52 research outputs found
The noncircular shape of FLOWATCH-PAB prevents the need for pulmonary artery reconstruction after banding
No full textObjective: To evaluate the differences between non-circular shape of FloWatch-PAB and conventional pulmonary artery (PA) banding. Methods: Geometrical analysis. Conventional banding and FloWatch-PAB perimeters were plotted against cross-sections. Computational fluid dynamics (CFD) model. CFD compared non-circular FloWatch-PAB cross-sections with conventional banding regarding pressure gradients. Clinical data. Seven children, median age 2 months (7 days to 3 years), median weight 4.2 kg (3.2–9.8 kg), with complex congenital heart defects underwent PA banding with FloWatch-PAB implantation. Results: Geometrical analysis. Conventional banding: progressive reduction of cross-sections was accompanied by progressive reduction of PA perimeters. FloWatch-PAB: with equal reduction of cross-sections the PA perimeter remained constant. CFD model. Non-circular and circular banding provided same trans-banding pressure gradients for same cross-sections at any given flow. Clinical data. Mean PA internal diameter at banding was 13.3 ± 4.5 mm. After a mean interval of 5.9 ± 3.7 months, all children underwent intra-cardiac repair and simple FloWatch-PAB removal without PA reconstruction. Mean PA internal diameter with FloWatch-PAB removal increased from 3.0 ± 0.8 to 12.4 ± 4.5 mm (normal mean internal diameter for the age = 9.9 ± 1.6). No residual pressure gradient was recorded in correspondence of the site of the previous FloWatch-PAB implantation in 6/7 patients, 10 mmHg peak and 5 mmHg mean gradient in 1/7. Conclusions: The non-circular shape of FloWatch-PAB can replace conventional circular banding with the following advantages: (a) the pressure gradient will remain essentially the same as for conventional circular banding for any given cross-section, but with significantly smaller reduction of PA perimeter; and (b) PA reconstruction at the time of de-banding for intra-cardiac repair can be avoided
Construction with wood-cement compounds and timber
No full textPourable lightweight wood-based concretes (or wood-cement compounds, WCCs, respectively) were developed and assessed with respect to struc tural properties, targeting their structural combination with timber. Composite slab and wall elements were conceived and evaluated experimentally and analytically in full-scale tests up to rupture and for long-term behaviour. Practical structural design approaches were also derived. Further assessments targeted properties of thermal and fire protection, recyclability, eco-balance and economic competitiveness. Possible use in residential, office and school buildings was proven
Propagation and reflection of pulse waves in flexible tubes and relation to wall properties
No full textThis thesis was submitted for the degree of Docter of Philosophy and awarded by Brunel University.The wall properties of the arteries play an important role in cardiovascular function. Stiffness of large artery is predictive of cardiovascular events. To understand the function of the cardiovascular system, special attention should be paid to the understanding of pulse wave propagation, because pulse waves carry information of the cardiovascular function, and provide information which can be useful for the prevention and diagnosis of diseases. This thesis presents a series of in vitro experimental studies of wave propagation, wave reflection and determination of mechanical properties of flexible vessels.
In this thesis, several studies have been included: 1) applied and compared foot-to-foot, PU-loop and lnDU-loop methods for determination of wave speed in flexible tubes and calf aortas; 2) investigated the variation of local wave speed determined by PU-loop with proximity to the reflection site; 3) investigated using wave intensity analysis (WIA) as the analytical technique to determine the reflection coefficient; 4) developed a new technique which based on one-point simultaneous measurements of diameter and velocity to determine the mechanical properties of flexible tubes and calf aortas.
In the first study, it is found wave speeds determined by PU-loop and lnDU-loop methods are very similar, and smaller than those determined by foot-to-foot method. The timing of arrival time of reflected wave based on diameter and velocity technique highly agreed with the corresponding timing based on pressure and velocity technique. The shapes of forward and backward non-invasive wave intensities based on diameter and velocity are very similar with the corresponding shapes based on pressure and velocity. Although the density term is not part of the equation, the lnDU-loop method for determining local wave speed is sensitive to the fluid density. In the second study, it is found wave speed measured by PU-loop is varied with proximity to the reflection site. The closer the measurement site to the reflection site, the greater the effect upon measured wave speed; a positive reflection caused an increase in measured wave speed; a negative reflection caused a decrease in measured wave speed. Correction iteration process was also considered to correct the affected measured wave speed. In the third study, it is found, reflection coefficient determined by pressure, square roots of wave intensity and wave energy are very close, but they are different from reflection coefficient determined by wave intensity and wave energy. Due to wave dissipation, the closer the measurement site to the reflection site, the greater is the value of the local reflection coefficient. The local reflection coefficient near the reflection site determined by wave intensity and wave energy are very close to the theoretical value of reflection coefficient. In the last study I found that distensibility determined by the new technique which utilising lnDU-loop is in agreement with that determined from the pressure and area which obtained from tensile test in flexible tubes; distensibility determined by the new technique is similar to those determined in the static and dynamic distensibility tests in calf aortas; Young’s modulus determined by the new technique are in agreement with that those determined by tensile tests in both flexible tubes and calf aortas.
In conclusion, wave speed determined by PU-loop and lnDU-loop methods are very similar, the new technique lnDU-loop provides an integrated noninvasive system for studying wave propagation; wave speed determined by PU-loop is affected by the reflection, the closer the measurement site to the reflection site, the greater the change in measured wave speed; WIA could be used to determine local reflection coefficient when the measurement site is close to the reflection site; the new technique using measurements of diameter and velocity at one point for determination of mechanical properties of arterial wall could potentially be non-invasive and hence may have advantage in the clinical setting
Lernen im Praktischen Jahr: Herausfordernde klinische Fälle jenseits des Bereichs des "Medical Expert". Eine Analyse studentischer Fallvignetten
No full textBackground: During clinical clerkships students experience complex and challenging clinical situations related to problems beyond the domain of the "Medical Expert". Workplace routine may leave little opportunity to reflect on these situations. The University of Zurich introduced a mandatory course directly after the clinical clerkship year (CCY) to work up these situations. Prior to the course each student submitted a vignette on a case he or she had perceived challenging during the CCY and which was not related to the domain of the "Medical Expert" role. In this paper we want to characterize these cases in respect to most prominent themes and related CanMEDS roles. The goal was to inform clinical supervisors about potential teaching demands during the CCY. Methods: All case vignettes submitted by a years' cohort were analysed by three researchers in two ways: for the clinical characteristics and the main theme of the underlying problem and the most prominent CanMEDS roles involved. Themes of the underlying problem were aggregated to overarching topics and subsequently to main categories by pragmatic thematic analysis.Results: 254 case vignettes covered the whole spectrum of clinical disciplines. A wide range of underlying themes could be assigned to five main categories: "communication within team" (23.2%), "communication with patients and relatives" (24.8%), "patient behavior and attitudes" (18.5%), "clinical decision making" (24.0%), and "social and legal issues" (9.4%). Most frequent CanMEDS roles were "Communicator" (26.9%) and "Professional" (23.5%).Conclusions: Cases students perceived as challenging beyond the "Medical Expert" were reported from all clinical disciplines. These were mainly related to communicational and professional issues, mirrored by the CanMEDS roles "Communicator" and "Professional". Therefore, supervisors in clinical clerkships should put an additional teaching focus on communication and professionalism.Hintergrund: Während des Praktischen Jahrs (in der Schweiz: Wahlstudienjahr, WSJ) werden die Studierenden mit komplexen Problemen konfrontiert, die oft nicht allein mit Mitteln im Bereich der CanMEDS-Rolle "Medical Expert" gelöst werden können. Während der Arbeit im Spital bleibt meist wenig Zeit diese Situationen aufzuarbeiten. Die Universität Zürich hat daher einen Pflichtkurs eingeführt, welcher den Studierenden direkt nach dem Wahlstudienjahr Raum zur Reflexion gibt. Als Kursgrundlage reichen alle Studierenden eine Vignette zu einem klinischen Fall ein, den sie im WSJ als besonders herausfordernd erlebt haben und dessen Problem ausserhalb des Bereichs des "Medical Experts" lag. Diese Arbeit untersucht, welche Themenbereiche in diesen Fallvignetten am häufigsten angesprochen wurden und im Bereich welcher CanMEDS-Rollen die Problematik angesiedelt war. Die Ergebnisse sollen klinischen Betreuenden helfen, mögliche herausfordernde Situationen zu erkennen und diese mit den Studierenden zu thematisieren.Methoden: Drei klinisch erfahrene Ärzte analysierten sämtliche Fallvignetten eines Studienjahres aus zwei Perspektiven: bezüglich der Hauptthematik des zugrundeliegenden Problems und bezüglich der hauptsächlich betroffenen CanMEDS-Rolle. Mittels induktiver Verfahren wurden die Hauptthematiken zu übergeordneten Kategorien zusammengefasst. Resultate: 254 eingereichte Fälle verteilten sich über sämtliche medizinische Fachgebiete. Die Hauptthematiken konnten fünf übergeordneten Kategorien zugewiesen werden: "Kommunikation im Team" (23.2%), "Kommunikation mit Patienten und Angehörigen" (24.8%), "Verhalten und Haltungen der Patienten" (18.5%), "ärztliche Entscheidungsfindung" (24.0%) und "Soziale und rechtliche Probleme" (9.4%). Die am häufigsten vertretenen CanMEDS-Rollen waren "Communicator" (26.9%) und "Professional" (23.5%).Fazit: Die Vignetten zu herausfordernden klinischen Fällen stammten aus sämtlichen medizinischen Fachgebieten. Am häufigsten wurden Probleme in den Bereichen "Kommunikation" und "Professionelles Handeln" identifiziert. Dies spiegelt sich wieder in den am häufigsten vertretenen CanMEDS-Rollen "Communicator" und "Professional". Diese Befunde sollten betreuende Ärztinnen und Ärzte dafür sensibilisieren, dass Studierende im Wahlstudienjahr herausfordernde Situationen in diesen Bereichen erleben. Die Thematisierung im klinischen Kontext erscheint daher sinnvoll
Doppler-guided regulation of a telemetrically operated adjustable pulmonary banding system
No full textObjectivesWe report on the Doppler-assessed regulation of an adjustable pulmonary artery band (PAB) in an animal model and in our first group of patients.BackgroundIndications for pulmonary artery banding have expanded to include patients requiring a late arterial switch. A telemetry-operated, fully implantable, adjustable PAB system (FloWatch- PAB, Endoart SA, Lausanne, Switzerland) has been developed to facilitate these operations.MethodsThe device was implanted in 13 minipigs (age one to five months, weights 3.2 to 12.0 kg). Themain study was performed on nine minipigs with adjustments of the PAB at implantation and at 1, 3, 5, 8, and 12 weeks after, assessed by Doppler pressure gradients. Explanation was performed 12 weeks after surgery. A long-term histology study (6 months and 14 months after surgery) was done on the other four minipigs. After approval by the ethics committee, the device was implanted in eight patients with weights between 2.8 and 9 kg to decrease pulmonary blood flow and pressure and to retrain the left ventricle beforearterial switch. The device was progressively tightened, with increasing transband Doppler gradients. Follow-up was one to three months.ResultsAn excellent correlation between transbanding systolic pressure gradient and degree of PAB constriction was encountered in the minipig study as well as in the human setting. No early or late deaths or reoperations occurred. Malfunction of the device was noted in three of 21 implanted devices. Two were related to surgically inflicted damage at implantation and one to an electronic problem that was fixed by resetting the control device.ConclusionsThe device offers a Doppler-controllable adjustment of pulmonary blood flow. It permits controlled tightening and release of the band, which improves perioperative and postoperative courses and decreases surgical interventions to adjust tightness of the band. It allows a protracted occlusion protocol, which may provide the best effect on retraining the left ventricle
On the monitoring of surface displacement in connection with volcano reactivation in Tenerife, Canary Islands, using space techniques
No full textGeodetic volcano monitoring in Tenerife has mainly focused on the Las Cañadas Caldera, where a geodetic micronetwork and a levelling profile are located. A sensitivity test of this geodetic network showed that it should be extended to cover the whole island for volcano monitoring purposes. Furthermore, InSAR allowed detecting two unexpected movements that were beyond the scope of the traditional geodetic network. These two facts prompted us to design and observe a GPS network covering the whole of Tenerife that was monitored in August 2000. The results obtained were accurate to one centimetre, and confirm one of the deformations, although they were not definitive enough to confirm the second one. Furthermore, new cases of possible subsidence have been detected in areas where InSAR could not be used to measure deformation due to low coherence. A first modelling attempt has been made using a very simple model and its results seem to indicate that the deformation observed and the groundwater level variation in the island may be related. Future observations will be necessary for further validation and to study the time evolution of the displacements, carry out interpretation work using different types of data (gravity, gases, etc) and develop models that represent the island more closely. The results obtained are important because they might affect the geodetic volcano monitoring on the island, which will only be really useful if it is capable of distinguishing between displacements that might be linked to volcanic activity and those produced by other causes. One important result in this work is that a new geodetic monitoring system based on two complementary techniques, InSAR and GPS, has been set up on Tenerife island. This the first time that the whole surface of any of the volcanic Canary Islands has been covered with a single network for this purpose. This research has displayed the need for further similar studies in the Canary Islands, at least on the islands which pose a greater risk of volcanic reactivation, such as Lanzarote and La Palma, where InSAR techniques have been used already
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