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At least 1,351 records · Page 75Linked to original sources
PubMed1986

Ocular histoplasmosis syndrome.

The Macular Photocoagulation Study (MPS) is a multi-center clinical trial supported by the National Eye Institute whose purpose is to assess argon laser photocoagulation as a treatment for choroidal neovascular membranes (NVMs) that do not involve the fovea. The MPS documented that in patients with ocular histoplasmosis syndrome argon laser photocoagulation in comparison with no treatment can reduce the risk of severe visual loss from 46 to 13% in the first two years. Accordingly, patients with ocular histoplasmosis and NVMs outside the fovea are advised to undergo prompt treatment with argon laser photocoagulation.

Clinical Trials as Topic↗
PubMed2004

In situ metrology of 85Kr plumes released by the COGEMA La Hague nuclear reprocessing plant.

The IRSN (Institut de Radioprotection et de Sûreté Nucléaire, France) has started an in situ study of the behaviour of atmospheric releases close-by the COGEMA La Hague nuclear reprocessing plant. The study is designed to improve information on the dispersion of radioactive pollutants very close to the emission point--a 100 m height chimney. In this situation, close to the emission and height of the emission, Gaussian models generally used to predict the behaviour of atmospheric releases are not well adapted. The study is based on the characterisation of the 85Kr emitted during normal operations of the reprocessing process. Temporal and spatial variations of the plume shape were investigated with intensive in situ measurements. Live in situ techniques to measure the electrons and the photons emitted by the 85Kr have been implemented and will be described. Preliminary results showing the interest of the techniques were presented. Variations of the dose rates created by the photon flux of a plume were directly measured and correlated to other quantities.

Belgium↗
PubMed2003

Cosmic ray measurements at aircraft altitudes and comparison with predictions of computer codes.

Extensive measurements of dose exposure of aircrew have been carried out in recent years using passive detectors on subsonic and supersonic air routes by DIAS (Dublin Institute for Advanced Studies). Studies were based on measurement of LET spectra using nuclear recoils produced in CR-39 nuclear track detectors by high energy neutrons and protons. The detectors were calibrated using energetic heavy ions. Data obtained were compared with the predictions of the EPCARD and CARI-6 codes. Good agreement has been found between the experimental and theoretical values.

Aircraft↗
PubMed2000

Comparison of in vitro and in vivo efficiencies of a novel unit-dose liquid aerosol generator and a pressurized metered dose inhaler.

Gamma scintigraphic imaging was employed in 10 healthy volunteers to compare the total and regional lung deposition of aerosols generated by two delivery platforms that permitted microprocessor-controlled actuation at an optimal point during inhalation. An aqueous solution containing 99mTc-DTPA was used to assess the deposition of aerosols delivered by inhalation from two successive unit-dosage forms (44 microl volume) using a prototype of a novel liquid aerosol system (AERx Pulmonary Delivery System). This was compared with aerosol deposition after inhalation of two 50 microl puffs of a 99mTc-HMPAO-labeled solution formulation from a pressurized metered dose inhaler (MDI). The in vitro size characteristics of the radiolabeled aerosols were determined by cascade impaction. For the AERx system, the predicted lung delivery efficiency based on the product of emitted dose (60.8%, coefficient of variation (CV)=12%) and fine particle fraction (% by mass of aerosol particles <5.7 microm in diameter) was 53.3% (CV=13%). For the solution MDI, the emitted dose was 62.9% (CV=13%) and the predicted lung dose was 44. 9% (CV=15%). The AERx system demonstrated efficient and reproducible dosing characteristics in vivo. Of the dose loaded into the device, the mean percent reaching the lungs was 53.3% (CV=10%), with only 6. 9% located in the oropharynx/stomach. In contrast, the lung deposition from the solution MDI was significantly less (21.7%) and more variable (CV=31%), with 42.0% of the radiolabel detected in the oropharynx/stomach. Analysis of the regional deposition of the radioaerosol indicated a homogeneous pattern of deposition after delivery from the AERx system. A predominantly central pattern of distribution occurred after MDI delivery, where the pattern of deposition was biased towards a central zone depicting the conducting airways. The AERx system, in contrast to MDIs, seems highly suited to the delivery of systemically active agents via pulmonary administration.

Adult↗
PubMedDate not supplied

Experimental validation of a new coronary guide wire labeled with rubidium 81/krypton 81m for continuous assessment of myocardial blood flow.

BACKGROUND: The rubidium 81/krypton 81m method was suggested for assessment of myocardial blood flow (MBF) three decades ago. This study investigates the novel concept of using 81Rb-/81mKr-labeled coronary guide wires with wire-attached 81Rb activity and diffusable 81mKr gas for assessment of lesion-specific impairment of MBF by evaluation of the 81Rb/81mKr activity ratio. The feasibility of wire production is tested, and application of the method is investigated in the canine model. METHODS AND RESULTS: Conventional coronary guide wires for angioplasty (0.014 in) were labeled with radioactive 81Rb/81mKr by ion bombardment of the wire tip. A total of 16 of the 18 wires labeled in series showed successful 81Rb fixation in combination with free 81mKr gas diffusability during quality control measurements. The suitability of the wires to assess MBF in combination with an external gamma ray detector was investigated in open-chested dogs. Electromagnetic measurement of coronary blood flow (CBF) was used as reference, providing a signal that is directly linked to volumetric MBF. The 81Rb/81mKr ratio tracked changes in CBF reliably in all 6 dogs. The found linear dependence of measured 81Rb/81mKr count rates on measured CBF supports the modeling assumptions made to apply the theoretic basis of the 81Rb/81mKr technique to 81Rb-labeled coronary guide wires. CONCLUSION: 81Rb-/81mKr-labeled coronary guide wires provide a signal that indicates volumetric MBF directly. This unique capability may qualify the technique as a valuable tool for research purposes and as an attractive method for invasive cardiology at centers where the logistic arrangements for short-lived isotope supply are provided.

Animals↗
PubMed2000

IR spectra of CH3F in liquid and solid noble gas solutions.

The IR absorption spectra of CH3F doped Ar, Kr and Xe solutions have been recorded near the melting point. The full widths at half maximum of fundamental bands increase noticeably after crystallization of the Xe and Kr solutions. A slight narrowing of the bands is observed just below the freezing point of the Ar solution. Treated in the framework of the Debye model for the J-diffusion of a symmetric top rotation, the results suggest a weaker perturbation of rotational motion of CH3F in the ordered Xe and Kr solids at least near the freezing point. At the same time, molecular rotation becomes more hindered when going to solid Ar. The broadening effect has been found to correlate with a hopping increase of the vibrational energy relaxation time, measured by the IR-IR double resonance method.

Argon↗
PubMed2002

The radial Hamiltonian for the ground electronic state of KrH+.

All literature vibration-rotational and pure rotational transitions belonging to ten isotopomers of KrH+ in the X'sigma+ state (in total 351 lines) have been used in a iterative nonlinear least-squares fit of compact analytic Born-Oppenheimer potential in the form of generalized potential energy function (GPEF). Additional functions describing the adiabatic and nonadiabatic corrections have also been determined. The obtained radial Hamiltonian reproduces the spectra with sufficiently good accuracy. The GPEF of KrH+ reproduces the experimental value of the dissociation energy, has a correct R(-4) asymptotic behaviour, and reproduces long-range inverse-power potential coefficient C4.

Electrons↗
PubMed2002

Laser spectroscopy of CdKr molecules in ultraviolet region.

Excitation spectra of the A0+(5(3)P1)<--X0+(5(1)S0), B1(5(3)P1)<--X0+ and D1(5(1)P1)<--X0+ transitions as well as a fluorescence spectrum of the D1(v') = 16 --> X0+ transition in CdKr van der Waals molecule has been recorded in an experiment of a continuous supersonic molecular beam crossed with a pulsed dye laser beam. A rigorous analysis of the excitation spectra based on Birge-Sponer and LeRoy-Bernstein methods aided with a computer calculation, utilizing a program of near dissociation expansion lead to the X0+- and improved A0+-, B1- and D1-state characterizations. Evidence of a theoretically predicted potential barrier within the B1-state well was found and discussed with regard to the latest result of ab initio calculation. An analysis of bound-bound and bound-free parts of the fluorescence spectrum confirmed a v'-assignment and indicated that Morse and Maitland-Smith M-S (n0, n1) functions are adequate representations of the bound well and repulsive wall of the X0+-state potential energy curve, respectively. All spectroscopic characteristics obtained in this work are compared with newest theoretical studies of this complex.

Cadmium↗
PubMed2002

Dissolved gases as partitioning tracers for determination of hydrogeological parameters.

In this study, dissolved Kr and SF6 gases were used to determine various hydrogeological parameters of laboratory columns under water-saturated and partially saturated conditions as a function of the flow velocity. The dissolved gases behaved conservatively in saturated columns but were significantly retarded in unsaturated conditions as a direct function of the Henry's law constant (KH) and the ratio of column pore spaces filled with air and water (Vg/Vw). Lower aqueous diffusion coefficients for SF6 compared to that for Kr also resulted in significant rate-limited mass transport across gas-water interface. This effect was exacerbated at higher flow velocities as was indicated by the asymmetric shape of breakthrough curves, more so in the case of SF6. A nonequilibrium advective-dispersive transport model accurately described tracer breakthrough and was used to estimate parameters such as final Vg/Vw under partially saturated conditions and partitioning rates. Internally consistent model results were obtained for both dissolved gases despite the wide range in physical properties (e.g., KH and aqueous diffusion coefficients), suggesting that dissolved Kr and SF6 may be used in conjunction to delineate and validate aquifer characteristics simultaneously from a single pulse injection of the tracer.

Geological Phenomena↗
PubMed2005

Theoretical prediction of noble gas containing anions FNgO- (Ng = He, Ar, and Kr).

The structures and energies of the noble gas containing anions FNgO- (Ng = He, Ar, and Kr) have been calculated by high-level ab initio calculations. The FNgO- anions were found to be deep-energy minima at the singlet electronic state, and their energies are significantly lower than those at the triplet state. High dissociation energy barriers to Ng + OF- were also predicted. The unexpected stability of the FNgO- was due to the dramatic ion-induced O=Ng bond formation. The calculated results suggested possible experimental identification of the anionic species and even some related "ionic compounds" under cryogenic conditions.

Anions↗
PubMed1986

Effects of clonidine on cerebral blood flow and the response to arterial CO2.

CBF, as measured by the clearance of 133Xe or 85Kr in the pentobarbital-anesthetized cat, displays a monotonic increase as the PaCO2 is elevated over a range of 20-60 mm Hg (slope Xe, 1.65 +/- 0.14 ml/100g/min/mm Hg; slope Kr, 1.40 +/- 0.11 ml/100 g/min/mm Hg). Clonidine (20 micrograms/kg i.v.), a centrally acting, alpha 2-preferring agonist, reduced the slope of the PaCO2-CBF response functions for Xe and Kr by 70 and 64%, respectively. Clonidine reduced normocarbic CBF-Xe by 36%, but had no effect on normocarbic CBF-Kr. ST-91, a polar structural analog of clonidine that does not cross the blood-brain barrier, did not reproduce the effects of clonidine when administered at an equivalent dose. This indicates that the effects of clonidine observed were secondary to its action on central rather than peripheral sites. In addition to the effects on the clearance of CBF markers, clonidine reduced the increased MABP otherwise evoked by elevated PaCO2. Reduction in the MABP response to PaCO2 did not account for the lowering of CBF during hypercarbia. In separate experiments where MABP was elevated to correspond with the PaCO2-MABP response observed in the absence of clonidine, a comparable reduction in the slope of the PaCO2 response was also observed. In addition, the pressure autoregulatory response was unaltered after clonidine treatment. These observations suggest that the central action of alpha 2-receptors on the CBF-CO2 response cannot be attributed to an altered perfusion pressure.

Animals↗
PubMed1987

Regional cerebral blood flow and focal cortical perfusion: a comparative study of 133Xe, 85Kr, and umbelliferone as diffusible indicators.

We report that regional CBF determined by the initial slope technique using 133Xe and 85Kr in cats and rabbits can be significantly influenced by the size of the field of measurement. The clearance curves of umbelliferone, a lipid-soluble intracellular pH fluorescent indicator, from a visually avascular 80-micron field were used to cross-correlate rCBF with focal cortical perfusion. Our findings indicate that in the cat, as the gamma or beta detector's field of volume was reduced, regional CBF (rCBF) measured by intraarterially injected 133Xe or 85Kr decreased in value by 33% and 28%, respectively, and the slope of the rCBF-PaCO2 response curve became less steep by 56% and 45%, respectively. Umbelliferone, measuring a much smaller volume of tissue, showed a lower normocapnic flow and a more oblique PaCO2 response curve. In the rabbits studied, the normocarbic rCBFs and the rCBF-PaCO2 response curves measured with the three techniques corresponded to those measured in the cat. These results suggest that large field/volume measurements assess a measure of flow that is a weighted average of several distinct flow compartments and that these compartments differ in their response to changes in PaCO2.

Animals↗