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PubMed1988

Oxygen diffusion distance in thyroxine-induced hypertrophic rabbit myocardium.

We studied the oxygen diffusion distance in the rabbit myocardium in untreated animals and in animals treated with thyroxine (T4) for 3 days and 16 days. The subepicardial and subendocardial regions were studied separately. Sixteen days of T4 treatment results in significant cardiac hypertrophy. After 16 days, the percentage of the myocardium occupied by myocytes decreases as the volume of extracellular matrix increases. After 3 days, the number of myocyte mitochondria per unit volume of myocardium increases without an increase in mitochondrial volume. After 16 days the volume density of the myocyte mitochondria increases. Oxygen diffusion distance was determined by measuring the distance between the myocardial capillaries and the cardiomyocyte mitochondria. The deposition of extracellular matrix results in an increase in the distance between the myocardial capillaries and the myocytes. The distribution of the mitochondria within the myocytes remains unchanged resulting in an increased distance between the capillaries and the mitochondria, hence, an increased oxygen diffusion distance. There is some evidence that the mitochondria most distant from the capillaries are the mitochondria in which division is most frequent with T4 stimulation. This may be related to the relative deprivation of oxygen of these mitochondria.

Animals↗

PubMed2002

Absolute distance perception during in-depth head movement: calibrating optic flow with extra-retinal information.

We investigated the ability of monocular human observer to scale absolute distance during sagittal head motion in the presence of pure optic flow information. Subjects were presented at eye-level computer-generated spheres (covered with randomly distributed dots) placed at several distances. We compared the condition of self-motion (SM) versus object-motion (OM) using equivalent optic flow field. When the amplitude of head movement was relatively constant, subjects estimated absolute distance rather accurately in both the SM and OM conditions. However, when the amplitude changed on a trial-to-trial basis, subjects' performance deteriorated only in the OM condition. We found that distance judgment in OM condition correlated strongly with optic flow divergence, and that non-visual cues served as important factors for scaling distances in SM condition. Absolute distance also seemed to be better scaled with sagittal head movement when compared with lateral head translation.

Adolescent↗

PubMed1989

Stroke distance in acute myocardial infarction: a simple measurement of left ventricular function.

Stroke distance was measured by means of doppler ultrasound in 100 consecutive patients with acute myocardial infarction. Mean stroke distance on days 1-5 after infarction was 72% of the predicted normal value for age and rose to 77% of normal by days 6-10. Stroke distance was lower after anterior (65%) than inferior infarction (75%), and was negatively correlated with peak serum aspartate aminotransferase (r = 0.47, p less than 0.001). Of 16 patients whose stroke distance on days 1-5 was below 50% of normal for age, 4 died, all within the first week. Of 84 patients whose stroke distance was 50% of normal or higher, only 1 died (at 13 days). The simple bedside measurement of stroke distance offers a practical method of monitoring left ventricular function in acute myocardial infarction: the measurement may have prognostic value.

Adult↗

PubMed1996

The step-size distance in muscle contraction: properties and estimates.

The step-size distance in muscle contraction is obtained using the step-size distance equation z = u/n, where z is the step-size distance, u is the actin filament velocity and n is the ATPase rate of splitting. In a previous study a step-size distance of about 17 A at no load was determined for intact frog muscle. Some properties of the step-size equation are described. We have now made estimates of the step-size distance z for a variety of muscles using existing physiological and biochemical data in the literature. The estimates are listed in Tables 1 and 2. We find that the step-size distances are clustered in the range 13-17 A for nearly all muscles.

Actins↗

PubMed2000

Errors in ultrasound digital image distance measurements.

Digital image distance measurements have two sources of error: they are the inherent image pixelation error and modality-specific registration errors. A theoretical analysis was performed to determine the pixelation error uncertainty in ultrasound (US) clinical and phantom digital image distance measurements. For horizontal or vertical phantom image distance measurements, the average absolute image pixelation error was found to be 0.5 pixel width. In the clinical horizontal case, the combined absolute distance measurement error due to pixel size and operator cursor placement errors was found to be 1.5 pixel widths (for a cursor placement error of 1 pixel width). For image clinical distance measurements, a formula is given for the dependence of the measurement error on the inclination of the measured structure in the pixel matrix. A protocol is recommended that minimizes all sources of error in clinical image distance measurements.

Humans↗

PubMed2002

Convergent beam electron diffraction extinction distance measurements for quantitative analysis of si(1-x),Ge(x).

A new method to determine the concentration of germanium in Si(1-x) Ge(x) single crystals is presented. It is based on extinction distance measurements by means of convergent beam electron diffraction (CBED). The two-beam condition CBED intensity oscillation (the so-called rocking curve) is measured for the 004 diffracted beam and compared with a numerical simulation. Using the two-beam dynamical diffraction approximation theory, this approach yields very precise values for both specimen thickness and effective extinction distance (Ultramicroscopy 87 (2001) 5). First a theoretical extinction distance zetag(x) for strain relaxed Si(1-x)Ge(x) is calculated assuming a solid solution and using tabulated atomic scattering factors of silicon and germanium atoms. It is found that for single crystals zetag(x) decreases from 156 nm in pure silicon to 90 nm in pure germanium. Measurements on calibrated strain relaxed SiGe layers with variable germanium concentrations show an excellent agreement between experimental and calculated extinction distances zetag(x). As a consequence the experimental extinction distance zetag(x) becomes an indirect measure of the germanium concentration with a 1-2 at % sensitivity. The method turns out to be insensitive to strain as experimental zetag(x) values obtained on strained SiGe layers fit the theoretical extinction distance curve calculated for strain relaxed SiGe.

Journal Article↗

PubMed1999

Midvastus approach in total knee arthroplasty: a description and a cadaveric study determining the distance of the popliteal artery from the patellar margin of the incision.

Total knee arthroplasty (TKA), one of the most efficacious procedures in orthopedics, requires complete exposure of the knee joint for precise instrumentation. Although most orthopedic surgeons agree that TKA is easily performed using a medial parapatellar approach, a large segment of the patellar blood flow is disrupted by this exposure. The southern or subvastus approach addresses these concerns; however, the procedure has the disadvantage of inadequate exposure in certain patients. A compromise between these two approaches, a midvastus approach, has been described. To decrease potential neurovascular injury, this cadaveric study of the midvastus approach determines the proximity of the incision to the popliteal vascular bundle and addresses the innervation pattern of the vastus medialis oblique. A midvastus arthrotomy was performed on 19 female and 15 male adult cadaveric knees. The midpoint of the superior pole of the patella and the superomedial patellar prominence were marked. After determining the midpoint between the 2 previously mentioned landmarks, an incision was made from that point paralleling the fibers of the vastus medialis oblique medially to the popliteal vascular bundle. The length of the incision was measured three times using calipers; measurements were averaged for each individual specimen, then by gender, and, finally, overall. Ninety-five percent confidence intervals were determined. Differences were assessed by an independent t-test with an alpha level of significance at .05. In addition, the terminal branches of the femoral nerve innervating the vastus medialis oblique were dissected in 5 cadavers. The femoral nerve branched extensively to innervate the vastus medialis oblique. The average distance between the patella and the popliteal vessels was 8.8 +/- 1.4 cm. The average distance in males, 9.5 +/- 1.4 cm, was significantly greater than the distance in females, 8.3 +/- 1.2 cm (P < .02). The distance appeared proportionate to the size of the extremity. The midvastus approach is a viable alternative for primary TKA in selected patients who are not obese and who have not had previous arthrotomy or osteotomy. The average distance (8.8 cm) and corresponding range (6.5 cm minimum to 12.3 cm maximum) are sufficient to suggest a maximal safe distance for sharp dissection of 4.5 cm from the patellar margin in an adult. For additional exposure, the muscle can be safely split further with blunt dissection.

Adult↗

PubMed2003

Distance and near contrast sensitivity function after multifocal intraocular lens implantation.

PURPOSE: To evaluate contrast sensitivity at distance and near after multifocal intraocular lens (IOL) implantation. SETTING: Ophthalmologic Institute of Alicante, University Miguel Hernández, Alicante, Spain. METHODS: Contrast sensitivity was measured with the Stereo Optical Functional Acuity Contrast Test at distance and near in 21 patients with a refractive multifocal IOL (Array SA-40N, AMO). A control group with a monofocal IOL (SI-40NB, AMO) was also studied to allow comparison of results. Contrast sensitivity was measured 1, 3, 6, 12, and 18 months after IOL implantation. RESULTS: There was a statistically significant greater reduction in contrast sensitivity at distance at all spatial frequencies in the multifocal group than in the monofocal group during the first month. At 3 months, contrast sensitivity at 12 and 18 cycles per deg remained reduced in the multifocal group; contrast sensitivity at the other frequencies did not differ from that in the monofocal group (P > 0.1). At 6, 12, and 18 months, contrast sensitivity at all spatial frequencies was not significantly different between groups (P > 0.1). There was a statistically significant greater reduction in near contrast sensitivity in the multifocal group than in the monofocal group at all spatial frequencies during the first and third month after surgery (P <.01). No statistically significant differences were found between groups after 6 months (P > 0.1). Contrast sensitivity at distance and near in the multifocal group improved over time (P <.01). CONCLUSIONS: The Array IOL provided contrast sensitivity at distance comparable to that obtained with the monofocal IOL between 3 and 6 months after implantation. Near contrast sensitivity improved over time but was always lower than at distance and in the monofocal near-corrected patients, which is acceptable to avoid near visual function degradation.

Aged↗

PubMed1999

Long-distance rotational echo double resonance measurements for the determination of secondary structure and conformational heterogeneity in peptides.

The utility of rotational echo double resonance (REDOR) NMR spectroscopy for determining the conformations of linear peptides has been examined critically using a series of crystalline and amorphous samples. The focus of the present work was the evaluation of long-distance (> 5 A) interactions using 13C-15N dephasing. Detailed studies of specifically labeled melanostatin and synthetic analogs of the alpha-factor yeast mating hormone show that nitrogen-dephased, carbon-observe REDOR measurements are reliable for distances up to 6.0 A, and that dipolar interactions can be detected for distances up to 7 A. By contrast, nitrogen-observe REDOR gives reliable results only for distances shorter than 5.0 A. To measure distances accurately, REDOR data must be corrected for the effects of natural-abundance spins. These corrections are particularly important for measuring long distances, which are of the greatest value for determining peptide secondary structure. We have developed a spherical shell model for calculating the effect of these background spins. The REDOR studies also indicate that in a lyophilized powder, the tridecapeptide alpha-factor mating pheromone from Saccharomyces cerevisiae (WHWLQLKPGQPMY) probably exists as a distribution of different turn structures around the KPGQ region. This finding revises previous solid-state NMR studies on this peptide, which concluded alpha-factor assumes a distorted type-I beta-turn in the Pro-Gly central region of the molecule [J.R. Garbow, M. Breslav, O. Antohi, F. Naider, Biochemistry, 33 (1994) 10094].

Algorithms↗

PubMed2002

Case-based distance measurements for the selection of controls in case-matched studies: application in coronary interventions.

In case-based studies, controls are retrospectively assigned to patients in order to permit a statistical evaluation of the study results through a comparison of the main outcome measures for the patient and retrieved control groups. Inappropriate selection of the controls by using false retrieval parameters or a false algorithm might lead to an incorrect data analysis and a false interpretation of the results. The main hypothesis of the presented study was that, if the matching baseline parameters were at least nearly perfectly selected, then the outcomes of the matched pairs should be similar, or no significant differences in study outcome should be observed between the patients and the matched controls. In the present study, the case-based domain was created from 1566 patients who had undergone intracoronary stent implantation. Uni- and multivariate logistic regression analysis determined nine significant predictors (matching variables) for the occurrence of major adverse cardiac events. An additional 425 consecutive patients undergoing intracoronary stent implantation were then matched with all the potential controls from the database by calculating the individual distance between the patient and the matched control on the basis of the elaborated retrieval algorithm. To test the matching hypothesis, different distance measurements, and an altered outcome and retrieval process were examined. With "flexible" distance measurements, the mean distance between the patients and the first matched controls was 1.31. The major adverse cardiac events were compared in the patient and matched control groups. The best sensitivity and specificity values of the matching system could be achieved in matched pairs with the distance < or =3.00 (95.1% of all patients). On the further stepwise exclusion of the matched pairs exhibiting a distance greater than 2 and 1, then the number of "matchable" controls and the specificity of our matching concept decreased considerably. When the short- or mid-term outcome was compared by using the long-term follow-up matching parameters, no correlation could be found between the treated subjects and controls, indicating that for the other study, main measures of other appropriate parameters must be selected, and demonstrating the importance of the outcome-oriented selection of the retrieval parameters. Furthermore, the outcome measures of the patients and randomly (non-systematically) selected controls did not correlate, revealing the impossibility of drawing correct study conclusions from a non-matched, randomly assigned pairs. In conclusion, the sensitivity and specificity of the matching program, and the study conclusions depend on the appropriately predefined matching parameters and retrieval algorithm.

Algorithms↗

PubMed1998

Increasing obstacle height and decreasing toe-obstacle distance affect the joint moments of the stance limb differently when stepping over an obstacle.

Foot placement during gait is important in regulating the dynamics of the joints of the supporting limb and in maintaining balance of the whole body. We hypothesized that increasing obstacle height and decreasing toe-obstacle distance (distance between the trailing foot and the obstacle during stance of the trailing foot just prior to stepping over the obstacle) would affect the joint moments of the stance limb differently when stepping over an obstacle. A total of 14 healthy young adults stepped over an obstacle 51, 102, 153, and 204 mm in height in a self-selected manner (i.e. toe-obstacle distance was not controlled) and for toe-obstacle distance targets of 10, 20, 30, and 40% of their step lengths measured during unobstructed gait. The adduction and internal rotation moments at the ankle joint increased as toe-obstacle distance decreased. The adduction and internal rotation moments at the hip joint during early stance, the internal rotation moment at the knee joint during late stance, and the dorsiflexion moment at the ankle joint during late stance increased with obstacle height. Reductions in toe-obstacle distance had greater effects on the moments of the ankle joint, and increases in obstacle height had greater effects on the moments of the hip joint. These greater demands on joint moments may affect the abilities of those elderly having decreased muscle strengths to safely step over obstacles. Copyright 1998 Elsevier Science B.V.

Journal Article↗

PubMed1999

Long-range oxidative damage to DNA: effects of distance and sequence.

INTRODUCTION: Oxidative damage to DNA in vivo can lead to mutations and cancer. DNA damage and repair studies have not yet revealed whether permanent oxidative lesions are generated by charges migrating over long distances. Both photoexcited *Rh(III) and ground-state Ru(III) intercalators were previously shown to oxidize guanine bases from a remote site in oligonucleotide duplexes by DNA-mediated electron transfer. Here we examine much longer charge-transport distances and explore the sensitivity of the reaction to intervening sequences. RESULTS: Oxidative damage was examined in a series of DNA duplexes containing a pendant intercalating photooxidant. These studies revealed a shallow dependence on distance and no dependence on the phasing orientation of the oxidant relative to the site of damage, 5'-GG-3'. The intervening DNA sequence has a significant effect on the yield of guanine oxidation, however. Oxidation through multiple 5'-TA-3' steps is substantially diminished compared to through other base steps. We observed intraduplex guanine oxidation by tethered *Rh(III) and Ru(III) over a distance of 200 A. The distribution of oxidized guanine varied as a function of temperature between 5 and 35 degrees C, with an increase in the proportion of long-range damage (> 100 A) occurring at higher temperatures. CONCLUSIONS: Guanines are oxidized as a result of DNA-mediated charge transport over significant distances (e.g. 200 A). Although long-range charge transfer is dependent on distance, it appears to be modulated by intervening sequence and sequence-dependent dynamics. These discoveries hold important implications with respect to DNA damage in vivo.

DNA↗

PubMed2003

Analysis of metabolic networks using a pathway distance metric through linear programming.

The solution of the shortest path problem in biochemical systems constitutes an important step for studies of their evolution. In this paper, a linear programming (LP) algorithm for calculating minimal pathway distances in metabolic networks is studied. Minimal pathway distances are identified as the smallest number of metabolic steps separating two enzymes in metabolic pathways. The algorithm deals effectively with circularity and reaction directionality. The applicability of the algorithm is illustrated by calculating the minimal pathway distances for Escherichia coli small molecule metabolism enzymes, and then considering their correlations with genome distance (distance separating two genes on a chromosome) and enzyme function (as characterised by enzyme commission number). The results illustrate the effectiveness of the LP model. In addition, the data confirm that propinquity of genes on the genome implies similarity in function (as determined by co-involvement in the same region of the metabolic network), but suggest that no correlation exists between pathway distance and enzyme function. These findings offer insight into the probable mechanism of pathway evolution.

Algorithms↗

PubMed1998

A combinatorial distance-constraint approach to predicting protein tertiary models from known secondary structure.

BACKGROUND: Distance geometry methods allow protein structures to be constructed using a large number of distance constraints, which can be elucidated by experimental techniques such as NMR. New methods for gleaning tertiary structural information from multiple sequence alignments make it possible for distance constraints to be predicted from sequence information alone. The basic distance geometry method can thus be applied using these empirically derived distance constraints. Such an approach, which incorporates a novel combinatoric procedure, is reported here. RESULTS: Given the correct sheet topology and disulfide formations, the fully automated procedure is generally able to construct native-like Calpha models for eight small beta-protein structures. When the sheet topology was unknown but disulfide connectivities were included, all sheet topologies were explored by the combinatorial procedure. Using a simple geometric evaluation scheme, models with the correct sheet topology were ranked first in four of the eight example cases, second in three examples and third in one example. If neither the sheet topology nor the disulfide connectivities were given a priori, all combinations of sheet topologies and disulfides were explored by the combinatorial procedure. The evaluation scheme ranked the correct topology within the top five folds for half the example cases. CONCLUSIONS: The combinatorial procedure is a useful technique for identifying a limited number of low-resolution candidate folds for small, disulfide-rich, beta-protein structures. Better results are obtained, however, if correct disulfide connectivities are known in advance. Combinatorial distance constraints can be applied whenever there are a sufficiently small number of finite connectivities.

Amino Acid Sequence↗

PubMed2003

Correlation between geographic distance and genetic similarity in an international collection of bovine faecal Escherichia coli O157:H7 isolates.

Evidence from epidemiological and molecular studies of bovine Escherichia coli O157:H7 suggests that strains are frequently transmitted across wide geographic distances. To test this hypothesis, we compared the geographic and genetic distance of a set of international bovine Escherichia coli O157:H7 isolates using the Mantel correlation. For a measure of genetic relatedness, pulsed-field gel electrophoresis of six different restriction enzyme digests was used to generate an average Dice similarity coefficient for each isolate pair. Geographic distance was calculated using latitude and longitude data for isolate source locations. The Mantel correlation between genetic similarity and the logarithm of geographic distance in kilometers was -0.21 (P<0.001). The low magnitude of the Mantel correlation indicates that transmission over long distances is common. The occurrence of isolates from different continents on the same cluster of the dendrogram also supports the idea that Escherichia coli O157:H7 strains can be transferred with considerable frequency over global distances.

Animals↗

PubMed2004

The distance from the Amplatzer septal occluder to the mitral valve in patients undergoing interventional closure of defects in the oval fossa increases with growth of the patient.

The Amplatzer septal occluder is an alternative to operative closure of atrial septal defects within the oval fossa. An issue when deploying the device is its distance from the mitral valve. The purpose of this study is to determine how this distance changes with growth of the patient. We identified, through a review of charts, all patients undergoing closure of defects within the oval fossa by insertion of an Amplatzer septal occluder. Data were obtained from the echocardiogram 24 hours after closure, and at most recent follow-up, including left ventricular end-diastolic diameter, left atrial diameter, degree of mitral valvar regurgitation, body surface area, and distance from the device to the mitral valve. We divided the patients into 2 groups based upon change in body surface area. The first group had an increase in body surface area of at least 10%. All others were in the second group. We inserted 55 Amplatzer septal occluders in 54 patients. Of these we excluded 17 patients, 1 because quality of images was inadequate, 1 who underwent placement of 2 devices, 1 in whom the device embolised to the left ventricle the day after deployment, and 14 who have not yet had a follow-up echocardiogram. The group which exhibited an increase in body surface area of greater than 10% demonstrated an increase in distance from the device to the mitral valve, left ventricular end-diastolic, and left atrial diameters. Those who did not undergo significant growth had no increase in distance from the device to the mitral valve, but did have an increase in left atrial and left ventricular end-diastolic diameters. No patient developed mitral regurgitation. We conclude that, when deploying an Amplatzer septal occluder close to the mitral valve in children, the distance from the device to the mitral valve can be expected to increase with growth of the patient.

Adolescent↗

PubMed1999

Adjusting the distance of electrochemical microsensors from secreting cell monolayers on the micrometer scale using impedance.

There are emerging applications of electrochemical microsensors where the distance of the sensor from an insulating plane needs to be adjusted and/or accurately known. The plane may be merely an obstruction or the source of a species whose release rate needs to be measured. An example is in cell secretion studies where a monolayer of cells is stimulated to secrete ions and/or other biochemical species which then diffuse away from the cells while being measured by a microsensor. Sensor response will thus depend on both the rate of release and the distance of the sensor from the cells. To obtain accurate release rates, the precision of the scheme to control electrode distance from the monolayer needs to be on the micrometer scale for species with ionic diffusivities. Optical (stereomicroscope and microruler) and mechanical (precalibrated micrometer screw) methods to precisely position the electrode are difficult to use under realistic circumstances (due to opaqueness of the chamber, and/or the medium, or irreproducible chamber depth). In this work we propose to correlate electrochemical cell impedance with sensor distance. This scheme has been used to adjust the distance of a chloride (tip diameter approximately 250 microns) and a potassium (tip diameter approximately 1000 microns) ion-selective microelectrode in the 0-250- and 0-2500-micron range, respectively, from a planar obstruction as well as from a monolayer of cells with a best precision of +/- 5 microns (n = 6) for the chloride and about +/- 20 microns for the potassium sensor. Larger electrodes have a broader range of distances over which they are sensitive, albeit with a poorer spatial resolution. This was verified by using Ag disk electrodes of 250 and 500 microns in diameters in AgNO3 solution.

Buffers↗

PubMed1993

Time-resolved energy transfer measurements of donor-acceptor distance distributions and intramolecular flexibility of a CCHH zinc finger peptide.

Time-resolved frequency-domain fluorescence energy transfer measurements have been used to investigate the solution structure of a single-domain CCHH-type zinc finger peptide. These measurements reveal not only the range of accessible distances for a given donor-acceptor pair within the molecule but also the degree of conformational flexibility that occurs in solution. Two donor-acceptor (D-A)-pair zinc finger peptides have been synthesized. A single tryptophan residue located at the midpoint of the sequence was the energy donor for two different acceptors. One acceptor, attached at the amino terminus was a 5-(dimethylamino)-1-naphthalenesulfonyl (DNS) group; the second acceptor was a 7-amino-4-methyl-coumarin-3-acetyl (AMCA) group, attached to the epsilon-amino function of a carboxy-terminal lysine residue. Distance distributions and the mutual site-to-site diffusion coefficients were determined for these two D-A-labeled peptides under zinc-bound, metal-free, and denatured conditions. The D-A distance distributions determined for these two peptides under metal-free and zinc-bound conditions indicated a shorter distance and a unique conformation (narrow distribution) when metal was bound and a longer distance with greater conformational flexibility when metal ion was absent. No site-to-site diffusion was detected for the zinc-bound peptide, whereas an appreciable amount of diffusion was measured for both metal-free and denatured peptide. Anisotropy measurements on the peptides indicated increased flexibility of all regions of the peptide chain in the absence of zinc and a more compact, less flexible structure when zinc was bound. It was concluded from these results that the metal-bound conformation represents a unique, well-defined structure. Comparison of distance distributions measured for metal-free and denatured peptide indicated that there is some residual structure present in the metal-free peptide.

Amino Acid Sequence↗