Biomedical subjects

A Held

Publications and source records attributed to A Held.

16 recordsLinked to original sources

PubMed2005

Homogeneity and stability study of the candidate reference material Adamussium colbecki for trace elements.

The preparation of a new candidate certified reference material (CRM) for trace elements based on the antarctic bivalve Adamussium colbecki(IRMM 813) was carried out by the Istituto Superiore di Sanità(ISS, Rome, Italy) in cooperation with the Institute for Reference Materials and Measurements, Joint Research Centre of the European Commission (EC-JRC-IRMM), in the frame of the Italian National Programme of Research in Antarctica (Programma Nazionale di Ricerca in Antartide, PNRA). Samples were collected at Terra Nova Bay (Ross Sea) during the 2000-2001 expedition in Antarctica. The preparation of a material suitable for certification was performed by the EC-JRC-IRMM. Measurements for homogeneity and short-term stability tests were carried out by ISS. The elements selected for the certification project were As, Cd, Cu, Cr, Fe, Mn, Ni and Zn. For the above-mentioned tests, the determination of the elements of interest was performed on samples mineralised by microwave-assisted acid digestion. The analytical techniques employed to this end were inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry (ICP-DRC-Q-MS). The candidate material was shown to be fit for purpose with regard to homogeneity and short-term stability, thus allowing the following phases of the certification project to be undertaken, in the first place the selection of expert laboratories for the accomplishment of the certification campaign.

Animals↗

PubMed2003

Differential effects of surgical sympathetic block on sudomotor and vasoconstrictor function.

OBJECTIVE: To assess the effects of a surgical block of the sympathetic chain at the T2 level on vasoconstriction and palmar sweating in patients with palmar hyperhidrosis. METHODS: In a prospective study, sympathetic vasoconstriction was measured by laser-Doppler imaging and by computer-assisted infrared thermography (rewarming kinetics following immersion of both hands in ice water [4 degrees C, 30 seconds]) in 61 patients with hyperhidrosis preoperatively and 2 days and 3 months postoperatively. In addition, palmar sweating preoperatively and 3 months postoperatively was assessed by quantitative sudometry. RESULTS: Before surgery, rewarming kinetics was significantly slower in the patients (n = 61) than in the healthy control subjects (n = 28). Two days after the block, baseline skin temperature increased by about 5 degrees C, and rewarming was massively accelerated in each of the patients. Three months postoperatively, rewarming kinetics was still accelerated in 36 hands, was unchanged from the preoperative condition in 42, and had worsened in 12. These changes were accompanied by parallel alterations of laser-Doppler flux. However, palmar sweating was massively reduced in all but one patient, irrespective of the different rewarming kinetics. CONCLUSIONS: T2 sympathectomy leads to long-lasting inhibition of palmar sweating, which does not correlate to loss of vasoconstriction. Recurrent and enhanced vasoconstrictor function 3 months following endoscopic sympathetic block has major implications for its use to treat enhanced vasoconstriction.

Adolescent↗

PubMed2000

Coordination polymerization in water affording amorphous polyethylenes.

The coordination polymerization of ethylene in water as a reaction medium was studied. Rubbery amorphous branched polyethylene was obtained when a known cationic diimine-substituted methyl complex was employed as a catalyst precursor. High rates of up to 900 TOh(-1) (turnover frequency) were observed. In contrast to solution polymerization in an organic solvent, the rate of suspension polymerization in water increases greatly with ethylene pressure in the range up to 20 bar; this indicates control of the polymerization rate by the concentration of the olefin monomer at the catalytically active site. The effect and mode of mass transfer phenomena were studied. A high catalyst stability in the aqueous coordination polymerization was observed. It was found to be due to an "encapsulation" of the water-insoluble catalyst precursor in the hydrophobic amorphous polymer during the polymerization reaction, and this resulted in strongly restricted accessibility for the aqueous phase. Surprisingly, exposure of the water-stable catalyst precursor to ethylene monomer in solution in the presence of water resulted in immediate decomposition. Polymer microstructure, and thermal and mechanical properties were investigated. The different degree of branching, molecular weight, and corresponding macroscopic properties of the polymers obtained in water as a reaction medium versus solution polymerization in methylene chloride under the same conditions are due to the different phase behavior during polymerization (suspension vs. solution), as opposed to an effect of water on the catalytically active centers.

Journal Article↗

PubMed2000

Mechanism of Ca(2+) overload in endothelial cells exposed to simulated ischemia.

OBJECTIVE: Several studies have shown that myocardial ischemia leads to functional failure of endothelial cells (EC) whereby disturbance of Ca(2+) homeostasis may play an important role. The mechanisms leading to Ca(2+) disbalance in ischemic EC are not fully understood. The aim of this study was to test effects of different components of simulated ischemia (glucose deprivation, anoxia, low extracellular pH (pH(o)) and lactate) on Ca(2+) homeostasis in EC. METHODS: Cytosolic Ca(2+) (Ca(i)), cytosolic pH (pH(i)) and ATP content were measured in cultured rat coronary EC. RESULTS: In normoxic cells 60 min glucose deprivation at pH(o) 7.4 had no effect on pH(i). It only slightly increased Ca(i) and decreased ATP content. Reduction of pH(o) to 6.5 under these conditions led to marked cytosolic acidosis and Ca(i) overload, but had no effect on ATP content. Anoxia at pH(o) 6.5 had no additional effect on Ca(i) overload, but significantly reduced cellular ATP. Addition of 20 mmol/l lactate to anoxia at pH(o) 6.5 accelerated Ca(i) overload due to faster cytosolic acidification. Acidosis-induced Ca(i) overload was prevented by inhibition of Ca(2+) release channels of endoplasmic reticulum (ER) with 3 micromol/l ryanodine or by pre-emptying the ER with thapsigargin. Re-normalisation of pH(o) for 30 min led to recovery of pH(i), but not of Ca(i). CONCLUSION: The ischemic factors leading to cytosolic acidosis (low pH(o) and lactate) cause Ca(i) overload in endothelial cells, while anoxia and glucose deprivation play only a minor role. The ER is the main source for this Ca(i) rise. Ca(i) overload is not readily reversible.

Adenosine Triphosphate↗

PubMed1991

Use of continuous noninvasive measurement of oxygen consumption in patients with adult respiratory distress syndrome following shock of various etiologies.

OBJECTIVE: To describe the patterns of cardiac index, oxygen delivery (DO2), oxygen consumption (VO2), and oxygen deficit (or excess) and to compare invasive and noninvasive monitoring systems for evaluation of these oxygen transport patterns. DESIGN: Descriptive study of oxygen transport interrelationships throughout critical illness in a consecutive series of surviving and nonsurviving patients with adult respiratory distress syndrome (ARDS). SETTING: University-affiliated city hospital. PATIENTS: A consecutive series of 55 critically ill patients with ARDS after shock of various etiologies. MEASUREMENTS AND RESULTS: Noninvasive VO2 was measured by a continuous, on-line, real-time device developed in our department. Inspired and expired oxygen concentrations were measured using a polarographic oxygen analyzer. Minute ventilation measurements were time integrated over 7-min intervals. Cardiac index, DO2, and VO2 were simultaneously measured invasively by pulmonary artery thermodilution catheters, together with arterial and mixed venous blood gases. There was good agreement (r2 = .60) in VO2 measured by the invasive and noninvasive methods. The estimated oxygen deficit or excess was calculated as the difference between the actual measured VO2 standardized for body temperature pressure saturated and the normative standard VO2 of each patient corrected for temperature and sedation (VO2 need). A total of 317 monitoring days in 55 patients were analyzed; 25 survivors were monitored for a mean of 4.6 +/- 2.9 days and 30 nonsurvivors were monitored for 6.9 +/- 6.6 days. Survivors had significantly higher cardiac index, DO2, and VO2 values. Generally, oxygen excesses were found in the survivors and oxygen deficit was observed in the nonsurvivors. Survivors did not reach a plateau in their DO2-VO2 patterns. In the septic nonsurviving patients and both nonseptic groups by contrast, a plateau was observed in the DO2-VO2 pattern. Surviving septic patients had a critical DO2 of 16 mL/min.kg (700 mL/min.m2) and a critical VO2 of 3.5 mL/min.kg (145 mL/min.m2). CONCLUSIONS: Monitoring of VO2 and DO2 variables is useful for evaluation of tissue oxygenation and titration of therapy in critically ill patients. Noninvasive monitoring of VO2 values are in good agreement with VO2 values calculated from invasive measurements of cardiac index. The increased DO2 and VO2 values are not attributable to mathematical coupling of erroneous cardiac index values.

Adult↗

PubMed1990

Interrelation between whole-body turnover rates of RNA and protein.

In our search for new non-invasive methods to determine metabolic and nutritional state, we have identified several specific, modified, urinary one-way catabolites of rRNA, tRNA and mRNA which permit the assessment of the whole-body turnover of these RNA classes. A comparison of the steady-state turnover of RNA and the proteins actin plus myosin (determined using urinary 3-methylhistidine) in preterm infants and adults showed that preterm infants have about 3 times higher average turnover rates per unit body weight than adults of tRNA and rRNA as well as of actin plus myosin, whereas calculated mRNA turnover was 6 times higher in preterm infants than in adults. These as well as our recent observations of RNA turnover in different mammals are compared here with data on whole-body protein turnover and basal metabolic rates (BMR) in different mammalian species including man, for which data are available. The turnover rates of tRNA, rRNA, protein and energy (BMR) can be described by the relation, turnover = const. x body mass (exp.), the extrapolated exponents being 0.69-0.78. This suggests a common underlying principle, possibly energy turnover, as cause for the coordinated whole-body turnover rates of RNA and protein in the steady state.

Adult↗

PubMed1981