighbors, Markov state approach, histograms, and Voronoi decomposition. The methods are compared by mapping the copula density into a time series (dependency level time series) and applying Sample Entropy estimates over the range of parameters. Application examples include systolic blood pressure and pulse interval signals recorded from conscious laboratory rats, treated either with vasopressin selective V1a and V2 receptor antagonists (100 ng and 500 ng) or with saline (control group). The signals are analyzed using composite multiscale entropy. It is shown that each estimation method suffers from bias, but, for each case, a stable working region can be found. It was also shown that the analysis of the dependency level time series could reveal the information that could not be extracted from the classical beat-to-beat time series, and that the copula density, transformed to real signals domain, visualizes the regions where the dependency of cardiovascular signals is exhibited the most, reflecting their mutual relationship and providing the possibility for further research. © 2021

Copula density is a function that quantifies the level of dependency between two, or more, related time series, and also visualizes their (non)linear dependency structures. This paper aims to analyze and compare different methods for copula density estimation: local (naïve) estimation, kernel estimation, K nearest neighbors, Markov state approach, histograms, and Voronoi decomposition. The methods are compared by mapping the copula density into a time series (dependency level time series) and applying Sample Entropy estimates over the range of parameters. Application examples include systolic blood pressure and pulse interval signals recorded from conscious laboratory rats, treated either with vasopressin selective V1a and V2 receptor antagonists (100 ng and 500 ng) or with saline (control group). The signals are analyzed using composite multiscale entropy. It is shown that each estimation method suffers from bias, but, for each case, a stable working region can be found. It was also shown that the analysis of the dependency level time series could reveal the information that could not be extracted from the classical beat-to-beat time series, and that the copula density, transformed to real signals domain, visualizes the regions where the dependency of cardiovascular signals is exhibited the most, reflecting their mutual relationship and providing the possibility for further research. © 2021