Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Distance”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed2007

Predicting biliary complications in right lobe liver transplant recipients according to distance between donor's bile duct and corresponding hepatic artery.

PURPOSE: To retrospectively determine whether biliary complications in recipients of living-donor right lobe liver grafts can be predicted at pretransplantation donor computed tomography (CT). MATERIALS AND METHODS: The human research committee approved this study. The requirement for informed consent was waived. Multi-detector row CT cholangiography and CT angiography were performed in 44 consecutive right lobe liver donors (25 men, 19 women; mean age, 37 years). When CT cholangiography in the donor demonstrated the right biliary anatomy (conventional or variant), the shortest distance between the right main (or second-order) hepatic artery and the corresponding right main (or second-order) bile duct was measured and compared with posttransplantation biliary complications in the transplant recipient by using generalized estimating equations. RESULTS: In 22 transplant recipients with one right main duct-to-common duct anastomosis (ie, conventional donor anatomy), the distance between the donor's right main bile duct and hepatic artery generally was small (mean distance, 3.8 mm; range, 1-14 mm) and unrelated (P=.46) to biliary complications (n=6). In 22 recipients who required two second-order right duct anastomoses (ie, with variant donor anatomy), the distance between the donor's second-order duct and corresponding hepatic artery was more variable (mean distance, 6.6 mm; range, 1-32.5 mm), and biliary complications were significantly more common when this distance was 10 mm or greater (in eight of 13 ducts with conventional anatomy and four of 31 ducts with variant anatomy, P<.05). CONCLUSION: Right lobe liver graft recipients who have variant right biliary anatomy and a second-order bile duct 10 mm or farther from the corresponding hepatic artery are at high risk for biliary complications, possibly because of a predisposition to ischemic injury.

Adult↗
PubMed1998

Effective diffusion distance of nitric oxide in the microcirculation.

Despite its well-documented importance, the mechanism for nitric oxide (NO) transport in vivo is still unclear. In particular, the effect of hemoglobin-NO interaction and the range of NO action have not been characterized in the microcirculation, where blood flow is optimally regulated. Using a mathematical model and experimental data on NO production and degradation rates, we investigated factors that determine the effective diffusion distance of NO in the microcirculation. This distance is defined as the distance within which NO concentration is greater than the equilibrium dissociation constant (0.25 microM) of soluble guanylyl cyclase, the target enzyme for NO action. We found that the size of the vessel is an important factor in determining the effective diffusion distance of NO. In approximately 30- to 100-micron-ID microvessels the luminal NO concentrations and the abluminal effective diffusion distance are maximal. Furthermore, the model suggests that if the NO-erythrocyte reaction rate is as fast as the rate reported for the in vitro NO-hemoglobin reaction, the NO concentration in the vascular smooth muscle will be insufficient to stimulate smooth muscle guanylyl cyclase effectively. In addition, the existence of an erythrocyte-free layer near the vascular wall is important in determining the effective NO diffusion distance. These results suggest that 1) the range of NO action may exhibit significant spatial heterogeneity in vivo, depending on the size of the vessel and the local chemistry of NO degradation, 2) the NO binding/ reaction constant with hemoglobin in the red blood cell may be much smaller than that with free hemoglobin, and 3) the microcirculation is the optimal site for NO to exert its regulatory function. Because NO exhibits vasodilatory function and antiatherogenic activity, the high NO concentration and its long effective range in the microcirculation may serve as intrinsic factors to prevent the development of systemic hypertension and atherosclerotic pathology in microvessels.

Animals↗
PubMed1995

Effects of muscle-to-electrode distance on the human diaphragm electromyogram.

It has been suggested that esophageal recordings of the diaphragm electromyogram (EMGdi) are influenced by changes in chest wall configuration. Whether the changes are of physiological or artifactual origin is unclear. For example, the distance between the esophageal electrode and the diaphragm is likely to alter with chest wall configuration and may lead to misinterpretations of EMGdi. The aims of this study were 1) to evaluate and quantify the effect of the muscle-to-electrode (ME) distance filter on EMGdi, as obtained with a multiple-array esophageal electrode, 2) to take advantage of the ME distance filter to locate the position of the diaphragm with respect to the electrode, and 3) to evaluate the influence of lung volume and chest wall configuration on EMGdi center frequency (CF) while controlling for the ME distance filter and signal quality. Five subjects performed six static contractions of the diaphragm at each of seven chest wall configurations, as evaluated by the method of K. Konno and J. Mead (J. Appl. Physiol. 22: 407-422, 1967). EMGdi was measured with seven pairs of electrodes mounted on an esophageal catheter. The pair of electrodes whose EMGdi power spectra were the least filtered by the ME distance was assumed to be closest to the diaphragm. The results of the study indicated that 1) EMGdi power spectra were strongly affected by the distance between the diaphragm and the electrodes. CF decreased by approximately 1 Hz/mm displacement away from the electrode pair closest to the diaphragm; and 2) no systematic relationship was found between changes in chest wall configuration and CF, when CF was measured from the electrode pair closest to the diaphragm. We conclude that the EMGdi CF can be reliably measured with a multiple-array esophageal electrode that covers the span of diaphragmatic excursion and by selecting the pair of electrodes that is the closest to the diaphragm.

Diaphragm↗
PubMed1999

The effect of cigarette smoking status on six-minute walk distance in patients with intermittent claudication.

The purposes of the study were threefold: (1) to compare 6-minute walk performance as a measure of exercise tolerance among three different groups of peripheral arterial occlusive disease (PAOD) patients with intermittent claudication-current smokers, former smokers, and patients who have never smoked; (2) to identify important covariates that might affect the relationship between smoking and exercise in the PAOD population; (3) to determine whether differences among the three groups in 6-minute walk performance persist after statistically controlling for the significant covariates. Recruited into the study were 415 PAOD patients with intermittent claudication between the ages of 42 and 88 years. The self-reported smoking status consisted of 182 current smokers, 196 former smokers, and 37 patients who had never smoked. The authors recorded 6-minute walk distance, a reliable measurement of exercise tolerance in PAOD patients, as well as age, body composition, self-reported ambulatory function, self-reported physical activity, and standard peripheral hemodynamics. Nonsmokers walked significantly farther (413 +/- 14 m; mean +/- standard error) and took more steps (665 +/- 14 steps) than either current (352 +/- 7 m; 563 +/- 9 steps) or former smokers 370 +/- 7 m; 600 +/- 8 steps) (p<0.05). The nonsmokers had a higher ankle-brachial index (ABI) value (0.70 +/- 0.03) than patients who actively smoked 0.62 +/- 0.01 (p<0.03); the authors observed an inverse relationship between smoking history and self-reported physical activity (WIQ Distance Score: nonsmokers 51 +/- 6%, former smokers 38 +/- 3%, and smokers 32 +/- 2%) (p<0.01). From a multivariate perspective, ABI, physical activity, and perceived walking ability were the only independent predictors of 6-minute walk distance. Differences in the adjusted 6-minute walk distance among the nonsmokers (388 +/- 13 m), current smokers (359 +/- 6 m), and former smokers (368 +/-6 m) no longer remained after controlling statistically for these covariates. The findings suggest that 6-minute walk distance is a sensitive measure to detect differences in submaximal exercise performance between smoking and nonsmoking PAOD patients with intermittent claudication. Moreover, the group difference in the 6-minute walk distance is explained by group differences in walking perception, PAOD severity, and physical activity level.

Adult↗
PubMed1978

Mean energy imparted in relation to the focus to object distance.

The relationship between the energy absorbed by the patient at the exposure of a radiographic image and the focus to object distance is analysed. It is found that the mean energy imparted, or the integral absorbed dose, is the same irrespective of the focus to object distance when the energy fluence and the field size are both normalized at the film plane. When the field size is kept constant within the object whilst the focus to object distance is varied a limited increase in the mean energy imparted occurs when the focus to object distance is decreased; this statement is valid for the focus to object distances which are usually applied in diagnostic radiology. When estimating radiation risks the importance of the focus to object distance is found to be of limited interest.

Absorption↗
PubMedDate not supplied

Risk of injury during alpine and telemark skiing and snowboarding. The equipment-specific distance-correlated injury index.

Estimation of injury risk in alpine sports is difficult. We present a new method of calculating an injury index related to the distance traveled on ski or snowboard. The distance-correlated injury index equals the number of injuries per 100,000 km traveled distance. This injury index can also be correlated to the type of equipment used. The equipment-specific distance-correlated injury index is the same as the distance-correlated injury index, but it is sport-specific. We found the distance-correlated injury index for alpine skiing to be 3.9 (95% Cl = 2.8 to 5.4); for snowboarding, 13.5 (95% Cl = 8.3 to 22.0); and for telemark skiing, 3.0 (95% Cl = 1.0 to 9.4), suggesting a three- to four-times higher incidence of injuries requiring hospital treatment among snowboarders than among alpine and telemark skiers.

Athletic Injuries↗
PubMed1995

Correlation of travel time on roads versus straight line distance.

Studies of hospital demand and choice of hospital have used straight line distance from a patient's home to hospitals as a measure of geographic access, but there is the potential for bias if straight line distance does not accurately reflect travel time. Travel times for unimpeded travel between major intersections in upstate New York were compared with distances between these points. The correlation between distance and travel time was 0.987 for all observations and 0.826 for distances less than 15 miles. These very high correlations indicate that straight line distance is a reasonable proxy for travel time in most hospital demand or choice models, especially those with large numbers of hospitals. The authors' outlier analyses show some exceptions, however, so this relationship may not hold for studies focusing on specific hospitals, very small numbers of hospitals, or studies in dense urban areas with high congestion and reliance on surface streets.

Catchment Area, Health↗
PubMed2002

Endoscopic telerobotics for neurosurgery: preliminary study for optimal distance between an object lens and a target.

To overcome limited maneuverability and procedures in the endoscopic neurosurgery, and to utilize its maximum potential ability, the HUMAN (hyper-utility mechatronic assistant) system has been developed. The system has a rigid three-dimensional endoscope with built-in three guiding-manipulators completely controlled as a slave robot by a surgeon in a remote place. To use this system most efficiently, we investigated the suitable distance between an object lens of the endoscope and a target. Actual working territory (AWT) and actual working angle (AWA) of the forceps in the endoscopical operative field (EOF) were measured by changing the distance between the lens and the target. AWT ratio (AWT/EOF) and AWA ratio (AWA/360) decreased from 58% to 12% and increased from 39% to 85% respectively as the distance became longer. When the distance exceeds 13 mm, AWA did not increase more than 85%, and AWT kept decreasing. For the effective use of the system, the optimal distance between the lens and the target should be within 13 mm, and the system will demonstrate its ability to the maximum at the distance of 8mm.

Endoscopes↗
PubMed2004

Inter-residue distances derived from fold contact propensities correlate with evolutionary substitution costs.

BACKGROUND: The wealth of information on protein structure has led to a variety of statistical analyses of the role played by individual amino acid types in the protein fold. In particular, the contact propensities between the various amino acids can be converted into folding energies that have proved useful in structure prediction. The present study addresses the relationship of protein folding propensities to the evolutionary relationship between residues. RESULTS: The contact preferences of residue types observed in a representative sample of protein structures are converted into a residue similarity matrix or inter-residue distance matrix. Remarkably, these distances correlate excellently with evolutionary substitution costs. Residue vectors are derived from the distance matrix. The residue vectors give a concrete picture of the grouping of residues into families sharing properties crucial for protein folding. CONCLUSIONS: Inter-residue distances have proved useful in showing the explicit relationship between contact preferences and evolutionary substitution rates. It is proposed that the distance matrix derived from structural analysis may be useful in aligning proteins where remote homologs share structural features. Residue vectors derived from the distance matrix illustrate the spatial arrangement of residues and point to ways in which they can be grouped.

Amino Acid Substitution↗
PubMed2005

Evolutionary distance estimation and fidelity of pair wise sequence alignment.

BACKGROUND: Evolutionary distances are a critical measure in comparative genomics and molecular evolutionary biology. A simulation study was used to examine the effect of alignment accuracy of DNA sequences on evolutionary distance estimation. RESULTS: Under the studied conditions, distance estimation was relatively unaffected by alignment error (50% or more of the sites incorrectly aligned) as long as 50% or more of the sites were identical among the sequences (observed P-distance < 0.5). Beyond this threshold, the alignment procedure artificially inflates the apparent sequence identity, skewing distance estimates, and creating alignments that are essentially indistinguishable from random data. This general result was independent of substitution model, sequence length, and insertion and deletion size and rate. CONCLUSION: Examination of the estimated sequence identity may yield some guidance as to the accuracy of the alignment. Inaccurate alignments are expected to have large effects on analyses dependent on site specificity, but analyses that depend on evolutionary distance may be somewhat robust to alignment error as long as fewer than half of the sites have diverged.

Algorithms↗
PubMed2006

PepDist: a new framework for protein-peptide binding prediction based on learning peptide distance functions.

BACKGROUND: Many different aspects of cellular signalling, trafficking and targeting mechanisms are mediated by interactions between proteins and peptides. Representative examples are MHC-peptide complexes in the immune system. Developing computational methods for protein-peptide binding prediction is therefore an important task with applications to vaccine and drug design. METHODS: Previous learning approaches address the binding prediction problem using traditional margin based binary classifiers. In this paper we propose PepDist: a novel approach for predicting binding affinity. Our approach is based on learning peptide-peptide distance functions. Moreover, we suggest to learn a single peptide-peptide distance function over an entire family of proteins (e.g. MHC class I). This distance function can be used to compute the affinity of a novel peptide to any of the proteins in the given family. In order to learn these peptide-peptide distance functions, we formalize the problem as a semi-supervised learning problem with partial information in the form of equivalence constraints. Specifically, we propose to use DistBoost, which is a semi-supervised distance learning algorithm. RESULTS: We compare our method to various state-of-the-art binding prediction algorithms on MHC class I and MHC class II datasets. In almost all cases, our method outperforms all of its competitors. One of the major advantages of our novel approach is that it can also learn an affinity function over proteins for which only small amounts of labeled peptides exist. In these cases, our method's performance gain, when compared to other computational methods, is even more pronounced. We have recently uploaded the PepDist webserver which provides binding prediction of peptides to 35 different MHC class I alleles. The webserver which can be found at http://www.pepdist.cs.huji.ac.il is powered by a prediction engine which was trained using the framework presented in this paper. CONCLUSION: The results obtained suggest that learning a single distance function over an entire family of proteins achieves higher prediction accuracy than learning a set of binary classifiers for each of the proteins separately. We also show the importance of obtaining information on experimentally determined non-binders. Learning with real non-binders generalizes better than learning with randomly generated peptides that are assumed to be non-binders. This suggests that information about non-binding peptides should also be published and made publicly available.

Algorithms↗
PubMed2006

PATRISTIC: a program for calculating patristic distances and graphically comparing the components of genetic change.

BACKGROUND: Phylogenies are commonly used to analyse the differences between genes, genomes and species. Patristic distances calculated from tree branch lengths describe the amount of genetic change represented by a tree and are commonly compared with other measures of mutation to investigate the substitutional processes or the goodness of fit of a tree to the raw data. Up until now no universal tool has been available for calculating patristic distances and correlating them with other genetic distance measures. RESULTS: PATRISTICv1.0 is a java program that calculates patristic distances from large trees in a range of file formats and allows graphical and statistical interpretation of distance matrices calculated by other programs. CONCLUSION: The software overcomes some logistic barriers to analysing signals in sequences. In additional to calculating patristic distances, it provides plots for any combination of matrices, calculates commonly used statistics, allows data such as isolation dates to be entered and reorders matrices with matching species or gene labels. It will be used to analyse rates of mutation and substitutional saturation and the evolution of viruses. It is available at http://biojanus.anu.edu.au/programs/ and requires the Java runtime environment.

Decision Trees↗
PubMed2006

Mixing of propagules from discrete sources at long distance: comparing a dispersal tail to an exponential.

BACKGROUND: Rare long distance dispersal events impact the demography and the genetic structure of populations. When dispersal is modelled via a dispersal kernel, one possible characterisation of long-distance dispersal is given by the shape of the tail of the kernel, i.e. its type of decay. This characteristic is known to directly act on the speed and pattern of colonization, and on the spatial structure of genetic diversity during colonization. In particular, colonization waves behave differently depending on whether the kernel decreases faster or slower than an exponential (i.e. is thin-tailed vs. fat-tailed). To interpret and extend published results on the impact of long-distance dispersal on the genetic structure of populations, we examine a classification of dispersal kernels based on the shape of their tails and formally demonstrate qualitative differences among them that can influence the predicted diversity of a propagule pool sampled far from two distinct sources. RESULTS: We show that a fat-tailed kernel leads asymptotically to a diverse propagule pool containing a balanced mixing of the propagules from the two sources, whereas a thin-tailed kernel results in all propagules originating from the closest source. We further show that these results hold for biologically relevant distances under certain circumstances, and in particular if the number of propagules is large enough, as would be the case for pollen or seeds. CONCLUSION: To understand the impact of long-distance dispersal on the structure and dynamics of a metapopulation, it might be less important to precisely estimate an average dispersal distance than to determine if the tail of the dispersal kernel is fatter or thinner than that of an exponential function. Depending solely on this characteristic, a metapopulation will behave similarly to an island model with a diverse immigrant pool or to a stepping-stone model with migrants from closest populations. Our results further help to understand why thin-tailed dispersal kernels lead to a colonization wave of constant speed, whereas fat-tailed dispersal kernels lead to a wave of increasing speed. Our results also suggest that the diversity of the pollen cloud of a mother plant should increase with increasing isolation for fat-tailed kernels, whereas it should decrease for thin-tailed kernels.

Demography↗
PubMed2006

Fast calculation of the quartet distance between trees of arbitrary degrees.

BACKGROUND: A number of algorithms have been developed for calculating the quartet distance between two evolutionary trees on the same set of species. The quartet distance is the number of quartets - sub-trees induced by four leaves - that differs between the trees. Mostly, these algorithms are restricted to work on binary trees, but recently we have developed algorithms that work on trees of arbitrary degree. RESULTS: We present a fast algorithm for computing the quartet distance between trees of arbitrary degree. Given input trees T and T', the algorithm runs in time O(n + /V/./V'/ min{id, id'}) and space O(n + /V/./V'/), where n is the number of leaves in the two trees, V and V are the non-leaf nodes in T and T', respectively, and id and id' are the maximal number of non-leaf nodes adjacent to a non-leaf node in T and T', respectively. The fastest algorithms previously published for arbitrary degree trees run in O(n3) (independent of the degree of the tree) and O(/V/./V'/.id.id'), respectively. We experimentally compare the algorithm with existing algorithms for computing the quartet distance for general trees. CONCLUSION: We present a new algorithm for computing the quartet distance between two trees of arbitrary degree. The new algorithm improves the asymptotic running time for computing the quartet distance, compared to previous methods, and experimental results indicate that the new method also performs significantly better in practice.

Journal Article↗
PubMed1995

The significance of head movements in distance discrimination in praying mantis larvae

1. When larvae of the praying mantis Polyspilota sp. and Tenodera sinensis want to leave an exposed position and can choose to move between stationary objects at different distances, they usually choose the nearest. Their ability to select the nearest object is greatest when the background has horizontal stripes and is least when it has vertical stripes. Object preference is based on a successive distance comparison, which may involve content-related memory processes. 2. Mantid larvae can determine the absolute distance to a stationary object. Vertical contrasting borders play an important role in this process. 3. Side-to-side head movements (peering) are directly involved in the distance measurement, as shown (i) by the peering behaviour itself and (ii) by the fact that mantids can be deceived in distance measurement by arbitrary movements of target objects during the peering movement. It is supposed that the distance measurement involves the larger and faster retinal image shifts that near, as opposed to more distant, objects evoke. 4. Mantid larvae can distinguish a black-and-white rectangle in the foreground from a black-and-white striped background, even when both are similar with respect to luminance, contrast and texture. The ability to distinguish between figures and background could be explained by motion parallaxes, i.e. by the fact that during peering movements the nearer object moves faster and by a larger angle than the background structure. 5. From birth onwards, even when the eyes have yet to develop foveal specialization, mantids are capable of this visually controlled behaviour.

Journal Article↗
PubMed1985

Velocity, stroke rate, and distance per stroke during elite swimming competition.

The mean velocity of 9 out of 10 women's events during the U.S. Olympic Swimming Trials was greater in 1984 as compared to 1976. Three of the 10 men's events showed improvement. In 9 out of these 12 events, the increased velocity was accounted for by increased distance per stroke (range, -3 to -13%). In the women's 100-m butterfly and 100-m backstroke, increased velocity was due solely to faster stroke rates. The finalists in each event were compared to those whose velocities were 3-7% slower. In almost all events and stroke styles, the finalists achieved greater distances per stroke than did the slower group. In the men's events increased distance per stroke was associated with decreased stroke rate, except in the backstroke, in which both were increased for the finalists. Although the faster women swimmers generally had greater distances per stroke, they were more dependent than men on faster stroke rates to achieve superiority. The profile of velocity for races of 200 m and longer indicated that as fatigue developed the distance per stroke decreased. The faster swimmers compensated for this change by maintaining or increasing stroke rate more than did their slower competitors. This study indicates that improvements and superiority in stroke mechanics are reflected in the stroke rate and distance per stroke used to swim a race.

Arm↗
PubMed1981

Recognition of the epicardial breakthrough on body surface isopotential maps: influence of the inter-electrode distance on the patterns reflecting the epicardial breakthrough.

The epicardial breakthrough can be recognized from the localized depression of the body surface potential, which is characterized by a localized bend of the equipotential lines or a send-minimum on isopotential maps. Recognition of epicardial breakthrough with isopotential maps enables us to diagnose location of the block site of the bundle branch blocks more precisely than by ECG or VCG. However, the optimum inter-electrode distance for detection of such a localized potential has not been determined. In the present study, influence of the inter-electrode distance on the characteristic patterns reflecting the epicardial breakthrough was studied on 16 healthy persons using 9 x 9 electrode arrays with inter-electrode distance of 1.25 cm, 5 x 5 with 2.5 cm, and 3 x 3 with 5 cm. Breakthrough was recognized in 15 out of 16 cases (94%) on maps recorded with electrode arrays with inter-electrode distance of 1.25 and 2.5 cm. However, detectability of the breakthrough was reduced to 10 out of 16 cases (63%) with electrode array having inter-electrode distance of 5 cm. In conclusion, it is preferable to use an electrode array with an inter-electrode distance of no more than 2.5 cm for the purpose of breakthrough recognition.

Adult↗
PubMed2002

Isonymy and isolation by distance in the Netherlands.

The isonymy structure of the Netherlands was studied using the surname distribution of 2.4 million private telephone users selected from a 1996 commercial CD-ROM containing the names of 6.3 million users in the country. The users were distributed in 226 towns selected on a geographic basis to form an approximately regular grid throughout the Netherlands. Names of telephone users in each town were downloaded from the CD-ROM, with private users being selected for inclusion in the analysis. The shortest linear distance between several nearest neighboring towns was less than 2 km (e.g., Kampen and Ijsselmuiden, Krommen and Zaandijk, Hendrikdo and Papendrecht) and the longest distance was 326 km (Delfzijl and Oostburg ZL). The number of different surnames revealed by the analysis was 126,485. Lasker's distance, the negative value of the logarithm of isonymy between localities, was found to be significantly correlated with linear geographic distance, with r = 0.47 +/- 0.006. A dendrogram built using the matrix of isonymy distances, using the nearest neighbor-joining method, separates the Dutch towns into several clusters, most of them correlated with traditional Dutch regions. Comparisons with the results of previous analyses of the structure of other European countries are given. From the present analysis, isolation by distance emerges clearly, and it is relevant, although much weaker than in Switzerland, Austria, Italy, and Germany. The random component of inbreeding estimated from isonymy indicates a considerable degree of homogeneity in the Netherlands.

CD-ROM↗