Maschinelle Beatmung kann eine vorbestehende Lungenerkrankung weiter aggravieren und das Lungenparenchym zuvor lungengesunder Patienten schädigen. Pulmonale Atelektasen können diese Schädigung noch verstärken. Aus diesem Grund ist es erstrebenswert das Auftreten von Atelektasen frühzeitig zu erkennen und zu quantifizieren, um Gegenmaßnahmen wie Rekrutierung oder PEEP-Applikation zu ergreifen. Den aktuellen Goldstandard zur Detektion und Quantifizierung von Belüftungsstörungen stellt die quantitative Analyse mittels Computertomographie (qCT) dar, welche jedoch nur mit hohem Aufwand und potenziellen Risiken für den Patienten durchführbar ist. Wir untersuchten daher anhand von 14 Schafen mit gesunden Lungen die Beziehung zwischen Atelektasen und intrapulmonaler Shuntfraktion sowie dem arteriellen Sauerstoffpartialdruck (PaO2) mit dem Hintergrund, eine möglichst bettseitig durchführbare Alternative zur qCT zum Zwecke der Quantifizierung der pulmonalen Atelektasen zu erhalten. Die Quantifizierung der Atelektasen könnte es ermöglichen, die Notwendigkeit einer Beatmungsoptimierung festzustellen und deren Erfolg zu beurteilen. Hierzu wurden die o.g. Schafe standardisiert mit einer inspiratorischen Sauerstofffraktion von 1 maschinell beatmet und das nichtbelüftete Lungengewebe mittels qCT quantifiziert. Parallel wurden der arterielle und gemischt-venöse Sauerstoffpartialdruck gemessen sowie die Shuntfraktion berechnet. Mittels Regressionsanalyse konnte eine starke Korrelation zwischen nichtbelüftetem Lungengewebe und natürlichem Logarithmus des PaO2 (R2=0,8) einerseits und der Shuntfraktion (R2=0,83) andererseits aufgezeigt werden. Aufgrund der Ergebnisse scheint es möglich über eine einfache Messung des PaO2 oder Berechnung des Shunts Rückschlüsse auf das Ausmaß der Atelektasen zu ziehen und so durch geeignete Gegenmaßnahmen die beatmungsassoziierte Schädigung von Lungenparenchym zu reduzieren.

Zugl.: Giessen, Universiẗat, Diss., 2008.

Zugl.: Giessen, Universiẗat, Diss., 2008.

Freie Universiẗat, Diss., 2004--Berlin. / Dateiformat: zip, Dateien im PDF-Format. Erscheinungsjahr an der Haupttitelstelle: 2004.

Intrapulmonary arteriovenous anastomoses (IPAVA) are vascular conduits through which blood flow bypasses the pulmonary circulation, and does not participate in pulmonary gas exchange. Blood flow through IPAVA (QIPAVA) is known to increase with increasing cardiac output, such as exercise, and while breathing normobaric, hypoxic gas at rest or during exercise. Previous studies demonstrate that QIPAVA is decreased at rest and during exercise in hypobaria compared to equivalent normobaric conditions. Studies involving postural changes have shown that QIPAVA may change with body position. In human studies, QIPAVA is measured either by transthoracic saline contrast echocardiography (TTSCE) or by injection of 99mTc-labeled macroaggregates of albumin (99mTc-MAA). It is unknown if discrepancies in measuring QIPAVA in normobaria and hypobaria, and in different body positions, represent real physiological changes or if they are methodological artifacts. In Chapter IV, the effect of hypobaria on QIPAVA was investigated. QIPAVA was reduced during exercise in hypobaria in normoxia and hypoxia compared to normobaric conditions, however gas exchange efficiency was unimpaired. This suggests that pulmonary blood flow may change in hypobaria such that blood flow is directed away from IPAVA. Alternatively, it may suggest that saline contrast is less stable at high altitude and not detected by TTSCE. In Chapter V, the effect of changing body position on QIPAVA as detected by TTSCE was investigated in human subjects at rest. No significant changes were observed in QIPAVA with postural changes. In Chapter VI, a perfusion model was used to investigate behavior of saline contrast microbubbles, MAA, and microspheres (20 µm and 50 µm diameter) encountering a vertical bifurcation. The results indicated that microbubbles and 20 µm microspheres tend to enter the upper branch of the bifurcation, whereas MAA and 50 µm microspheres tend to enter the lower branch. In Chapter VII, the effect of atmospheric pressure on the initial microbubble radius (Ro) of agitated saline contrast microbubbles was investigated. The results of this study demonstrated that the Ro of microbubbles created at sea level pressure was significantly smaller than Ro of microbubbles created at higher altitudes (1,668 m and 5,260 m). / 2019-01-09

Proefschrift Maastricht. / Lit.opg. en samenvatting in het Nederlands.

<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e., if it is made of passive components such as resistors and inductors.</p> <p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p> <p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p> <p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p>

No description available.

Resumo: Os sistemas de drenagem externa são componentes empregados para drenagem do excesso do fluido cefalorraquidiano (produzido no cérebro e contido nos ventrículos cerebrais) para um recipiente coletor, disposto fora do corpo humano. Em geral esses sistemas são compostos de um cateter ventricular, uma tubagem e uma bolsa de drenagem. Esses sistemas são utilizados em determinados procedimentos médicos e permitem, adicionalmente, a monitoração da pressão intracraniana, a coleta de materiais para análise e infusão de medicamentos. Entretanto, tais dispositivos não possuem um mecanismo que interrompa o escoamento do líquido cefalorraquidiano, quando o sistema é submetido a sensíveis variações de pressões hidrostáticas, seja pelo posicionamento indevido da bolsa de drenagem muito abaixo da cabeça do paciente, ou quando o paciente levanta-se subitamente, favorecendo a ocorrência do chamado efeito sifão e, como resultado, a hiperdrenagem desse fluido. A exposição do usuário à hiperdrenagem, mesmo que em curto intervalo de tempo, provoca lesões irreversíveis ao sistema nervoso do paciente. No presente trabalho, é proposto e ensaiado um mecanismo anti-sifão, com diferentes características construtivas, acoplado a um determinado sistema de drenagem externa, com o objetivo de fornecer maior proteção ao usuário. Experimentalmente, para a obtenção do desempenho hidrodinâmico do conjunto, utilizou-se a coleta automatizada de dados referentes à vazão de fluido com relação aos gradientes de pressão impostos. Parte dos modelos de mecanismo anti-sifão sugeridos demonstram adequada funcionalidade quando acoplados ao sistema de drenagem externa, oferecendo, assim, a possibilidade de uma proteção adicional ao usuário. / Abstract: Neurosurgical devices known as "External drainage systems" are hermetic devices employed to accomplish continuous or intermittent drainage of cerebrospinal fluid (CSF) excess caused by production /absorption imbalance. This hermetic system stores the CSF through a tubing and collection bag. In addition, this system allows for intracranial pressure monitoring (ICP), obtention of CSF sampling for biochemical analysis and intrathecal infusion of drugs. However, such devices do not incorporate a safe mechanism which would interrupt the flux in case of excessive drainage. This clinical situation is not uncommon, ocurring whenever the system is open and submitted to a sudden pressure drop, generated by the undue relative positioning of the collection bag, either by situating below the patientþs head or because the patient suddenly uprighting in the bed. Both conditions favors a physical phenomenon called syphoning effect, well known in neurosurgery. This undesirable side-effect, even for a short period of time, may compromise and even lead to irreversible damage to the brain. This project refers to the development of an anti-siphon device to prevent such side-effects. In order to accomplish this task, a special bench test has been developed. An automated data acquisition system has been employed in order to develop the experiments. Several models of anti-siphon device and pressure gradients were tested. Some models have shown a good performance and were suitable for clinical use, offering an additional protection to the patient. / Orientador: Edson Del Rio Vieira / Coorientador: Sérgio Said Mansur / Banca: José Luiz Gasche / Banca: Ricardo Augusto Mazza / Mestre

Regensburg, Univ., Diss., 2009