Biomedical subjects
Michael Mayer
Publications and source records attributed to Michael Mayer.
Cardiac troponin after major vascular surgery: the role of perioperative ischemia, preoperative thallium scanning, and coronary revascularization.
OBJECTIVES: We sought to determine the role of preoperative predictors, particularly ischemia, on preoperative thallium scanning (PTS) and coronary revascularization on low-level and conventional troponin elevations after major vascular surgery. BACKGROUND: Postoperative cardiac troponin (cTn) elevations have recently been shown to predict both short- and long-term mortality after vascular surgery. METHODS: The perioperative data, including PTS and subsequent coronary revascularization, continuous perioperative 12-lead ST-segment trend monitoring, cTn-I and/or cTn-T, and creatine kinase-MB fraction in the first three postoperative days, were prospectively collected in 501 consecutive elective major vascular procedures. RESULTS: Moderate to severe inducible ischemia on PTS was associated with a 49.0% incidence of low-level (cTn-I >0.6 and/or cTn-T >0.03 ng/ml) and 22.4% conventional (cTn-I >1.5 and/or cTn-T >0.1 ng/ml) troponin elevation. In contrast, patients with preoperative coronary revascularization had 23.4% and 6.4% low-level and conventional troponin elevations, respectively, similar to patients without ischemia on PTS. By multivariate logistic regression, ischemia on PTS was the most important predictor of both low-level and conventional troponin elevations (adjusted odds ratios [ORs] 2.5 and 2.7, p = 0.02 and 0.04, respectively), whereas preoperative coronary revascularization predicted less troponin elevations (adjusted ORs 0.35 and 0.16, p = 0.045 and 0.022, respectively). Postoperative ischemia (>10 min), the more so prolonged (>30 min) ischemia was the only independent predictor of troponin elevation if added with the preoperative predictors to the multivariate analysis (ORs 15.8 and 22.8, respectively, p < 0.001). CONCLUSIONS: Troponin elevations occur frequently after vascular surgery. They are strongly associated with postoperative ischemia, predicted by inducible ischemia on PTS, and reduced by preoperative coronary revascularization.
Self-assembled aggregates of IgGs as templates for the growth of clusters of gold nanoparticles.
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Micropatterned agarose gels for stamping arrays of proteins and gradients of proteins.
We describe a method for repetitive and rapid formation of planar microarrays and gradients of proteins using patterned agarose stamps. It demonstrates: (i) micropatterning of agarose gels with feature sizes as small as 2 microm; (ii) inking of posts (diameter 50-1000 microm) on patterned agarose stamps with one or multiple (here, eight) proteins and repetitive stamping of patterns (>100 times in the case of one protein) and arrays (20 times in the case of eight proteins) without the need for intermediate re-inking; (iii) transferring spots of proteins with good homogeneity in surface coverage to glass slides; (iv) applying this technique to surface-based immunoassays; (v) stamping that requires only sub-nanomolar amounts of protein (typically approximately 3 microg in approximately 0.6 microL of solution); (vi) stamping without the need for drying of the proteins, as opposed to stamping with stamps made of poly(dimethylsiloxane); and (vii) patterning gradients of proteins by allowing two proteins to diffuse toward each other in an agarose stamp, followed by printing the protein gradients onto a surface.
Lyme neuroborreliosis mimicking primary CNS lymphoma.
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Association of cardiac troponin, CK-MB, and postoperative myocardial ischemia with long-term survival after major vascular surgery.
OBJECTIVES: The aim of this study was to determine the long-term prognosis with postoperative markers of myocardial ischemia and infarction. BACKGROUND: Cardiac troponins (cTn) are superior to creatine kinase-MB fraction (CK-MB) in detecting perioperative myocardial infarction (PMI). However, their threshold levels signifying PMI and their long-term prognostic value are not yet determined. METHODS: A cohort of 447 consecutive patients who underwent 501 major vascular procedures was prospectively studied. Perioperative continuous 12-lead electrocardiogram monitoring, cardiac troponin-I (cTn-I) and/or cardiac troponin-T (cTn-T), and CK-MB levels on the first three postoperative days, and long-term survival were determined. The association of different cutoff levels of CK-MB, troponin, and ischemia duration with long-term survival was investigated. RESULTS: Between 14 (2.9%) and 107 (23.9%) of the patients sustained PMI, depending on the biochemical criteria used. Elevated postoperative CK-MB, cTn, and prolonged (>30 min) ischemia, at all cutoff levels examined, predicted long-term mortality independent of the preoperative predictors: patient's age, type of vascular surgery, previous myocardial infarction, and renal failure (Cox multivariate analysis). Both CK-MB >10% and cTn-I >1.5 ng/ml and/or cTn-T >0.1 ng/ml independently predicted a 3.75-fold and 2.06-fold increase in long-term mortality (p = 0.006 and 0.012, respectively). Similarly, both CK-MB >5% and cTn-I >0.6 ng/ml and/or cTn-T >0.03 ng/ml independently predicted a 2.15-fold and 1.89-fold increase in mortality (p = 0.018 and 0.01, respectively). Patients with both these markers elevated had a 4.19-fold increase in mortality (p < 0.001). CONCLUSIONS: Postoperative CK-MB and troponin, even at low cutoff levels, are independent and complementary predictors of long-term mortality after major vascular surgery.
Reversible immobilization of peptides: surface modification and in situ detection by attenuated total reflection FTIR spectroscopy.
A generic method is described for the reversible immobilization of polyhistidine-bearing polypeptides and proteins on attenuated total reflecting (ATR) sensor surfaces for the detection of biomolecular interactions by FTIR spectroscopy. Nitrilotriacetic acid (NTA) groups are covalently attached to self-assembled monolayers of either thioalkanes on gold films or mercaptosilanes on silicon dioxide films deposited on germanium internal reflection elements. Complex formation between Ni2+ ions and NTA groups activates the ATR sensor surface for the selective binding of polyhistidine sequences. This approach not only allows a stable and reversible immobilization of histidine-tagged peptides (His-peptides) but also simultaneously allows the direct in situ quantification of surface-adsorbed molecules from their specific FTIR spectral bands. The surface concentrations of both NTA and His-peptide on silanized surfaces were determined to be 1.1 and 0.4 molecules nm-2, respectively, which means that the surface is densely covered. A comparison of experimental FTIR spectra with simulated spectra reveals a surface-enhancement effect of one order of magnitude for the gold surfaces. With the presented sensor surfaces, new ways are opened up to investigate, in situ and with high sensitivity and reproducibility, protein-ligand, protein-protein, protein-DNA interactions, and DNA hybridization by ATR-FTIR spectroscopy.
Monitoring expression and clustering of the ionotropic 5HT3 receptor in plasma membranes of live biological cells.
The ionotropic 5HT(3) receptor was expressed in transiently transfected mammalian cells, yielding an unprecedented high concentration of up to 12 million receptors per cell. Receptor traffic in the plasma membrane of live cells was observed continuously over 24 h by fluorescence scanning confocal microscopy. This was possible by using 5HT(3) receptor-specific fluorescent ligands with high binding affinity and low off-rate to pulse label receptors at any time after appearance on the cell surface, and label subsequently those receptors expressed later by another, spectrally distinguishable, high-affinity fluorescent ligand. Having reached a critical cell surface concentration of approximately 3000 receptors/microm(2), the receptors started to aggregate in patches with a 4-fold increased surface concentration. The clusters were constantly delivered from a pool of freshly expressed receptors isotropically distributed within the basolateral region of the cell membrane. From there, they migrated to and accumulated on the apical cell surface approximately 9 h after transfection. Individual clusters grew until they reached a critical size of 1-2 microm when they merged to form with 3-5 microm large macroclusters. Clustered receptors were immobile on the minute time scale but always coexisted with monomeric receptors in the regions surrounding the clusters as revealed by fluorescence correlation spectroscopy. Because the receptor density of 12 000 receptors/microm(2) in the patches is as high as that found in two-dimensional crystals of certain membrane proteins, such patches might be a proper source for direct crystallization of membrane proteins without prior purification.
Microfabricated teflon membranes for low-noise recordings of ion channels in planar lipid bilayers.
We present a straightforward, accessible method for the fabrication of micropores with diameters from 2 to 800 micro m in films of amorphous Teflon (Teflon AF). Pores with diameters </=40 micro m made it possible to record ion fluxes through ion channels in planar bilayers with excellent signal characteristics. These pores afforded: i), stable measurements at transmembrane voltages up to 460 mV; ii), recordings at low noise levels (0.4 pA rms at 4.3 kHz bandwidth); iii), recordings at high effective bandwidth (10.7 kHz); and iv), formation of multiple planar lipid bilayers in parallel. Microfabricated pores in films of Teflon AF made it possible to examine, experimentally and theoretically, the influence of the pore diameter on the current noise in planar bilayer recordings. Reducing the pore diameter below 40 micro m mainly increased the stability of the planar bilayers, but had only a small effect on the level of the current noise. The low-noise properties of bilayer recordings on micropores in Teflon AF films were exploited to record the smallest conductance state of alamethicin (24 pS) at an unprecedentedly high bandwidth of 10.7 kHz.
Direct estimation of Cole parameters in multifrequency EIT using a regularized Gauss-Newton method.
A major drawback of electrical impedance tomography is the poor quality of the conductivity images, i.e., the low spatial resolution as well as large errors in the reconstructed conductivity values. The main reason is the necessity for regularization of the ill-conditioned inverse problem which results in excessive spatial low-pass filtering. A novel regularization method (SMORR (spectral modelling regularized reconstructor)) is proposed, which is based on the inclusion of spectral a priori information in the form of appropriate tissue models (e.g. Cole models). This approach reduces the ill-posedness of the inverse problem, when multifrequency data are available. An additional advantage is the direct reconstruction of the (physiological) tissue parameters of interest instead of the conductivities. SMORR was compared with posterior fitting of a Cole model to the conductivity spectra obtained with a classical iterative reconstruction scheme at various frequencies. SMORR performed significantly better than the reference method concerning robustness against noise in the data.
Membraneless vanadium redox fuel cell using laminar flow.
This paper describes the design and characterization of a small, membraneless redox fuel cell. The smallest channel dimensions of the cell were 2 mm x 50 mum or x 200 mum; the cell was fabricated in poly(dimethylsiloxane) using soft lithography. This all-vanadium fuel cell took advantage of laminar flow to obviate the need for a membrane to separate the solutions of oxidizing and reducing components.
Spine arthroplasty: a historical review.
Degenerative disc disease is one of the most frequently encountered spinal disorders. The intervertebral disc is a complex anatomic and functional structure, which makes the development of an efficient and reliable artificial disc a complex challenge. Not only is the disc function arduous to reproduce, but there are important consequences associated with the conception and the choice of materials that will have to bear the loads. Biochemical problems have complicated things even more. Two different principles have been applied in the realisation of a discal replacement: a metallic and/or polyethylene prosthesis allowing mainly mobility or a prosthesis enabling the reproduction of viscoelastic properties. Of course some devices attempt to combine both principles. In this paper we will try to present, in chronological order, an overview of the designs published in the literature as well as in the patents granted in this field. The very fact that such a long list of implants, based on highly varied principles, has been proposed, and that only very few have reached the level of animal models, let alone human implantation, clearly demonstrates how challenging the task of designing an intervertebral disc replacement is. Proper randomized controlled trials are now on the way, and should help in assessing the efficacy and real place of spine arthroplasty in the treatment of spinal disorders. Only then will spinal surgery join the list of successful joint replacements.
Immunoaffinity screening with capillary electrochromatography.
Highly efficient capillary electrochromatographic separations of cardiac glycosides and other steroids are presented. Employing butyl-derivatized silica particles as stationary phase resulted in a nearly three times faster electroosmotic flow (EOF) compared to capillary electrochromatography (CEC) with octadecyl silica particles. On-column focusing with a preconcentration factor of 180 was performed and separation efficiencies of up to 240,000 plates per meter were obtained. Using label-free standard UV absorbance, detection limits of 10-80 nM were reached for all steroids tested. For screening of cardiac glycosides, e.g., digoxin and digitoxin in mixtures of steroids, CEC was combined with immunoaffinity extraction using immobilized polyclonal anti-digoxigenin antibodies and F(ab) fragments. Simply adding small amounts of antibody carrying particles to the samples and comparing chromatograms before and after antibody addition allowed screening for high affinity antigens in mixtures with moderate numbers of compounds. Under conditions of competing antigens, affinity fingerprints of immobilized anti-digoxigenin and anti-digitoxin antibodies were obtained, reflecting the cross-reactivity of eleven steroids. The method provides high selectivity due to the combination of bioaffinity interaction with highly efficient CEC separation and UV detection at several wavelengths in parallel. This selectivity was exploited for the detection of four cardiac glycosides in submicromolar concentrations in an untreated urine sample.
C-reactive protein concentrations in cerebral spinal fluid in gram-positive and gram-negative bacterial meningitis.
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