Intelligent Biosignal Processing in Wearable and Implantable Sensors

This reprint provides a collection of papers illustrating the state-of-the-art of smart processing of data coming from wearable, implantable or portable sensors. Each paper presents the design, databases used, methodological background, obtained results, and their interpretation for biomedical applications. Revealing examples are brain–machine interfaces for medical rehabilitation, the evaluation of sympathetic nerve activity, a novel automated diagnostic tool based on ECG data to diagnose COVID-19, machine learning-based hypertension risk assessment by means of photoplethysmography and electrocardiography signals, Parkinsonian gait assessment using machine learning tools, thorough analysis of compressive sensing of ECG signals, development of a nanotechnology application for decoding vagus-nerve activity, detection of liver dysfunction using a wearable electronic nose system, prosthetic hand control using surface electromyography, epileptic seizure detection using a CNN, and premature ventricular contraction detection using deep metric learning. Thus, this reprint presents significant clinical applications as well as valuable new research issues, providing current illustrations of this new field of research by addressing the promises, challenges, and hurdles associated with the synergy of biosignal processing and AI through 16 different pertinent studies. Covering a wide range of research and application areas, this book is an excellent resource for researchers, physicians, academics, and PhD or master students working on (bio)signal and image processing, AI, biomaterials, biomechanics, and biotechnology with applications in medicine

Intestinal innervation and its role in mucosal damage and inflammation

The regulatory role of the autonomic nervous system (ANS) in intestinal inflammation and immunity is widely acknowledged. In this thesis, we investigated mediating pathways and demonstrated a pivotal role for the spleen. We studied the effect of electrical splenic nerve bundle stimulation (SpNS) in a mouse model of experimental colitis induced by dextran sulfate sodium and showed that SpNS reduced colitis. Further, we elucidated effects of sympathetic activity on intestinal mucosal homeostasis. Chemical sympathetic denervation through 6-hydroxydopamine led to enhanced intestinal inflammation, and impaired barrier integrity. In contrast, adrenergic receptor stimulation through UK 14,304, a specific receptor agonist, led to increased proliferation and stem cell function. Adrenergic receptor α2A was found to act as molecular delegate of intestinal epithelial sympathetic activity controlling cell proliferation, differentiation, and host defense. The ANS is a complex network activating numerous pathways and therefore effects can be ambiguous and are often challenging to interpret. Our studies increased the understanding of effects of autonomic neuronal activity on intestinal processes, and future studies should continue investigations with not only experimental, but also clinical research. Ultimately, a role for bioelectronic medicine in intestinal immunity and mucosal healing can be allocated and neuromodulatory techniques are to be examined as a plausible treatment modality

Intestinal innervation and its role in mucosal damage and inflammation

The regulatory role of the autonomic nervous system (ANS) in intestinal inflammation and immunity is widely acknowledged. In this thesis, we investigated mediating pathways and demonstrated a pivotal role for the spleen. We studied the effect of electrical splenic nerve bundle stimulation (SpNS) in a mouse model of experimental colitis induced by dextran sulfate sodium and showed that SpNS reduced colitis. Further, we elucidated effects of sympathetic activity on intestinal mucosal homeostasis. Chemical sympathetic denervation through 6-hydroxydopamine led to enhanced intestinal inflammation, and impaired barrier integrity. In contrast, adrenergic receptor stimulation through UK 14,304, a specific receptor agonist, led to increased proliferation and stem cell function. Adrenergic receptor α2A was found to act as molecular delegate of intestinal epithelial sympathetic activity controlling cell proliferation, differentiation, and host defense. The ANS is a complex network activating numerous pathways and therefore effects can be ambiguous and are often challenging to interpret. Our studies increased the understanding of effects of autonomic neuronal activity on intestinal processes, and future studies should continue investigations with not only experimental, but also clinical research. Ultimately, a role for bioelectronic medicine in intestinal immunity and mucosal healing can be allocated and neuromodulatory techniques are to be examined as a plausible treatment modality

Noninvasive Stroke Volume Monitoring by Electrical Impedance Tomography

In clinical practice it is of vital importance to track the health of a patient's cardiovascular system via the continuous measurement of hemodynamic parameters. Cardiac output (CO) and the related stroke volume (SV) are two such parameters of central interest as they are closely linked with oxygen delivery and the health of the heart. Many techniques exist to measure CO and SV, ranging from highly invasive to noninvasive ones. However, none of the noninvasive approaches are reliable enough in clinical settings. To overcome this limitation, we investigated the feasibility and practical applicability of noninvasively measuring SV via electrical impedance tomography (EIT), a safe and low-cost medical imaging modality. In a first step, the unclear origins of cardiosynchronous EIT signals were investigated in silico on a 4D bioimpedance model of the human thorax. Our simulations revealed that the EIT heart signal is dominated by ventricular activity, giving hope for a heart amplitude-based SV estimation. We further showed via simulations that this approach seems feasible in controlled scenarios but also suffers from some limitations. That is, EIT-based SV estimation is impaired by electrode belt displacements and by changes in lung conductivity (e.g. by respiration or liquid redistribution). We concluded that the absolute measurement of SV by EIT is challenging, but trending - that is following relative changes - of SV is more promising. In a second step, we investigated the practical applicability of this approach in three experimental studies. First, EIT was applied on 16 mechanically ventilated patients in the intensive care unit (ICU) receiving a fluid challenge to improve their hemodynamic situation. We showed that the resulting relative changes in SV could be tracked using the EIT lung amplitude, while this was not possible via the heart amplitude. The second study, performed on patients in the operating room (OR), had to be prematurely terminated due to too low variations in SV and technical challenges of EIT in the OR. Finally, the third experimental study aimed at testing an improved measurement setup that we designed after having identified potential limitations of available clinical EIT systems. This setup was tested in an experimental protocol on 10 healthy volunteers undergoing bicycle exercises. Despite the use of subject-specific 3D EIT, neither the heart nor the lung amplitudes could be used to assess SV via EIT. Changes in electrode contact and posture seem to be the main factors impairing the assessment of SV. In summary, based on in silico and in vivo investigations, we revealed various challenges related to EIT-based SV estimation. While our simulations showed that trending of SV via the EIT heart amplitude should be possible, this could not be confirmed in any of the experimental studies. However, in the ICU, where sufficiently controlled EIT measurements were possible, the EIT lung amplitude showed potential to trend changes in SV. We concluded that EIT amplitude-based SV estimation can easily be impaired by various factors such as electrode contact or small changes in posture. Therefore, this approach might be limited to controlled environments with the least possible changes in ventilation and posture. Future research should scrutinize the lung amplitude-based approach in dedicated simulations and clinical trials