07 / 2023 – 12 / 2023
Aging populations worldwide are contributing to an increasing number of people suffering from cardiovascular diseases . In hospitals, the health status of patients at risk for deterioration is assessed using vital sign monitoring . Changes in vital parameters, especially those evaluating the hemodynamics of the heart, can reveal the presence of critical medical conditions. With each heartbeat, a mechanical pulse wave propagates through the vessels accompanied by the vibrations generated by contraction and valve closure .
Current gold standard methods, including the electrocardiogram (ECG) for evaluating the heart’s electrical activity , demand permanent skin contact, entailing trained medical staff to ensure correct placement and wiring to diagnostic machines. Since this setup restricts patients’ movements and therefore limits their autonomy and participation in daily life activities, it is mainly feasible in intensive care facilities. Conversely, a large collective of patients could also benefit from continuous monitoring in general care units  and homecare scenarios .
One potential solution which has been extensively researched over the last four decades is vital sign monitoring using radar systems . Evaluation of reflected electromagnetic waves allows the distance estimation between radar antenna and body surface, which is modulated by movements, respiration, and cardiac vibrations. Employing this method, Schellenberger et al. developed a system for continuous and contactless in-bed monitoring of heart and respiration rate . Will et al. discovered in their investigation of diverging radar-recorded pulse wave shapes that their configuration is highly dependent on the measured region of interest . Taking the analysis one step further, they introduced heart sound detection using radar, reporting a high correlation in time of occurrence and signal shape between radar-recorded high-frequency components and the phonocardiogram (PCG) signal . Furthermore, they showed based on measurements on both neck and thorax that the timing of heart sounds is dependent on the distance to their origin.
Apart from the work by Will et al.  , most research in this field concentrates on the development of algorithms for heart and respiration rate determination or heartbeat segmentation solely from measurements acquired from the chest region, e.g.,  . Nevertheless, considering that variations in pulse wave configuration can indicate pathophysiological changes , investigating local signal shapes and timings could offer valuable insights into the presence or progression of cardiovascular diseases.
Therefore, the goal of this master’s thesis is to extend the knowledge about pulse wave and heart sound propagation within the human body. In the scope of this work, a study with healthy participants will be conducted as a part of the EmpkinS collaborative research center . Radar recordings will be performed at distinct locations across the body with nearby photoplethysmogram (PPG), reference for pulse waves, and PCG, reference for heart sounds, measurements while the participants are laying at rest on a mattress. Synchronously, ECG and an impedance cardiogram to determine respiration will be recorded. Using this multimodal dataset, the feasibility of detecting cardiac activity at distal body locations will be analyzed. Given the feasibility, morphology and temporal properties among measurement locations will be investigated to derive descriptive parameters capable of effectively characterizing the observed alterations.
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