2,709 research outputs found
Interpreting ambiguous âtraceâ results in Schistosoma mansoni CCA Tests: Estimating sensitivity and specificity of ambiguous results with no gold standard
Background The development of new diagnostics is an important tool in the fight against disease. Latent Class Analysis (LCA) is used to estimate the sensitivity and specificity of tests in the absence of a gold standard. The main field diagnostic for Schistosoma mansoni infection, Kato-Katz (KK), is not very sensitive at low infection intensities. A point-of-care circulating cathodic antigen (CCA) test has been shown to be more sensitive than KK. However, CCA can return an ambiguous âtraceâ result between âpositiveâ and ânegativeâ, and much debate has focused on interpretation of traces results. Methodology/Principle findings We show how LCA can be extended to include ambiguous trace results and analyse S. mansoni studies from both CĂŽte dâIvoire (CdI) and Uganda. We compare the diagnostic performance of KK and CCA and the observed results by each test to the estimated infection prevalence in the population. Prevalence by KK was higher in CdI (13.4%) than in Uganda (6.1%), but prevalence by CCA was similar between countries, both when trace was assumed to be negative (CCAtn: 11.7% in CdI and 9.7% in Uganda) and positive (CCAtp: 20.1% in CdI and 22.5% in Uganda). The estimated sensitivity of CCA was more consistent between countries than the estimated sensitivity of KK, and estimated infection prevalence did not significantly differ between CdI (20.5%) and Uganda (19.1%). The prevalence by CCA with trace as positive did not differ significantly from estimates of infection prevalence in either country, whereas both KK and CCA with trace as negative significantly underestimated infection prevalence in both countries. Conclusions Incorporation of ambiguous results into an LCA enables the effect of different treatment thresholds to be directly assessed and is applicable in many fields. Our results showed that CCA with trace as positive most accurately estimated infection prevalence
Intravenous lidocaine infusion as a component of multimodal analgesia for colorectal surgery-measurement of plasma levels
Abstract Background Growing evidence suggests that intravenous lidocaine as a component of multimodal analgesia improves recovery after major colorectal surgery. There is little published data regarding ideal dosing and target plasma concentration in this context, and we wanted to establish our dosing schedule was safe by measuring blood levels of lidocaine. Methods We measured the plasma lidocaine concentration of 32 patients at 30âmin, 6âh and 12âh after starting intravenous lidocaine infusion for analgesia after major colorectal surgery. Patients received a bolus of 1.5âmgâkgâ1 over 20âmin at the time of induction of anaesthesia. This was followed by a continuous infusion of 2% w/v lidocaine at 3âmlâhrâ1 (60âmgâhrâ1) for patients weighing up to 70âkg and 6âmlâhrâ1 (120âmgâhrâ1) for patients weighing over 70âkg, using actual body weight. Results The overall mean plasma lidocaine concentration was 4.0âÎŒgâmlâ1 (range 0.6â12.3âÎŒgâmlâ1). In patients treated with the higher infusion dose, the mean concentration was 4.6âÎŒgâmlâ1 compared to 3.2âÎŒgâmlâ1 in those patients on the lower dose. Mean levels were higher at 6âh than 30âmin and higher again at 12âh. There were no adverse events or reports of symptoms of local anaesthetic toxicity. Conclusions Whilst there were no signs or symptoms of lidocaine toxicity in our patients, there was a wide range of plasma concentrations including some over 10âÎŒgâmlâ1; a level above which symptoms of toxicity may be expected. We have changed our dosing protocol to using ideal rather than actual body weight based on these results
Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
We present an angle-resolved photoemission study of Na0.7CoO2, the host
cobaltate of the NaxCoO2.yH2O series. Our results show a large hexagonal-like
hole-type Fermi surface, an extremely narrow strongly renormalized
quasiparticle band and a small Fermi velocity. Along the Gamma to M high
symmetry line, the quasiparticle band crosses the Fermi level from M toward
Gamma consistent with a negative sign of effective single-particle hopping (t
): t is estimated to be about 8 meV which is on the order of exchange coupling
J in this system. This suggests that t ~ J ~ 10 meV is an important energy
scale in the system. Quasiparticles are well defined only in the T-linear
resistivity regime. Small single particle hopping and unconventional
quasiparticle dynamics may have implications for understanding the unusual
behavior of this new class of compounds.Comment: Revised text, Added Figs, Submitted to PR
Curie Temperatures for Three-Dimensional Binary Ising Ferromagnets
Using the Swendsen and Wang algorithm, high accuracy Monte Carlo simulations
were performed to study the concentration dependence of the Curie temperature
in binary, ferromagnetic Ising systems on the simple-cubic lattice. Our results
are in good agreement with known mean-field like approaches. Based on former
theoretical formulas we propose a new way of estimating the Curie temperature
of these systems.Comment: nr. of pages:13, LATEX. Version 2.09, Scientific Report :02/1994
(Univ. of Bergen, Norway), 7 figures upon reques
Spatial structure increases the waiting time for cancer
Cancer results from a sequence of genetic and epigenetic changes which lead
to a variety of abnormal phenotypes including increased proliferation and
survival of somatic cells, and thus, to a selective advantage of pre-cancerous
cells. The notion of cancer progression as an evolutionary process has been
experiencing increasing interest in recent years. Many efforts have been made
to better understand and predict the progression to cancer using mathematical
models; these mostly consider the evolution of a well-mixed cell population,
even though pre-cancerous cells often evolve in highly structured epithelial
tissues. We propose a novel model of cancer progression that considers a
spatially structured cell population where clones expand via adaptive waves.
This model is used to asses two different paradigms of asexual evolution that
have been suggested to delineate the process of cancer progression. The
standard scenario of periodic selection assumes that driver mutations are
accumulated strictly sequentially over time. However, when the mutation supply
is sufficiently high, clones may arise simultaneously on distinct genetic
backgrounds, and clonal adaptation waves interfere with each other. We find
that in the presence of clonal interference, spatial structure increases the
waiting time for cancer, leads to a patchwork structure of non-uniformly sized
clones, decreases the survival probability of virtually neutral (passenger)
mutations, and that genetic distance begins to increase over a characteristic
length scale, determined here. These characteristic features of clonal
interference may help to predict the onset of cancers with pronounced spatial
structure and to interpret spatially-sampled genetic data obtained from
biopsies. Our estimates suggest that clonal interference likely occurs in the
progressing colon cancer, and possibly other cancers where spatial structure
matters.Comment: 21 page
Charge Fluctuations in Geometrically Frustrated Charge Ordering System
Effects of geometrical frustration in low-dimensional charge ordering systems
are theoretically studied, mainly focusing on dynamical properties. We treat
extended Hubbard models at quarter-filling, where the frustration arises from
competing charge ordered patterns favored by different intersite Coulomb
interactions, which are effective models for various charge transfer-type
molecular conductors and transition metal oxides. Two different lattice
structures are considered: (a) one-dimensional chain with intersite Coulomb
interaction of nearest neighbor V_1 and that of next-nearest neighbor V_2, and
(b) two-dimensional square lattice with V_1 along the squares and V_2 along one
of the diagonals. From previous studies, charge ordered insulating states are
known to be unstable in the frustrated region, i.e., V_1 \simeq 2V_2 for case
(a) and V_1 \simeq V_2 for case (b), resulting in a robust metallic phase even
when the interaction strenghs are strong. By applying the Lanczos exact
diagonalization to finite-size clusters, we have found that fluctuations of
different charge order patterns exist in the frustration-induced metallic
phase, showing up as characteristic low energy modes in dynamical correlation
functions. Comparison of such features between the two models are discussed,
whose difference will be ascribed to the dimensionality effect. We also point
out incommensurate correlation in the charge sector due to the frustration,
found in one-dimensional clusters.Comment: 8 pages, 9 figure
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