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The flow control of inspiratory valves for mechanical ventilation is a crucial element of the overall functionality as it mainly governs precision and safety. However, control tuning can be challenging as the widely used magnetic actuation principle comes with a hysteresis shaped characteristic. As a result, the production of ventilators is highly dependent on specific valves and therefore vulnerable if supply chains are interrupted as during the pandemic. An approach which is capable of providing a reliable control for a variety of standard solenoid valves would be beneficial. Therefore, this work examines different models of hysteresis and their precision when being applied to actual measurement data of high pressure solenoid valves as a foundation for a following model-based control approach which can be either feedback or feedforward. Regarding the precision, the Prandtl-Ishlinskii (PI) model outperformed alternative approaches (MAEbelow2.5 L/ min) for the chosen parameters which is why the model is described for fitting both the forward and inverse case.

Cardiovascular diseases are a leading cause of mortality worldwide. Thus, critically ill patients require continuous monitoring of cardiovascular indicators, such as the left ventricular volume (LVV). Although continuous hemodynamic monitoring of patients is desirable, due to technical limitations, current measurement technologies either require manual intervention of the physician or only provide inaccurate results. Intracardiac impedance measurements are a promising approach for continuous assessment of cardiac function. However, developing and evaluating these methods requires a simulation model of the left ventricle with cardiac motion during an entire cardiac cycle. While many models exist for a fixed ventricle size, to date, no freely available models incorporate time and represent the cardiac motion during a complete cardiac cycle. Therefore, we developed four cardiacmechanical left ventricular models with varying ventricle sizes and complexities. Each model focuses on a different aspect of the geometric shape, thus allowing an isolated analysis of the different influences. This paper presents the development of the models and initial results of the impedance analysis. All measured admittances exhibit a high resemblance for all models and a strong, non-linear correlation with the LVV. A comparison between the models shows how the different geometries affect the impedance. The models, thus, provide a useful basis for the development of LVV estimation algorithms.

Pacemaker spike detection is an important step in monitoring paced patients. Capacitive ECG facilitates unobtrusive monitoring of subjects during daily routines such as driving. Robust algorithms are required to deal with low signal quality and artifacts, e.g. by employing fusion of multiple signal channels. Due to the low signal-to-noise ratio of the measurement, there are limitations to detection accuracy compared to conventional ECG monitors. Especially low voltage stimulations such as bipolar pacemaker spikes are hard to detect. We present a convolutional network approach to improve on recent signal processing algorithms.We show a realistic evaluation of its performance using leave-one-subject-out cross validation (LOOCV), its dependence on the size of the receptive field, and an estimation of an upper performance bound.

Bioimpedance measurements use current or voltage sources to inject an excitation signal into the body. These sources require a high bandwidth, typically from 1 kHz to 1 MHz. Besides a low common mode, current limitation is necessary for patient safety. In this paper, we compare a symmetric enhanced Howland current source (EHCS) and a symmetric voltage source (VS) based on a non-inverting amplifier between 1 kHz and 1 MHz. A common mode reduction circuit has been implemented in both sources. The bandwidth of each source was optimized in simulations and achieved a stable output impedance over the whole frequency range. In laboratory measurements, the output impedance of the EHCS had its -3 dB point at 400 kHz. In contrast, the VS reached the +3 dB point at 600 kHz. On average over the observed frequency range, the active common mode compensation achieved a common mode rejection of -57.7 dB and -71.8 dB for the EHCS and VS, respectively. Our modifications to classical EHCS and VS circuits achieved a low common mode signal between 1 kHz and 1 MHz without the addition of complex circuitry, like general impedance converters. As a conclusion we found VSs to be superior to EHCSs for bioimpedance spectroscopy due to the higher bandwidth performance. However, this only applies if the injected current of the VS can be measured.

Volume measurement is beneficial in left ventricular assist device (LVAD) therapy to quantify patient demand. In principle, an LVAD could provide a platform that allows bioimpedance measurements inside the ventricle without requiring additional implants. Conductance measured by the LVAD can then be used to estimate the ventricular radius, which can be applied to calculate ventricular volume. However, established methods that estimate radius from conductance require elaborate individual calibration or show low accuracy.

Nowadays, rotary blood pumps for the treatment of end-stage heart failure patients are usually fixed-speed controlled. Therefore, without sufficient heart activity, patients may reveal reduced blood flow pulsatility. However, there is evidence that pulsatile flow reduces adverse events. Furthermore, optimized pump flow profiles could be used to achieve certain control objectives. Therefore, a pump flow model is identified and subsequently used to design a control system with an iterative learning controller to generate desired pump flow patterns. Either a flow sensor is required for direct measurement or the flow can be estimated from pressure sensor readings using the proposed pump flow model. For comparison, a PID controller with disturbance feedforward control is also designed. Furthermore, the robustness against respiratory sinus arrhythmia is analyzed.

Ventricular Assist Devices (VADs) are used to treat patients with cardiogenic shock. As the heart is unable to supply the organs with sufficient oxygenated blood and nutrients, a VAD maintains the circulation to keep the patient alive. The observation of the patient's hemodynamics is crucial for an individual treatment; therefore, sensors to measure quantifiable hemodynmaic parameters are desirable.

The feasibility of bioimpedance spectroscopy (BIS) techniques for monitoring intradialytic changes in body fluids is advancing. The aim of this study was to compare the knee-to-knee (kkBIS) with the traditional whole-body (whBIS) with respect to continuous assessment of fluid volume status in hemodialysis patients. Twenty patients divided into two groups, hemodynamically stable and unstable, were recruited. Bioimpedance data from two different electrodes configurations (hand-to-foot and knee-to-knee) were collected and retrospectively analysed. A good correlation between the two methods with respect to changes in extracellular resistance (Re) and Re normalized for ultrafiltration volume (ΔRe/UFV) with p < 0.001 was observed. The relationship between relative change (%) in ΔRe and that in patient weight was most notable with kkBIS (4.82 ± 3.31 %/kg) in comparison to whBIS (3.69 ± 2.90 %/kg) in unstable patients. Furthermore, results based on kkBIS showed a reduced ability of the thigh compartments to keep up with the volume changes in the trunk for unstable patients. kkBIS provided a comparable sensitivity to whBIS even in patients at risk of intradialytic hypotension while avoiding the need for the complex implementation imposed by whBIS or other configurations.

Lung pathologies such as edema, atelectasis or pneumonia are potentially life threatening conditions. Especially in critically ill and mechanically ventilated patients, an early diagnosis and treatment is crucial to prevent an Acute Respiratory Distress Syndrome [1]. Thus, continuous monitoring tool for the lung condition available at the bedside would be highly appreciated. One concept for this is Electrical Impedance Tomography (EIT). In EIT, an electrode belt of typically 16 or 32 electrodes is attached at the body surface and multiple impedance measurements are performed. From this, the conductivity change inside the body is reconstructed in a two-dimensional image. In various studies, EIT proved to be a useful tool for quantifying recruitment maneuvers, the assessment of the ventilation homogeneity, the detection of lung edema or perfusion monitoring [2, 3, 4, 5]. Nevertheless, the main problem of EIT is the low spatial resolution (compared to CT) and the limitation to two dimensional images. In this paper, we try to address the latter issue: Instead of projecting conductivity changes onto a two-dimensional image, we adjust electrode positions to focus single tetrapolar measurements to specific, three-dimensional regions of interest. In earlier work, we defined guidelines to achieve this focusing [6, 7]. In this paper, we demonstrate in simulations and in a water tank experiment that applying these guidelines can help to detect pathologies in specific lung regions.

The weakened heart is supported by a left ventricular assist device (LVAD) to supply the heart muscle with oxygenated blood. In case the heart muscle recovers during LVAD therapy, the patient has to be weaned from the device. To date, there is no adequate method to detect heart muscle recovery in LVAD therapy. In order to establish a novel method based on the measurement of electric conductivity, this study presents a silicone model of a ventricle mock-up to simulate the electrical properties of cardiac muscle tissue. Previously, it has been shown that the electrical properties of myocardial tissue change during ischemia, so that these changes are a possible estimate for measuring the condition of myocardial tissue. To this purpose, this study presents a casting process for a ventricle model and describes the materials used to imitate the electrical properties of the heart muscle to obtain conductive material. Initial results showed that the higher the carbon concentration in the silicone, the higher the conductivity of the silicone samples. The measurements were performed at different frequencies and the samples were analyzed for homogenization.

A medical expert system of automatic artificial ventilation is set up in a star topology with additional closed-loop hemodynamic control. Arterial blood pressure (MAP) is controlled by noradrenaline (NA) as a controlling variable. The overall patient-in-the-loop expert system can intensively and intelligently perform a long-term treatment based on the Acute Respiratory Distress Syndrome Network (ARDSNet) protocol. Three main goals are actively carried out, namely the stabilization and regulation of oxygenation, plateau pressure and blood pH value. The developed system shows a distinctive experimental result based on a 31.5-kg pig, in order to fulfil the ventilatory goals and to ensure proper systemic perfusion. Hence, this system has enormous potentials to realize a commercial system for individual patient with ARDS.

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