Influence on fluid dynamics of coronary artery outlet angle variation in artificial aortic root prosthesis

<p>Abstract</p> <p>Background</p> <p>Because of higher life expectancy, the number of elderly patients today with degenerative aortic diseases is on the increase. Often artificial aortic roots are needed to replace the native tissue. This surgical procedure requires re-implantation of the previous separated coronary arteries into the wall of the prosthesis. Regardless of the prosthesis type, changes in the reinsertion technique, e.g., the variation of the outlet angle of the coronary arteries, could influence the coronary blood flow. Whether the prosthesis type or the outlet angle variation significantly improves the blood circulation and lowers the risk of coronary insufficiency is still an open question. The numerical calculations presented can help to clear up these disputable questions.</p> <p>Methods</p> <p>Two simplified base geometries are used for simulating the blood flow in order to determine velocity and pressure distributions. One model uses a straight cylindrical tube to approximate the aortic root geometry; the other uses a sinus design with pseudosinuses of Valsalva. The coronary outlet angle of the right coronary artery was discretely modified in both models in the range from 60° to 120°. The pressure and velocity distributions of both models are compared in the ascending aorta as well as in the right and the left coronary artery.</p> <p>Results</p> <p>The potentially allowed and anatomic limited variation of the outlet angle influences the pressure only a little bit and shows a very slight relative maximum between 70° and 90°. The sinus design and variations of the outlet angle of the coronary arteries were able to minimally optimize the perfusion pressure and the velocities in the coronary circulation, although the degree of such changes is rather low and would probably not achieve any clinical influence.</p> <p>Conclusion</p> <p>Our results show that surgeons should feel relatively free to vary the outlet angle within the anatomic structural conditions when employing the technique of coronary reinsertion.</p

Feasibility of rapid and automated importation of 3D echocardiographic left ventricular (LV) geometry into a finite element (FEM) analysis model

BACKGROUND: Finite element method (FEM) analysis for intraoperative modeling of the left ventricle (LV) is presently not possible. Since 3D structural data of the LV is now obtainable using standard transesophageal echocardiography (TEE) devices intraoperatively, the present study describes a method to transfer this data into a commercially available FEM analysis system: ABAQUS(©). METHODS: In this prospective study TomTec LV Analysis TEE(© )Software was used for semi-automatic endocardial border detection, reconstruction, and volume-rendering of the clinical 3D echocardiographic data. A newly developed software program MVCP FemCoGen(©), written in Delphi, reformats the TomTec file structures in five patients for use in ABAQUS and allows visualization of regional deformation of the LV. RESULTS: This study demonstrates that a fully automated importation of 3D TEE data into FEM modeling is feasible and can be efficiently accomplished in the operating room. CONCLUSION: For complete intraoperative 3D LV finite element analysis, three input elements are necessary: 1. time-gaited, reality-based structural information, 2. continuous LV pressure and 3. instantaneous tissue elastance. The first of these elements is now available using the methods presented herein

Personality and Vulnerability to Depression in Stroke Patients

Conclusions¿ Neuroticism is an important predictor of PSD, a finding that emphasizes the need to take personality into account as a potential vulnerability factor for depression in stroke patients. Research on PSD should aim at delineating the interplay between neurological and psychological factors in the development of PSD.

Implementation outcomes of cognitive behavioural therapy delivered by non-specialists for common mental disorders and substance-use disorders in low- and middle-income countries: a systematic review.

Due to severe shortages of specialist mental health personnel in low- and middle-income countries (LMICs), psychological therapies are increasingly being delivered by non-specialist health workers (NSHWs). Previous reviews have investigated the effectiveness of NSHW-delivered psychological therapies, including cognitive behavioural therapy (CBT), in LMIC settings. This systematic review aims to synthesise findings on the implementation outcomes of NSHW-delivered CBT interventions addressing common mental disorders and substance-use disorders in LMICs. Four databases were searched, yielding 3211 records, 18 of which met all inclusion criteria. We extracted and synthesised qualitative and quantitative data across eight implementation outcomes: acceptability, adoption, appropriateness, feasibility, fidelity, implementation cost, penetration and sustainability. Findings suggest that delivery of CBT-based interventions by NSHWs can be acceptable, appropriate and feasible in LMIC settings. However, more research is needed to better evaluate these and other under-reported implementation outcomes

The use of standard calendar software by individuals with acquired brain injury and cognitive complaints: a mixed methods study

PURPOSE: To explore the actual use of standard calendar software by people with acquired brain injury (ABI) and healthy individuals. METHOD: Mixed methods design with qualitative and quantitative analyses of the respondents' use of calendar software. Fifteen individuals with ABI and 15 healthy participants were enrolled. Participants were asked to execute five consecutive tasks using standard calendar software, which resembled everyday use of an electronic calendar. RESULTS: The core processes "task execution" and "information processing" were influenced by internal factors (cognitive and emotional processes and fatigue) as well as environmental factors (software features and distractions). Results obtained by qualitative and quantitative methods showed similar reaction patterns in both groups. However, ABI patients had more cognitive problems and showed stronger emotions during task performance than healthy participants. Healthy participants were more successful and needed less time and mental effort to perform a task. CONCLUSIONS: Although ABI patients were able to use standard calendar software, they became upset more easily, needed more effort, became tired sooner and more suddenly. Strategies to support ABI patients in the use of calendar software are suggested from multi-disciplinary perspectives

Characterization of Propellant Flow and Bias Required to Initiate an Arc Discharge in a Heaterless Hollow Cathode

Heaterless hollow cathodes provide an opportunity to reduce complexity and improve reliability in electric propulsion systems. While removal of the heater has little effect on steady-state operation of a hollow cathode, it has a considerable effect on the ignition process. To successfully integrate a heaterless hollow cathode into a spaceflight electric propulsion system, it will be necessary to establish definitive requirements for the propellant feed and electrical subsystems so that ignition of a plasma discharge can be achieved reliably. The aim of this research was to form a better understanding of these requirements by performing an investigation of the propellant flow and voltage conditions required for the ignition of a plasma arc discharge. This aim was achieved by performing discharge initiation experiments using both a specially designed experimental apparatus and a functional heaterless hollow cathode assembly. It was demonstrated that there is a distinct difference in the voltage required to initiate a plasma discharge between two common electric propulsion propellants, xenon and krypton, which suggests that the developmental testing of heaterless hollow cathodes needs to be performed with the appropriate propellant gas species. Heaterless hollow cathode ignition experiments showed that the keeper orifice diameter has a strong effect on the voltage required to ignite a plasma discharge at a given propellant mass flow rate, while the effect of keeper-cathode separation distance was only strong at flow rates below 25 sccm (Xe)

Dynamic concentration of motors in microtubule arrays

We present experimental and theoretical studies of the dynamics of molecular motors in microtubule arrays and asters. By solving a convection-diffusion equation we find that the density profile of motors in a two-dimensional aster is characterized by continuously varying exponents. Simulations are used to verify the assumptions of the continuum model. We observe the concentration profiles of kinesin moving in quasi two-dimensional artificial asters by fluorescent microscopy and compare with our theoretical results.Comment: 4pages, 4 figures revte