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At least 1,207 records · Page 67Linked to original sources
PubMed1981

Argon endolaser.

We developed an endolaser probe that is capable of delivering argon laser light for photocoagulation of retinal breaks or vascular fronds. Energy is transmitted through a fiberoptic cord from a console outside of the surgical area to an endolaser probe inside the operating suite. The probe can be fired into fluid- or gas-filled media. With the use of this system, panretinal photocoagulation can be performed rapidly and conveniently during a vitrectomy procedure. We have also successfully managed posterior retinal tears and bleeding fibrovascular fronds with this system.

Argon↗
PubMed1977

Liver atrophy, hypertrophy and regenerative hyperplasia in the rat: the relevance of blood flow.

Liver perfusion can be measured sequentially by monitoring the clearance of 85krypton injected into the portal circulation. Preliminary studies in dogs show that the method reflects gas clearance from a homogeneously perfused liver parenchyma and correlates well with measurements of total hepatic blood flow. The method has been adapted to measurement of liver blood flow in normal rats, partially hepatectomized rats and after portacaval transposition with and without partial hepatectomy. There is a marked rise of approximately 250% in the first four hours after partial hepatectomy in the rat. After portacaval trans-position, liver blood flow remains within the normal range and no great rise occurs after partial hepatectomy. In animals subjected to portacaval transposition, there is a reduction in relative liver weight (liver weight/body weight ratio) and when partial hepatectomy is performed three weeks after portacaval transposition, the relative liver weight is regained within three weeks, and does not differ from that of non-hepatectomized controls. DNA synthetic activity, studied during the 72 hours after partial hepatectomy performed three weeks after portacaval transposition, shows an uptake of tritiated thymidine into liver DNA of the same magnitude as and contemporaneous with that of controls. Liver atrophy after portal diversion is not a result of a decrease in absolute liver blood flow. Regenerative hyperplasia appears to be independent of a direct supply of portal blood and occurs in the absence of the post-hepatectomy rise in liver blood flow seen in normal rats.

Adrenalectomy↗
PubMed1978

Myocardial imaging with extractable cations and inert tracers: the effects of flow and metabolism.

The physical and biological properties of 201thallium (Tl) have been investigated and are discussed in this review. A new technique using the ultra-short lived 81mkrypton (81mKr) as a continuous infusion into the aortic root in dogs and man is described. This provides a dynamic assessment of changes in regional myocardial perfusion. Experiments using 201Tl and 81mKr in dogs have shown that regional decreases in myocardial perfusion alone cannot be detected in images of the heart using 201Tl. The effects of perfusion and a variety of factors on the energy dependent cellular uptake of 201Tl are discussed as being of primary importance in changing the regional myocardial distribution of this tracer. The constant infusion of 81mKr in patients with anginal chest pain provides continuous measurement of regional myocardial perfusion in high spatial resolution images. This dynamic method provides a physiological assessment of stenosed coronary arteries at rest and during stress.

Animals↗
PubMed1980

The effects of propranolol on myocardial perfusion and metabolism during acute regional ischaemia.

The unique physical properties of the short-lived inert and freely diffusing isotope 81mkrypton allow a continuous observation to be made of regional myocardial perfusion. Eighteen dogs were anaesthetised and a reversible snare placed on the left anterior descending coronary artery (LAD). 81mKrypton was used to study regional myocardial perfusion, and myocardial metabolism was assessed using the epicardial ECG and release of creatine kinase activity (CK). Six dogs did not undergo LAD occlusion ("sham operated"); in six other dogs the LAD was occluded (controls), and another six dogs were given propranolol, 0.5 mg/kg, 20 min after LAD occlusion. All the parameters were measured before and for 5 h after LAD occlusion. When compared to controls, dogs treated with propranolol showed significant improvement (p less than 0.01) in regional myocardial perfusion; smaller loss of electrically active myocardium for any given degree of early ST-segment elevation; and a delay in the release of CK activity from a local coronary vein. These results suggest that propranolol exerts a beneficial effect following the development of acute myocardial infarction.

Animals↗
PubMed2001

Gas-phase binding of non-covalent protein complexes between bovine pancreatic trypsin inhibitor and its target enzymes studied by electrospray ionization tandem mass spectrometry.

The potential of electrospray ionization (ESI) mass spectrometry (MS) to detect non-covalent protein complexes has been demonstrated repeatedly. However, questions about correlation of the solution and gas-phase structures of these complexes still produce vigorous scientific discussion. Here, we demonstrate the evaluation of the gas-phase binding of non-covalent protein complexes formed between bovine pancreatic trypsin inhibitor (BPTI) and its target enzymes over a wide range of dissociation constants. Non-covalent protein complexes were detected by ESI-MS. The abundance of the complex ions in the mass spectra is less than expected from the values of the dissociation constants of the complexes in solution. Collisionally activated dissociation (CAD) tandem mass spectrometry (MS/MS) and a collision model for ion activation were used to evaluate the binding of non-covalent complexes in the gas phase. The internal energy required to induce dissociation was calculated for three collision gases (Ne, Ar, Kr) over a wide range of collision gas pressures and energies using an electrospray ionization source. The order of binding energies of the gas-phase ions for non-covalent protein complexes formed by the ESI source and assessed using CAD-MS/MS appears to differ from that of the solution complexes. The implication is that solution structure of these complexes was not preserved in the gas phase.

Animals↗
PubMed2001

Stage-specific skeletal and visceral defects of the I(Kr)-blocker almokalant: further evidence for teratogenicity via a hypoxia-related mechanism.

BACKGROUND: As a class effect, potent I(Kr)-blockers have been shown to induce stage-specific external malformations. The aim of this study was to investigate whether I(Kr)-blockers also induce stage-specific visceral and skeletal defects and to further elucidate a proposed arrhythmia-hypoxia hypothesis. METHODS: Single oral doses of the selective I(Kr)-blocker almokalant (ALM) 25-150 micromol/kg, 7-14 dams/group, were given to Sprague-Dawley rats on gestation days (GD) 10-14, and the fetuses were examined for malformations on GD 21. One group was pretreated with the spin-trapping agent, alpha-phenyl-N-t-butylnitrone (PBN), given intraperitoneally 1 hr before ALM on GD 11. RESULTS: Cardiac ventricular septum defects and vascular malformations were observed after dosing on GD 10-11 and, to a lesser degree, on GD 12-13. Urogenital defects, absence/malposition of the postcaval lung lobe, and attenuated diaphragm were observed mainly on GD 10-11. Skeletal examination showed a high incidence of vertebral abnormalities on thoracic level on GD 10, on lower thoracic to caudal level on GD 11, and sternebral defects were observed all days. On GD 13 brachy-, oligo-, and syndactyly of the forepaw were induced, and of the hindpaw on GD 14. PBN reduced the incidence of both visceral and skeletal defects. CONCLUSIONS: The stage specificity of observed visceral and skeletal defects correlates well with what has been reported in the literature after temporary interruption of oxygen supply during the same stages of development. The protective effect by PBN present further evidence that the teratogenicity of potent I(Kr)-blockers is related to induction of hypoxia- reoxygenation injury due to embryonic cardiac arrhythmia.

Abnormalities, Drug-Induced↗
PubMed2000

Modeling protein-small molecule interactions: structure and thermodynamics of noble gases binding in a cavity in mutant phage T4 lysozyme L99A.

The complexes of phage T4 lysozyme L99A with noble gases have been studied by molecular dynamics simulation. In a long simulation of the complex with one Xe atom, the structure was found to undergo global conformation change involving a reversible opening and closing of the entrance to the substrate-binding site, during which the conformations of the N and C-terminal domains varied little. The distributions of Xe positions sampled in dynamics simulations were refined in terms of anisotropic Gaussian distributions via least-squares minimization of the difference between Fourier transforms. In addition, molecular transformation simulations have been applied in order to calculate the binding free energies of Xe, Kr and Ar relative to a standard state at a pressure of 1 bar. A single bound Xe is found to assume an equilibrium distribution over three adjacent preferred sites, while in a two-Xe complex, the two Xe atoms preferentially occupy two of these. The positions of the three sites agree closely with the positions of bound Xe determined in the refined crystal structure of a complex formed at a pressure of 8 bar Xe, and the calculated affinities agree well with the observed partial occupancies. At a pressure of 8 bar, a mixture of one-Xe and two-Xe complexes is present, and similarly for complexes with Kr and Ar, with single occupancy relatively more prevalent with Kr and Ar. (Binding of a third Xe atom is found to be quite unfavorable.) A comparison with simulation results for the binding of benzene to the same site leads to the conclusion that binding of Xe within cavities in proteins is common because of several favorable factors: (1) Xe has a large atomic polarizability; (2) Xe can be applied at a relatively high pressure, i.e. high chemical potential; (3) an unfavorable entropic term related to the need to orient the ligand in the binding site is absent. Finally, it is found that the model's binding energy of a water molecule in the cavity is insufficient to overcome the unfavorable binding entropy.

Amino Acid Substitution↗
PubMed1996

Comets, meteorites and atmospheres.

The relatively low value of Xe/Kr in the atmospheres of Earth and Mars seems to rule out meteorites as the major carriers of noble gases to the inner planets. Laboratory experiments on the trapping of gases in ice forming at low temperatures suggest that comets may be a better choice. It is then possible to develop a model for the origin of inner planet atmospheres based on volatiles delivered by comets added to volatiles originally trapped in planetary rocks. The model will be tested by results from the Galileo Entry Probe.

Argon↗
PubMed1985

Regional specific mean expiratory gas flow from 81mKr equilibrium inhalation data.

A new method of analysing the data available from routine 81m Kr equilibrium inhalation investigations has been developed. The data for analysis are acquired from a gamma camera in the form of a sequential series of images from which multiple breath activity-time curves are generated for eight regions in the lung. The method is based on a description of the behaviour of the radioactive gas in the lung using a mathematical model. Values of specific mean expiratory gas flow, that is mean expiratory gas flow per unit lung volume, are calculated from the application of the model to the expiratory phase only of a single breath activity-time curve which is generated from the multiple breath activity-time curve using post-acquisition gating. This method overcomes the problem of non-uniform inspiratory concentration of tracer gas experienced in previously reported techniques of analysing inhalation data obtained using poorly soluble radioactive gases. The model is shown, in simulation studies, to be an adequate description of the behaviour of radioactive gas in the lung and the analysis technique is shown, in clinical studies, to be both reproducible and sensitive to disease state.

Humans↗
PubMed1980

81mKr gas generator for lung ventilation study.

A generator of 81mKr was designed and tested. The parent nuclide 81Rb was produced by the 70 MeV proton induced reactions on a Rb2SO4 target. 81mKr was bubbled out with oxygen gas from the 81Rb solution, and collected in a reservoir for lung ventilation studies. The generator was continuously operated at the high flow rate up to 10 1/min. The generator efficiency was 86%. The collection rates in the reservoir were examined under several flow rates. The pure 81mKr isomer was observed wih a NaI (T1) detector at the reservoir.

Humans↗
PubMed1980

Kr-81m for determination of right ventricular ejection fraction (RVEF).

A 10--12 mCi 81Rb leads to 81mKr generator was connected to a specially designed short-period infusion set, to produce an equilibrium activity distribution in the right heart. This procedure was tested in 25 individuals to calculate the right ventricular ejection fraction (RVEF). On average 30 heart cycles were analyzed per study. No background activity from the left heart was visualized because of the radionuclide exhalation. The background from the lungs could be neglected, which is partially due to the ultra-short half-life of the nuclide (t 1/2 = 13 S). Thus, an easy automatic procedure can be applied to delineate the ventricle and to calculate the RVEF. The data showed excellent reproducibility, when investigations were repeated. The method would benefit from use of higher activity generators.

Adult↗