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Jan J Zebrowski

Publications and source records attributed to Jan J Zebrowski.

6 recordsLinked to original sources
PubMed2006

Nonstationary Pomeau-Manneville intermittency in systems with a periodic parameter change.

Pomeau-Manneville intermittency in nonstationary systems is investigated. If one of the parameters characterizing a dynamical system is changed periodically, periodic orbits may appear even when the value of this parameter remains in a range which, in the stationary case, yields chaotic behavior. This property may be used for the control of systems exhibiting intermittency. If the parameter change is not large enough, a periodic orbit does not appear but the distribution of the laminar phases is modified. In the case of type I intermittency, this means a broadening of such a distribution or, alternatively, a splitting of its right peak. We present a theory of these phenomena. Numerical simulations both for one-dimensional maps and for flows support our predictions. Some of the phenomena discussed here were observed earlier in time series of heart rate variability.

Journal Article↗
PubMed2006

Autonomic information flow improves prognostic impact of task force HRV monitoring.

Heart rate variability (HRV) represents the cardiovascular control mediated by the autonomic nervous system and other mechanisms. In the established task force HRV monitoring different cardiovascular control mechanisms can approximately be identified at typical frequencies of heart rate oscillations by power spectral analysis. HRV measures assessing complex and fractal behavior partly improved clinical risk stratification. However, their relationship to (patho-)physiology is not sufficiently explored. Objective of the present work is the introduction of complexity measures of different physiologically relevant time scales. This is achieved by a new concept of the autonomic information flow (AIF) analysis which was designed according to task force HRV. First applications show that different time scales of AIF improve the risk stratification of patients with multiple organ dysfunction syndrome and cardiac arrest patients in comparison to standard HRV. Each group's significant time scales correspond to their respective pathomechanisms.

Adult↗
PubMed2006

Analysis of complex physiological systems by information flow: a time scale-specific complexity assessment.

In the last two decades conventional linear methods for biosignal analysis have been substantially extended by non-stationary, non-linear, and complexity approaches. So far, complexity is usually assessed with regard to one single time scale, disregarding complex physiology organised on different time scales. This shortcoming was overcome and medically evaluated by information flow functions developed in our research group in collaboration with several theoretical, experimental, and clinical partners. In the present work, the information flow is introduced and typical information flow characteristics are demonstrated. The prognostic value of autonomic information flow (AIF), which reflects communication in the cardiovascular system, was shown in patients with multiple organ dysfunction syndrome and in patients with heart failure. Gait information flow (GIF), which reflects communication in the motor control system during walking, was introduced to discriminate between controls and elderly patients suffering from low back pain. The applications presented for the theoretically based approach of information flow confirm its value for the identification of complex physiological systems. The medical relevance has to be confirmed by comprehensive clinical studies. These information flow measures substantially extend the established linear and complexity measures in biosignal analysis.

Adult↗
PubMed2006

Complex autonomic dysfunction in cardiovascular, intensive care, and schizophrenic patients assessed by autonomic information flow.

BACKGROUND: The cardiovascular control system is mediated by mechanisms acting at different time scales, such as heart period, vagal, sympathetic, and other slower controllers. Since these elements are interrelated in a complex manner, classical control theory fails and information-based description, based on autonomic information flow (AIF) functions, is appropriate. We investigated the hypothesis that AIF functions of typical time scales specifically characterize autonomic dysfunction and prognosis. MATERIALS AND METHODS: Holter recordings of patients with multiple organ dysfunction syndrome (MODS) (26 survivors, 10 non-survivors), heart failure (13 low risk, 13 high risk of cardiac arrest), idiopathic dilated cardiomyopathy (IDC) (26 low risk, 11 high risk), after abdominal aorta surgery (AAS) [32 with length of stay in hospital (LOS) >7 days; 62 with LOS < or =7 days] or with schizophrenia (n=20) were assessed and compared to 20 control subjects. RESULTS: We found different AIF time scales discriminating risk. AIF measures of heart beat period had predominant prognostic value in heart failure patients, those of vagal communication in MODS and IDC, and those of long-term communication after AAS. Schizophrenic patients were discriminated from controls by vagally mediated communication. CONCLUSION: Different time scales of AIF represent specific pathophysiological aspects of altered complex autonomic control (communication) and consequently have predictive implications.

Autonomic Nervous System↗
PubMed2002

Assessment of the RR versus QT relation by a new symbolic dynamics method. Gender differences in repolarization dynamics.

A new method based on symbolic dynamics was applied to assess RR-QT dynamics and to compare gender differences. Segments of 10,000 RR and QT from the night were selected. The values of RR and QT were coded as follows. Each RR and QT interval was compared with their means in the last 50 beats [xRR, xQT]; when the interval was larger than x + delta then it was coded as a "2", where delta is the tolerance parameter; when it was less than x - delta-the code was a "0"; when it was larger than x-delta and and the less than x+delta-then it was coded as a "1." The tolerance parameter "delta" was equal to 10 ms for RR and 4 ms for QT. We obtained pairs of symbols representing the values of RR and QT-symbolic words. The results were presented in form of the probability density of the symbolic words. Mean RR, mean QT, SDRR, SDQT, QTc (Bazett formula) were also calculated. Electrocardiogram data of healthy individuals: 20 women and 20 men (mean age 39 +/- 12) were analyzed. There were significant gender differences in RR-QT dynamics. During heart rate acceleration the probability of QT shortening (the probability of the word "00") was higher in men than in women (P =.003). During heart rate deceleration QT lengthening (the word "22") was more frequently observed in men than in women (P =.003) as well. The QT reaction to RR interval changes is less complex in women than in men. In discriminant analysis, when QTc was ignored in the model, the RR-QT dynamics separated genders with 67% accuracy (chi(2) = 9.1, P <.003). RR-QT dynamics can be analyzed with symbolic dynamics methods. The gender differences in repolarization are not only due to QTc duration alone but also result from the dependence of the duration of QT on the RR duration.

Adult↗