Papers by Christopher Mayer
Cardiovascular Engineering and Technology
Attractor reconstruction is a new way to quantify the morphology of a cardiovascular waveform by ... more Attractor reconstruction is a new way to quantify the morphology of a cardiovascular waveform by plotting all data points in the three-dimensional phase space, generating a trajectory of overlapping loops. The aim of this study is to show the feasibility of an automatic approach to quantify pulse wave attractors from a device-guided breathing study, and to link attractor features to pulse waveform features. The recently developed feature extraction technique is applied to arterial pulse waveform data of 30 patients with treated hypertension. The patients performed a device-guided slow breathing exercise. The generated attractors were categorized into three different shapes: triangular attractors, bent attractors and attractors with overlapping arms. The average height of the attractors continuously and progressively dropped from 41.8 [35.4, 55.1] AU to 34.5 [25.4, 47.3] AU (p < 0.001) during the breathing exercise. We have shown that the novel approach to quantify pulse wave attr...
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Journal of Nephrology, 2021
Background In hemodialysis patients, left ventricular hypertrophy (LVH) contributes to high cardi... more Background In hemodialysis patients, left ventricular hypertrophy (LVH) contributes to high cardiovascular mortality. We examined cardiovascular mortality prediction by the recently proposed Peguero-Lo Presti voltage since it identifies more patients with electrocardiographic (ECG) LVH than Cornell or Sokolow-Lyon voltages. Methods A total of 308 patients on hemodialysis underwent 24 h ECG recordings. LVH parameters were measured before and after dialysis. The primary endpoint of cardiovascular mortality was recorded during a median 3-year follow up. Risk prediction was assessed by Cox regression, both unadjusted and adjusted for the Charlson Comorbidity Index and the Cardiovascular Mortality Risk Score. Results The Peguero-Lo Presti voltage identified with 21% the most patients with positive LVH criteria. All voltages significantly increased during dialysis. Factors such as ultrafiltration rate, Kt/V, body mass index, sex, and phosphate were the most relevant for these changes. Dur...
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Nowadays, we use a variety of devices to interact with local and cloud-based systems and services... more Nowadays, we use a variety of devices to interact with local and cloud-based systems and services and are used to aesthetic and tailored user interfaces. This fact induces challenges for user interface designers regarding additional efforts for the development of multiple user interfaces for (all) available devices. Model-based user interface design tackles this challenge by creating abstract models for a transformation to various devices, but with the disadvantage of additional efforts for using and learning these techniques. Thus, we propose a transformation process deriving an abstract model on the basis of an integrated mockup and wireframe design tool. This allows combining the advantages of model-based user interface design with the world of the classical user interface design process. The engine transfers sketches to an abstract task model in ConcurTaskTrees notation. The model is the input for a separate model interpretation layer generating concrete user interfaces for vari...
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Heart rate variability (HRV) analysis is a non-invasive tool for assessing cardiac health. Entrop... more Heart rate variability (HRV) analysis is a non-invasive tool for assessing cardiac health. Entropy measures quantify the chaotic properties of HRV, but they are sensitive to the choice of their required parameters. Previous studies therefore have performed parameter optimization, targeting solely their particular patient cohort. In contrast, this work aimed to challenge entropy measures with recently published parameter sets, without time-consuming optimization, for risk prediction in end-stage renal disease patients. Approximate entropy, sample entropy, fuzzy entropy, fuzzy measure entropy, and corrected approximate entropy were examined. In total, 265 hemodialysis patients from the ISAR (rISk strAtification in end-stage Renal disease) study were analyzed. Throughout a median follow-up time of 43 months, 70 patients died. Fuzzy entropy and corrected approximate entropy (CApEn) provided significant hazard ratios, which remained significant after adjustment for clinical risk factors ...
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Models in general, but especially in medicine, need extensive testing and verification to ensure ... more Models in general, but especially in medicine, need extensive testing and verification to ensure that they do not contain errors and produce correct results. Traditionally, this happens after completing the development. In this work an approach to automated and continuous testing, verification and documentation based on a continuous integration tool is presented. This practice has several advantages in comparison to the traditional way of verification. As the model is verified after every single change that is made to it, one benefit is the earlier and more precise tracing of errors. Another advantage is the aggregation of code generation, software building, testing, verifying and documentation in one tool to ensure maximum automation and to reduce expenditure of time. Furthermore, due to the integration of central versioning systems, it makes working in development teams easier. In this work, the development processes of two cardiovascular models are incorporated into a continuous ...
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The user interface is the most important feature of interaction between users and (AAL) services.... more The user interface is the most important feature of interaction between users and (AAL) services. Explicitly defined user interfaces are bound to a specific toolkit and programming language or markup language. Thus a separate user interface definition has to be created manually for different classes of I/O devices to be supported. Compared to manual user interface creation, the automatic or semiautomatic generation of user interfaces based on interaction descriptions considerably reduces the manual effort necessary for integrating a large number of devices and therefore automatically increases the number of supported devices. The main goal of this paper is to provide an overview of selected existing solutions for the definition of generic user interactions and the generation of user interfaces. The comparison shows that the aspect of adaptability is partly covered by the presented User Interaction Description Languages. Nevertheless it is important to analyze them with respect to ad...
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The analysis of aortic blood pressure and flow represent an important tool to predict cardiovascu... more The analysis of aortic blood pressure and flow represent an important tool to predict cardiovascular risk. A Windkessel model relating pressure and flow, together with an optimal performance criterion of left-ventricular work, is used to generate the aortic flow pattern for a given central pressure curve. For the corresponding optimization problem, different physiologically relevant constraints are specified, but due to the limited number of degrees of freedom not all of them can be included at once. The optimization problem is solved with every possible combination of constraints and the resulting flow and pressure curves are analyzed. These waveforms show that the choice of constraints strongly affects the accuracy of the generated curves. Constraining aortic flow during diastole appears to be the best choice, but a physiologically shaped flow and pressure pattern cannot be achieved simultaneously with the applied objective function and constraints.
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Hypertension, 2021
Central (aortic) systolic blood pressure (cSBP) is the pressure seen by the heart, the brain, and... more Central (aortic) systolic blood pressure (cSBP) is the pressure seen by the heart, the brain, and the kidneys. If properly measured, cSBP is closer associated with hypertension-mediated organ damage and prognosis, as compared with brachial SBP (bSBP). We investigated 24-hour profiles of bSBP and cSBP, measured simultaneously using Mobilograph devices, in 2423 untreated adults (1275 women; age, 18–94 years), free from overt cardiovascular disease, aiming to develop reference values and to analyze daytime-nighttime variability. Central SBP was assessed, using brachial waveforms, calibrated with mean arterial pressure (MAP)/diastolic BP (cSBP MAP/DBPcal ), or bSBP/diastolic blood pressure (cSBP SBP/DBPcal ), and a validated transfer function, resulting in 144 509 valid brachial and 130 804 valid central measurements. Averaged 24-hour, daytime, and nighttime brachial BP across all individuals was 124/79, 126/81, and 116/72 mm Hg, respectively. Averaged 24-hour, daytime, and nighttime va...
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Aging Clinical and Experimental Research, 2021
Background Assistive technologies have the potential to facilitate everyday life of people with d... more Background Assistive technologies have the potential to facilitate everyday life of people with dementia and their families. Close collaboration with affected people and interdisciplinary research are essential to understand and address the needs of prospective users. In this study, we present the results of the evaluation of such an assistive system prototype. Aims Challenges from the patient and caregiver side, technical and design problems and acceptance and usability with regard to our special target group were evaluated. Methods MEMENTO, a system of two e-ink tablets and a smartwatch, was tested in the domestic environment of dementia patients. Thirty participants from Italy, Spain and Austria took part in a 3-month field trial and compared the MEMENTO system to traditional strategies in everyday life. Quantitative and qualitative data were collected and frequency of use of the system was monitored. Results There were no significant changes in quantitative measurements, such as...
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Artery Research, 2020
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SNE Simulation Notes Europe, Apr 1, 2012
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Artery Research, 2020
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Artery Research, 2020
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Artery Research, 2020
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Frontiers in Cardiovascular Medicine, 2019
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Nephrology Dialysis Transplantation, 2019
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Artery Research, 2016
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Proceedings of the 10th EAI International Conference on Pervasive Computing Technologies for Healthcare, 2016
The work-in-progress paper presents an application driven approach to create a versatile toolchai... more The work-in-progress paper presents an application driven approach to create a versatile toolchain to create avatars. It targets the lack of an economic solution that enables the integration of avatars on multiple platforms and multiple devices. The requirements are based on Active and Assisted Living (AAL) domain-specific research and application-experiences of avatar-based user-interaction in the last decade. The created toolchain consists of phases: i) pre-processing, ii) processing and iii) optional post-processing. To achieve a high level of anthropomorphism not only the visual representation and synchronized voice is required but also combined movements, emotions and in particular affective reactions on the user's behavior. The flexible toolchain enables an integration of ongoing and future improvements. The first results are promising and show that an economic but high-quality solution that can be integrated easily in different services can be developed.
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Entropy, 2016
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Journal of Ambient Intelligence and Smart Environments, 2016
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Papers by Christopher Mayer