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Thromboelastography in the assessment of coagulation changes in peripheral vascular disease
Full text linkStudies up to date in the western literature involving changes in coagulation
in patients with peripheral vascular disease(PVD) have consistently reported
activation of coagulation based on measurement of raised levels of markers
of activation of coagulation(clot formation), decreased fibrinolysis (breakdown
of fibrin), platelet activation leading to increased aggregation and defective
endothelial (arterial wall) function in patients with PVD that leads to
thrombosis in arterial circulation thus designating this group of patients as
hypercoagulable.‘ Interestingly these patients are not deemed as such in
clinical practice as the routine coagulation tests(RCTs) currently employed do
not identify these abnormalities. The overall purpose of the research
described in this thesis was to identify changes in coagulation in patients with
peripheral vascular disease using Thromboelastography (TEG), a technique
which exploits the visco-elastic properties of a blood clot as it forms, retracts
or lyses (breaks down) using a small volume of whole blood.
Validation of TEG technique employing citrated whole blood (CWB) and
heparinase modified (hepTEG) methods and standardisation of analysis to
overcome variability in TEG analysis, blood sample instability due to storage
times was carried out. TEG analysis after sample storage between 1-2 hours
showed no significant inter or intra sample assay variability confirming
excellent reproducibility( (p= NS; reliability coefficients (Alpha) greater than
0.9 for R time, K time, Angle, Maximal Amplitude (MA) and Coagulation
Index(CI)). hepTEG method confirmed complete reversal of heparin effect in
blood samples obtained from participants following heparin administration.(R
ii time: 9.16+/- 1.68 Vs 8.90 +/- 1.48 p=NS; K time: 2.98+/- 0.87 Vs 3.20 +/-
1.05 p=NS; Angle: 56.86+/- 6.39 Vs 56.90 +/- 5.30 p=NS; MA 56.34+/- 6.39
Vs 56.79+/-6.23 p=NS; CI: 0.59+/-1.19 Vs 0.88+/-1.00 p=NS). 50 age
matched controls to obtain reference values for comparison and
documentation of any significant changes in TEG parameters due to age,
gender anaesthesia and surgery was completed. Preparation /induction of
anaesthesia led to a significant trend towards activation of coagulation in all
age groups and gender (Angle 56.23 +/-0.89, CI 54.42, 58.04 Vs 58.21+/-
0.83, CI 56.54, 59.88;p=0.003 and MA 56.40 +/- 0.79 CI 54.80, 58.01 Vs
59.36 +/- 0.89, CI 57.56, 61.15; p=0.003 and CI 0.71 +/- 0.14, CI 0.42, 1.00
Vs 1.35 +/- 0.17, CI 1.00, 1.69;p=0.003)
Surgical stimulus led to a further activation of coagulation that followed
induction of anaesthesia (Angle: 58.21+/- 0.83, CI 56.54, 59.88 Vs 60.98 +/-
0.69, CI 59.59, 62.37; p=0.001). TEG parameter values obtained from
healthy controls aged over 45 are used as reference values for this study.
TEG showed no significant differences in TEG parameters when samples
obtained from an upper limb artery and a vein were analysed. However when
samples from the main lower limb artery (common femoral artery/CFA) and
the major vein that drains the same limb (common femoral vein/CFV) in
patients with symptomatic PVD, TEG identified significant activation of
coagulation in samples obtained from the vein that drains an ischaemic limb
(decrease in R time (p0.05), an increase in MA (p0.05) and an increase in
CI (p0.002)). This interesting finding led to a hypothesis that ischaemic
tissue has a prominent role in the activation of coagulation observed in
iii patients with PVD. To test this hypothesis, common femoral venous and
arterial samples from 30 patients with symptomatic PVD were analysed using
TEG. TEG identified significant activation of coagulation in samples obtained
from an artery downstream (CFA) when compared to those obtained from an
artery that is proximal (Aorta). This change towards hypercoagulation was
also found to be positively related to the degree of narrowing or stenotic
disease (quantified using angiography) between these two sampling
points(R, r=0.442, p0.05 / MA, r=0.379, p0.05 / CI r=0.429, p0.05). A
significant positive relationship in between degree of ischaemia (ABPI) and
difference in TEG parameter values in between arterial and venous blood
samples obtained from an ischaemic limb (ABPI) on that side (CI v ABPI r =
-0.427 p0.05, MA v ABPI r =-0.370 p0.05) was also found in this study.
These findings suggest activation of coagulation as the blood flows down an
atherosclerotic vessel and in combination with the observed changes due to
the presence of peripheral ischemia tissue suggested that the
hypercoagulability observed in PVD may have its origins in the ishaemic limb
itself.
To clarify the role of non-ionic contrast media (NICM) in the context of
conflicting findings regarding its thrombogenic potential especially in patients
with PVD undergoing angiography, aortic blood samples(n=30) were
obtained before and after injection of NICM. Heparinase modified TEG
analysis showed that there was no activation of coagulation immediately after
NICM exposure and in fact there was a significant trend towards
hypocoagulation in contrast to the published reports of increased
iv thrombogenicity after NICM exposure (increase in R time (time to fibrin
formation) (CI 7.8,10.18 minutes) (p=0.036), in K time (dynamics of clot
formation) (CI 2.2,2.8 minutes) (p=0.028), and a reduction in Angle
(decreased acceleration of fibrin build up) (CI 53.10,62.7 degrees)
(p=0.013),MA (reduced ultimate clot strength) (CI 54.5,62.7 mm) (p=0.013)
and (CI) (decreased overall coagulation status) (0.31,1.95) (p=0.032)). This
study also showed that despite this significant reduction in the activation of
coagulation after NICM exposure, PVD patients were consistently
procoagulant when compared to age- matched controls(n=30) who were not
exposed to NICM (R time: p=0.029/K time: p=0.001/Angle: p=0.003/MA:
p=0.020 and CI: p=0.014)
Patients with ischaemic heart disease, a consequence of significant coronary
artery atherosclerosis have reduced amounts of naturally occurring
anticoagulant substances like heparan, heparan-sulphate proteoglycan and
endogenous heparin. Since patients with PVD exhibit similar pathology in
addition to the presence of peripheral ischaemic tissue, to identify any similar
defect in PVD, blood samples from patients with symptomatic PVD(n=28)
and age matched control subjects were analysed using hepTEG. Heparinase
modified TEG analysis identified for the first time, heparinase sensitive
heparin-like activity in peripheral venous samples in patients with PVD (R
time 7.50 0.44 min / CI 6.54, 8.46 Vs 7.17 0.40 min / CI 6.30, 8.05 /
p=0.041). Endogenous heparin-like activity is found to be reduced in PVD
and this reduction also correlated with the degree of peripheral ischaemia
v(ABPI) (correlation coefficient: abpi: 1.000 / change in R time 0.350 /
p=0.021)TEG analysis of samples from 30 patients with aortic aneurysmal disease
and 14 aortic occlusive disease undergoing revascularisation and 30 controls
were carried out using hepTEG method. Baseline TEG parameter values in
the aneurysm group showed significant activation of coagulation when
compared to the controls (R time (p=0.001); K time (p=0.008) and (CI)
(p=0.047)). Following release of the aortic cross-clamp a significant trend
towards activation of coagulation was noted in the aneurysm group and a
similar but pronounced activation of coagulation was noted in the occlusive
group, confirming activation of coagulation following reperfusion of ischaemic
tissues (R time (p=0.042); K time (p=0.043) MA (p= 0.034) and CI (p=0.026)).
Further TEG analysis during postoperative period showed that both these
patient groups exhibit sustained periods of hypercoagulability. In addition to
these findings hepTEG method further revealed underlying
hypercoagulability, despite exogenous heparin administration, confirming
presence and activation of non- AT-III dependent pathways of activation of
coagulation in these patients.
TEG analysis of blood samples from 86 patients admitted with symptoms
peripheral ischaemia requiring revascularisation surgery or amputation were
carried out and TEG parameter values obtained from control group was used
for compari
A Cross European Comparison of Price Levels and Price Dispersion Among Bricks-and-Clicks, Pure Play and Multichannel Retailers
No full textthe paper offers a comparison of internet pricing strategies of three different types of retailers: online, multichannel and traditional retailers.
An empirical analysis is developed in France and Ital
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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