Cortical somatosensory evoked potential amplitudes and severity of hypoxic-ischemic encephalopathy after cardiac arrest

Introduction: Bilaterally absent median nerve cortical somatosensory evoked potentials (SSEPs) are a reliable prognostic parameter to early predict poor outcome in comatose cardiac arrest (CA) patients if sufficient recording criteria are fulfilled. However, the prognostic significance of cortical SSEP amplitudes and tolerable cortical noise level remain uncertain. Methods: We investigated the prognostic value of cortical SSEP amplitudes to predict poor and good outcome after CA. First, we prospectively determined cortical broadband SSEP amplitudes and clinical outcome upon intensive care unit discharge. Clinical outcome was assessed according to cerebral performance category (CPC) scale and dichotomized in good (CPC 1 – 3) and poor outcome (CPC 4 – 5). Second, we retrospectively studied amplitudes of high-frequency (600 Hz) SSEP components. Third, we retrospectively investigated cortical broadband SSEP amplitudes and severity of hypoxic-ischemic encephalopathy (HIE) in CPC 5 patients histopathologically evaluated by postmortem brain autopsies and dichotomized into no/mild and severe HIE. Results: Of 293 CA patients, 0.62 μV was the lowest cortical broadband SSEP amplitude of 156 good outcome patients whereas all 78 patients with lower amplitudes had a poor outcome. Prognostic parameters, case reviews and amplitude distribution of CPC 4 patients strongly indicated absence of severe HIE in patients with cortical broadband SSEP amplitudes above 2.5 μV. We detected early and late high-frequency (600 Hz) SSEP components in 146 and 95 of 302 included patients. High amplitudes of late high-frequency (600 Hz) SSEP components were mainly found in patients with high cortical broadband SSEP amplitudes. We assessed severe HIE unlikely in patients with late high- frequency (600 Hz) SSEP component amplitudes above 70 nV. Of 187 deceased CA patients with brain autopsy, the lowest cortical broadband SSEP amplitude in 24 patients with no/mild histopathological HIE was 0.5 μV. We found severe histopathological HIE in all 26 patients with cortical broadband SSEP amplitudes below 0.5 μV of whom 21 patients had bilaterally absent cortical SSEPs. Conversely, considering confounders the highest cortical broadband SSEP amplitude in patients with severe histopathological HIE was 2.7 μV. Conclusion: Cortical noise levels should not exceed 0.5 μV to avoid falsely classifying cortical SSEPs as bilaterally absent in good outcome patients. Bilaterally absent cortical SSEPs and cortical broadband SSEPs below 0.5 μV are reliable prognostic parameters for severe HIE evaluated by clinical outcome and brain autopsy. Cortical broadband SSEP amplitudes above 2.7 μV and late high- frequency (600 Hz) SSEP component amplitudes above 70 nV suggest absence of severe HIE.Einleitung: Bilateral fehlende kortikale somatosensorisch evozierte Potentiale (SSEPs) nach Nervus medianus Stimulation sind unter Beachtung ausreichender Aufnahmestandards ein zuverlässiger Prognoseparameter um frühzeitig ein schlechtes Outcome bei komatösen Patienten nach Herzstillstand vorherzusagen. Allerdings ist die prognostische Bedeutung von kortikalen SSEP Amplituden und tolerierbare kortikale Rauschlevel ungewiss. Methodik: Wir untersuchten die prognostische Wertigkeit von kortikalen SSEP Amplituden um nach Herzstillstand ein schlechtes und gutes Outcome vorherzusagen. Erstens untersuchten wir prospektiv kortikale Breitband-SSEP Amplituden und das klinische Outcome bei Entlassung von der Intensivstation. Das klinische Outcome wurde mit der Cerebral Performance Category (CPC) Skala erfasst und in gutes (CPC 1 – 3) und schlechtes Outcome (CPC 4 – 5) dichotomisiert. Zweitens studierten wir retrospektiv die Amplituden von hochfrequenten (600 Hz) SSEP Komponenten. Drittens evaluierten wir retrospektiv kortikale Breitband-SSEP Amplituden und den Schweregrad der hypoxisch-ischämischen Enzephalopathie (HIE) bei CPC 5 Patienten histopathologisch mit postmortem Hirnautopsien und dichotomisierten in keine/milde und schwere HIE. Ergebnisse: Von 293 Herzstillstandpatienten war 0.62 μV die niedrigste kortikale Breitband-SSEP Amplitude unter 156 Patienten mit gutem Outcome wohingegen alle 78 Patienten mit niedrigeren Amplituden ein schlechtes Outcome hatten. Prognostische Parameter, Fallübersichten und die Amplitudenverteilung von CPC 4 Patienten deuteten stark auf die Abwesenheit schwerer HIE bei Patienten mit kortikalen Breitband-SSEP Amplituden über 2.5 μV hin. Frühe und späte hochfrequente (600 Hz) SSEP Komponenten wurden bei 146 und 95 von 302 inkludierten Patienten detektiert. Hohe Amplituden von späten hochfrequenten (600 Hz) SSEP Komponenten wurden vor allem bei Patienten mit hohen kortikalen Breitband-SSEP Amplituden gefunden. Eine schwere HIE erschien bei Patienten mit späten hochfrequenten (600 Hz) SSEP Komponentamplituden über 70 nV unwahrscheinlich. Von 187 verstorbenen Herzstillstandpatienten mit Hirnautopsie war 0.5 μV die niedrigste kortikale Breitband-SSEP Amplitude bei 24 Patienten mit keiner/milder histopathologischer HIE. Alle 26 Patienten mit kortikalen Breitband-SSEP Amplituden unter 0.5 μV zeigten eine schwere histopathologische HIE von denen 21 bilateral fehlende kortikale SSEPs hatten. Umgekehrt war nach Ausschluss von Störfaktoren 2.7 μV die höchste kortikale Breitband-SSEP Amplitude von Patienten mit schwerer histopathologischer HIE. Schlussfolgerung: Kortikale Rauschlevel sollten 0.5 μV nicht überschreiten um fälschlicherweise SSEPs als bilateral kortikal fehlend zu klassifizieren bei Patienten mit gutem klinischem Outcome. Bilateral fehlende kortikale SSEPs und kortikale Breitband-SSEP Amplituden unter 0.5 μV sind zuverlässige Prognoseparameter für schwere HIE anhand des klinischen Outcomes und Hirnautopsien. Kortikale Breitband-SSEP Amplituden über 2.7 μV und späte hochfrequente (600 Hz) SSEP Komponentamplituden über 70 nV sprechen für die Abwesenheit von schwerer HIE

Survival, but not the severity of hypoxic–ischemic encephalopathy, is associated with higher mean arterial blood pressure after cardiac arrest: a retrospective cohort study

BackgroundThis study investigates the association between the mean arterial blood pressure (MAP), vasopressor requirement, and severity of hypoxic–ischemic encephalopathy (HIE) after cardiac arrest (CA).MethodsBetween 2008 and 2017, we retrospectively analyzed the MAP 200 h after CA and quantified the vasopressor requirements using the cumulative vasopressor index (CVI). Through a postmortem brain autopsy in non-survivors, the severity of the HIE was histopathologically dichotomized into no/mild and severe HIE. In survivors, we dichotomized the severity of HIE into no/mild cerebral performance category (CPC) 1 and severe HIE (CPC 4). We investigated the regain of consciousness, causes of death, and 5-day survival as hemodynamic confounders.ResultsAmong the 350 non-survivors, 117 had histopathologically severe HIE while 233 had no/mild HIE, without differences observed in the MAP (73.1 vs. 72.0 mmHg, pgroup = 0.639). Compared to the non-survivors, 211 patients with CPC 1 and 57 patients with CPC 4 had higher MAP values that showed significant, but clinically non-relevant, MAP differences (81.2 vs. 82.3 mmHg, pgroup < 0.001). The no/mild HIE non-survivors (n = 54), who regained consciousness before death, had higher MAP values compared to those with no/mild HIE (n = 179), who remained persistently comatose (74.7 vs. 69.3 mmHg, pgroup < 0.001). The no/mild HIE non-survivors, who regained consciousness, required fewer vasopressors (CVI 2.1 vs. 3.6, pgroup < 0.001). Independent of the severity of HIE, the survivors were weaned faster from vasopressors (CVI 1.0).ConclusionsAlthough a higher MAP was associated with survival in CA patients treated with a vasopressor-supported MAP target above 65 mmHg, the severity of HIE was not. Awakening from coma was associated with less vasopressor requirements. Our results provide no evidence for a MAP target above the current guideline recommendations that can decrease the severity of HIE

Bewertung des Energieverbrauchs beim Schweißen von Kupfer

In der vorliegenden Arbeit geht es um das Laserschweißen von Kupfer. Dabei wird besonders auf die Nahtqualität geachtet und der Energieverbrauch registriert. Durch die speziellen Materialeigenschaften gestaltet sich das Schweißen dieses Materials sehr schwierig deshalb ist es auch notwendig durch grundlegende Untersuchungen geeignete Prozessparameter zu finden. In dieser Arbeit werden die speziellen Eigenschaften von Kupfer hinsichtlich des Laserschweißens erläutert, geeignete Laserparameter abgeleitet und die Schweißnahtqualität bewertet. Wesentlich sind noch die Durchführung von Schweißversuchen, die Bewertung des Energieverbrauchs und die Bewertung der optischen Eigenschaften der Kupferoberfläche. Anschließend werden die Ergebnisse ausgewertet

Entwicklung eines Technologiekonzeptes zum Laserscribing von Dünnschichtmodulen

In dieser Masterarbeit wird die praktische Umsetzbarkeit eines Konzeptes zur Grabenstrukturierung in Dünnschichtsolarzellen untersucht. Im konkreten handelt es sich um den Ersten von vier Strukturierungsschritten (P1). Es werden die speziellen Anforderungen an den Laserprozess und das Bearbeitungskonzept beschrieben. Ausgehend von Vorversuchen mit verschiedenen Lasergeräten werden praktische Versuche durchgeführt und entsprechend den Anforderungen ausgewertet. Daraus werden die Parameter für ein optimales Ergebnis bestimmt

Float Current Analysis for Fast Calendar Aging Assessment of 18650 Li(NiCoAl)O2/Graphite Cells

Float currents are steady-state self-discharge currents after a transient phase—caused by anode overhang, polarization, etc.—is accomplished. The float current is measured in this study with a standard test bench for five 18650 cells (Samsung 25R) at potentiostatic conditions while the temperature is changed in 5 K steps from 5 °C to 60 °C. The entire test is performed in about 100 days resulting in 12 measurement points per cell potential for an Arrhenius representation. The float current follows the Arrhenius law with an activation energy of about 60 kJ/mol. The capacity loss measured at reference condition shows a high correlation to the results of float currents analysis. In contrast to classical calendar aging tests, the performed float current analysis enables determining the aging rate with high precision down to at least 10 °C. Returning from higher temperatures to 30 °C reference temperature shows reducing float currents at 30 °C for increasing temperature steps that may originate from an hysteresis effect that has to be investigated in future publications

Kalman Filter Tuning Using Multi-Objective Genetic Algorithm for State and Parameter Estimation of Lithium-Ion Cells

To ensure a reliable and safe operation of battery systems in various applications, the system’s internal states must be observed with high accuracy. Hereby, the Kalman filter is a frequently used and well-known tool to estimate the states and model parameters of a lithium-ion cell. A strong requirement is the selection of a suitable model and a reasonable initialization, otherwise the algorithm’s estimation might be insufficient. Especially the process noise parametrization poses a difficult task, since it is an abstract parameter and often optimized by an arbitrary trial-and-error principle. In this work, a traceable procedure based on the genetic algorithm is introduced to determine the process noise offline considering the estimation error and filter consistency. Hereby, the parameters found are independent of the researcher’s experience. Results are validated with a simulative and experimental study, using an NCA/graphite lithium-ion cell. After the transient phase, the estimation error of the state-of-charge is lower than 0.6% and for internal resistance smaller than 4mΩ while the corresponding estimated covariances fit the error well

Optimization of inverse model identification for multi-axial test rig control

Laboratory testing of multi-axial fatigue situations improves repeatability and allows a time condensing of tests which can be carried out until component failure, compared to field testing. To achieve realistic and convincing durability results, precise load data reconstruction is necessary. Cross-talk and a high number of degrees of freedom negatively affect the control accuracy. Therefore a multiple input/multiple output (MIMO) model of the system, capturing all inherent cross-couplings is identified. In a first step the model order is estimated based on the physical fundamentals of a one channel hydraulic-servo system. Subsequently, the structure of the MIMO model is optimized using correlation of the outputs, to increase control stability and reduce complexity of the parameter optimization. The identification process is successfully applied to the iterative control of a multi-axial suspension rig. The results show accurate control, with increased stability compared to control without structure optimization

Optimization of inverse model identification for multi-axial test rig control

Laboratory testing of multi-axial fatigue situations improves repeatability and allows a time condensing of tests which can be carried out until component failure, compared to field testing. To achieve realistic and convincing durability results, precise load data reconstruction is necessary. Cross-talk and a high number of degrees of freedom negatively affect the control accuracy. Therefore a multiple input/multiple output (MIMO) model of the system, capturing all inherent cross-couplings is identified. In a first step the model order is estimated based on the physical fundamentals of a one channel hydraulic-servo system. Subsequently, the structure of the MIMO model is optimized using correlation of the outputs, to increase control stability and reduce complexity of the parameter optimization. The identification process is successfully applied to the iterative control of a multi-axial suspension rig. The results show accurate control, with increased stability compared to control without structure optimization