2,037 research outputs found
Ward Round - Paediatric bowel obstruction: A surprising and rare cause of a common problem
A four year old boy presented to Kamuzu Central Hospital for evaluation of five days of progressive nausea, vomiting, and obstipation. History was obtained from the child and mother. For several months prior to presentation he suffered from abdominal discomfort and distension, without diarrhoea, constipation, fevers, chills, or weight loss. Malawi Medical Journal Vol. 20 (3) 2008: pp. 101-10
Defunct brain stem cardiovascular regulation underlies cardiovascular collapse associated with methamphetamine intoxication
<p>Abstract</p> <p>Background</p> <p>Intoxication from the psychostimulant methamphetamine (METH) because of cardiovascular collapse is a common cause of death within the abuse population. For obvious reasons, the heart has been taken as the primary target for this METH-induced toxicity. The demonstration that failure of brain stem cardiovascular regulation, rather than the heart, holds the key to cardiovascular collapse induced by the pesticide mevinphos implicates another potential underlying mechanism. The present study evaluated the hypothesis that METH effects acute cardiovascular depression by dampening the functional integrity of baroreflex via an action on brain stem nuclei that are associated with this homeostatic mechanism.</p> <p>Methods</p> <p>The distribution of METH in brain and heart on intravenous administration in male Sprague-Dawley rats, and the resultant changes in arterial pressure (AP), heart rate (HR) and indices for baroreflex-mediated sympathetic vasomotor tone and cardiac responses were evaluated, alongside survival rate and time.</p> <p>Results</p> <p>Intravenous administration of METH (12 or 24 mg/kg) resulted in a time-dependent and dose-dependent distribution of the psychostimulant in brain and heart. <b/>The distribution of METH to neural substrates associated with brain stem cardiovascular regulation was significantly larger than brain targets for its neurological and psychological effects; the concentration of METH in cardiac tissues was the lowest among all tissues studied. In animals that succumbed to METH, the baroreflex-mediated sympathetic vasomotor tone and cardiac response were defunct, concomitant with cessation of AP and HR. On the other hand, although depressed, those two indices in animals that survived were maintained, alongside sustainable AP and HR. Linear regression analysis further revealed that the degree of dampening of brain stem cardiovascular regulation was positively and significantly correlated with the concentration of METH in key neural substrate involved in this homeostatic mechanism.</p> <p>Conclusions</p> <p>We conclude that on intravenous administration, METH exhibits a preferential distribution to brain stem nuclei that are associated with cardiovascular regulation. We further found that the concentration of METH in those brain stem sites dictates the extent that baroreflex-mediated sympathetic vasomotor tone and cardiac responses are compromised, which in turn determines survival or fatality because of cardiovascular collapse.</p
Quantum jumps of light recording the birth and death of a photon in a cavity
A microscopic system under continuous observation exhibits at random times
sudden jumps between its states. The detection of this essential quantum
feature requires a quantum non-demolition (QND) measurement repeated many times
during the system evolution. Quantum jumps of trapped massive particles
(electrons, ions or molecules) have been observed, which is not the case of the
jumps of light quanta. Usual photodetectors absorb light and are thus unable to
detect the same photon twice. They must be replaced by a transparent counter
'seeing' photons without destroying them3. Moreover, the light has to be stored
over a duration much longer than the QND detection time. We have fulfilled
these challenging conditions and observed photon number quantum jumps.
Microwave photons are stored in a superconducting cavity for times in the
second range. They are repeatedly probed by a stream of non-absorbing atoms. An
atom interferometer measures the atomic dipole phase shift induced by the
non-resonant cavity field, so that the final atom state reveals directly the
presence of a single photon in the cavity. Sequences of hundreds of atoms
highly correlated in the same state, are interrupted by sudden
state-switchings. These telegraphic signals record, for the first time, the
birth, life and death of individual photons. Applying a similar QND procedure
to mesoscopic fields with tens of photons opens new perspectives for the
exploration of the quantum to classical boundary
Quantum field theoretic approach to neutrino oscillations in matter
We consider neutrino oscillations in non-uniform matter in a quantum field
theoretic (QFT) approach, in which neutrino production, propagation and
detection are considered as a single process. We find the conditions under
which the oscillation probability can be sensibly defined and demonstrate how
the properly normalized oscillation probability can be obtained in the QFT
framework. We derive the evolution equation for the oscillation amplitude and
discuss the conditions under which it reduces to the standard
Schr\"odinger-like evolution equation. It is shown that, contrary to the common
usage, the Schr\"odinger-like evolution equation is not applicable in certain
cases, such as oscillations of neutrinos produced in decays of free pions
provided that sterile neutrinos with eV exist.Comment: LaTeX, 24 pages + 16 pages of appendices, 1 figure. V2: typos
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Bespoke Biomolecular Wires for Transmembrane Electron Transfer: Spontaneous Assembly of a Functionalized Multiheme Electron Conduit.
Shewanella oneidensis exchanges electrons between cellular metabolism and external redox partners in a process that attracts much attention for production of green electricity (microbial fuel cells) and chemicals (microbial electrosynthesis). A critical component of this pathway is the outer membrane spanning MTR complex, a biomolecular wire formed of the MtrA, MtrB, and MtrC proteins. MtrA and MtrC are decaheme cytochromes that form a chain of close-packed hemes to define an electron transfer pathway of 185 Å. MtrA is wrapped inside MtrB for solubility across the outer membrane lipid bilayer; MtrC sits outside the cell for electron exchange with external redox partners. Here, we demonstrate tight and spontaneous in vitro association of MtrAB with separately purified MtrC. The resulting complex is comparable with the MTR complex naturally assembled by Shewanella in terms of both its structure and rates of electron transfer across a lipid bilayer. Our findings reveal the potential for building bespoke electron conduits where MtrAB combines with chemically modified MtrC, in this case, labeled with a Ru-dye that enables light-triggered electron injection into the MtrC heme chain
The Epidemiology, Management, Outcomes and Areas for Improvement of Burn Care in Central Malawi: An Observational Study
This report describes the epidemiology of burn injuries and quantifies the appropriateness of use of available interventions at Kamuzu Central Hospital, Malawi, between July 2008 and June 2009 (370 burn patients). Burns accounted for 4.4% of all injuries and 25.9% of all burns presenting to the hospital were admitted. Most patients (67.6%) were < 15 years old and 56.2% were male. The most frequent cause was scalding (51.4%). Burns occurred most frequently in the cool, dry season and in the evening. The mean burn surface area (second/third degree) was 14.1% and most burns (74%) presented within 8 h. The commonest procedure was debridement and/or amputation. The mean hospital stay was 21.1 days, in-hospital mortality was 27% and wound infection rate was 31%. Available interventions (intravenous fluids, nutrition therapy, physiotherapy) were misapplied in 59% of cases. It is concluded that primary prevention should address paediatric and scald burns, and secondary prevention should train providers to use available interventions appropriately
A method for quantifying sectoral optic disc pallor in fundus photographs and its association with peripapillary RNFL thickness
Purpose: To develop an automatic method of quantifying optic disc pallor in
fundus photographs and determine associations with peripapillary retinal nerve
fibre layer (pRNFL) thickness.
Methods: We used deep learning to segment the optic disc, fovea, and vessels
in fundus photographs, and measured pallor. We assessed the relationship
between pallor and pRNFL thickness derived from optical coherence tomography
scans in 118 participants. Separately, we used images diagnosed by clinical
inspection as pale (N=45) and assessed how measurements compared to healthy
controls (N=46). We also developed automatic rejection thresholds, and tested
the software for robustness to camera type, image format, and resolution.
Results: We developed software that automatically quantified disc pallor
across several zones in fundus photographs. Pallor was associated with pRNFL
thickness globally (\b{eta} = -9.81 (SE = 3.16), p < 0.05), in the temporal
inferior zone (\b{eta} = -29.78 (SE = 8.32), p < 0.01), with the nasal/temporal
ratio (\b{eta} = 0.88 (SE = 0.34), p < 0.05), and in the whole disc (\b{eta} =
-8.22 (SE = 2.92), p < 0.05). Furthermore, pallor was significantly higher in
the patient group. Lastly, we demonstrate the analysis to be robust to camera
type, image format, and resolution.
Conclusions: We developed software that automatically locates and quantifies
disc pallor in fundus photographs and found associations between pallor
measurements and pRNFL thickness.
Translational relevance: We think our method will be useful for the
identification, monitoring and progression of diseases characterized by disc
pallor/optic atrophy, including glaucoma, compression, and potentially in
neurodegenerative disorders.Comment: 44 pages, 20 figures, 7 tables, submitte
P-rex1 cooperates with PDGFRβ to drive cellular migration in 3D microenvironments
Expression of the Rac-guanine nucleotide exchange factor (RacGEF), P-Rex1 is a key determinant of progression to metastasis in a number of human cancers. In accordance with this proposed role in cancer cell invasion and metastasis, we find that ectopic expression of P-Rex1 in an immortalised human fibroblast cell line is sufficient to drive multiple migratory and invasive phenotypes. The invasive phenotype is greatly enhanced by the presence of a gradient of serum or platelet-derived growth factor, and is dependent upon the expression of functional PDGF receptor β. Consistently, the invasiveness of WM852 melanoma cells, which endogenously express P-Rex1 and PDGFRβ, is opposed by siRNA of either of these proteins. Furthermore, the current model of P-Rex1 activation is advanced through demonstration of P-Rex1 and PDGFRβ as components of the same macromolecular complex. These data suggest that P-Rex1 has an influence on physiological migratory processes, such as invasion of cancer cells, both through effects upon classical Rac1-driven motility and a novel association with RTK signalling complexes
Acute effects of nicotine on visual search tasks in young adult smokers
Rationale Nicotine is known to improve performance on tests involving sustained attention and recent research suggests that nicotine may also improve performance on tests involving the strategic allocation of attention and working memory. Objectives We used measures of accuracy and response latency combined with eye-tracking techniques to examine the effects of nicotine on visual search tasks. Methods In experiment 1 smokers and non-smokers performed pop-out and serial search tasks. In experiment 2, we used a within-subject design and a more demanding search task for multiple targets. In both studies, 2-h abstinent smokers were asked to smoke one of their own cigarettes between baseline and tests. Results In experiment 1, pop-out search times were faster after nicotine, without a loss in accuracy. Similar effects were observed for serial searches, but these were significant only at a trend level. In experiment 2, nicotine facilitated a strategic change in eye movements resulting in a higher proportion of fixations on target letters. If the cigarette was smoked on the first trial (when the task was novel), nicotine additionally reduced the total number of fixations and refixations on all letters in the display. Conclusions Nicotine improves visual search performance by speeding up search time and enabling a better focus of attention on task relevant items. This appears to reflect more efficient inhibition of eye movements towards task irrelevant stimuli, and better active maintenance of task goals. When the task is novel, and therefore more difficult, nicotine lessens the need to refixate previously seen letters, suggesting an improvement in working memory
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