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At least 631 records · Page 35Linked to original sources
PubMed1999

[Rationale and limits of echo planar magnetic resonance imaging].

INTRODUCTION: The use of Echo Planar Imaging (EPI) techniques has extensively increased in the last few years. The technical improvements in new Magnetic Resonance Imaging (MRI) systems satisfy the instrumental requirements for these complex high-speed methods. The latest commercial systems are provided with standard EPI sequences. The increased data acquisition speed which characterizes EPI opens new and interesting perspectives, although the resolution is lower than the one typically achieved with conventional imaging. MATERIALS AND METHODS: The description of the data sampling process in terms of the k-space is a powerful tool for planning or understanding complex sequence diagrams like EPI. The basic concepts of the method are reported and discussed, pointing out the most noteworthy feature of the k-space, i.e., its Fourier inverse yield to the image. A generic pulse sequence has been considered to explain the sampling of k-space trajectories. Examples of ultrafast imaging techniques are subsequently considered and discussed. CONCLUSIONS: EPI improves the resolution time of MRI, which is an intrinsically slow imaging procedure. Images can be obtained in few tenth of a second so that MRI suits the short temporal range of many interesting physiological processes. Recently the main goal of functional Magnetic Resonance Imaging (fMRI) has been the study of brain activity related to local changes in brain hemodynamics. These changes cause MR signal intensity variations. In the last years, several brain activity studies have been performed by means of Positron Emission Tomography (PET) which involves the administration of radioactive substances; fMRI has the advantage that it is a noninvasive technique, although peripheral nerve stimulation effects should be considered.

Humans↗
PubMed1978

[The computed tomography of the malignant thoracic space-occupying process under special consideration of radiotherapeutic points of view (author's transl)].

The data of 70 patients with a malignant thoracic space-occupying process were compared in order to find out the differences between computed tomography and conventional X-ray diagnosis (thorax radiography, hilum tomography), the radiotherapeutic aspects of these methods being taken under special consideration. Computed tomography is excellently suited for the establishment of therapeutic schemes because it is the only technique producing individual cross-sectional views of the thorax which are in correct scale and have a high resolving power. Contrary to thorax radiography and hilum shadow, the computed tomography offers some additional diagnostic information in several special fields.

Bronchial Neoplasms↗
PubMedDate not supplied

Core temperature monitoring of firefighters during hazardous materials training sessions.

OBJECTIVE: To determine core temperature (Tc) elevations in hazardous materials (HazMat) technicians wearing level-A fully encapsulated, chemically resistive suits (FECRSs) during training scenarios. DESIGN: Cross-sectional, observational feasibility study with Institutional Review Board approval. SETTING: HazMat training scenarios held during the summer of 1994. Weather conditions included both rainy and sunny days, with a mean ambient temperature of 75.8 degrees F (24.3 degrees C) (range 69-83 degrees F [20.6-28.3 degrees C). PARTICIPANTS: Nine male firefighters participating in training scenarios in the Midwestern United States. INTERVENTIONS: Each volunteer swallowed a capsule containing a Tc sensor developed by the National Aeronautics and Space Administration. The capsule continuously monitored Tc and stored data in an ambulatory recorder worn under the level-A FECRS during training. RESULTS: Mean age of the volunteers was 34 years, mean weight was 92.6 kg, and average baseline Tc was 36.7 degrees C (97.1 degrees F) (range 35.3-38.2 degrees C [95.5-100 degrees F]). Time in the FECRS averaged 25.4 minutes (range 14-35 minutes). All subjects demonstrated increased Tc while in the suit; the mean Tc increase was 0.8 degree C (1.4 degrees F) (range 0.2-1.3 degrees C [0.4-2.3 degrees F]). The Tc continued to increase during wet decontamination procedures and after suit removal. Mean heat storage values (delta Tcx LBMx 3.47 kJ) were calculated, and found to be moderately elevated to 3.6 kJ/kg (range 2.1-4.6 kJ/kg). CONCLUSION: These observations support the validity and significance of implementing prophylactic measures for firefighters using protective clothing. Simple protective measures include enforced time limitations, hydration, and efforts to minimize heat buildup by avoiding both direct sunlight and unnecessary time encapsulated in the suit.

Adult↗
PubMed1976

Physiologic and anti-G suit performance data from YF-16 flight tests.

Biomedical data were collected during high-G portions of 11 YF-16 test flights. Test pilots monitored revealed increased respiratory rate and volume, decreased tidal volume, and increased heart rate at higher G levels, with one pilot exhibiting various cardiac arrhythmias. Anti-G suit inflation and pressurization lags varied inversely with G-onset rate, and suit pressurization slope was near the design value.

Adaptation, Physiological↗
PubMed1989

[Optimizing carbon monoxide detection in biological material].

The determination of the CO-content is difficult in heated or putrified samples of blood and tissues. The preparation of these materials and a sensitive gas-chromatographic detection of small amounts of carbon-monoxide with head-space technique are described. The iron-content of a sample is a measure for the complete saturation with carbon-monoxide. This content is measured with AAS in the same vessel used before to determine CO. The presented method is suited too for ecological studies.

Carbon Monoxide↗
PubMed1975

Distribution of ventilation-perfusion ratios in dogs with normal and abnormal lungs.

We have recently described a new method for measuring distributions of ventilation-perfusion ratios (VA/Q) based on inert gas elimination. Here we report the initial application of the method in normal dogs and in dogs with pulmonary embolism, pulmonary edema, and pneumonia. Characteristic distributions appropriate to the known effects of each lesion were observed. Comparison with traditional indices of gas exchange revealed that the arterial PO2 calculated from the distributions agreed well with measured values, as did the shunts indicated by the method and by the arterial PO2 while breathing 100 per cent 02. Also the Bohr dead space closely matched the dispersion of ventilation in realtion to VA/Q. Assumptions made in the method were critically evaluated and appear justified. These include the existence of a steady state of gas exchange, an alveolar-end-capillary diffusion equilibration, and the fact that all of the observered VA/Q inequality occurs between gas exchange units in parallel. However, theoretical analysis suggests that the method can detect failure of diffusion equilbration across the blood-gas barrier should it exist. These results suggest that the method is well-suited to clinical investigation of patients with pulmonary disease.

Acute Disease↗
PubMed1982

Preparation of cell-free extracellular matrix from human peripheral nerve.

The extracellular matrix of human peripheral nerve, which is mainly basement membrane and fibrillar collagen, has been prepared by a procedure involving extensive detergent extraction of isolated endoneurium and perineurium obtained from various nerves. The ultrastructure of the isolated nerve extracellular matrix was indistinguishable from that seen in sections of intact nerve, indicating that the extraction procedure preserved the morphological integrity of these connective tissue components. The amino acid and carbohydrate compositions of the nerve extracellular matrix preparations were typically collagenous in nature containing a high content of glycine, proline, 4-hydroxyproline, and alanine and significant amounts of lysine and hydroxylysine. The preparations contained virtually no 3-hydroxyproline and low content of glucose and galactose compared to pure basement membranes, indicating that interstitial rather than basement membrane collagens predominated. This preparation appears well-suited to both the ultrastructural and biochemical study of the extracellular matrix of peripheral nerve.

Cell Fractionation↗
PubMed1995

Use of TSAR as a new tool to analyze the molecular dynamics trajectories of proteins.

There is a lack of tools to analyze simulations of protein molecular dynamics quantitatively. Our aim is to use calmodulin, a prototypical calcium-binding protein, to describe a strategy and some tools for extracting relevant information from dynamics calculations. Our main conclusions are as follows: Autocorrelation vectors may be used to represent a 3D conformation in an n-dimensional space, where n is variable (n < or = 20-30). On such a transformation, classic statistical tools (PCA, clustering, etc.) may be used to differentiate or characterize dynamics trajectories quantitatively. TSAR, an integrated package used for quantitative structure-activity relationships, is well suited (after minor modifications) for such a purpose. Finally, this type of strategy is able to point out the effects of the solvent screening parameters of the Amber software on the dynamics trajectories of calmodulin.

Calmodulin↗
PubMed1990

Two structural states of the vertebrate Z band.

Ultrastructural analysis of the vertebrate Z band suggests that two reversible states of a single intricate lattice are essential for the contractile process. The two structural states of the Z band lattice (ss and bw) have been described in cross section in skeletal and cardiac muscle in different physiological states. The lattice responds to active tension but resists passive deformation. Changes in Z band form and dimension are correlated with cross-bridge binding. Two-dimensional image processing techniques show enhanced structural features that vary with the observed changes in lattice dimension. All projected images from all lattices show an approximate four-fold symmetry. Each image reveals differences in the appearance of axial filaments which enter from opposite sides of the Z band and cross-connecting filaments of similar curvature which appear to connect each axial filament to four nearest axial filaments. In the ss images, the apparent diameter of cross-cut axial filaments and the Z band interaxial filament spacing are smaller than in bw images. Cross-connecting filaments appear to overlap in the region half-way between axial filaments in ss images. We conclude that the Z band is an essential and dynamic part of the sarcomere, uniquely suited to transmit tension while maintaining dimensions appropriate for cross-bridge interaction.

Animals↗
PubMed1998

Percutaneous epidural and nerve root block and percutaneous lumbar sympatholysis.

Epidural steroid injections and selective nerve root blocks currently are considered standard techniques in the diagnosis and treatment of back pain. The targeted epidural and perineural steroid injection with nerve block is a new technique that combines an epidural steroid injection and a nerve block. Radiologists are best suited for performing these procedures because of their training and skills in fluoroscopy and needle procedures.

Epidural Space↗
PubMed1993

Heart rate and workload variations in actual and simulated flight.

The monitoring of heart rate in aviation research provides a global index of pilot workload. Heart rate variability is a promising measure but more complex to assess and therefore less often used, especially in dynamic task environments. The application of spectral analysis techniques of heart rate for workload assessment in aviation is illustrated and discussed. Ideally, workload assessment includes real-time or continuous measures to reveal variations in workload as pilots accomplish their tasks. Four studies are discussed that used heart rate measures for the assessment of: (1) training effectiveness; (2) stress of flight instruction; (3) simulator realism; and (4) flight task difficulty. Results indicate that cardiovascular measures are well suited to index different mental states of pilots as well as their dynamic responses to variations in workload.

Adult↗
PubMed2006

It looks easy! Heuristics for combinatorial optimization problems.

Human performance on instances of computationally intractable optimization problems, such as the travelling salesperson problem (TSP), can be excellent. We have proposed a boundary-following heuristic to account for this finding. We report three experiments with TSPs where the capacity to employ this heuristic was varied. In Experiment 1, participants free to use the heuristic produced solutions significantly closer to optimal than did those prevented from doing so. Experiments 2 and 3 together replicated this finding in larger problems and demonstrated that a potential confound had no effect. In all three experiments, performance was closely matched by a boundary-following model. The results implicate global rather than purely local processes. Humans may have access to simple, perceptually based, heuristics that are suited to some combinatorial optimization tasks.

Attention↗
PubMed1988

Optimizing release from peptide hormone secretory nerve terminals.

Secretion of the peptide neurohormones oxytocin and vasopressin from terminals of magnocellular neurones in the mammalian neurohypophysis is elicited by conduction of depolarizing action potentials into terminal membranes, inducing opening of voltage-sensitive Ca2+ channels, entry of Ca2+ from the extracellular space and a rise in cytoplasmic Ca2+ concentration. The amount of peptide released per action potential is not immutable. In particular, the patterns in which action potentials are generated at the cell somata of the two types of neurone each appear exquisitely suited to optimize the release process at the terminal by utilizing a frequency-facilitation mechanism and by minimizing a mechanism of fatigue in the release process. The different properties of oxytocin and vasopressin neurones are of important physiological significance. The secretory terminals are also a site of receptor-mediated influences of neuromodulators which can greatly alter release efficiency. The mechanisms underlying facilitation and fatigue are not clearly understood. The evidence suggests that processes both prior to depolarization of the terminals (propagation and form of the action potentials) and directly at the terminals (frequency/pattern-dependent Ca2+ entry and channel openings) are involved. Transient activity-related increases in extracellular K+ concentration may be involved at both sites. Two types of neuromodulation have been partly characterized. Kappa-Opioid receptors in secretory terminal membranes directly modulate depolarization-evoked peptide release probably via interactions with Ca2+ channels. beta-Adrenergic receptors localized on neurohypophyseal astroglial cells mediate more subtle effects of noradrenaline. In the more chronic situation the neurohypophyseal astroglia alter their morphological relationships with neurosecretory elements and the basal lamina at release sites, changes which may also serve to optimize the secretory process.

Animals↗
PubMed1996

Sex-related engagement of the hemispheres in visuospatial processing.

Hemispheric asymmetries in visuospatial functions were investigated in women and men with a tachistoscopic task using lateralized presentation of "Necker" cubes. A lexical decision task served as control. In either of the two tasks the procedure involved a bilateral presentation of correct and distorted items and responses had to be given by means of a nonverbal decision task. The analysis of hits in the cube task showed a right visual field advantage for women and a left visual field advantage for men, but women had more false alarms in the right visual field, whereas men showed the reverse pattern again. The lexical decision task showed similar response patterns for men and women. The distinct response behavior supports the hypothesis that tasks allowing for various strategies to choose from obviously are better suited to elicit a differential engagement of the two hemispheres in women and men.

Adult↗
PubMed2000

Anti-Vascular endothelial growth factor treatment augments tumor radiation response under normoxic or hypoxic conditions.

Recent studies in experimental animals have shown that combining antiangiogenic therapy with radiation can enhance tumor response. Whether this enhancement is mainly attributable to angiogenesis inhibition, endothelial cell radiosensitivity, tumor cell apoptosis, or a decrease in the number of hypoxic cells (improved oxygenation) is not known. We designed this study to discern the role of tumor oxygenation. We chose an anti-vascular endothelial growth factor (anti-VEGF) monoclonal antibody (mAb) which has a known target, human VEGF. We also measured interstitial fluid pressure (IFP) to test the hypothesis that the decreased vascular permeability induced by the anti-VEGF mAb can lower IFP. The effect of anti-VEGF mAb on vascular density, partial oxygen tension (pO2), and apoptosis was also measured. Athymic NCr/Sed nu/nu mice bearing 6-mm xenograft of the human glioblastoma multiforme (U87), or colon adenocarcinoma (LS174T) were treated with anti-VEGF mAb injected i.p. on alternate days for a total of six injections at a dosage of 100 microg/injection/mouse. For combined anti-VEGF and radiation, single radiation doses were given under normal blood flow (20 and 30 Gy) or clamped hypoxic conditions (30 and 40 Gy) 24 h after the sixth injection of mAb. The inhibition of the growth of U87 and LS174T tumors by the anti-VEGF mAb was associated with a significant reduction in tumor vascular density and a relatively small increase in the number of apoptotic cells. Compared with size-matched controls, IFP decreased by 74% in LS174T, and 73% in U87 in mice treated with anti-VEGF mAb. After antibody treatment PO2 increased significantly in U87, but did not change in LS174T tumors. Combined treatment induced in U87 tumors a tumor-growth delay (TGD) which was greater than additive; in LS174T except for the 40-Gy hypoxic group, the effect was only additive. In both U87 and LS174T the TGD induced by the antibody was independent of oxygen levels in the tumor at the time of radiation. The fact that the increase in TGD occurred under both normoxic and hypoxic conditions suggests that anti-VEGF mAb treatment can compensate for the resistance to radiation induced by hypoxia.

Adenocarcinoma↗