PD Dr. Niels Wessel erforscht die Analyse und Vorhersage von Herzrhythmus- und autonomen Regulationsstörungen durch nicht-invasive Biosignalmessungen, insbesondere mittels Magnetokardiographie und Herzratenvariabilität. Sein aktueller Fokus liegt auf der Anwendung von Deep Learning und selbstüberwachtem Lernen zur Erkennung von Herzkrankheiten (Koronararterienerkrankung, Herzinsuffizienz, Arrhythmien) sowie auf der Analyse zirkadianer Rhythmen bei Schlafstörungen und deren Auswirkungen auf kardiovaskuläre Risiken. Die Methoden ermöglichen Kliniken und Medizingeräteherstellern verbesserte, strahlungsfreie Diagnostik und Früherkennung von Herzerkrankungen sowie die Entwicklung präventiver Interventionen (z. B. akustische Stimulation bei Schlafapnoe). Relevant sind die Arbeiten für Kardiologie, Schlafmedizin, medizinische Geräteentwicklung und klinische Diagnostik.
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PD Dr. rer. nat. Niels Wessel
HU-FIS-Profil ↗Förderer: Bundesministerium für Wirtschaft und Energie Zeitraum: 09/2009 - 08/2012 Projektleitung: PD Dr. rer. nat. Niels Wessel
Zeitraum: 04/2010 - 10/2010 Projektleitung: PD Dr. rer. nat. Niels Wessel
Förderer: DFG sonstige Programme Zeitraum: 04/2010 - 10/2010 Projektleitung: PD Dr. rer. nat. Niels Wessel
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics · DOI
The knowledge of transitions between regular, laminar or chaotic behaviors is essential to understand the underlying mechanisms behind complex systems. While several linear approaches are often insufficient to describe such processes, there are several nonlinear methods that, however, require rather long time observations. To overcome these difficulties, we propose measures of complexity based on vertical structures in recurrence plots and apply them to the logistic map as well as to heart-rate-variability data. For the logistic map these measures enable us not only to detect transitions between chaotic and periodic states, but also to identify laminar states, i.e., chaos-chaos transitions. The traditional recurrence quantification analysis fails to detect the latter transitions. Applying our measures to the heart-rate-variability data, we are able to detect and quantify the laminar phases before a life-threatening cardiac arrhythmia occurs thereby facilitating a prediction of such an event. Our findings could be of importance for the therapy of malignant cardiac arrhythmias.
Chaos An Interdisciplinary Journal of Nonlinear Science · DOI
In the modern industrialized countries every year several hundred thousands of people die due to sudden cardiac death. The individual risk for this sudden cardiac death cannot be defined precisely by common available, noninvasive diagnostic tools like Holter monitoring, highly amplified ECG and traditional linear analysis of heart rate variability (HRV). Therefore, we apply some rather unconventional methods of nonlinear dynamics to analyze the HRV. Especially, some complexity measures that are based on symbolic dynamics as well as a new measure, the renormalized entropy, detect some abnormalities in the HRV of several patients who have been classified in the low risk group by traditional methods. A combination of these complexity measures with the parameters in the frequency domain seems to be a promising way to get a more precise definition of the individual risk. These findings have to be validated by a representative number of patients. (c) 1995 American Institute of Physics.
Cardiovascular Research · DOI
OBJECTIVES: This study introduces new methods of non-linear dynamics (NLD) and compares these with traditional methods of heart rate variability (HRV) and high resolution ECG (HRECG) analysis in order to improve the reliability of high risk stratification. METHODS: Simultaneous 30 min high resolution ECG's and long-term ECG's were recorded from 26 cardiac patients after myocardial infarction (MI). They were divided into two groups depending upon the electrical risk, a low risk group (group 2, n = 10) and a high risk group (group 3, n = 16). The control group consisted of 35 healthy persons (group 1). From these electrocardiograms we extracted standard measures in time and frequency domain as well as measures from the new non-linear methods of symbolic dynamics and renormalized entropy. RESULTS: Applying discriminant function techniques on HRV analysis the parameters of non-linear dynamics led to an acceptable differentiation between healthy persons and high risk patients of 96%. The time domain and frequency domain parameters were successful in less than 90%. The combination of parameters from all domains and a stepwise discriminant function separated these groups completely (100%). Use of this discriminant function classified three patients with apparently low (no) risk into the same cluster as high risk patients. The combination of the HRECG and HRV analysis showed the same individual clustering but increased the positive value of separation. CONCLUSIONS: The methods of NLD describe complex rhythm fluctuations and separate structures of non-linear behavior in the heart rate time series more successfully than classical methods of time and frequency domains. This leads to an improved discrimination between a normal (healthy persons) and an abnormal (high risk patients) type of heart beat generation. Some patients with an unknown risk exhibit similar patterns to high risk patients and this suggests a hidden high risk. The methods of symbolic dynamics and renormalized entropy were particularly useful measures for classifying the dynamics of HRV.