3,790 research outputs found
Advanced Three-Dimensional Echocardiography
__Abstract__
During the development of echocardiography, 3D echocardiography imaging represents
a major innovation in cardiovascular ultrasound (Figure 1). Advancements in computer
and transducer technologies permit real-time 3D acquisition and presentation
of cardiac structures from any view. An important milestone in the history of real-time
3D echocardiography was reached shortly after the year 2000, with the development
of fully sampled matrix-array transducers (Figure 2). These transducers provide excellent
real-time imaging of the beating heart in three dimensions and require significant technological developments in both hardware and software
Case report: Concomitant MitraClip implantation for severe mitral regurgitation and plug closure of endocarditis induced fistula between aortic root and left atrium after transcatheter aortic valve implantation
Background: Infective endocarditis (IE) after transcatheter aortic valve implantation (TAVI) occurs in up to 1.5% of patients within the first year. The development of an aorto-atrial fistula (AAF) is a rare but problematic complication of IE, which can be confirmed with transoesophageal echocardiography (TOE). We present an exceptional case of occluding an aorto-left atrial fistula only diagnosed with intraprocedural TOE during a subsequent procedure of MitraClip implantation. Case summary: A 79-year-old symptomatic male patient with multiple comorbidities was referred due to severe mitral regurgitation (MR). He has had prior TAVI which was complicated with streptococcal IE for which he had received prolonged antibacterial therapy. Transthoracic echocardiography (TTE) revealed severe MR. The patient was accepted for a MitraClip procedure by the heart team. Intra-procedural TOE revealed also a significant continuous shunt through an AAF which was likely caused by the endocarditis. The strategy was therefore defined as to occlude the fistula with an Amplatzer Vascular Plug II 12 mm. The plug was released in the fistula leaving an insignificant residual shunt. After the transseptal puncture one MitraClip XTR was implanted, reducing the MR to mild. After the procedure, the patient's general clinical condition improved without signs of haemolysis. The pre-discharge TTE confirmed trace residual shunt, mild residual MR and mild paravalvular leakage. Discussion: Our case illustrates a complex transcatheter structural heart intervention with improvised procedural strategies based on the intra-procedural TOE findings. We conclude that the pre-procedural TOE needs to be comprehensive rather than exclusive, particularly in the context of bioprosthesis-related endocarditis
Determinants of changes in pulmonary artery pressure in patients with severe aortic stenosis treated by tr
Background: Elevated pulmonary artery pressure (PAP) in patients with severe aortic stenosis (AS) is a strong predictor of adverse prognosis. This study sought to assess the relation between PAP and clinical and echocardiographic parameters in elderly patients with severe AS, as well as to identify the determinants of the change in PAP after transcatheter aortic valve implantation (TAVI). Methods: The study included 170 subjects (age 81 ± 7 years, 45% men) with symptomatic severe AS who were treated by TAVI. They underwent a clinical evaluation and a transthoracic echocardiography before the TAVI procedure and 6 months after. Results: In a multivariable analysis, the independent predictors for baseline PAP were the body mass index (BMI) (β = 0.21, p =.006), COPD GOLD class (β = 0.20; p =.009), the E/e′ ratio (β = 0.20; p =.02) and the degree of aortic regurgitation (β = 0.20; p =.01). After TAVI, there was significantly less (51% vs. 29%, p<.0001) pulmonary hypertension, defined as a tricuspid regurgitation velocity ≥2.8 m/s. The baseline variables related to an improvement in PAP were the tricuspid regurgitation velocity (p =.0001) and the E/e′ (p =.005). From the parameters potentially modified with TAVI, the only independent predictor of PAP variation was the change in the E/e′ ratio (β = 0.23; p =.01). Conclusions: Independent predictors for baseline PAP in elderly patients with symptomatic AS were the BMI, GOLD class, the aortic regurgitation and the E/e′ ratio. The baseline predictors for a change in PAP 6 months after TAVI were the baseline PAP and E/e′, with only the change in the E/e′ ratio being correlated to the change in PAP
Security and Privacy Issues in Wireless Mesh Networks: A Survey
This book chapter identifies various security threats in wireless mesh
network (WMN). Keeping in mind the critical requirement of security and user
privacy in WMNs, this chapter provides a comprehensive overview of various
possible attacks on different layers of the communication protocol stack for
WMNs and their corresponding defense mechanisms. First, it identifies the
security vulnerabilities in the physical, link, network, transport, application
layers. Furthermore, various possible attacks on the key management protocols,
user authentication and access control protocols, and user privacy preservation
protocols are presented. After enumerating various possible attacks, the
chapter provides a detailed discussion on various existing security mechanisms
and protocols to defend against and wherever possible prevent the possible
attacks. Comparative analyses are also presented on the security schemes with
regards to the cryptographic schemes used, key management strategies deployed,
use of any trusted third party, computation and communication overhead involved
etc. The chapter then presents a brief discussion on various trust management
approaches for WMNs since trust and reputation-based schemes are increasingly
becoming popular for enforcing security in wireless networks. A number of open
problems in security and privacy issues for WMNs are subsequently discussed
before the chapter is finally concluded.Comment: 62 pages, 12 figures, 6 tables. This chapter is an extension of the
author's previous submission in arXiv submission: arXiv:1102.1226. There are
some text overlaps with the previous submissio
Prediction of paravalvular leakage after transcatheter aortic valve implantation
Significant paravalvular leakage (PVL) after transcatheter aortic valve implantation (TAVI) is related to patient mortality. Predicting the development of PVL has focused on computed tomography (CT) derived variables but literature targeting CoreValve devices is limited, controversial, and did not make use of standardized echocardiographic methods. The study included 164 consecutive patients with severe aortic stenosis that underwent TAVI with a Medtronic CoreValve system©, with available pre-TAVI CT and pre-discharge transthoracic echocardiography. The predictive value for significant PVL of the CT-derived Agatston score, aortic annulus size and eccentricity, and “cover index” was assessed, according to both echocardiographic Valve Academic Research Consortium (VARC) criteria and angiographic Sellers criteria. Univariate predictors for more than mild PVL were the maximal diameter of the aortic annulus size (for both angiographic and echocardiographic assessment of PVL), cover index (for echocardiographic assessment of PVL only), and Agatston score (fo
The role of experience in echocardiographic identification of location and extent of mitral valve prolapse with 2D and 3D echocardiography
Contradiction exists on the incremental value of two-dimensional (2D) and 3D transoesophageal echocardiography (TOE) over 2D transthoracic echocardiography (TTE) for the detection of mitral valve (MV) prolapse in readers with different echocardiographic experience. Twenty patients and five healthy persons were retrospectively identified who had undergone 2D-TTE, 2D-TOE and 3D-TOE. Fifteen (75 %) patients had surgical evidence of prolapse of the posterior MV leaflet and five patients (25 %) had a dilated MV annulus without prolapse. Three reader groups with different echocardiographic expertise (novice, trainees, cardiologists) scored thus in total 675 posterior scallops. Overall there was an improvement in agreement and Kappa values from novice to trainees to cardiologists. Diagnostic accuracies of 2D-TOE were higher than those of 2D-TTE mainly in novice readers. The incremental value of 3D-TOE over 2D-TOE was mainly seen in specificities. Time to diagnosis was dramatically reduced from 2D to 3D-TEE in all reader groups (all P < 0.001). 3D-TOE also improved the agreement (+12 to +16 %) and Kappa values (+0.14 to +0.21) in all reader groups for the exact description of P2 prolapse. Differences between readers with variable experience in determining the precise localization and extent of the prolapsing posterior MV scallops exist in particular in 2D-TTE analysis. 3D-TOE analysis was extremely fast compared to the 2D analysis methods and showed the best diagnostic accuracy (mainly driven by specificity) with identification of P1 and P3 prolapse still improving from novice to trainees to cardiologists and provided optimal description of P2 prolapse extent
Social networks and political participation in a Sicilian community context
AbstractThis study shows the linkage between political and social participation, underlining the relevance of the motivational sphere. The aim is to evaluate politically relevant social capital by adopting a relational perspective and ego-network measures, so that we can understand the interdependence between cognitive maps, motivational factors and relational dimension, both in qualitative and quantitative dimensions
Fatigue evaluation in maintenance and assembly operations by digital human simulation
Virtual human techniques have been used a lot in industrial design in order
to consider human factors and ergonomics as early as possible. The physical
status (the physical capacity of virtual human) has been mostly treated as
invariable in the current available human simulation tools, while indeed the
physical capacity varies along time in an operation and the change of the
physical capacity depends on the history of the work as well. Virtual Human
Status is proposed in this paper in order to assess the difficulty of manual
handling operations, especially from the physical perspective. The decrease of
the physical capacity before and after an operation is used as an index to
indicate the work difficulty. The reduction of physical strength is simulated
in a theoretical approach on the basis of a fatigue model in which fatigue
resistances of different muscle groups were regressed from 24 existing maximum
endurance time (MET) models. A framework based on digital human modeling
technique is established to realize the comparison of physical status. An
assembly case in airplane assembly is simulated and analyzed under the
framework. The endurance time and the decrease of the joint moment strengths
are simulated. The experimental result in simulated operations under laboratory
conditions confirms the feasibility of the theoretical approach
Enhancement of Canonical Wnt/β-Catenin Signaling Activity by HCV Core Protein Promotes Cell Growth of Hepatocellular Carcinoma Cells
BACKGROUND: The Hepatitis C virus (HCV) core protein has been implicated as a potential oncogene or a cofactor in HCV-related hepatocellular carcinoma (HCC), but the underlying mechanisms are unknown. Overactivation of the Wnt/β-catenin signaling is a major factor in oncogenesis of HCC. However, the pathogenesis of HCV core-associated Wnt/β-catenin activation remains to be further characterized. Therefore, we attempted to determine whether HCV core protein plays an important role in regulating Wnt/β-catenin signaling in HCC cells. METHODOLOGY: Wnt/β-catenin signaling activity was investigated in core-expressing hepatoma cells. Protein and gene expression were examined by Western blot, immunofluorescence staining, RT-qPCR, and reporter assay. PRINCIPAL FINDINGS: HCV core protein significantly enhances Tcf-dependent transcriptional activity induced by Wnt3A in HCC cell lines. Additionally, core protein increases and stabilizes β-catenin levels in hepatoma cell line Huh7 through inactivation of GSK-3β, which contributes to the up-regulation of downstream target genes, such as c-Myc, cyclin D1, WISP2 and CTGF. Also, core protein increases cell proliferation rate and promotes Wnt3A-induced tumor growth in the xenograft tumor model of human HCC. CONCLUSIONS/SIGNIFICANCE: HCV core protein enhances Wnt/β-catenin signaling activity, hence playing an important role in HCV-associated carcinogenesis
On-sky speckle nulling through a single-mode fiber with the Keck Planet Imager and Characterizer
The Keck Planet Imager and Characterizer (KPIC) is an instrument at the Keck
II telescope that enables high-resolution spectroscopy of directly imaged
exoplanets and substellar companions. KPIC uses single-mode fibers to couple
the adaptive optics system to Keck's near-infrared spectrometer (NIRSPEC).
However, KPIC's sensitivity at small separations is limited by the leakage of
stellar light into the fiber. Speckle nulling uses a deformable mirror to
destructively interfere starlight with itself, a technique typically used to
reduce stellar signal on a focal-plane imaging detector. We present the first
on-sky demonstration of speckle nulling through an optical fiber with KPIC,
using NIRSPEC to collect exposures that measure speckle phase for
quasi-real-time wavefront control while also serving as science data. We repeat
iterations of measurement and correction, each using at least 5 exposures. We
show a decrease in the on-sky leaked starlight by a factor of 2.6 to 2.8 in the
targeted spectral order, at a spatial separation of 2.0 {\lambda}/D in K-band.
This corresponds to an estimated factor of 2.6 to 2.8 decrease in the required
exposure time to reach a given SNR, relative to conventional KPIC observations.
The performance of speckle nulling is limited by instability in the speckle
phase: when the loop is opened, the null-depth degrades by a factor of 2 on the
timescale of a single phase measurement, which would limit the suppression that
can be achieved. Future work includes exploring gradient-descent methods, which
may be faster and thereby able to achieve deeper nulls. In the meantime, the
speckle nulling algorithm demonstrated in this work can be used to decrease
stellar leakage and improve the signal-to-noise of science observations.Comment: 18 pages, 4 figure
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