Search PubMed⌕ Search

Biomedical subjects

R Dressler

Publications and source records attributed to R Dressler.

15 recordsLinked to original sources
PubMed2002

Chemical investigation of hassium (element 108).

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

Journal Article↗
PubMed2002

Rho(0) meson production in the pp-->pppi(+)pi(-) reaction at 3.67 GeV/c.

Total and differential cross sections for the exclusive reaction pp-->pp rho observed via the pi(+)pi(-) decay channel have been measured at p(beam)=3.67 GeV/c. The observed total meson production cross section is determined to be (23.4+/-0.8+/-8) mu b and is significantly lower than typical cross sections used in model calculations for heavy-ion collisions. The differential cross sections measured indicate a strong anisotropy (approximately cos(theta(CM)(rho)) in the rho(0) meson production.

Journal Article↗
PubMed2000

Chemical characterization of bohrium (element 107)

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available. In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table, whereas element 106 behaves in accordance with the expected periodicity. Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elements of group VII, thus confirming relativistic calculations that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.

Journal Article↗
PubMed1999

First Measurement of a Thermochemical Property of a Seaborgium Compound.

With only a few atoms of seaborgium (Sg, element 106), in the form of volatile SgO(2)Cl(2), it was possible to determine the sublimation enthalpy of this compound using gas chromatography. Furthermore, it was demonstrated that in Group 6 Sg is chemically more similar to W than to Mo.

Journal Article↗
PubMed1999

The effects of target and distractor familiarity on visual search in de novo Parkinson's disease patients: latent inhibition and novel pop-out.

De novo Parkinson's disease (PD) patients identified presence or absence of a unique shape presented with homogeneous distractors. Response time (RT) was examined as a function of prior experience with target and/or distractor assessing latent inhibition (LI; slower RTs to a target that was formerly a distractor against a background of distractors that were formerly targets as compared with a novel target with distractors that were formerly targets) and novel pop-out effects. PD patients were slower than controls in detecting test-phase targets compared with preexposure-phase targets. Female PD patients with right-side motor symptoms had elevated LI compared with female controls and female PD patients with left-side symptoms. Male PD patients with right-side symptoms did not exhibit LI. Results are discussed in terms of the dopamine hypothesis and the reciprocal relationship between PD and schizophrenia.

Exploratory Behavior↗
PubMed1998

Enhanced fatigue during motor performance in patients with Parkinson's disease.

OBJECTIVE: To measure fatigue quantitatively during continuous motor performance in patients with PD. BACKGROUND: Enhanced fatigue on performance of motor tasks is a very frequent and disabling complaint of PD patients, and is poorly characterized and understood. Recent evidence suggests a role for mitochondrial dysfunction in the pathogenesis of PD. Reduced exercise capacity is one of the hallmarks of systemic mitochondrial impairment. METHODS: The authors used an automated system to measure muscle fatigue during a continuous (30-second), maximal, isometric forearm flexion in 17 PD patients and 10 age-matched control subjects. A fatigue index (FI) was then calculated. Peak force (PF) was measured as an internal standard of the examination. Measurements were performed before and 2 hours after an oral dose of levodopa/carbidopa (125 mg/12.5 mg). RESULTS: In PD patients there was a 50% increase in FI. The increased FI was often asymmetric and more pronounced on the side more affected by the disease. FI was significantly responsive to, and improved after, an oral dose of levodopa. The rate of improvement in FI induced by levodopa correlated with disease severity, as measured by the Unified Parkinson's Disease Rating Scale. No significant alterations in PF were observed. CONCLUSIONS: Enhanced muscle fatigue should be recognized as an integral part of the spectrum of motor impairment of PD. However, our data argue for its association with a central dopamine deficiency rather than with a muscle mitochondrial abnormality.

Adult↗
PubMed1997

Membranous lupus nephritis with antineutrophil cytoplasmic antibody-associated segmental necrotizing and crescentic glomerulonephritis.

Focal segmental necrotizing and crescentic lupus nephritis accompanied by perinuclear antineutrophil cytoplasmic antibody (P-ANCA) seropositivity is an unusual occurrence. We report the first biopsy-documented cases of membranous lupus nephritis class V with associated "pauci-immune" segmental necrotizing glomerulonephritis and P-ANCA seropositivity. The absence of subendothelial electron-dense deposits favored a manifestation of superimposed ANCA-associated glomerulonephritis rather than class III lupus nephritis. The pathogenetic implications of this association are explored.

Adult↗
PubMed1995

Hypervitaminosis A in two hemodialysis patients.

We present two cases of hemodialysis patients developing vitamin A toxicity related to excessive consumption of nutritional supplements containing large quantities of vitamin A. In one patient, severe hypercalcemia was the lone presenting sign; in the other, hypercalcemia was associated with unusual neurologic manifestations. We will discuss the reason why hemodialysis patients are at special risk for the development of hypervitaminosis A and review the mechanism leading to the associated hypercalcemia.

Adult↗
PubMed1995

Long-term high dose intravenous calcitriol therapy in end-stage renal disease patients with severe secondary hyperparathyroidism.

We prospectively studied the long-term effects of intravenous calcitriol in 17 hemodialysis patients with severe secondary hyperparathyroidism (HPT) for 25.7 +/- 3.4 (+/- SE) months. Calcitriol was given thrice weekly after dialysis. Subsequently, changes were made every 3-4 weeks based upon serum chemistries. Total calcium and inorganic phosphorus were measured weekly; alkaline phosphatase (AP) and IRMA-PTH were measured monthly. Inorganic phosphate was controlled with calcium supplements. With calcitriol therapy both IRMA-PTH and AP decreased from 876 +/- 113 to 65 +/- 13 pg/ml (p < or = 0.001) and 432 +/- 106 to 103 +/- 15 U/ml (p < or = 0.001), respectively. Each patient had a reduction in IRMA-PTH and AP. Nadir IRMA-PTH occurred at 55.4 +/- 7.3 weeks. The maximum and mean maximum doses of calcitriol were 8.0 and 4.1 +/- 0.4 micrograms thrice weekly, respectively. Hypercalcemia tended to occur in those patients who were hypercalcemic prior to the initiation of intravenous calcitriol therapy. All hypercalcemic episodes were asymptomatic and reversed either by temporary withdrawal or lowering of the calcitriol dose. Hyperphosphatemia developed in those patients with a history of elevated serum phosphates and was mostly related to dietary and medication noncompliance. We conclude that intravenous calcitriol was uniformly effective and safe for the long-term therapy of severe HPT in ESRD. Careful attention to serum phosphate control is required.

Calcitriol↗
PubMed1993

Short-term beneficial effect of deprenyl monotherapy in early Parkinson's disease: a quantitative assessment.

It was recently shown that early treatment with deprenyl in patients with Parkinson's disease can delay the need for initiation of levodopa therapy. It was therefore suggested that deprenyl may slow down disease progression. Alternatively, the observed stabilization of clinical disability may merely reflect drug-induced symptomatic benefit. We therefore examined a possible short-term beneficial effect of deprenyl (10 mg/day) as the first and only drug in 15 consecutive de novo patients. Bradykinesia was quantitatively assessed by computerized analysis of isometric force/time curves of biceps and triceps bilaterally and by calculation of simple reaction time (RT) and maximal muscle contraction rate (MMCR). We also measured maximal muscle force, evaluated clinical status by the Unified Parkinson's Disease Rating Scale (UPDRS) motor score, and recorded patients' subjective reports. All tests were carried out before and at 1 and 2 months of treatment. Only one patient reported a beneficial effect. No significant changes in the UPDRS or score or muscle force were observed. In contrast, MMCR and RT improved at 1 month by an average of 12.1 and 7.2%, respectively (p < 0.01, paired t test). This improvement persisted after 2 months of treatment. Study shows that deprenyl monotherapy exerts a short-term beneficial effect in de novo parkinsonian patients. This effect, however, appears to be small, subclinical, and probably cannot account for the observed delay in the need to start levodopa therapy.

Aged↗
PubMed1989

Pseudomonal and candidal peritonitis as a complication of continuous ambulatory peritoneal dialysis in human immunodeficiency virus-infected patients.

PURPOSE: To our knowledge, there has been no report documenting the spectrum of peritonitis in human immunodeficiency virus (HIV)-infected persons. We therefore analyzed our records to confirm our previous observation of a higher incidence of pseudomonal and fungal peritonitis in a group of HIV antibody-positive (HIV+) patients undergoing continuous ambulatory peritoneal dialysis (CAPD). PATIENTS AND METHODS: During a 22-month period, we retrospectively studied 71 patients with end-stage renal disease undergoing CAPD. Of these, seven were HIV+, five were at high risk for HIV infection but antibody-negative, and 59 were at low risk for HIV infection. Organisms isolated in episodes of peritonitis were classified microbiologically as one of the following: gram-positive, non-pseudomonal gram-negative, pseudomonal, fungal, or culture-negative. RESULTS: The total peritonitis rate was higher in both the high-risk (p less than or equal to 0.01) and the HIV+ (p less than or equal to 0.02) groups when compared with that in the low-risk population. These differences were attributable to the following: (1) the high-risk group's two-fold increase in gram-positive infections (p less than or equal to 0.01), and (2) a 24-fold increase in pseudomonal (p less than 0.001) infections and seven-fold increase in fungal (p less than 0.005) infections in the HIV+ group. These infections were invariably associated with catheter loss and frequently resulted in conversion to hemodialysis. CONCLUSION: We believe that the use of CAPD in HIV+ patients may be limited by this increased occurrence of pseudomonal and fungal peritonitis.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Survival of human immunodeficiency virus-infected patients on maintenance dialysis.

It has recently been reported that patients on maintenance dialysis with the acquired immune deficiency syndrome (AIDS) survive only 1 to 3 months. We studied all patients on maintenance dialysis at the Baumritter Kidney Center who were known to be infected with the human immunodeficiency virus (HIV). Five patients met the criteria for AIDS; another ten had anti-HIV antibodies but no opportunistic infections. The AIDS patients survived 8 to 18 months, and two are still alive. Mean survival in the AIDS group was 13.2 +/- 1.9 months, while the HIV(+) non-AIDS group survived 15.7 +/- 3.0 months. While these data are not statistically different, the survival curve in the AIDS group predicted a shorter survival than for the HIV(+) patients without AIDS. In fact, the survival of our dialyzed AIDS patients was similar to that reported for AIDS patients in general. Our experience suggests that dialysis may have no adverse effect on survival in AIDS. We conclude that dialysis patients with AIDS may survive 8 to 12 months or more and that the approach to such patients should be individualized.

Acquired Immunodeficiency Syndrome↗