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At least 775 records · Page 43Linked to original sources
PubMed1997

Guided bone regeneration: integration of a resorbable membrane and a bone graft material.

Guided bone regeneration relies primarily on four principles--exclusion of unwanted tissues and cells, space creation and maintenance, protection of the underlying blood clot, and wound stabilization. For successful bone regeneration to occur, large bony defects require an underlying grafting material and a cell-occlusive membrane. The learning objective of this article is to review the history and principles of guided bone regeneration and describe the characteristics of a slowly resorbing bilayer collagen membrane, well suited for bone regeneration procedures. An osteoconductive bone grafting material and its ability to support the overlying collagen membrane and serve as a matrix for the ingrowth of vascular and bone-forming cells are discussed.

Absorbable Implants↗
PubMedDate not supplied

Caustics mapping: an image-space technique for real-time caustics.

In this paper, we present a simple and practical technique for real-time rendering of caustics from reflective and refractive objects. Our algorithm, conceptually similar to shadow mapping, consists of two main parts: creation of a caustic map texture, and utilization of the map to render caustics onto nonshiny surfaces. Our approach avoids performing any expensive geometric tests, such as ray-object intersection, and involves no precomputation; both of which are common features in previous work. The algorithm is well suited for the standard rasterization pipeline and runs entirely on the graphics hardware.

Algorithms↗
PubMed1979

A rose by any other name... on 'naming of neurones' by Rowe and Stone.

Rowe and Stone dispose of descriptive terminologies for retinal units as 'essentialist' and argue for a 'neutral' multifactorial system redefined from previous W, X. Y nomenclatures. It is argued here that descriptive terminology need not be either essentialist or undesirable and that the W, X, Y terminology is too confused with false associations to be satisfactory. The synthetic power of the W, X, Y nomenclature was lost with the discovery of concentric W cell receptive fields, the projection of the W cells to the LGN and the suggestion of overlap between X and W conduction velocity groups. It was made methodologically unsound by its employment for the naming of Nissl stained soma classes before the identity of individual somas with the physiological entities can be demonstrated. Although now redefined, the identity of symbols in the several vintages of the W, X, Y system leads to inevitable confusion. The current tripartite division of a multidimensional quality space without cluster analysis is not neutral because it emphasises conduction velocity but represses the diversity of W receptive fields. The concise, apt and memorable descriptive receptive field terminologies are more desirable in that they are operationally based and approximate the unit's transfer function--the parameter most significant to the central nervous system in its information processing task; thus they are more suited for cross species comparison because of a probably bountiful source of functional hypotheses. The lack of taxonomic neutrality in the W, X, Y system has recently been emphasised by its failure to adequately classify rabbit retinal receptive field categories.

Animals↗
PubMed1999

Categorical and metric spatial processes distinguished by task demands and practice.

In this study we examined Kosslyn's (1987) claim that the right hemisphere exhibits a relative superiority for processing metric spatial relations, whereas the left hemisphere exhibits a relative superiority for processing categorical spatial relations. In particular, we examined whether some failures to observe strong visual field (VF) advantages in previous studies might be due to practice effects that allowed individuals to process tasks in alternative manners (e.g., to process a metric task using a categorical strategy). We used two versions of a task previously employed by Hellige and Michimata (1989)in which individuals judge the metric (distance) or categorical (above/below) spatial relations between a bar and a dot. In one version, the position of the bar was held static. In another, the bar's position varied. This manipulation prevented participants from using the computer screen as a reference frame, forcing them to compute the spatial relationships on the basis of the relevant items only (i.e., the bar and the dot). In the latter, but not the former version of the task we obtained evidence supporting Kosslyn's hypothesis, namely, a significant right visual field (RVF) advantage for categorical spatial processing and a trend toward a left visual field (LVF) advantage for metric spatial processing. Furthermore, the pattern of results for trials on which information was presented centrally (CVF trials) was similar to that observed on RVF trials, whereas the pattern for trials in which identical information was presented in each visual field (BVF trials) was similar to that observed on LVF trials. Such a pattern is consistent with Kosslyn's suggestion that categorical processing is better suited for cells with small receptive fields and metric processing for cells with larger receptive fields.

Adult↗
PubMed2002

Temporal transformation of multiunit activity improves identification of single motor units.

This report describes a temporally based method for identifying repetitive firing of motor units. This approach is ideally suited to spike trains with negative serially correlated inter-spike intervals (ISIs). It can also be applied to spike trains in which ISIs exhibit little serial correlation if their coefficient of variation (COV) is sufficiently low. Using a novel application of the Hough transform, this method (i.e. the modified Hough transform (MHT)) maps motor unit action potential (MUAP) firing times into a feature space with ISI and offset (defined as the latency from an arbitrary starting time to the first MUAP in the train) as dimensions. Each MUAP firing time corresponds to a pattern in the feature space that represents all possible MUAP trains with a firing at that time. Trains with stable ISIs produce clusters in the feature space, whereas randomly firing trains do not. The MHT provides a direct estimate of mean firing rate and its variability for the entire data segment, even if several individual MUAPs are obscured by firings from other motor units. Addition of this method to a shape-based classification approach markedly improved rejection of false positives using simulated data and identified spike trains in whole muscle electromyographic recordings from rats. The relative independence of the MHT from the need to correctly classify individual firings permits a global description of stable repetitive firing behavior that is complementary to shape-based approaches to MUAP classification.

Action Potentials↗
PubMed2003

[Plastic surgery procedures in the treatment of mediastinitis in adult].

Closed vacuum drainage is becoming the standard technique in most early postoperative mediastinitis, open wound treatment being only necessary in case of failure of the previous technique or in high grade mediastinitis. The reconstruction technique to be chosen depends on both resulting wound presentation after debridement and thorax morphology. Mediastinal dead space obliteration is a "sine qua non" for success often requiring multiple flap transposition. Since 1983, reconstructive procedures were carried out in 205 patients, of them 95 had bilateral pectoralis major turn-over transposition flaps on internal pedicules, following internal mammary artery coronary revascularisation in 45. Trapezius and latissimus dorsi were the next most used flaps. Transposition of the omentum although especially well suited for torpid wounds was to often precluded by bad abdominal risk factors. Conservative closed drainage salvaged by reconstructive procedures when necessary has greatly improved both survival and functional outcome of these patients.

Drainage↗
PubMed2001

Field assessment of nanoscale bimetallic particles for groundwater treatment.

A field demonstration was performed in which nanoscale bimetallic (Fe/Pd) particles were gravity-fed into groundwater contaminated bytrichloroethene and other chlorinated aliphatic hydrocarbons at a manufacturing site. With diameters on the order of 100-200 nm, the nanoparticles are uniquely suited to rapidly degrade redox-amenable contaminants and for optimal subsurface delivery and dispersion. Approximately 1.7 kg of the nanoparticles was fed into the test area over a 2-day period, resulting in minimal clogging of the injection well. The test area was located within a well-characterized region of the contaminant plume and included an injection well and three piezometer couplets spaced 1.5 m apart. Despite the low nanoparticle dosage, trichloroethene reduction efficiencies of up to 96% were observed over a 4-week monitoring period with the highest values observed at the injection well and adjacent piezometers. Data from the field assessment were consistent with the results of pre-injection laboratory studies, which showed rapid dechlorination of target chlorinated compounds accompanied by a sharp decrease of standard oxidation potential and an increase in pH.

Biotransformation↗
PubMedDate not supplied

[Verification of the effectiveness of preventing altitude decompression disorders by nitrogen desaturation of the organism through surrounding the body with an oxygen envelope].

The purpose of the present investigation was to assess the effect of nitrogen penetrating the human skin from the ambient atmosphere on the level of denitrogenization achieved by oxygen breathing. Young healthy male test subjects were exposed to denitrogenization for 5, 6 or 8 hours by breathing pure oxygen. During that time they wore an oxygen filled suit. Then they ascended an altitude of 11,000 m and remained there for 6 hours doing exercises. Altogether 38 investigations were carried out on 13 subjects, with and without a pressure suit. The investigation did not demonstrate any specific differences in the occurrence of decompression disease at an altitude of 11,000 m with or without a pressure suit. Nitrogen penetrating through the skin from the ambient atmosphere during oxygen breathing did not influence the level of denitrogenization.

Adult↗
PubMed1982

[Problems of microsurgery in lymphedema].

Microsurgery for primary and secondary lymphedema at present consists of shunts between lymphatic vessels and veins. The surgical technique has been well established for more than a decade. The problems consist of the irreversible changes in the peripheral lymphatic system and in the connective tissues, as well as the obliteration of the deep lymphatics, best suited for lymphaticovenous anastomoses. These changes are recognized only late, after clinical swelling becomes manifest. Therefore, lymphaticovenous shunts should be performed prophylactically. Their number should be sufficiently high to solve the quantitative problem, caused by the reduced lymphatic transport capacity.

Extracellular Space↗
PubMed1986

Scanning electron microscopy of isolated epithelium of the murine gastrointestinal tract: morphology of the basal surface and evidence for paracrinelike cells.

By using the method of Bjerknes and Cheng, isolated murine gastrointestinal epithelial sheets were prepared for scanning electron microscopy. Examination of isolated epithelium from fundic stomach revealed numerous branched gastric glands. Parietal cells were easily detected bulging from the basal surface of the glandular epithelium. The basal surface membrane of parietal cells appeared smooth, with only sparse microvilluslike projections, whereas adjacent glandular cells had numerous 1- to 2-micron fingerlike projections which interdigitated laterally with similar processes from adjacent cells. Occasionally, paracrinelike cells having long cytoplasmic processes ranging from 10 to 20 micron in length were observed on the basal epithelial surface of the stomach and the colon, but not the small intestine. In isolated intestinal epithelia, the basal surface of crypt epithelial cells showed extensive cytoplasmic interdigitations, but no distinct morphology permitting recognition of individual cell types. Various stages of intestinal crypt bifurcation were seen. Craterlike spaces in the basal surface of crypt epithelium, presumably due to migrating leukocytes, were also numerous. Examination of the luminal surface of the isolated intestinal epithelium revealed that intimate associations between epithelium and mucosal-associated microorganisms were maintained, thus suggesting that minimal alterations in surface morphology were incurred by epithelial isolation. These observations on epithelial structure suggest that isolated gastrointestinal epithelia may be well suited for physiological studies of epithelial function and interactions with the microbial flora.

Animals↗
PubMed1993

Intratracheal pulmonary ventilation and congenital diaphragmatic hernia: a report of two cases.

Previous studies from our institution have shown that neonates with congenital diaphragmatic hernia (CDH), whose best postductal PaO2 (BPDPO2) was less than 100 mm Hg while on maximal conventional mechanical ventilation (CMV), had a mortality exceeding 90%. When combined with extracorporeal membrane oxygenation (ECMO), the mortality rose to 100% in those infants who developed hypercarbia following decannulation. Historically, those patients have required increasing ventilator support, leading to iatrogenic lung damage, and eventual death. Intratracheal pulmonary ventilation (ITPV) using the reverse thrust catheter (RTC) developed by Kolobow incorporates a continuous flow of humidified gas through a reverse Venturi catheter positioned at the distal end of the endotracheal tube. In animal studies, ITPV was shown to result in a reduced physiological dead-space (VD), to facilitate expiration, and to enhance CO2 elimination. In our current study, we have applied ITPV in two neonates with CDH who could not be weaned from ECMO because of uncontrollable hypercapnia, and who met above criteria for 100% mortality. In both cases, ITPV restored normal PaCO2 at low peak inspiratory pressure (PIP) with a substantial decrease in VD. We believe ITPV is suited to ventilating newborns with CDH in whom barotrauma is known to be common. Beyond its present use, ITPV may be useful to ventilate children with other forms of respiratory failure, and should be so considered along with other now available methods of mechanical pulmonary ventilation.

Hernia, Diaphragmatic↗
PubMedDate not supplied

X-ray microtomography (microCT) using phase contrast for the investigation of organic matter.

PURPOSE: We show that microtomography (microCT) using synchrotron radiation (SR) can be extended to include X-ray phase contrast, which is two to three orders of magnitude more sensitive than conventional attenuation contrast and better suited for the investigation of specimens consisting chiefly of light elements for photon energies ranging at least from 1 to 100 keV. METHOD: Phase contrast is generated by placing the specimen in one of the interfering beams of an X-ray interferometer. With use of 12-keV X-rays, phase projections of the specimen are recorded at 180 or 360 angular settings equally spaced between 0 and 180 degrees. One phase projection consists of four pairs of "associated" radiograms in the sense that one is taken with and the other without the specimen in the beam. Between pairs a parallel-sided phase-shifter plate is rotated for changing the relative phase of the two interfering beams by multiples of pi/2 rad. By calculating phase-weighted sums of all associated pairs of radiograms, true phase-shift projections are obtained for all angular settings of the specimen, which are then reconstructed. RESULTS: Three-dimensional images have been obtained from rat cerebrum and rat trigeminal nerve, showing cell structures at 8- to 15-micron spatial resolution. Gray and white matter of cerebrum and neurons in the trigeminal nerve are clearly visible. CONCLUSION: X-ray phase-contrast microCT is becoming a valuable tool for studies of organic samples in medicine and biology.

Animals↗
PubMed2002

Vector algebra in the analysis of genome-wide expression data.

BACKGROUND: Data from thousands of transcription-profiling experiments in organisms ranging from yeast to humans are now publicly available. How best to analyze these data remains an important challenge. A variety of tools have been used for this purpose, including hierarchical clustering, self-organizing maps and principal components analysis. In particular, concepts from vector algebra have proven useful in the study of genome-wide expression data. RESULTS: Here we present a framework based on vector algebra for the analysis of transcription profiles that is geometrically intuitive and computationally efficient. Concepts in vector algebra such as angles, magnitudes, subspaces, singular value decomposition, bases and projections have natural and powerful interpretations in the analysis of microarray data. Angles in particular offer a rigorous method of defining 'similarity' and are useful in evaluating the claims of a microarray-based study. We present a sample analysis of cells treated with rapamycin, an immunosuppressant whose effects have been extensively studied with microarrays. In addition, the algebraic concept of a basis for a space affords the opportunity to simplify data analysis and uncover a limited number of expression vectors to span the transcriptional range of cell behavior. CONCLUSIONS: This framework represents a compact, powerful and scalable construction for analysis and computation. As the amount of microarray data in the public domain grows, these vector-based methods are relevant in determining statistical significance. These approaches are also well suited to extract biologically meaningful information in the analysis of signaling networks.

Cluster Analysis↗
PubMed2002

CECILIA, a versatile research tool for cellular responses to gravity.

We describe a centrifuge designed and constructed according to current demands for a versatile instrument in cellular gravitational research, in particular protists (ciliates, flagellates). The instrument (called CECILIA, centrifuge for ciliates) is suited for videomonitoring, videorecording, and quantitative evaluation of data from large numbers of swimming cells in a ground-based laboratory or in a drop tower/drop shaft under microgravity conditions. The horizontal rotating platform holds up to six 8mm-camcorders and six chambers holding the experimental cells. Under hypergravity conditions (up to 15 g) chambers can be rotated about 2 axes to adjust the swimming space at right angles or parallel to the resulting gravity vector. Evaluations of cellular responses to central acceleration-- in the presence of gravitational 1 g--are used for extrapolation of cellular behaviour under hypogravity conditions. CECILIA is operated and monitored by computer using a custom-made software. Times and slopes of rising and decreasing acceleration, values and and quality of steady acceleration are supervised online. CECILIA can serve as an on-ground research instrument for precursor investigations of the behaviour of ciliates and flagellates under microgravity conditions such as long-term experiments in the International Space Station.

Acceleration↗
PubMed2003

Flexible ligand docking using evolutionary algorithms: investigating the effects of variation operators and local search hybrids.

The docking of ligands to proteins can be formulated as a computational problem where the task is to find the most favorable energetic conformation among the large space of possible protein-ligand complexes. Stochastic search methods such as evolutionary algorithms (EAs) can be used to sample large search spaces effectively and is one of the commonly used methods for flexible ligand docking. During the last decade, several EAs using different variation operators have been introduced, such as the ones provided with the AutoDock program. In this paper we evaluate the performance of different EA settings such as choice of variation operators, population size, and usage of local search. The comparison is performed on a suite of six docking problems previously used to evaluate the performance of search algorithms provided with the AutoDock program package. The results from our investigation confirm that the choice of variation operators has an impact on the search-capabilities of EAs. The introduced DockEA using the best settings found obtained the overall best docking solutions compared to the Lamarckian GA (LGA) provided with AutoDock. Furthermore, the DockEA proved to be more robust than the LGA (in terms of reproducing the results in several runs) on the more difficult problems with a high number of flexible torsion angles.

Algorithms↗
PubMed2001

A kinematic analysis of hand selection in a reaching task.

A group of left- and right-handers was tested on a task requiring them to reach out and pick up an object with either the left or the right hand. We varied the eccentricity of the target object (a small glass) and the required accuracy level, by filling the glass with liquid. We recorded (a) frequency of left or right hand use, (b) hand preference using a handedness questionnaire, and (c) the trajectories of the reaches using a movement registration system. It was found that the stronger the hand preference, the further in contralateral space the shift occurred between left and right hand use. Not only did the transition point corresponding to the shift between the two hands correlate with the point where their deceleration times were equal, but these locations closely coincided. These findings suggest that people are highly skilled perceivers of their own action capabilities, and that they are able to select the action mode that is most suited to perform a given task. We argue that laterality should be understood in terms of asymmetries in action modes.

Journal Article↗
PubMed1998

Statistical analysis of functional MRI data in the wavelet domain.

The use of the wavelet transform is explored for the detection of differences between brain functional magnetic resonance images (fMRI's) acquired under two different experimental conditions. The method benefits from the fact that a smooth and spatially localized signal can be represented by a small set of localized wavelet coefficients, while the power of white noise is uniformly spread throughout the wavelet space. Hence, a statistical procedure is developed that uses the imposed decomposition orthogonality to locate wavelet-space partitions with large signal-to-noise ratio (SNR), and subsequently restricts the testing for significant wavelet coefficients to these partitions. This results in a higher SNR and a smaller number of statistical tests, yielding a lower detection threshold compared to spatial-domain testing and, thus, a higher detection sensitivity without increasing type I errors. The multiresolution approach of the wavelet method is particularly suited to applications where the signal bandwidth and/or the characteristics of an imaging modality cannot be well specified. The proposed method was applied to compare two different fMRI acquisition modalities. Differences of the respective useful signal bandwidths could be clearly demonstrated; the estimated signal, due to the smoothness of the wavelet representation, yielded more compact regions of neuroactivity than standard spatial-domain testing.

Adult↗
PubMed2004

Computerized tomography evaluation of a resorbable implant after transforaminal lumbar interbody fusion.

OBJECT: Synthetic bioabsorbable implants have recently been introduced in spinal surgery; consequently, the indications, applications, and results are still evolving. The authors used absorbable interbody spacers (Medtronic Sofamor Danek, Memphis, TN) packed with recombinant bone morphogenetic protein (Infuse; Medtronic Sofamor Danek) for single- and multiple-level transforaminal lumbar interbody fusion (TLIF) procedures over a period of 18 months. This is a consecutive case series in which postoperative computerized tomography (CT) scanning was used to assess fusion status. METHODS: There were 22 patients (17 men, five women; 39 fusion levels) whose mean age was 41.6 years (range 23-70 years) and in whom the mean follow-up duration was 12.4 months (range 6-18 months). Bridging bone was noted as early as the 3-month postoperative CT scan when obtained; solid arthrodesis was routinely noted between 6 and 12 months in 38 (97.4%) of 39 fusion levels. In patients who underwent repeated CT scanning, the fusion mass appeared to increase with time, whereas the disc space height remained stable. Although the results are early (mean 12-month follow-up duration), there was only one noted asymptomatic delayed union/nonunion at L5-S1 in a two-level TLIF with associated screw breakage. There were no infections or complications related to the cages. CONCLUSIONS: The bioabsorbable cages appear to be a viable alternative to metal interbody spacers, and may be ideally suited to spinal interbody applications because of their progressive load-bearing properties.

Absorbable Implants↗