26 research outputs found
Failed coronary artery bypass anastomosis detected by intraoperative coronary flow measurement
No full textObjectives: To assess intraoperative flow of arterial and venous coronary grafts after myocardial revascularization which may allow early detection of low flow situations, especially during minimally invasive coronary bypass surgery (MIDCAB), and lead to immediate correction of technical problems. Methods: In two patients with severe and diffuse multi-vessel disease the left internal mammary artery (IMA) was connected to the left anterior descending artery (LAD). During reperfusion, the flow was measured in the IMA and vein grafts using a transit time flow meter. Results: In both cases the IMA showed only a systolic pendulating flow curve with a mean flow of 0–1 ml/min and a high resistance. Manual IMA assessment revealed an adequate pulsation. Both distal IMA anastomoses were re-explored on cardiopulmonary bypass yielding an initial flow of 7 and 14 ml/min, respectively. After treatment with papaverine/adenosine the IMA flow increased from 7 to 26 ml/min (coronary flow reserve (CFR)=3.7) and from 14 to 46 ml/min (CFR=3.3), respectively. Conclusion: Intraoperative flow assessment of IMA and venous bypass grafts can be recommended to monitor flow; especially during MIDCAB procedures
Modelling effect of coarse aggregates on oxygen transport and corrosion products precipitation in reinforced concrete
No full textThe structure of concrete, in particular the microstructure of the steel-concrete interface (SCI), can significantly affect corrosion of rebars. To support corrosion, oxygen needs to diffuse from the ambient environment to the steel surface. Meanwhile, corrosion products transport through the SCI and precipitate in concrete. Transport properties of concrete play an important role in these two processes. However, the effect of the heterogeneous structure of concrete especially coarse aggregates on oxygen transport and corrosion products precipitation in reinforced concrete is rarely studied in the literature. This study employed a numerical model to investigate such effect. Simulation domains in 2D were created with different aggregate contents and sizes. The model included oxygen diffusion, ions diffusion and migration, corrosion products oxidation and precipitation. The simulation results showed that the presence of aggregates significantly reduces oxygen diffusion. It becomes more pronounced for high aggregate contents which lead to more corrosion products formed at the interface. Furthermore, results showed that the interfacial transition zone (ITZ) around aggregates can enhance oxygen diffusion
Oral rehydration therapy--Qualitative studies of balance between pragmatism and scientific rigour in managing diarrhoea
No full textIn the experience of the author, oral rehydration therapy has proven effective at home, in the ambulatory and in the institutional care setting. A series of anecdotal reports on the successful use of oral rehydration on refugees, in famine and poverty, on medical students, prisoners, and the well-off people of western countries, is presented. The essential principles of oral rehydration are identified and we show how these can be adapted to a particular health care setting. A clear understanding of local attitudes and beliefs about diarrhoea is essential to professional health workers if they are to act as agents of change.oral rehydration therapy applied technology qualitative studies
Engineering of cartilage tissue constructs in a 3-dimensional perfusion bioreactor culture system under controlled oxygen tension
No full textThe most relevant results generated in this thesis can be summarized as follow:
· Adult human articular chondrocytes (AHAC) from elderly individuals expanded in culture
medium supplemented with the growth factors TGFβ-1, FGF-2 and PDGF and subsequently
cultured in 3-d pellets had an enhanced chondrogenic capacity when exposed to more
physiological (i.e. 5%) oxygen levels.
· In correlation with the enhanced tissue forming capacity of AHAC from elderly donors under
low oxygen tension, the mRNA expression levels of selective matrix degrading enzymes
were reduced as compared to conventional in vitro oxygen culture condition.
· We developed an integrated bioreactor system, which streamlines within a single device the
phases of perfusion cell seeding and prolonged perfusion culture of cell seeded scaffolds in
vitro.
· The culturing of uniformly seeded adult human articular chondrocytes under direct perfusion,
where cells are continuously exposed to a normoxic range of oxygen levels, can maintain a
uniform distribution of viable cells throughout thick porous scaffolds as compared to
statically cultured constructs.
· The culturing of constructs uniformly seeded with adult human articular chondrocytes under
a more physiological range of oxygen resulted in a higher chondrogenic differentiation as
compared to culture under normoxic levels. Anyhow, this effect was less pronounced as
compared to statically cultured cell constructs or micromass cell pellets, possibly due to the
flow induced shear forces.
· Reduced perfusion flow rates applied to chondrocytes on porous scaffolds significantly
induced more cartilaginous tissue in the presents of low vs. high oxygen levels. However the
effects of low oxygen were not as marked as in pellet culture
Modelling of Cathodic Protection of Steel in Concrete Considering Time and Location-dependent Influencing Factors
No full textCathodic protection (CP) is an electrochemical repair technique for reinforced concrete (RC) structures affected by chloride induced corrosion. The underlying concept is based on a shift of the free corrosion potential of the reinforcement towards negative (cathodic) potentials, in order to force the reinforcement to act as a cathode and therefore suppress the anodic dissolution of iron. This is achieved via the application of an additional CP anode system to the structure. For CP, different types of anode system (galvanic, impressed current, laminar or discrete), made from different materials (e.g. zinc, mixed metal oxide coated titanium, carbon) exist. The protective effect of this method depends on the effective protection current density obtained on the active surfaces of the reinforcement. The continuous construction of the usual reinforcing cages impedes a direct measurement of this parameter. As no reliable test method for the corrosion state of reinforcement during CP exists, the application is based on(semi-) empirical criteria. While this is sufficient for successful application of CP for a wide range of common geometries and CP anode systems, the applicability of CP for unconventional geometrical arrangements of active and passive rebar or the use of new anode materials cannot be assessed this way. For these cases, numerical studies provide the opportunity to predict the current and potential distribution within the structure on a theoretical basis in order to support the design process. Within this thesis, the theoretical background of the numerical simulation of corrosion processes in RC is described and the modifications necessary for the modelling of impressed current cathodic protection (ICCP) are presented. A key focus in this work is the implementation of ICCP anode systems. Proposed models of this author are discussed versus those obtained from the literature. In the course of this work, influencing parameters such as the geometrical arrangement of reinforcement (active/passive) and CP anode system, concrete resistivity and conductivity of the anode material are investigated by means of parametrical studies and discussed IV regarding their specific impact on the applicability of CP against the backdrop of the common protection criteria. An additional focus is set on the implementation of the time-dependency of the current and potential distribution into the numerical models. It is known, that the permanent cathodic polarization of the reinforcement can provide beneficial side effects such as migration of chloride ions away from the surface of the reinforcement, or the evolution of hydroxyl ions caused by the cathodic reaction. A method for the consideration of these processes within a numerical study is proposed and the impact of these side effects versus those of the influencing parameters given above is discussed by means of a parametrical study
The effect of the steel–concrete interface on chloride-induced corrosion initiation in concrete: a critical review by RILEM TC 262-SCI
No full textThe steel–concrete interface (SCI) is known to influence corrosion of steel in concrete. However, due to the numerous factors affecting the SCI—including steel properties, concrete properties, execution, and exposure conditions—it remains unclear which factors have the most dominant impact on the susceptibility of reinforced concrete to corrosion. In this literature review, prepared by members of RILEM technical committee 262-SCI, an attempt is made to elucidate the effect of numerous SCI characteristics on chloride-induced corrosion initiation of steel in concrete. We use a method to quantify and normalize the effect of individual SCI characteristics based on different literature results, which allows comparing them in a comprehensive context. It is found that the different SCI characteristics have received highly unbalanced research attention. Parameters such as w/b ratio and cement type have been studied most extensively. Interestingly, however, literature consistently indicates that those parameters have merely a moderate effect on the corrosion susceptibility of steel in concrete. Considerably more pronounced effects were identified for (1) steel properties, including metallurgy, presence of mill scale or rust layers, and surface roughness, and (2) the moisture state. Unfortunately, however, these aspects have received comparatively little research attention. Due to their apparently strong influence, future corrosion studies as well as developments towards predicting corrosion initiation in concrete would benefit from considering those aspects. Particularly the working mechanisms related to the moisture conditions in microscopic and macroscopic voids at the SCI is complex and presents major opportunities for further research in corrosion of steel in concrete.Accepted Author ManuscriptMaterials and Environmen
Failed coronary artery bypass anastomosis detected by intraoperative coronary flow measurement
No full textObjectives: To assess intraoperative flow of arterial and venous coronary grafts after myocardial revascularization which may allow early detection of low flow situations, especially during minimally invasive coronary bypass surgery (MIDCAB), and lead to immediate correction of technical problems. Methods: In two patients with severe and diffuse multi-vessel disease the left internal mammary artery (IMA) was connected to the left anterior descending artery (LAD). During reperfusion, the flow was measured in the IMA and vein grafts using a transit time flow meter. Results: In both cases the IMA showed only a systolic pendulating flow curve with a mean flow of 0-1 ml/min and a high resistance. Manual IMA assessment revealed an adequate pulsation. Both distal IMA anastomoses were re-explored on cardiopulmonary bypass yielding an initial flow of 7 and 14 ml/min, respectively. After treatment with papaverine/adenosine the IMA flow increased from 7 to 26 ml/min (coronary flow reserve (CFR)=3.7) and from 14 to 46 ml/min (CFR=3.3), respectively. Conclusion: Intraoperative flow assessment of IMA and venous bypass grafts can be recommended to monitor flow; especially during MIDCAB procedure
Correction to: Insemination with border disease virus-infected semen results in seroconversion in cows but not persistent infection in fetuses
No full textThe original article [1] contained an error whereby a co-author, Sarah Züblin had their name displayed incorrectly. This error has now been corrected
