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Biomedical subjects

E Bucher

Publications and source records attributed to E Bucher.

At least 19 recordsLinked to original sources
PubMed2004

The effect of epidural analgesia in labour on maternal respiratory function.

Lumbar epidural analgesia during labour has gained widespread acceptance. The impact of epidural analgesia based on mixtures of low-dose local anaesthetic solutions and lipophilic opioids on most clinically relevant obstetric outcomes is minimal. Since the pregnant state per se is associated with important alterations in respiration, we assessed whether a subtle degree of motor blockade brought about by epidural analgesia might compromise respiratory function as assessed by spirometry. Sixty consenting parturients receiving epidural analgesia were consecutively included in this prospective study. We performed spirometry during the antepartum visit and in labour after effective epidural analgesia was established; at both assessments the women were pain-free. Values were within normal ranges but increased significantly after effective epidural analgesia; median (IQR [range]) increase for vital capacity 7.4 (3.0-13 [-12-27])% (p < 0.001); forced vital capacity 4.4 (1.7-9.8 [-13-26])% (p < 0.001); forced expiratory volume in 1 s 5.5 (1.7-8.6 [-14-28])% (p < 0.001); and peak expiratory flow rate 2.3 (-1.6-5.8 [-18-16])% (p = 0.01)). We conclude that epidural analgesia for labour significantly improved respiratory function.

Adult↗
PubMed2004

Impact of spinal anaesthesia and obesity on maternal respiratory function during elective Caesarean section.

Spinal anaesthesia for Caesarean section has gained widespread acceptance. We assessed the impact of spinal anaesthesia and body mass index (BMI) on spirometric performance. In this prospective study, we consecutively assessed 71 consenting parturients receiving spinal anaesthesia with hyperbaric bupivacaine and fentanyl for elective Caesarean section. We performed spirometry during the antepartum visit (baseline), immediately after spinal anaesthesia, 10-20 min, 1 h, 2 h after the operation, and after mobilisation (3 h). Baseline values were within normal ranges. There was a significant decrease in all spirometric parameters after effective spinal anaesthesia that persisted throughout the study period. The decrease in respiratory function was significantly greater in obese (BMI > 30 kg x m(-2)) than in normal-weight parturients (BMI < 25 kg x m(-2)), e.g. median (IQR) vital capacity directly after spinal anaesthesia; -24 (-16 to -31)% vs. -11 (-6 to -16)%, p < 0.001 and recovery was significantly slower. We conclude that both spinal anaesthesia and obesity significantly impair respiratory function in parturients.

Adult↗
PubMed2001

Oxygen nonstoichiometry and ionic transport properties of La0.4Sr0.6CoO3-delta .

Homogeneous samples of La0.4Sr0.6CoO3-delta were obtained by the glycine nitrate process. The oxygen nonstoichiometry was determined from oxygen exchange measurements as a function of oxygen partial pressure (10(-4) bar < PO2 < 10(-2) bar) and temperature (300 degrees C < T< 900 degrees C). The chemical diffusion coefficient D was obtained from oxygen exchange measurements applying a stepwise variation of the oxygen partial pressure of the ambient atmosphere of a disk-shaped sample. The amount of oxygen absorbed or desorbed by the perovskite was analyzed as a function of time. Chemical diffusion data were evaluated using simplified and exact fitting procedures taking into account the surface exchange coefficient. Alternatively, galvanostatic polarization measurements were performed in a PO2-range between 10(-4) and 10(-2) bar to yield D and the ionic conductivity sigma(i) from the long time solution of the diffusion equation. Values for D from polarization measurements at T= 775 degrees C and from oxygen exchange measurements at T= 725 degrees C are in good agreement with each other. D and sigma(1) increase with increasing PO2 (10(-4) to 10(-2) bar). The ionic conductivity shows a maximum at 3-delta approximately 2.82 and decreases with decreasing oxygen content indicating the possible formation of vacancy ordered structures.

Kinetics↗
PubMed2001

High performance thermoelectric Tl9BiTe6 with an extremely low thermal conductivity.

Tl 9BiTe (6) exhibits a thermoelectric figure of merit of ZT approximately 1.2 around 500 K, which significantly exceeds the state-of-the-art materials in this temperature range. The extraordinary thermoelectric performance is mainly due to the extremely low thermal conductivity of Tl 9BiTe (6) [ 0.39 W/(m times K) at 300 K]. In fact, the minimum lifetime of the phonons has to be taken into account to describe the thermal conductivity data.

Journal Article↗
PubMed2000

Ferromagnetic hcp chromium in Cr/Ru(0001) superlattices.

We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices, based on magnetic hysteresis and corroborated by x-ray magnetic circular dichroism at the CrL(2,3) edges. In situ reflection high-energy electron diffraction, x-ray diffraction, and Cr K-edge polarized x-ray absorption investigations have shown that the Cr layers thinner than 8 angstroms adopt a slightly distorted hcp structure, accompanied by a large atomic volume expansion of up to 14% compared to the bcc packing volume. The expanded hcp structure clearly induces the observed ferromagnetism, in agreement with theory.

Journal Article↗
PubMed2000

Observation of a BCS spectral function in a conventional superconductor by photoelectron spectroscopy

We present high-resolution photoelectron spectra on the A15-type conventional superconductor V 3Si, where-for the first time-both singularities of the BCS density of states can be resolved by photoemission spectroscopy (PES). With a transition temperature of about T(c) approximately 17 K the gap Delta(gap) of this compound has a magnitude of approximately 5 meV. A measurement by PES on this small energy scale requires a very high energy resolution (DeltaE less, similar5 meV) and sample temperatures significantly below T(c).

Journal Article↗
PubMed2000

Onset of antiferromagnetism in heavy-fermion metals

There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second description, based on the physics of electron fluids or 'Fermi liquids' states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave. It is at present unknown which view is appropriate at a 'quantum critical point' where the antiferromagnetic transition temperature vanishes. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu(6-x)Au(x), which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (x(c) = 0.1), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.

Journal Article↗
PubMed2000

Efficient organic photovoltaic diodes based on doped pentacene.

Recent work on solar cells based on interpenetrating polymer networks and solid-state dye-sensitized devices shows that efficient solar-energy conversion is possible using organic materials. Further, it has been demonstrated that the performance of photovoltaic devices based on small molecules can be effectively enhanced by doping the organic material with electron-accepting molecules. But as inorganic solar cells show much higher efficiencies, well above 15 per cent, the practical utility of organic-based cells will require their fabrication by lower-cost techniques, ideally on flexible substrates. Here we demonstrate efficiency enhancement by molecular doping in Schottky-type photovoltaic diodes based on pentacene--an organic semiconductor that has received much attention as a promising material for organic thin-film transistors, but relatively little attention for use in photovoltaic devices. The incorporation of the dopant improves the internal quantum efficiency by more than five orders of magnitude and yields an external energy conversion efficiency as high as 2.4 per cent for a standard solar spectrum. Thin-film devices based on doped pentacene therefore appear promising for the production of efficient 'plastic' solar cells.

Journal Article↗
PubMed2000

Spondylodiscitis associated with bacteraemia due to coagulase-negative staphylococci.

Three cases are reported of spondylodiscitis caused by coagulase-negative staphylococci in patients without osteosynthetic material. All three patients had bacteraemia associated with an infected intravascular device left in place. On the basis of this observation, it is concluded that such devices should be removed promptly in cases of prolonged or relapsing bacteraemia. Furthermore, spondylodiscitis should be suspected in patients with back pain after bacteraemia caused by coagulase-negative staphylococci.

Aged↗
PubMed1998

T-cell independent IgM and enduring protective IgG antibodies induced by chimeric measles viruses.

B-cell activation depends on the intensity of B-cell receptor cross-linking. Studies of haptenated antigens and vesicular stomatitis virus (VSV) have demonstrated a correlation between antigen repetitiveness and the degree to which B-cell activation is independent of T cells. Here, we compare neutralizing antibody responses to inactivated VSV with those to two inactivated human pathogenic viruses: highly cytopathic poliovirus (PV) and poorly cytopathic measles virus (MV). The rigidly structured PV efficiently induced neutralizing IgM antibodies independent of T cells. In contrast, neutralizing antibodies to the pleomorphic MV were dependent on helper T cells. To test whether this resulted from the differences in virus structure or the capacity of MV to induce cell fusion and/or immunosuppression, we analyzed antibody responses to chimeric MV expressing VSV glycoprotein instead of MV fusion protein and hemagglutinin. IgM antibodies were independent of T cells; in addition, we found IgG responses dependent on T-cell help that were enduring and protective against lethal VSV infection. Because chimeric MV viruses look like MV ultrastructurally, we conclude that not only structural differences in the envelope but also the ability of MV to induce immunosuppression may limit its capacity to directly activate B cells. These findings are relevant for our understanding of B-cell activation by two prototypic human pathogenic viruses and for the design of new recombinant vaccines.

Animals↗
PubMed1997

Role of repetitive antigen patterns for induction of antibodies against antibodies.

Antibody responses against antibodies, such as rheumatoid factors, are found in several immunopathological diseases and may play a role in disease pathogenesis. Experience shows that they are usually difficult to induce experimentally. Antibodies specific for immunoglobulin constant regions (anti-allotypic) or for variable regions (anti-idiotypic) have been investigated in animal models; the latter have even been postulated to regulate antibody and T cell responses via network-like interactions. Why and how such anti-antibodies are induced during autoimmune diseases, has remained largely unclear. Because repetitively arranged epitopes in a paracrystalline structure of a viral envelope cross-link B cell receptors efficiently to induce a prompt T-independent IgM response, this study used immune complexes containing viruses or bacteria to evaluate the role of antigen pattern for induction of anti-antibody responses. We present evidence that antibodies bound to strictly ordered, but not to irregularly arranged, antigens dramatically enhance induction of anti-antibodies, already after a single immunization and without using adjuvants. The results indicate a novel link between anti-antibody responses and infectious agents, and suggest a similar role for repetitive self-antigens such as DNA or collagen involved in chronic immunopathological diseases.

Animals↗
PubMed1996

Monovalent single-chain Fv fragments and bivalent miniantibodies bound to vesicular stomatitis virus protect against lethal infection.

Several antibody-dependent mechanisms have been postulated to mediate neutralization of different animal viruses, including blocking of docking to receptors, induction of conformational changes in the virus coat, and Fc-dependent opsonization. We have studied the molecular requirements for antibody-mediated neutralization of vesicular stomatitis virus (VSV) in vitro and protection against lethal disease in vivo with a single-chain Fv fragment (scFv) and the corresponding bivalent miniantibody (scFv-dHLX) generated from a VSV-neutralizing monoclonal antibody. Both monovalent scFv and bivalent scFv-dHLX miniantibodies were able to neutralize VSV in vitro and to protect interferon-alphabeta receptor-deficient (IFN-alphabeta R-/-) mice against lethal disease after intravenous injection of 50 plaque-forming units (pfu) VSV pre-incubated with the scFv reagents. Similarly, severe-combined immunodeficient (SCID) mice infected with immune complexes of 10(8) pfu VSV and bivalent scFv-dHLX were protected against lethal disease; however, mice infected with immune complexes of 10(8) pfu VSV and monovalent scFv were not. Although repeated scFv-dHLX treatment reduced virus quantities in the blood, neither SCID nor IFN-alphabeta R-/- mice were protected against lethal disease after passive immunization and subsequent VSV infection. This was due to the short half-life of 17 min of scFv-dHLX in the circulation. These data demonstrate that neutralization of VSV and protection against lethal disease do not require Fc-mediated mechanisms and that cross-linking is not crucial for protection against physiologically relevant virus doses in vivo.

Amino Acid Sequence↗