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Biomedical subjects

G Ertl

Publications and source records attributed to G Ertl.

At least 37 records · Page 2Linked to original sources

Electronic excitation and dynamic promotion of a surface reaction.

The mechanism of recombinative desorption of hydrogen from a Ru(0001) surface induced by femtosecond-laser excitation has been investigated and compared to thermally initiated desorption. For the laser-driven process, it is shown that hot substrate electrons mediate the reaction within a few hundred femtoseconds resulting in a huge isotope effect between H2 and D2 in the desorption yield. In mixed saturation coverages, this ratio crucially depends on the proportions of H and D. Deviations from second order desorption kinetics demonstrate that the recombination is dynamically promoted by excitation of neighboring, but nonreacting adatoms. A concentration dependent rate constant which accounts for the faster excitation of H versus D is proposed.

Journal Article↗

Detection of myocardial viability in acute infarction using contrast-enhanced (1)H magnetic resonance imaging.

BACKGROUND: Reperfusion strategies salvage myocardium at risk in acute myocardial infarction (MI). This clinical study was performed to determine whether areas without evidence of delayed MRI contrast enhancement in MI correspond to viability by means of percent systolic wall thickening (%SWT) and enddiastolic wall thickness (EDWT) in chronic infarction. METHODS: Twenty MRI studies were performed in ten patients within 6 days of MI and 3 months post-MI. On a segmental basis the percentage of viable myocardium as defined by contrast-enhanced MRI (no delayed MRI contrast enhancement) in acute MI was measured and was compared with %SWT and EDWT in chronic MI. RESULTS: Of the 1718 segments in acute infarction in which the percentage of viable myocardium was measured 1333 were found to be completely viable by means of contrast-enhanced MRI (no delayed MRI contrast enhancement). All of these segments revealed %SWT on day 90 post-MI, and 97% of segments were viable by means of an EDWT of more than 5.5 mm. In 85 segments the proportion of viable myocardium was 50-99% (mean 56+/-8%), with 92% segments found to be viable by means of %SWT and 92% by EDWT, and of 156 segments with viable myocardium between 1-49% (36+/-8%) 79% were found to be viable by means of %SWT and 82% by EDWT. Corresponding proportions of 144 segments with transmural delayed MRI contrast enhancement in acute MI were 45% and 17%. CONCLUSIONS: In acute reperfused MI viable myocardium as delineated by contrast-enhanced MRI is correlated with clinical parameters of viability. Delayed MRI contrast enhancement resolves nontransmural MI and may become a valuable clinical tool when planning revascularization procedures.

Adult↗

Controlling turbulence in a surface chemical reaction by time-delay autosynchronization.

A global time-delay feedback scheme is implemented experimentally to control chemical turbulence in the catalytic CO oxidation on a Pt(110) single crystal surface. The reaction is investigated under ultrahigh vacuum conditions by means of photoemission electron microscopy. We present results showing that turbulence can be efficiently suppressed by applying time-delay autosynchronization. Hysteresis effects are found in the transition regime from turbulence to homogeneous oscillations. At optimal delay time, we find a discontinuity in the oscillation period that can be understood in terms of an analytical investigation of a phase equation with time-delay autosynchronization. The experimental results are reproduced in numerical simulations of a realistic reaction model.

Journal Article↗

Wave initiation through spatiotemporally controllable perturbations.

We study the initiation of pulses and fronts in a two-dimensional catalytic reaction-diffusion system: CO oxidation on Pt(110). Using a computer-controlled mobile focused laser beam, we impart various patterns (in space and time) of localized temperature "kicks" to the surface. We explore, and also rationalize through modeling, the cooperativity of such individually subcritical perturbations in both the excitable and the bistable regime.

Journal Article↗

Gentle dragging of reaction waves.

Using a recently realized "addressable catalyst surface" [Science 294, 134 (2001)]] we study the interaction of chemical reaction waves with prescribed spatiotemporal fields. In particular, we study how a traveling chemical pulse is "dragged" by a localized, moving temperature heterogeneity as a function of its intensity and speed. The acceleration and eventual "detachment" of the wave from the heterogeneity is also explored through simulation and stability analysis.

Journal Article↗

[Documentation in the cardiac catheterization laboratory using electronic databases--experiences in 176 German cath labs].

Due to the introduction of a variety of new features to the German health system, such as a new reimbursement system for inpatient work based on diagnosis-related groups, an obligation to detailed documentation for total quality management, as well as due to the continuing increase in the amount of imaging and other data within invasive cardiology, the use of electronic databases for documentation in the cardiac cath lab is of significant importance. The user friendliness and robustness of the software system for daily clinical practice is crucial for the acceptance of electronic documentation systems by physicians, nurses and technicians. This survey was aimed to explore the current practice and experiences of German cardiac catheterization labs with electronic databases particularly designed for documentation in invasive cardiology, including report generation of cath studies, risk and complication management and logistics for medical material ordering for the cath lab. Of the 176 hospitals and practices having agreed in taking part in this surveillance 165, are currently using an electronic database for administration of medical data and study reports. In 64% of the cath labs, a sub-specialized software system for detailed documentation of the course and the results of an invasive procedure, the human and material resources used, generation of the cath report, and documentation of procedural and post-procedural complications for total quality management is used. The acceptance and satisfaction with the software solutions currently available reveals to be rather inhomogeneous. While user-friendliness and flexibility of a number of software products were positively mentioned, main issues, such as missing hardware of software interfaces with the hospital information system for patient administration, missing stability of several systems, image management too complex and report configuration too inconvenient for daily clinical practice, were criticized. In general, in the light of continuing increase of the amount of clinical and imaging data as well as due to the legal obligation of detailed procedural documentation in all areas of invasive cardiology, a documentation system based on electronic databases bears the potential of an enormous economization of the daily workload of a cardiac cath lab. Prerequisites for the acceptance of such a system in clinical practice is not only the stability and reliability of the system but also the ability to link such a sub-system to existing databases via suitable interfaces and the flexibility of the system for modification of its features to meet the individual requirements of each user.

Adult↗

Selective modulation of endogenous nitric oxide formation in ischemia/reperfusion injury in isolated rat hearts--effects on regional myocardial flow and enzyme release.

The role of nitric oxide (NO) in ischemia/reperfusion injury is controversial. We tested the role of inducible NOS (iNOS) in the ischemia/reperfusion injury in isolated rat hearts using the selective iNOS inhibitor S-methylisothiourea sulfate (SMT) and the non-selective NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). After 15 min of stabilization in Langendorff mode, hearts were perfused either with normal Krebs-Henseleit buffer, buffer containing 100 microM L-NAME, 0.5 microM SMT or 50 microM SMT for 5 min and were subjected to 25 min of ischemia followed by 30 min of reperfusion. Left ventricular developed pressure (LVDP) and total coronary flow (CF) were recorded continuously. After ischemia/reperfusion, a marked expression of iNOS protein was demonstrated by Western blotting, while virtually no iNOS protein was present in hearts without ischemia/reperfusion. Regional myocardial blood flow (RMBF) was measured with colored microspheres. Coronary vasoactive concentration of L-NAME and SMT depressed myocardial function as shown by decreased LVDP, dP/dt(max) and coronary.ow before ischemia. After ischemia the recovery of the total CF was impaired in L-NAME and 50 microM SMT pretreated hearts which was related to homogenous RMBF decrease in the right and left ventricle compared to that in control group. Low concentration SMT (0.5 microM) showed no coronary vasoactive effects before ischemia and attenuated ischemia/reperfusion injury indicated by lower ischemic contracture at 25 min of ischemia and reduced CK and LDH release during reperfusion. Thus, NOS inhibition did not affect blood flow distribution in rat hearts either in the pre-ischemic or reperfusion period. Selective iNOS inhibition reduced ischemic injury by reducing ischemic contracture and CK as well as LDH release during reperfusion.

Animals↗

Cardiac magnetic resonance imaging in small animal models of human heart failure.

The aim of this study was to test the feasibility of cine magnetic resonance imaging (MRI) for assessment of the infarcted rat and mouse heart and to compare the results with established methods. These models have been proven to predict genesis and prevention of heart failure in patients. The value of cine MRI was tested in studies investigating interventions to change the course of the remodeling process. MRI was performed for determination of left ventricular (LV) volumes and mass, myocardial infarct (MI) size and cardiac output. LV wet weight was determined after MRI. Rats underwent conventional hemodynamic measurements for determination of cardiac output and LV volumes by electromagnetic flowmeter and pressure-volume curves. Infarct size was determined by histology. MRI-acquired MI-size (18.5+/-2%) was smaller than that found by histology (22.8+/-2.5%, p<0.05) with close correlation (r=0.97). There was agreement in LV mass between MRI and wet weight (r=0.97, p<0.05) and in the MRI- and flowmeter measurements of cardiac output (r=0.80, p<0.05). Volume by MRI differed from pressure-volume curves with good correlation (r=0.96, p<0.05). In a serial study of mice after coronary ligation, LV hypertrophy at 8 weeks was detected (Sham 105.1+/-7.9 mg, MI 144.4+/-11.7 mg, p<0.05). Left ventricles were enlarged in infarcted mice (end-diastolic volume, week 8: Sham 63.5+/-4 microl, MI 94.2 microl, p<0.05). In conclusion, cine MRI is a valuable diagnostic tool applicable to the rat and mouse model of MI. Being non-invasive and exact it offers new insights into the remodeling process after MI because serial measurements are possible. The technique was applied to study several interventions and proved its usefulness.

Animals↗

Energetics and vibrational states for hydrogen on Pt(111).

We present a combination of theoretical calculations and experiments for the low-lying vibrational excitations of H and D atoms adsorbed on the Pt(111) surface. The vibrational band states are calculated based on the full three-dimensional adiabatic potential energy surface obtained from first-principles calculations. For coverages less than three quarters of a monolayer, the observed experimental high-resolution electron peaks at 31 and 68 meV are in excellent agreement with the theoretical transitions between selected bands. Our results convincingly demonstrate the need to go beyond the local harmonic oscillator picture to understand the dynamics of this system.

Journal Article↗

Cytochrome P450 2C expression and EDHF-mediated relaxation in porcine coronary arteries is increased by cortisol.

OBJECTIVES/METHODS: In addition to nitric oxide (NO) and prostacyclin, endothelium-dependent dilation is mediated by the endothelium-derived hyperpolarizing factor (EDHF) which, in the coronary circulation, has been characterised as a metabolite of arachidonic acid synthesised by an cytochrome P450 (CYP) epoxygenase homologous to CYP 2C8/9. As the promotor regions of CYP 2C8 and 2C9 contain consensus sequences for glucocorticoid response elements, we determined the effect of cortisol on EDHF-mediated relaxations as well as on the expression of CYP 2C in isolated segments of porcine coronary artery. RESULTS: Bradykinin-induced NO-mediated relaxation of KCl-constricted arterial rings was slightly attenuated following exposure to cortisol. However, EDHF-mediated relaxations of U46619-constricted arterial rings assessed in the presence of the cyclo-oxygenase inhibitor diclofenac and the NO synthase inhibitor N(omega)nitro-L-arginine (0.3 mM), were significantly enhanced (maximum relaxation: 66+/-7%, P<0.05 vs. control rings: 36+/-8%). Cortisol treatment (0.1 microM, 24 h) did not affect the endothelium-independent relaxation elicited by sodium nitroprusside and acute incubation with cortisol (0.1 microM, 30 min) did not alter either NO- or EDHF-mediated responses. The expression of CYP 2C (quantified by RT-PCR, Western blot analysis and confocal microscopy) was enhanced in porcine coronary endothelial cells following incubation with cortisol for 18-24 h. CONCLUSIONS: These results demonstrate the concomitant upregulation of EDHF-mediated relaxations and CYP 2C expression by long-term treatment with cortisol. These observations support the concept that an epoxygenase homologous to CYP 2C8/9 plays a crucial role in the generation of EDHF-mediated responses in the coronary endothelium.

Animals↗

Spatiotemporal addressing of surface activity.

We have modified surface catalytic activity in real time and space by focusing an addressable laser beam to differentially heat a platinum (110) single-crystal surface. Ellipsomicroscopy imaging of local conditions (such as reactant and product local coverages) enabled us to close the loop between sensing and actuation (both spatiotemporally resolved). Pulses and fronts, the basic building blocks of patterns, could be formed, accelerated, modified, guided, and destroyed at will. Real-time image processing and feedback allow the design and implementation of new classes of nonlocal evolution rules.

Journal Article↗

Spatiotemporal self-organization in a surface reaction: from the atomic to the mesoscopic scale.

Scanning tunneling microscopy data revealed the atomic processes in propagating reaction fronts that occur in the catalytic oxidation of hydrogen on Pt(111). The fronts were also characterized on mesoscopic length scales with respect to their velocity and width. Simulations on the basis of a reaction-diffusion model reproduce the experimental findings qualitatively well. The quantitative comparison reveals the limitations of this traditional approach to modeling spatiotemporal pattern formation in nonlinear dynamics.

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Improvement of left ventricular remodeling and function by hydroxymethylglutaryl coenzyme a reductase inhibition with cerivastatin in rats with heart failure after myocardial infarction.

BACKGROUND: Hydroxymethylglutaryl coenzyme A reductase inhibitors (statins) attenuate angiotensin II-induced cellular signaling. Because angiotensin II is involved in left ventricular (LV) remodeling after myocardial infarction (MI), we examined the effects of statin treatment in an experimental model of chronic heart failure after MI. METHODS AND RESULTS: Rats with extensive MI were treated with placebo or cerivastatin (0.3 mg/kg per day) as a dietary supplement or via gavage for 11 weeks starting on the 7th postoperative day. Infarct size and cholesterol levels were similar among all groups. LV cavity area, an index of LV dilatation, was reduced in MI rats on cerivastatin compared with placebo. LV end-diastolic pressure was increased in MI rats on placebo (24.1+/-4.1 mm Hg versus sham: 5.1+/-0.3 mm Hg; P<0.01), and it was significantly reduced by cerivastatin treatment (13.7+/-2.7 mm Hg; P<0.05 versus placebo). Cerivastatin partially normalized LV dP/dt(max) and dP/dt(min), indices of LV systolic and diastolic function, which were significantly reduced in MI rats on placebo. Improvement of LV function by cerivastatin was accompanied by a reduced expression of collagen type I and beta-myosin heavy chain. LV endothelial nitric oxide synthase was increased, whereas the nitrotyrosine protein level was decreased in MI rats by cerivastatin treatment. CONCLUSIONS: Cerivastatin improved LV remodeling and function in rats with heart failure. This effect was associated with an attenuated LV expression of fetal myosin heavy chain isoenzymes and collagen I. Statin treatment may retard the progression of chronic heart failure.

Animals↗

Prevention of endothelial dysfunction in heart failure by vitamin E: attenuation of vascular superoxide anion formation and increase in soluble guanylyl cyclase expression.

OBJECTIVES: Enhanced vascular superoxide anion generation contributes to endothelial dysfunction in heart failure. However, the effect of long-term treatment with the antioxidant vitamin E is unknown. METHODS AND RESULTS: Relaxant responses were determined in aortic rings from Wistar rats with heart failure 12 weeks after myocardial infarction (MI) and compared with responses in tissues from sham-operated animals. From the seventh post-operative day, rats were given either a standard chow or a chow enriched in vitamin E (approximate intake 100 mg/day). In rings from rats with heart failure, acetylcholine-induced relaxation was attenuated (maximum relaxation, R(max) 54 +/- 3%) when compared with rings from sham-operated animals (79 +/- 3%, n=12, P < 0.01), while endothelium-independent relaxation elicited by sodium-nitroprusside was unchanged. Aortic superoxide generation was significantly enhanced in rats with heart failure. Vitamin E supplementation significantly improved acetylcholine-induced relaxation in rats with heart failure (R(max) 75 +/- 4%, P < 0.01) and led to a leftward shift in sodium-nitroprusside-induced relaxation curve. Aortic expression of the beta(1)-subunit of soluble guanylyl cyclase was significantly enhanced by vitamin E supplementation. In addition, the elevated vascular superoxide formation was normalised by vitamin E. CONCLUSIONS: These results demonstrate that dietary supplementation with the antioxidant vitamin E restores normal endothelial function, reduces vascular superoxide anion formation and increases the expression of the soluble guanylyl cyclase in rats with heart failure.

Acetylcholine↗

Formation of two-dimensional concentration pulses on microdesigned composite catalyst surfaces.

We study the effect of microdesigned composite geometries on pattern formation during the catalytic oxidation of CO on Pt-Ti, Pt-Rh, and Pt-Pd composite catalysts. In particular, we find experimentally (and rationalize through modeling) that adsorbate surface transport through the second (active) component drastically affects the shapes and interactions of concentration patterns (traveling pulses) observed on pure Pt.

Journal Article↗

Controlling chemical turbulence by global delayed feedback: pattern formation in catalytic CO oxidation on Pt(110).

Control of spatiotemporal chaos is one of the central problems of nonlinear dynamics. We report on suppression of chemical turbulence by global delayed feedback using, as an example, catalytic carbon monoxide oxidation on a platinum (110) single-crystal surface and carbon monoxide partial pressure as the controlled feedback variable. When feedback intensity was increased, spiral-wave turbulence was transformed into new intermittent chaotic regimes with cascades of reproducing and annihilating local structures on the background of uniform oscillations. The global feedback further led to the development of cluster patterns and standing waves and to the stabilization of uniform oscillations. These findings are reproduced by theoretical simulations.

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Ag8 fluorescence in argon.

The fluorescence of Ag8 in an argon matrix and in argon droplets is reported. This is the first unambiguous assignment of the fluorescence of a metal cluster larger than the tetramer, indicating that the excited state lifetime is longer than previously thought. It is discussed as a possible result of a matrix cage effect. The excitation spectrum is compared with two-photon-ionization measurements of Ag8 in helium droplets and to known absorption data. The agreement is excellent. We propose that the excited states relax rapidly through vibrational coupling to a long-lived state, from which the fluorescence occurs.

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