TY  - JOUR
AU  - Kalauzi, Aleksandar
AU  - Vučković, Aleksandra
AU  - Bojić, Tijana
PY  - 2018
UR  - http://link.springer.com/10.1007/s11517-017-1746-3
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/7746
AB  - A number of measures, stemming from nonlinear dynamics, exist to estimate complexity of biomedical objects. In most cases they are appropriate, but sometimes unconventional measures, more suited for specific objects, are needed to perform the task. In our present work, we propose three new complexity measures to quantify complexity of topographic closed loops of alpha carrier frequency phase potentials (CFPP) of healthy humans in wake and drowsy states. EEG of ten adult individuals was recorded in both states, using a 14-channel montage. For each subject and each state, a topographic loop (circular directed graph) was constructed according to CFPP values. Circular complexity measure was obtained by summing angles which directed graph edges (arrows) form with the topographic center. Longitudinal complexity was defined as the sum of all arrow lengths, while intersecting complexity was introduced by counting the number of intersections of graph edges. Wilcoxon's signed-ranks test was used on the sets of these three measures, as well as on fractal dimension values of some loop properties, to test differences between loops obtained in wake vs. drowsy. While fractal dimension values were not significantly different, longitudinal and intersecting complexities, as well as anticlockwise circularity, were significantly increased in drowsy.
T2  - Medical & Biological Engineering & Computing
T1  - New complexity measures reveal that topographic loops of human alpha phase potentials are more complex in drowsy than in wake
VL  - 56
IS  - 6
SP  - 967
EP  - 978
DO  - 10.1007/s11517-017-1746-3
ER  - 

@article{
author = "Kalauzi, Aleksandar and Vučković, Aleksandra and Bojić, Tijana",
year = "2018",
abstract = "A number of measures, stemming from nonlinear dynamics, exist to estimate complexity of biomedical objects. In most cases they are appropriate, but sometimes unconventional measures, more suited for specific objects, are needed to perform the task. In our present work, we propose three new complexity measures to quantify complexity of topographic closed loops of alpha carrier frequency phase potentials (CFPP) of healthy humans in wake and drowsy states. EEG of ten adult individuals was recorded in both states, using a 14-channel montage. For each subject and each state, a topographic loop (circular directed graph) was constructed according to CFPP values. Circular complexity measure was obtained by summing angles which directed graph edges (arrows) form with the topographic center. Longitudinal complexity was defined as the sum of all arrow lengths, while intersecting complexity was introduced by counting the number of intersections of graph edges. Wilcoxon's signed-ranks test was used on the sets of these three measures, as well as on fractal dimension values of some loop properties, to test differences between loops obtained in wake vs. drowsy. While fractal dimension values were not significantly different, longitudinal and intersecting complexities, as well as anticlockwise circularity, were significantly increased in drowsy.",
journal = "Medical & Biological Engineering & Computing",
title = "New complexity measures reveal that topographic loops of human alpha phase potentials are more complex in drowsy than in wake",
volume = "56",
number = "6",
pages = "967-978",
doi = "10.1007/s11517-017-1746-3"
}

Kalauzi, A., Vučković, A.,& Bojić, T.. (2018). New complexity measures reveal that topographic loops of human alpha phase potentials are more complex in drowsy than in wake. in Medical & Biological Engineering & Computing, 56(6), 967-978.
https://doi.org/10.1007/s11517-017-1746-3

Kalauzi A, Vučković A, Bojić T. New complexity measures reveal that topographic loops of human alpha phase potentials are more complex in drowsy than in wake. in Medical & Biological Engineering & Computing. 2018;56(6):967-978.
doi:10.1007/s11517-017-1746-3 .

Kalauzi, Aleksandar, Vučković, Aleksandra, Bojić, Tijana, "New complexity measures reveal that topographic loops of human alpha phase potentials are more complex in drowsy than in wake" in Medical & Biological Engineering & Computing, 56, no. 6 (2018):967-978,
https://doi.org/10.1007/s11517-017-1746-3 . .

TY  - JOUR
AU  - Platiša, Mirjana M.
AU  - Bojić, Tijana
AU  - Pavlović, Siniša U.
AU  - Radovanovic, Nikola N.
AU  - Kalauzi, Aleksandar
PY  - 2016
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/941
AB  - Classical Poincare plot is a standard way to measure nonlinear regulation of cardiovascular control. In our work we propose a generalized form of Poincare plot where we track correlation between the duration of j preceding and k next RR intervals. The investigation was done in healthy subjects and patients with atrial fibrillation, by varying j,k LT = 100. In cases where j = k, in healthy subjects the typical pattern was observed by paths that were substituting scatterplots and that were initiated and ended by loops of Poincare plot points. This was not the case for atrial fibrillation patients where Poincare plot had a simple scattered form. More, a typical matrix of Pearsons correlation coefficients, r(j,k), showed different positions of local maxima, depending on the subjects health condition. In both groups, local maxima were grouped into four clusters which probably determined specific regulatory mechanisms according to correlations between the duration of symmetric and asymmetric observed RR intervals. We quantified matrices degrees of asymmetry and found that they were significantly different: distributed around zero in healthy, while being negative in atrial fibrillation. Also, Pearsons coefficients were higher in healthy than in atrial fibrillation or in signals with reshuffled intervals. Our hypothesis is that by this novel method we can observe heart rate regimes typical for baseline conditions and defense reaction in healthy subjects. These data indicate that neural control mechanisms of heart rate are operating in healthy subjects in contrast with atrial fibrillation, identifying it as the state of risk for stress-dependent pathologies. Regulatory regimes of heart rate can be further quantified and explored by the proposed novel method.
T2  - Frontiers in Neuroscience
T1  - Generalized Poincare Plots-A New Method for Evaluation of Regimes in Cardiac Neural Control in Atrial Fibrillation and Healthy Subjects
VL  - 10
SP  - 38
DO  - 10.3389/fnins.2016.00038
ER  - 

@article{
author = "Platiša, Mirjana M. and Bojić, Tijana and Pavlović, Siniša U. and Radovanovic, Nikola N. and Kalauzi, Aleksandar",
year = "2016",
abstract = "Classical Poincare plot is a standard way to measure nonlinear regulation of cardiovascular control. In our work we propose a generalized form of Poincare plot where we track correlation between the duration of j preceding and k next RR intervals. The investigation was done in healthy subjects and patients with atrial fibrillation, by varying j,k LT = 100. In cases where j = k, in healthy subjects the typical pattern was observed by paths that were substituting scatterplots and that were initiated and ended by loops of Poincare plot points. This was not the case for atrial fibrillation patients where Poincare plot had a simple scattered form. More, a typical matrix of Pearsons correlation coefficients, r(j,k), showed different positions of local maxima, depending on the subjects health condition. In both groups, local maxima were grouped into four clusters which probably determined specific regulatory mechanisms according to correlations between the duration of symmetric and asymmetric observed RR intervals. We quantified matrices degrees of asymmetry and found that they were significantly different: distributed around zero in healthy, while being negative in atrial fibrillation. Also, Pearsons coefficients were higher in healthy than in atrial fibrillation or in signals with reshuffled intervals. Our hypothesis is that by this novel method we can observe heart rate regimes typical for baseline conditions and defense reaction in healthy subjects. These data indicate that neural control mechanisms of heart rate are operating in healthy subjects in contrast with atrial fibrillation, identifying it as the state of risk for stress-dependent pathologies. Regulatory regimes of heart rate can be further quantified and explored by the proposed novel method.",
journal = "Frontiers in Neuroscience",
title = "Generalized Poincare Plots-A New Method for Evaluation of Regimes in Cardiac Neural Control in Atrial Fibrillation and Healthy Subjects",
volume = "10",
pages = "38",
doi = "10.3389/fnins.2016.00038"
}

Platiša, M. M., Bojić, T., Pavlović, S. U., Radovanovic, N. N.,& Kalauzi, A.. (2016). Generalized Poincare Plots-A New Method for Evaluation of Regimes in Cardiac Neural Control in Atrial Fibrillation and Healthy Subjects. in Frontiers in Neuroscience, 10, 38.
https://doi.org/10.3389/fnins.2016.00038

Platiša MM, Bojić T, Pavlović SU, Radovanovic NN, Kalauzi A. Generalized Poincare Plots-A New Method for Evaluation of Regimes in Cardiac Neural Control in Atrial Fibrillation and Healthy Subjects. in Frontiers in Neuroscience. 2016;10:38.
doi:10.3389/fnins.2016.00038 .

Platiša, Mirjana M., Bojić, Tijana, Pavlović, Siniša U., Radovanovic, Nikola N., Kalauzi, Aleksandar, "Generalized Poincare Plots-A New Method for Evaluation of Regimes in Cardiac Neural Control in Atrial Fibrillation and Healthy Subjects" in Frontiers in Neuroscience, 10 (2016):38,
https://doi.org/10.3389/fnins.2016.00038 . .

TY  - JOUR
AU  - Platiša, Mirjana M.
AU  - Bojić, Tijana
AU  - Pavlović, Siniša U.
AU  - Radovanovic, Nikola N.
AU  - Kalauzi, Aleksandar
PY  - 2016
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/1332
AB  - Rearranged origin of heart rhythm in patients with atrial fibrillation (AF) influences the regulation of the heart and consequently the respiratory rhythm, and the bidirectional interaction of these rhythms not documented. Hence, we examined coupling of the RR interval and the respiration (Resp) signal by coherence, Granger causality and the cross-sample entropy method of time series analysis in patients with AF and a healthy control group. In healthy subjects, the influence of respiration on cardiac rhythm was found as increased coherence at the breathing frequency (BF) range, significantly stronger interaction and synchrony from Resp to RR than from RR to Resp. On the contrary, in patients with AF, coherence at BF diminished, there were no causal interactions between signals in both directions, which resulted in equally great asynchrony between them. In AF, the absence of full functionality of the sinoatrial node, as an integrator of neural cardiac control, resulted in diminished vagal modulation of heart periods and consequently impaired bidirectional cardio-respiratory interaction.
T2  - Biomedical Engineering / Biomedizinische Technik
T1  - Uncoupling of cardiac and respiratory rhythm in atrial fibrillation
VL  - 61
IS  - 6
SP  - 657
EP  - 663
DO  - 10.1515/bmt-2016-0057
ER  - 

@article{
author = "Platiša, Mirjana M. and Bojić, Tijana and Pavlović, Siniša U. and Radovanovic, Nikola N. and Kalauzi, Aleksandar",
year = "2016",
abstract = "Rearranged origin of heart rhythm in patients with atrial fibrillation (AF) influences the regulation of the heart and consequently the respiratory rhythm, and the bidirectional interaction of these rhythms not documented. Hence, we examined coupling of the RR interval and the respiration (Resp) signal by coherence, Granger causality and the cross-sample entropy method of time series analysis in patients with AF and a healthy control group. In healthy subjects, the influence of respiration on cardiac rhythm was found as increased coherence at the breathing frequency (BF) range, significantly stronger interaction and synchrony from Resp to RR than from RR to Resp. On the contrary, in patients with AF, coherence at BF diminished, there were no causal interactions between signals in both directions, which resulted in equally great asynchrony between them. In AF, the absence of full functionality of the sinoatrial node, as an integrator of neural cardiac control, resulted in diminished vagal modulation of heart periods and consequently impaired bidirectional cardio-respiratory interaction.",
journal = "Biomedical Engineering / Biomedizinische Technik",
title = "Uncoupling of cardiac and respiratory rhythm in atrial fibrillation",
volume = "61",
number = "6",
pages = "657-663",
doi = "10.1515/bmt-2016-0057"
}

Platiša, M. M., Bojić, T., Pavlović, S. U., Radovanovic, N. N.,& Kalauzi, A.. (2016). Uncoupling of cardiac and respiratory rhythm in atrial fibrillation. in Biomedical Engineering / Biomedizinische Technik, 61(6), 657-663.
https://doi.org/10.1515/bmt-2016-0057

Platiša MM, Bojić T, Pavlović SU, Radovanovic NN, Kalauzi A. Uncoupling of cardiac and respiratory rhythm in atrial fibrillation. in Biomedical Engineering / Biomedizinische Technik. 2016;61(6):657-663.
doi:10.1515/bmt-2016-0057 .

Platiša, Mirjana M., Bojić, Tijana, Pavlović, Siniša U., Radovanovic, Nikola N., Kalauzi, Aleksandar, "Uncoupling of cardiac and respiratory rhythm in atrial fibrillation" in Biomedical Engineering / Biomedizinische Technik, 61, no. 6 (2016):657-663,
https://doi.org/10.1515/bmt-2016-0057 . .

TY  - JOUR
AU  - Kalauzi, Aleksandar
AU  - Vučković, Aleksandra
AU  - Bojić, Tijana
PY  - 2015
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/475
AB  - Organization of resting state cortical networks is of fundamental importance for the phenomenon of awareness, which is altered in the first part of hypnagogic period (Hori stages 1-4). Our aim was to investigate the change in brain topography pattern of EEG alpha attractor correlation dimension (CD) in the period of transition from Hori stage 1 to 4. EEG of ten healthy adult individuals was recorded in the wake and drowsy states, using a 14 channel average reference montage, from which 91 bipolar channels were derived and filtered in the wider alpha (6-14 Hz) range. Sixty 1 s long epochs of each state and individual were subjected to CD calculation according to the Grassberger-Procaccia method. For such a collection of signals, two embedding dimensions, d = {5,10}, and 22 time delays 7 = 2-23 samples were explored. Optimal values were d = 10 and 7 = 18, where both saturation and second zero crossing of the autocorrelation function occurred. Bipolar channel CD underwent a significant decrease during the transition and showed a positive linear correlation with electrode distance, stronger in the wake individuals. Topographic distribution of bipolar channels with above median CD changed from longitudinal anterior-posterior pattern (awake) to a more diagonal pattern, with localization in posterior regions (drowsiness). Our data are in line with the literature reporting functional segregation of neuronal assemblies in anterior and posterior regions during this transition. Our results should contribute to understanding of complex reorganization of the cortical part of alpha generators during the wake/drowsy transition. (C) 2014 Elsevier B.V. All rights reserved.
T2  - International Journal of Psychophysiology
T1  - Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans
VL  - 95
IS  - 3
SP  - 278
EP  - 291
DO  - 10.1016/j.ijpsycho.2014.11.008
ER  - 

@article{
author = "Kalauzi, Aleksandar and Vučković, Aleksandra and Bojić, Tijana",
year = "2015",
abstract = "Organization of resting state cortical networks is of fundamental importance for the phenomenon of awareness, which is altered in the first part of hypnagogic period (Hori stages 1-4). Our aim was to investigate the change in brain topography pattern of EEG alpha attractor correlation dimension (CD) in the period of transition from Hori stage 1 to 4. EEG of ten healthy adult individuals was recorded in the wake and drowsy states, using a 14 channel average reference montage, from which 91 bipolar channels were derived and filtered in the wider alpha (6-14 Hz) range. Sixty 1 s long epochs of each state and individual were subjected to CD calculation according to the Grassberger-Procaccia method. For such a collection of signals, two embedding dimensions, d = {5,10}, and 22 time delays 7 = 2-23 samples were explored. Optimal values were d = 10 and 7 = 18, where both saturation and second zero crossing of the autocorrelation function occurred. Bipolar channel CD underwent a significant decrease during the transition and showed a positive linear correlation with electrode distance, stronger in the wake individuals. Topographic distribution of bipolar channels with above median CD changed from longitudinal anterior-posterior pattern (awake) to a more diagonal pattern, with localization in posterior regions (drowsiness). Our data are in line with the literature reporting functional segregation of neuronal assemblies in anterior and posterior regions during this transition. Our results should contribute to understanding of complex reorganization of the cortical part of alpha generators during the wake/drowsy transition. (C) 2014 Elsevier B.V. All rights reserved.",
journal = "International Journal of Psychophysiology",
title = "Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans",
volume = "95",
number = "3",
pages = "278-291",
doi = "10.1016/j.ijpsycho.2014.11.008"
}

Kalauzi, A., Vučković, A.,& Bojić, T.. (2015). Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans. in International Journal of Psychophysiology, 95(3), 278-291.
https://doi.org/10.1016/j.ijpsycho.2014.11.008

Kalauzi A, Vučković A, Bojić T. Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans. in International Journal of Psychophysiology. 2015;95(3):278-291.
doi:10.1016/j.ijpsycho.2014.11.008 .

Kalauzi, Aleksandar, Vučković, Aleksandra, Bojić, Tijana, "Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans" in International Journal of Psychophysiology, 95, no. 3 (2015):278-291,
https://doi.org/10.1016/j.ijpsycho.2014.11.008 . .

TY  - JOUR
AU  - Kapidžić, Ana
AU  - Platiša, Mirjana M.
AU  - Bojić, Tijana
AU  - Kalauzi, Aleksandar
PY  - 2014
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/188
AB  - Our aim was to model the dependence of respiratory sinus arrhythmia (RSA) on the respiratory waveform and to elucidate underlying mechanisms of cardiorespiratory coupling. In 30 subjects, RR interval and respiratory signal were recorded during spontaneous and paced (0.1 Hz/0.15 Hz) breathing and their relationship was modeled by a first order linear differential equation. This model has two parameters: a0 (related to the instantaneous degree of abdominal expansion) and a1 (referring to the speed of abdominal expansion). Assuming that a0 represents slowly adapting pulmonary stretch receptors (SARs) and a1 SARs in coordination with other stretch receptors and central integrative coupling; then pulmonary stretch receptors relaying the instantaneous lung volume are the major factor determining cardiovagal output during inspiration. The models results depended on breathing frequency with the least error occurring during slow paced breathing. The role of vagal afferent neurons in cardiorespiratory coupling may relate to neurocardiovascular diseases in which weakened coupling among venous return, arterial pressure, heart rate and respiration produces cardiovagal instability. (C) 2014 Elsevier B.V. All rights reserved.
T2  - Respiratory Physiology and Neurobiology
T1  - RR interval-respiratory signal waveform modeling in human slow paced and spontaneous breathing
VL  - 203
SP  - 51
EP  - 59
DO  - 10.1016/j.resp.2014.08.004
ER  - 

@article{
author = "Kapidžić, Ana and Platiša, Mirjana M. and Bojić, Tijana and Kalauzi, Aleksandar",
year = "2014",
abstract = "Our aim was to model the dependence of respiratory sinus arrhythmia (RSA) on the respiratory waveform and to elucidate underlying mechanisms of cardiorespiratory coupling. In 30 subjects, RR interval and respiratory signal were recorded during spontaneous and paced (0.1 Hz/0.15 Hz) breathing and their relationship was modeled by a first order linear differential equation. This model has two parameters: a0 (related to the instantaneous degree of abdominal expansion) and a1 (referring to the speed of abdominal expansion). Assuming that a0 represents slowly adapting pulmonary stretch receptors (SARs) and a1 SARs in coordination with other stretch receptors and central integrative coupling; then pulmonary stretch receptors relaying the instantaneous lung volume are the major factor determining cardiovagal output during inspiration. The models results depended on breathing frequency with the least error occurring during slow paced breathing. The role of vagal afferent neurons in cardiorespiratory coupling may relate to neurocardiovascular diseases in which weakened coupling among venous return, arterial pressure, heart rate and respiration produces cardiovagal instability. (C) 2014 Elsevier B.V. All rights reserved.",
journal = "Respiratory Physiology and Neurobiology",
title = "RR interval-respiratory signal waveform modeling in human slow paced and spontaneous breathing",
volume = "203",
pages = "51-59",
doi = "10.1016/j.resp.2014.08.004"
}

Kapidžić, A., Platiša, M. M., Bojić, T.,& Kalauzi, A.. (2014). RR interval-respiratory signal waveform modeling in human slow paced and spontaneous breathing. in Respiratory Physiology and Neurobiology, 203, 51-59.
https://doi.org/10.1016/j.resp.2014.08.004

Kapidžić A, Platiša MM, Bojić T, Kalauzi A. RR interval-respiratory signal waveform modeling in human slow paced and spontaneous breathing. in Respiratory Physiology and Neurobiology. 2014;203:51-59.
doi:10.1016/j.resp.2014.08.004 .

Kapidžić, Ana, Platiša, Mirjana M., Bojić, Tijana, Kalauzi, Aleksandar, "RR interval-respiratory signal waveform modeling in human slow paced and spontaneous breathing" in Respiratory Physiology and Neurobiology, 203 (2014):51-59,
https://doi.org/10.1016/j.resp.2014.08.004 . .

TY  - JOUR
AU  - Kapidžić, Ana
AU  - Platiša, Mirjana M.
AU  - Bojić, Tijana
AU  - Kalauzi, Aleksandar
PY  - 2014
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/338
AB  - We examined the effects of gender and age in young and middle-aged subjects on the level of cardiorespiratory interaction by analyzing properties of cardiac, respiratory and cardiac-respiratory regulatory mechanisms under paced breathing. In 56 healthy subjects, ECG (RR interval) and respiratory signal were simultaneously acquired in supine position at paced (0.1-0.45 Hz, steps of 0.05 Hz) and spontaneous breathing. The participants were divided into gender matched group of young adults (19-25 years old) and middle-aged adults (35-44 years old). Power spectral analysis was applied on RR interval time series and spectral components in very low frequency (VLF), low frequency (LF) and high frequency (HF) ranges were computed. We also calculated Sample entropy of RR interval series (SampEnRR), respiratory series (SampEnResp), and their cross-sample entropy (cross-SampEn). Under paced breathing, reduction of all spectral powers with age (p LT 0.05) is not gender dependent but reduction of some entropy measures is; SampEnRR and SampEnResp were lower only in men (p LT 0.05). In the middle-aged subjects, effect of gender on spectral measures is significant; males had lower HF (p LT 0.05). Pattern of dependencies of SampEn and cross-SampEn on paced breathing frequency were significantly different in men (young vs. middle-aged, p = 0.001 and p = 0.037) and in middle-aged subjects (females vs. males, p = 0.011 and p = 0.008). In middle-aged males, lower entropy measures indicated reduced and less complex partial cardiac and respiratory control, and central cardio-respiratory control. In conclusion, in healthy middle-aged subjects changes in cardio-respiratory coupling are detectable only in males. (C) 2014 IPEM. Published by Elsevier Ltd. All rights reserved.
T2  - Medical Engineering and Physics
T1  - Nonlinear properties of cardiac rhythm and respiratory signal under paced breathing in young and middle-aged healthy subjects
VL  - 36
IS  - 12
SP  - 1577
EP  - 1584
DO  - 10.1016/j.medengphy.2014.08.007
ER  - 

@article{
author = "Kapidžić, Ana and Platiša, Mirjana M. and Bojić, Tijana and Kalauzi, Aleksandar",
year = "2014",
abstract = "We examined the effects of gender and age in young and middle-aged subjects on the level of cardiorespiratory interaction by analyzing properties of cardiac, respiratory and cardiac-respiratory regulatory mechanisms under paced breathing. In 56 healthy subjects, ECG (RR interval) and respiratory signal were simultaneously acquired in supine position at paced (0.1-0.45 Hz, steps of 0.05 Hz) and spontaneous breathing. The participants were divided into gender matched group of young adults (19-25 years old) and middle-aged adults (35-44 years old). Power spectral analysis was applied on RR interval time series and spectral components in very low frequency (VLF), low frequency (LF) and high frequency (HF) ranges were computed. We also calculated Sample entropy of RR interval series (SampEnRR), respiratory series (SampEnResp), and their cross-sample entropy (cross-SampEn). Under paced breathing, reduction of all spectral powers with age (p LT 0.05) is not gender dependent but reduction of some entropy measures is; SampEnRR and SampEnResp were lower only in men (p LT 0.05). In the middle-aged subjects, effect of gender on spectral measures is significant; males had lower HF (p LT 0.05). Pattern of dependencies of SampEn and cross-SampEn on paced breathing frequency were significantly different in men (young vs. middle-aged, p = 0.001 and p = 0.037) and in middle-aged subjects (females vs. males, p = 0.011 and p = 0.008). In middle-aged males, lower entropy measures indicated reduced and less complex partial cardiac and respiratory control, and central cardio-respiratory control. In conclusion, in healthy middle-aged subjects changes in cardio-respiratory coupling are detectable only in males. (C) 2014 IPEM. Published by Elsevier Ltd. All rights reserved.",
journal = "Medical Engineering and Physics",
title = "Nonlinear properties of cardiac rhythm and respiratory signal under paced breathing in young and middle-aged healthy subjects",
volume = "36",
number = "12",
pages = "1577-1584",
doi = "10.1016/j.medengphy.2014.08.007"
}

Kapidžić, A., Platiša, M. M., Bojić, T.,& Kalauzi, A.. (2014). Nonlinear properties of cardiac rhythm and respiratory signal under paced breathing in young and middle-aged healthy subjects. in Medical Engineering and Physics, 36(12), 1577-1584.
https://doi.org/10.1016/j.medengphy.2014.08.007

Kapidžić A, Platiša MM, Bojić T, Kalauzi A. Nonlinear properties of cardiac rhythm and respiratory signal under paced breathing in young and middle-aged healthy subjects. in Medical Engineering and Physics. 2014;36(12):1577-1584.
doi:10.1016/j.medengphy.2014.08.007 .

Kapidžić, Ana, Platiša, Mirjana M., Bojić, Tijana, Kalauzi, Aleksandar, "Nonlinear properties of cardiac rhythm and respiratory signal under paced breathing in young and middle-aged healthy subjects" in Medical Engineering and Physics, 36, no. 12 (2014):1577-1584,
https://doi.org/10.1016/j.medengphy.2014.08.007 . .

TY  - JOUR
AU  - Kalauzi, Aleksandar
AU  - Bojić, Tijana
AU  - Vučković, Aleksandra
PY  - 2012
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/4908
AB  - The exact mathematical relationship between FFT spectrum and fractal dimension (FD) of an experimentally recorded signal is not known. In this work, we tried to calculate signal FD directly from its Fourier amplitudes. First, dependence of Higuchis FD of mathematical sinusoids on their individual frequencies was modeled with a two-parameter exponential function. Next, FD of a finite sum of sinusoids was found to be a weighted average of their FDs, weighting factors being their Fourier amplitudes raised to a fractal degree. Exponent dependence on frequency was modeled with exponential, power and logarithmic functions. A set of 280 EEG signals and Weierstrass functions were analyzed. Cross-validation was done within EEG signals and between them and Weierstrass functions. Exponential dependence of fractal exponents on frequency was found to be the most accurate. In this work, signal FD was for the first time expressed as a fractal weighted average of FD values of its Fourier components, also allowing researchers to perform direct estimation of signal fractal dimension from its FFT spectrum.
T2  - Medical and Biological Engineering and Computing
T1  - Modeling the relationship between Higuchis fractal dimension and Fourier spectra of physiological signals
VL  - 50
IS  - 7
SP  - 689
EP  - 699
DO  - 10.1007/s11517-012-0913-9
ER  - 

@article{
author = "Kalauzi, Aleksandar and Bojić, Tijana and Vučković, Aleksandra",
year = "2012",
abstract = "The exact mathematical relationship between FFT spectrum and fractal dimension (FD) of an experimentally recorded signal is not known. In this work, we tried to calculate signal FD directly from its Fourier amplitudes. First, dependence of Higuchis FD of mathematical sinusoids on their individual frequencies was modeled with a two-parameter exponential function. Next, FD of a finite sum of sinusoids was found to be a weighted average of their FDs, weighting factors being their Fourier amplitudes raised to a fractal degree. Exponent dependence on frequency was modeled with exponential, power and logarithmic functions. A set of 280 EEG signals and Weierstrass functions were analyzed. Cross-validation was done within EEG signals and between them and Weierstrass functions. Exponential dependence of fractal exponents on frequency was found to be the most accurate. In this work, signal FD was for the first time expressed as a fractal weighted average of FD values of its Fourier components, also allowing researchers to perform direct estimation of signal fractal dimension from its FFT spectrum.",
journal = "Medical and Biological Engineering and Computing",
title = "Modeling the relationship between Higuchis fractal dimension and Fourier spectra of physiological signals",
volume = "50",
number = "7",
pages = "689-699",
doi = "10.1007/s11517-012-0913-9"
}

Kalauzi, A., Bojić, T.,& Vučković, A.. (2012). Modeling the relationship between Higuchis fractal dimension and Fourier spectra of physiological signals. in Medical and Biological Engineering and Computing, 50(7), 689-699.
https://doi.org/10.1007/s11517-012-0913-9

Kalauzi A, Bojić T, Vučković A. Modeling the relationship between Higuchis fractal dimension and Fourier spectra of physiological signals. in Medical and Biological Engineering and Computing. 2012;50(7):689-699.
doi:10.1007/s11517-012-0913-9 .

Kalauzi, Aleksandar, Bojić, Tijana, Vučković, Aleksandra, "Modeling the relationship between Higuchis fractal dimension and Fourier spectra of physiological signals" in Medical and Biological Engineering and Computing, 50, no. 7 (2012):689-699,
https://doi.org/10.1007/s11517-012-0913-9 . .

TY  - JOUR
AU  - Kalauzi, Aleksandar
AU  - Vučković, Aleksandra
AU  - Bojić, Tijana
PY  - 2012
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/5215
AB  - Phases of alpha oscillations recorded by EEG were typically studied in the context of event or task related experiments, rarely during spontaneous alpha activity and in different brain states. During wake-to-drowsy transition they change unevenly, depending on the brain region. To explore their dynamics, we recorded ten adult healthy individuals in these two states. Alpha waves were treated as stable frequency and variable amplitude signals with one carrier frequency (CF). A method for calculating their CF phase shifts (CFPS) and CF phase potentials (CFPP) was developed and verified on surrogate signals as more accurate than phase shifts of Fourier components. Probability density estimate (PDE) of CFPS, CFPP and CF phase locking showed that frontal and fronto-temporal areas of the cortex underwent more extensive changes than posterior regions. The greatest differences were found between pairs of channels involving F7, F8, F3 and F4 (PDE of CFPS); F7, F8. T3 and 14 (CFPP); F7, F8, F3, F4, C3, C4 and T3 (decrease in CF phase locking). A topographic distribution of channels with above the average phase locking in the wake state revealed two separate regions occupying anterior and posterior brain areas (with intra regional and inter hemispheric connections). These regions merged and became mutually phase locked longitudinally in the drowsy state. Changes occurring primarily in the frontal and fronto-temporal regions correlated with an early decrease of alertness. Areas of increased phase locking might be correlated with topography of synchronous neuronal assemblies conceptualized within neural correlates of consciousness. (C) 2012 Elsevier B.V. All rights reserved.
T2  - International Journal of Psychophysiology
T1  - EEG alpha phase shifts during transition from wakefulness to drowsiness
VL  - 86
IS  - 3
SP  - 195
EP  - 205
DO  - 10.1016/j.ijpsycho.2012.04.012
ER  - 

@article{
author = "Kalauzi, Aleksandar and Vučković, Aleksandra and Bojić, Tijana",
year = "2012",
abstract = "Phases of alpha oscillations recorded by EEG were typically studied in the context of event or task related experiments, rarely during spontaneous alpha activity and in different brain states. During wake-to-drowsy transition they change unevenly, depending on the brain region. To explore their dynamics, we recorded ten adult healthy individuals in these two states. Alpha waves were treated as stable frequency and variable amplitude signals with one carrier frequency (CF). A method for calculating their CF phase shifts (CFPS) and CF phase potentials (CFPP) was developed and verified on surrogate signals as more accurate than phase shifts of Fourier components. Probability density estimate (PDE) of CFPS, CFPP and CF phase locking showed that frontal and fronto-temporal areas of the cortex underwent more extensive changes than posterior regions. The greatest differences were found between pairs of channels involving F7, F8, F3 and F4 (PDE of CFPS); F7, F8. T3 and 14 (CFPP); F7, F8, F3, F4, C3, C4 and T3 (decrease in CF phase locking). A topographic distribution of channels with above the average phase locking in the wake state revealed two separate regions occupying anterior and posterior brain areas (with intra regional and inter hemispheric connections). These regions merged and became mutually phase locked longitudinally in the drowsy state. Changes occurring primarily in the frontal and fronto-temporal regions correlated with an early decrease of alertness. Areas of increased phase locking might be correlated with topography of synchronous neuronal assemblies conceptualized within neural correlates of consciousness. (C) 2012 Elsevier B.V. All rights reserved.",
journal = "International Journal of Psychophysiology",
title = "EEG alpha phase shifts during transition from wakefulness to drowsiness",
volume = "86",
number = "3",
pages = "195-205",
doi = "10.1016/j.ijpsycho.2012.04.012"
}

Kalauzi, A., Vučković, A.,& Bojić, T.. (2012). EEG alpha phase shifts during transition from wakefulness to drowsiness. in International Journal of Psychophysiology, 86(3), 195-205.
https://doi.org/10.1016/j.ijpsycho.2012.04.012

Kalauzi A, Vučković A, Bojić T. EEG alpha phase shifts during transition from wakefulness to drowsiness. in International Journal of Psychophysiology. 2012;86(3):195-205.
doi:10.1016/j.ijpsycho.2012.04.012 .

Kalauzi, Aleksandar, Vučković, Aleksandra, Bojić, Tijana, "EEG alpha phase shifts during transition from wakefulness to drowsiness" in International Journal of Psychophysiology, 86, no. 3 (2012):195-205,
https://doi.org/10.1016/j.ijpsycho.2012.04.012 . .