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Diagnosis and epidemiology of osteoporosis.

PURPOSE OF REVIEW: Osteoporosis remains a major public health problem through its association with fragility fractures. Recent data suggest that the annual cost in Europe is 13 billion euros, mainly accounted for by hospitalisation after fracture. Understanding the epidemiology of osteoporosis is an essential step in developing strategies to reduce the burden of osteoporotic fracture in the population. RECENT FINDINGS: This article will review recent advances surrounding the epidemiology of osteoporosis, the burden of fracture in children and adults in this country and abroad, morbidity associated with such fractures, associations of disease and medication with fragility fracture, and advances in diagnostic techniques and identification of at-risk groups. SUMMARY: The papers studied highlight the wealth of high-quality research in this field, and they help in the visualisation of strategies to identify individuals at high risk of fragility fracture and to quantify fracture risk by measurement of bone density, bone quality, and risk factor algorithms.

Adolescent↗

Visualisation by low-angle shadowing of the leucocyte-common antigen. A major cell surface glycoprotein of lymphocytes.

The leucocyte-common antigen (L-CA) from rat thymocytes is a cell surface glycoprotein of 180 000 apparent mol. wt. with an 80-kd cytoplasmic domain. This paper reports the molecular dimensions of the molecule visualised by electron microscopy after low-angle shadowing. The L-CA monomer consists of a globular head region of approximately 12 nm diameter and a short tail approximately 18 nm long. In deoxycholate both monomers and multimers are seen with aggregation occurring at the head groups. When the detergent is removed, larger clusters are formed with tails extending from a central aggregate. A 100-kd tryptic fragment of L-CA that is known to include the extracellular parts of the molecule also exists in monomer and multimer forms and is seen to have a rod-like structure of length 28 nm without evidence of the head group. Altogether the data indicate that the rod-like structure is found outside the cell and that the extra sequence that forms the head is inside. The tryptic fragment is likely to be derived by cleavage after the transmembrane sequence.

Animals↗

Statistical test for peri-stimulus time histograms in assessing motor neuron activity.

The peri-stimulus time histogram is a valuable tool for evaluating neural connections in humans. To detect the degree to which a conditioning stimulus to a sensory nerve modulates motor neuron activity, a histogram of motor unit spike intervals after a conditioning stimulus is measured. This histogram allows the effect of the conditioning stimulus to be visualised. By comparison with a reference histogram of motor unit spike intervals after a sham stimulus, the noise caused by spontaneous firing sway can be removed. However, no valid statistical test has yet been developed to separate the physiological effect from the spontaneous sway and statistical noise. A computational method has been proposed to detect modulation caused by a conditioning stimulus. To clarify the effect of a conditioning stimulus, this new method used reference histograms to calculate a confidence interval. A simulated experiment demonstrated that about 2000 re-samplings were sufficient to estimate a confidence interval for a histogram with 1 ms bin width constructed from 300 triggers. Testing of the experimental data, measured from the tibialis anterior muscles during the elicitation of the excitatory spinal reflex, confirmed that significant peaks were produced at 30, 34, 35 and 38ms after the conditioning stimulus. These correspond appropriately to the delay of the spinal reflex.

Electric Stimulation↗

Sulphation of the salivary mucin MG1 (MUC-5B) is not correlated to the degree of its sialylation and is unaffected by cystic fibrosis.

Defective acidification of intracellular organelles, particularly the trans-Golgi network, has been proposed to explain the decreased sialylation and increased sulphation of secreted proteins in cystic fibrosis (CF). To test this hypothesis we compared expression of sulphate and sialic acid on three salivary mucins namely MG1 (MUC-5B), MG2 (MUC-7) and GL. Proteins in whole mouth saliva (WMS) from four individuals were separated by fast protein liquid chromatography (FPLC) on a Superdex 200 column and the partially purified mucins slot-blotted and assayed for sulphate content by staining with Alcian Blue. Sulphation varied with the individual and with the mucin: MG1 was the most sulphated and contributed almost the entire sulphate content of WMS. These results allowed us to test small volumes of WMS from 20 CF patients and age- and sex-matched controls for estimates of sulphate content on MG1. Wherever possible sulphate on MG1 was also visualised by staining washed SDS-PAGE gels with Alcian Blue at pH 1.0. To assess the sialic acid content of salivary mucins, electroblots of SDS-PAGE gels were probed with labelled Triticum vulgaris agglutinin. In summary, our results show MG1 to be the main sulphated protein in whole mouth saliva and there are large differences in the expression of sulphate and of sialic acid on this mucin, both in control and CF groups. CF led neither a decrease in sialylation nor an increase in sulphation and direct comparisons of sialic acid content with sulphate in MG1 failed to reveal any obvious link between the two in health or in disease. Our data thus do not support the hypothesis of defective acidification as the underlying cause of altered glycosylation in CF, but point instead to inter-individual differences in expression/functioning of terminal glycosyltransferases for published observations. We thank the European Union Biomed II programme for support.

Acids↗

Subcellular localization of neuronal nitric oxide synthase in the rat nucleus of the solitary tract in relation to vagal afferent inputs.

In the nucleus of the solitary tract (NTS), nitric oxide (NO) modulates neuronal circuits controlling autonomic functions. A proposed source of this NO is via nitric oxide synthase (NOS) present in vagal afferent fibre terminals, which convey visceral afferent information to the NTS. Here, we first determined with electron microscopy that neuronal NOS (nNOS) is present in both presynaptic and postsynaptic structures in the NTS. To examine the relationship of nNOS to vagal afferent fibres the anterograde tracer biotinylated dextran amine was injected into the nodose ganglion and detected in brainstem sections using peroxidase-based methods. nNOS was subsequently visualised using a pre-embedding immunogold procedure. Ultrastructural examination revealed nNOS immunoreactivity in dendrites receiving vagal afferent input. However, although nNOS-immunoreactive terminals were frequently evident in the NTS, none were vagal afferent in origin. Dual immunofluorescence also confirmed lack of co-localisation. Nevertheless, nNOS immunoreactivity was observed in vagal afferent neurone cell bodies of the nodose ganglion. To determine if these labelled cells in the nodose ganglion were indeed vagal afferent neurones nodose ganglion sections were immunostained following application of cholera toxin B subunit to the heart. Whilst some cardiac-innervating neurones were also nNOS immunoreactive, nNOS was never detected in the central terminals of these neurones. These data show that nNOS is present in the NTS in both pre- and postsynaptic structures. However, these presynaptic structures are unlikely to be of vagal afferent origin. The lack of nNOS in vagal afferent terminals in the NTS, yet the presence in some vagal afferent cell bodies, suggests it is selectively targeted to specific regions of the same neurones.

Animals↗

Calprotectin inhibits matrix metalloproteinases by sequestration of zinc.

BACKGROUND/AIMS: Calprotectin, a 36 kDa protein present in neutrophil cytoplasm, has antimicrobial and apoptosis inducing activities, which are reversed by the addition of zinc. Matrix metalloproteinases (MMPs), a family of zinc dependent enzymes, are important in many normal biological processes including embryonic development, angiogenesis, and wound healing, but also pathological processes such as inflammation, cancer, and tissue destruction. The aim of this study was to investigate whether calprotectin can inhibit MMP activity, and whether such inhibition could be overcome by the addition of zinc. METHODS: MMP activity was measured by the degradation of substrates precoated on to microwells, and visualised by Coomassie blue staining of residual substrate. Seven metalloproteinases (MMP-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9, and MMP-13) were tested against two substrates: gelatin and alpha-casein. RESULTS: All MMPs except MMP-1 were active against gelatin, whereas MMP-7 was the only enzyme active against alpha-casein. The addition of calprotectin inhibited the activity of all the MMPs, but different concentrations of the protein, from 0.3 microM to > 11microM, were necessary to produce a 50% inhibition of the MMPs. Inhibition by calprotectin was largely overcome by the addition of zinc. CONCLUSIONS: The findings suggest that calprotectin inhibits MMPs by sequestration of zinc. The data also suggest that MMPs have different affinities for zinc and that calprotectin has a lower zinc affinity than the MMPs.

Caseins↗

Voltage sensing in ion channels: a 50-year-old mystery resolved?

CONTEXT: Membrane-protein ion channels control electrical activity in the nervous system. Voltage-gated channels have four-fold symmetry, with a central pore domain surrounded by voltage-sensor regions. Each voltage-sensor region has a positively charged transmembrane helix, S4, which carries gating charges through the membrane on opening or closing. How S4 moves at gating is debated: either S4 moves in a helical screw or in a helical twist pattern. In both cases S4 is assumed to move inside the densely packed channel protein. The pore region was visualised when Roderick MacKinnon's group crystallised a bacterial K+ channel in 1998. The voltage-sensor region and the S4 movement are more difficult to visualise, because voltage-gated channels are harder to crystallise. STARTING POINT: Recently, Yuoxing Jiang and colleagues in MacKinnon's group reported the first successful crystallisation and X-ray analysis of a voltage-gated channel (Nature 2003; 423: 33-41, 42-48), with unexpected results. S4 forms a hairpin loop with another helix, stretching out from the channel perimeter rather than being located inside the densely-packed protein core. This finding suggests a novel type of S4 movement at gating, a paddle sweeping through the lipid bilayer in response to voltage changes. WHERE NEXT? Jiang and colleagues' unexpected results are controversial. Several predictions of the model are incompatible with other experimental data. However, if the paddle configuration is real, it opens up a new field for pharmacological rethinking. Such a configuration may help to understand certain aspects of the action of lipid-soluble gating modifiers, such as local and general anaesthetics and antiarrythmic and antiepileptic agents.

Crystallography, X-Ray↗

Effect of pyrolysis temperature on composition, surface properties and thermal degradation rates of Brazil Nut shells.

Changes in chemical and surface characteristics of Brazil Nut shells (Bertholletia excelsa) due to pyrolysis at different temperatures (350 degrees C, 600 degrees C, 850 degrees C) were examined. For this purpose, proximate and ultimate analyses, physical adsorption measurements of N2 (-196 degrees C) and CO, (25 degrees C) as well as samples visualisation by scanning electronic microscopy (SEM) were performed. Appreciable differences in the residue characteristics, depending markedly on the pyrolysis temperature, were observed. Release of volatile matter led to the development of pores of different sizes. Progressive increases in micropore development with increasing pyrolysis temperature took place, whereas a maximum development of larger pores occurred at 600 degrees C. Furthermore, kinetics measurements of Brazil Nut shells pyrolysis from ambient temperature up to 900 degrees C were performed by non-isothermal thermogravimetric analysis. A model taking into account the significant changes in the residue during pyrolysis, through an increase in the activation energy with temperature and solid conversion, were found to properly fit the kinetics data over the wide range of degradation investigated.

Kinetics↗

Application of non-parametric regression to quantitative structure-activity relationships.

Several non-parametric regressors have been applied to modelling quantitative structure-activity relationship (QSAR) data. Performances were benchmarked against multilinear regression and the nonlinear method of smoothing splines. Variable selection was explored through systematic combinations of different variables and combinations of principal components. For the training set examined--539 inhibitors of the tyrosine kinase, Syk--the best two-descriptor model had a 5-fold cross-validated q2 of 0.43. This was generated by a multi-variate Nadaraya-Watson kernel estimator. A subsequent, independent, test set of 371 similar chemical entities showed the model had some predictive power. Other approaches did not perform as well. A modest increase in predictive ability can be achieved with three descriptors, but the resulting model is less easy to visualise. We conclude that non-parametric regression offers a potentially powerful approach to identifying predictive, low-dimensional QSARs.

Databases, Factual↗

Spatial scale interactions in stereo sensitivity and the neural representation of binocular disparity.

How are binocular disparities encoded and represented in the human visual system? An 'encoding cube' diagram is introduced to visualise differences between competing models. To distinguish the models experimentally, the depth-increment-detection function (discriminating disparity d from d +/- delta d) was measured as a function of standing disparity (d) with spatially filtered random-dot stereograms of different centre spatial frequencies. Stereothresholds degraded more quickly as standing disparity was increased with stimuli defined by high rather than low centre spatial frequency. This is consistent with a close correlation between the spatial scale of detection mechanisms and the disparities they process. It is shown that a simple model, where discrimination is limited by the noisy ratio of outputs of three disparity-selective mechanisms at each spatial scale, can account for the data. It is not necessary to invoke a population code for disparity to model the depth-increment-detection function. This type of encoding scheme implies insensitivity to large interocular phase differences. Might the system have developed a strategy to disambiguate or shift the matches made at fine scales with those made at the coarse scales at large standing disparities? In agreement with Rohaly and Wilson, no evidence was found that this is so. Such a scheme would predict that stereothresholds determined with targets composed of compounds of high and low frequency should be superior to those of either component alone. Although a small stereoacuity benefit was found at small disparities, the more striking result was that stereothresholds for compound-frequency targets were actually degraded at large standing disparities. The results argue against neural shifting of the matching range of fine scales by coarse-scale matches posited by certain stereo models.

Computer Graphics↗

3D structure of relaxed fish muscle myosin filaments by single particle analysis.

To understand the structural changes involved in the force-producing myosin cross-bridge cycle in vertebrate muscle it is necessary to know the arrangement and conformation of the myosin heads at the start of the cycle (i.e. the relaxed state). Myosin filaments isolated from goldfish muscle under relaxing conditions and viewed in negative stain by electron microscopy (EM) were divided into segments and subjected to three-dimensional (3D) single particle analysis without imposing helical symmetry. This allowed the known systematic departure from helicity characteristic of vertebrate striated muscle myosin filaments to be preserved and visualised. The resulting 3D reconstruction reveals details to about 55 A resolution of the myosin head density distribution in the three non-equivalent head 'crowns' in the 429 A myosin filament repeat. The analysis maintained the well-documented axial perturbations of the myosin head crowns and revealed substantial azimuthal perturbations between crowns with relatively little radial perturbation. Azimuthal rotations between crowns were approximately 60 degrees , 60 degrees and 0 degrees , rather than the regular 40 degrees characteristic of an unperturbed helix. The new density map correlates quite well with the head conformations analysed in other EM studies and in the relaxed fish muscle myosin filament structure modelled from X-ray fibre diffraction data. The reconstruction provides information on the polarity of the myosin head array in the A-band, important in understanding the geometry of the myosin head interaction with actin during the cross-bridge cycle, and supports a number of conclusions previously inferred by other methods. The observed azimuthal head perturbations are consistent with the X-ray modelling results from intact muscle, indicating that the observed perturbations are an intrinsic property of the myosin filaments and are not induced by the proximity of actin filaments in the muscle A-band lattice. Comparison of the axial density profile derived in this study with the axial density profile of the X-ray model of the fish myosin filaments which was restricted to contributions from the myosin heads allows the identification of a non-myosin density peak associated with the azimuthally perturbed head crown which can be interpreted as a possible location for C-protein or X-protein (MyBP-C or -X). This position for C-protein is also consistent with the C-zone interference function deduced from previous analysis of the meridional X-ray pattern from frog muscle. It appears that, along with other functions, C-(X-) protein may have the role of slewing the heads of one crown so that they do not clash with the neighbouring actin filaments, but are readily available to interact with actin when the muscle is activated.

Animals↗

Alterations of CAP audiogram by increased endolymphatic pressure and its relation to hydrops.

Most current theories regarding the inner ear pathology of Menières disease assume that there is an augmentation of the endolymphatic pressure due to the presence of hydrops. In this study normal hearing pigmented guinea pigs were employed to investigate the effect of increased endolymphatic pressure on the compound action potential (CAP) audiogram. All animals were implanted with an electrode on the round window and the CAP audiogram was determined prior to further surgery. The endolymphatic canal was then visualised by a posterior fossa intra-dural surgical approach. A hole was pierced in the canal and a cannula inserted. The CAP audiogram was again determined before, and at frequent intervals after, the application of hydrostatic pressure (0.5-1 cm Hg). A similar sequence of CAP sensitivity losses was observed within 2 h for 0.5 cm Hg or 15 min for 1 cm Hg. There was at first a very high frequency loss, followed by a very low frequency loss and finally a mid frequency sensitivity loss rendered the audiogram flat and lying around 50 dB sound pressure level. Given that the first characteristic index for experimental hydrops is a low frequency loss the present data suggest that an increase in endolymphatic pressure, as in these experiments, is likely to be a rather late pathological feature of hydrops. Indeed we have shown that a high frequency loss develops at a second phase during the evolution of hydrops.

Action Potentials↗

Evaluation of virtual reality bronchoscopy as a learning and assessment tool.

BACKGROUND: Conventional training in bronchoscopy involves a trainee performing on a real patient under supervision. This method of training is not only expensive, but there is also potential for increased patient discomfort. Simulators permit the acquisition of necessary technical skills required for the procedure. Virtual reality (VR) has been an integral part of training in aviation, and the application of this technology in medical training needs to be evaluated. OBJECTIVE: This study was conducted to evaluate the efficacy of a VR bronchoscopy simulator as a learning and assessment tool. METHODS: The bronchoscopic simulator (HT Medical Systems, Maryland, USA) is a VR computer programme. The simulator has the ability to assess competence by a set of parameters, which formed the data for the study. Nine novices without previous bronchoscopic experience formed the study group (group 1). Nine experienced bronchoscopists having performed between 200 and 1000 bronchoscopies formed the other group (group 2). We assessed the efficacy of the system as a learning tool by studying whether there was a significant difference between the first and subsequent sessions of the subjects from group 1 and by comparing the performance of the two groups. Statistical analysis was done using the Mann-Whitney U test and the Wilcoxon signed ranks test. RESULTS: There was a significant difference in performance between the first attempt of group 1 and the performance of the experts in terms of percentage of segments visualised and number of wall collisions and the economy of performance. Among the subjects from group 1, there was a significant improvement in percentage of segments visualised by the third attempt (p = 0.04), in the economy of performance by the sixth attempt (0.008) and in the number of wall collisions by the sixth attempt (0.024). When each attempt of the novices was compared with the performance of group 2, the significance in the difference of the percentage of segments studied (p = 0.09) and the economy of performance disappeared by the third attempt (0.06), while the difference in the number of wall collisions disappeared by the fifth attempt (p = 0.06). CONCLUSIONS: This study has been able to establish the face, construct and content validity of the simulator and the potential for it to be an effective training tool.

Bronchoscopy↗

Fatal head injury in children: a new approach to scoring axonal and vascular damage.

As part of a multidisciplinary study of brain damage in children fatally injured in motor vehicle accidents, a simple method to quantify and visualise the distribution and extent of injury has been developed. Vascular and axonal injury were assessed using coronal brain sections stained for haematoxylin and eosin, or reacted immunohistochemically for beta-amyloid precursor protein. Subsequent analysis was carried out using NIH Image software, and the resulting information is displayed in schematic diagrams. These summary diagrams simply and clearly show the distribution of injury in both the coronal and horizontal planes. This technique offers an advantage over previous scoring methods in that it provides both a quantitative and a visual summary of the distribution and extent of brain injury. This information can then be used to compare the injury distribution and severity with estimated impact points and acceleration data.

Accidents, Traffic↗

Differential vulnerability of the rat retina, suprachiasmatic nucleus and intergeniculate leaflet to malnutrition induced during brain development.

We investigated in young rats the effects of malnutrition on the main structures of the circadian timing system: retina, hypothalamic suprachiasmatic nuclei (SCN), thalamic intergeniculate leaflet, retinohypothalamic- and geniculohypothalamic tracts. Control rats were born from mothers fed a commercial diet since gestation, and malnourished rats from mothers fed a multideficient diet since gestation (GLA group) or lactation (LA group). After weaning, pups received the same diet as their mothers, and were analysed at postnatal days 27, 30-33 and 60-63. Brain sections were processed to visualise in the SCN neuropeptide Y immunoreactivity and terminal labeling after intraocular tracer injections. Nissl staining was used to assess cytoarchitectonic boundaries of the SCN and cell features in retinal whole mounts. Cell counts, morphometric and densitometric analysis were performed. Compared with controls, the total retinal surface was reduced and the topographical distribution of retinal ganglion cells was altered in malnourished rats, with changes in their density. Alterations were also detected in the SCN dimensions in the GLA and LA groups at one and two postnatal months, as well as in the SCN portion occupied by the retinal input in the GLA group at days 30-33, but not in the NPY-containing geniculohypothalamic tract. The present data point to subtle changes, with a low and differential vulnerability to early malnutrition, of structures involved in circadian timing regulation. Furthermore, the present findings suggest that the altered circadian rhythmicity previously documented in malnourished rats cannot be ascribed to impaired development of the retino- and geniculohypothalamic projections to the SCN.

Age Factors↗

Chemical composition of the attachment pad secretion of the locust Locusta migratoria.

This study is the first attempt to characterise the chemical composition of the secretion of the smooth pads of the locust Locusta migratoria and to relate this to the composition of the cuticle coverage of the pads and the wings. Gas-chromatography and mass-spectrometry (GC-MS) were the principal techniques used for the characterization of these materials. Secretion droplets were visualised and quantified with the aid of diverse microscopic techniques. The chemical composition of prints is shown to differ from the cuticle coverage, in particular, with respect to the fatty acid distribution: in the secretion, saturated and unsaturated fatty acids with chain lengths between C(16) and C(20) in both the free form and as glycerides predominate, whereas cuticle coverage contains waxes of long-chained fatty-acids bound to long-chain primary alcohols. The second important difference is the significant amount of glucose and other saccharides found in methanolyzates of the pad fluid. A considerable amount of the amino acids (up to 53%) was detected in the non-volatile portion of the fluid. Data obtained from the shock-freezing, carbon-platinum coating and replica preparation show that the secretory droplets contain nano-droplets on their surfaces. The results lead us to suggest that the pad secretion is an emulsion consisting of lipidic nano-droplets dispersed in an aqueous liquid. According to the chemical composition of the secretion, a high-viscosity of the fluid may be suggested. Presumably, the fluid is a kind of a coupling agent, promoting and strengthening adhesion between otherwise incompatible materials by providing the proximity of contact for intermolecular forces.

Amino Acids↗

[New data in cardiology: the electric charge of the heart].

This study emerging from profound consideration of the basis of vectorcardiography reveals a new electric model of the heart, the starting point for a computer programme of which only the principle is described. Noting inadequacies of vectorcardiography linked to necessary but possibly excessive simplifications, the author suggests a solution based only on Einthoven's postulate of a single dipole: at each instant during the cardiac revolution, the positions of point N, the centre of negative charges and origin of the dipole, of point P, the centre of positive charges and extremity of the dipole, and the value of the load borne by this dipole are calculated. The classical orientations of septal, parietal and basal vectors are thus found. It is shown that electric charge follows a bell-shaped curve and that the velocity of the dipole is compatible with that of the depolarisation wave, in contrast to velocities given by vectorcardiography. The trajectory of the dipole, a veritable "dipologram" visualises breaks in continuity which are interpreted. This new method has the advantage of being entirely confirmable: the dipole provided by the programme enables the calculation of potentials. Comparison between measured potentials and calculated potentials ensures the reliability of results provided by this programme. This method is totally in contrast with conventional vectorcardiography: the dipole is entirely mobile regarding both its origin and extremity, its site in the thorax is precisely identified, and its length is calculated, together with its velocity and the charge which it carries.(ABSTRACT TRUNCATED AT 250 WORDS)

Electricity↗

Characterisation of three-dimensional anatomic shapes using principal components: application to the proximal tibia.

The objective of the research is to determine if principal component analysis (PCA) provides an efficient method to characterise the normative shape of the proximal tibia. Bone surface data, converted to analytical surface descriptions, are aligned, and an auto-associative memory matrix is generated. A limited subset of the matrix principal components is used to reconstruct the bone surfaces, and the reconstruction error is assessed. Surface reconstructions based on just six (of 1452) principal components have a mean root-mean-square (RMS) reconstruction error of 1.05% of the mean maximum radial distance at the tibial plateau. Surface reconstruction of bones not included in the auto-associative memory matrix have a mean RMS error of 2.90%. The first principal component represents the average shape of the sample population. Addition of subsequent principal components represents the shape variations most prevalent in the sample and can be visualised in a geometrically meaningful manner. PCA offers an efficient method to characterise the normative shape of the proximal tibia with a high degree of dimensionality reduction.

Adult↗