PubMed Health⌕ Search

Biomedical subjects

P Hess

Publications and source records attributed to P Hess.

At least 19 recordsLinked to original sources
PubMed2006

Infrared spectroscopic ellipsometry of n-alkylthiol (C5-C18) self-assembled monolayers on gold.

The infrared spectroscopic ellipsometry (IRSE) of n-alkylthiol (CH3(CH2)xSH, x = 4, 6, 7, 8, 10, 13, 15, and 17, self-assembled monolayers (SAMs), with 5-18 carbon atoms (C5-C18), grown on gold-coated Si(100) substrates) was investigated at room temperature. The C-H stretching vibrations could be resolved even for pentathiol, the shortest chain studied. The symmetric and asymmetric stretching vibrations of the CH2 groups are located at about 2850 and 2920 cm(-1), and those of CH3 are at about 2877 and 2962 cm(-1), respectively; they show a slight shift with the number of CH2 units. In addition, Fermi resonance of the symmetric CH3 stretching vibration at 2940 cm(-1) appears with decreasing chain length due to weak coupling with the asymmetric CH2 stretching vibration. The "odd-even effect" of the n-alkylthiol SAMs with varying CH2 units could be distinguished by the two interactive IRSE parameters. The relative ellipsometric spectra for the four longest chains could be reproduced quite well by using a Lorentz multioscillator model with a three-phase optical model (air/SAMs/gold). On the basis of the theoretical calculations, the vibrational strength of these oscillators is very weak, its magnitude being 10(-4)-10(-5). The full width at half-maximum (fwhm) of the peaks varies from 7 to 33 cm(-1). Moreover, the intensity of the C-H vibrations increases with the number of methylene units, due to strong lateral interactions and ordering effects occurring for longer chains.

Journal Article↗
PubMed2006

Influence of oxygen on the elastic properties of nanocrystalline diamond films studied by laser-induced surface acoustic waves.

Laser-induced surface acoustic waves (SAWs) were used to study the influence of oxygen on the elastic properties of nanocrystalline diamond films. A series of samples was grown by chemical vapor deposition (CVD) on the (100) plane of p-type silicon for 3h under different O(2)/(CH(4)+H(2)) flow ratios from 0% to 8%. The elastic properties of these nanocrystalline diamond films were determined from the SAW dispersion curves. The maximum frequency realized was about 310 MHz in wideband SAW experiments and about 700 MHz using a narrowband mask method with several higher harmonics. It was found that the densities of all samples were surprisingly high, approaching the ideal value of diamond, whereas the Young's modulus increased from 700 to 950 GPa with the addition of oxygen. It is concluded that oxygen has a significant positive effect on the elastic properties of nanocrystalline diamond.

Journal Article↗
PubMed2004

Solitary surface acoustic waves.

Solitary acoustic pulses can propagate along the surface of a coated homogeneous and inhomogeneous medium. It is shown how these nonlinear surface acoustic waves evolve out of initial pulselike conditions generated by pulsed laser excitation and how they can be monitored by optical detection. The solitary pulse shapes at the surface are computed on the basis of an evolution equation with nonlocal nonlinearity. They depend on the anisotropy of the substrate. Various approaches for the derivation of the evolution equation from nonlinear elasticity theory are critically compared. The behavior of the solitary pulses in collisions is investigated and is found to strongly depend on the linear dispersion law. The nontrivial depth dependence of these solitary pulses is also analyzed.

Journal Article↗
PubMed2002

Impulsive fracture of silicon by elastic surface pulses with shocks.

During nonlinear evolution of surface acoustic waves (SAWs) stress increases with propagation, and may cause fracture of brittle materials. This effect was used to evaluate the strength of crystalline silicon with respect to impulsive load in the nanosecond time scale without using seed cracks. Short SAW pulses propagating in the [11(macro)2] direction on the Si(111) plane induce fracture at significantly lower SAW amplitudes than the mirror symmetric wave propagating in the [112(macro)] direction. This effect is explained by the differences in elastic nonlinearity of the two propagation directions.

Journal Article↗
PubMed2002

Observation of solitary elastic surface pulses.

The formation of solitary elastic surface pulses from laser-generated pulselike initial conditions is reported. The nonlinearity of the medium is compensated by both normal dispersion and anomalous dispersion, which were realized by coating isotropic fused silica by a metal and titanium nitride film, respectively. As an anisotropic material, silicon covered with an oxide layer was studied. The experimental results agree with numerical simulations carried out with a nonlocal evolution equation, which describes nonlinear propagation of surface acoustic waves in a dispersive medium.

Journal Article↗
PubMed2002

Present status of infrainguinal arterial bypass procedures following an all autogenous policy--long-term results of a single center.

OBJECTIVES: The direction of vein grafts for infrainguinal arterial reconstruction is controversial. Long-term results of a single center following an all autogenous tissue policy in infrainguinal arterial reconstruction are reported with special attention to possible advantages for the in situ and non-reversed bypass using angioscopy. METHODS: From 10/88 until 12/00 540 bypasses with autogenous veins were performed on 497 patients. Veins were used in a non-reversed or in-situ direction, valve disruption was performed under angioscopic control. All grafts were prospectively included in our data base and follow-up was scheduled in our vascular lab before discharge and after 3, 6, 9, 12, 24 etc. months. RESULTS: Primary patency of all bypasses after 108 months was 55.2%, primary assisted 76.9% (SE +/- 9.87), survival 58.4% (SE +/- 8.88) and limb salvage 81.3% (SE +/- 9.75). Perioperative mortality was 0.9% (5 pat). Patency rates (primary assisted patency) after 72 months were 81.7% (98.2%) for supragenicular, 61.5% (79.4%) for infragenicular and 56.6% (78.1%) for tibial anastomoses and for pedal reconstructions after 48 months 49.3% (68.6%). CONCLUSION: Reviewing the literature neither the in situ and non-reversed nor the reversed grafts yielded better long-term results. Absence of size mismatch may be an advantage in smaller veins. Angioscopy may detect unsuspected vein disease.

Aged↗
PubMed2002

Does fibrin glue reduce complications after femoral artery surgery? A randomised trial.

OBJECTIVES: to determine whether application of fibrin glue before closure of inguinal wounds reduces the incidence of lymphatic complications. DESIGN: we a prospective randomised trial. MATERIALS AND METHODS: 224 consecutive patients were enrolled. The wounds were randomly assigned to standard closure (group A, n = 134) or closure with application of fibrin glue (group B, n = 132). The incidence of local lymphatic and non-lymphatic complications, the amount of lymphatic fluid collected, and the time to drain removal were compared in the groups. RESULTS: the incidence of lymphatic complications was 19% in group A and 10% in group B (p = 0.027). The average drain output and the time to drain removal did not differ in the two groups. The total incidence of non-lymphatic local complications was 10% and did not differ in the two groups. CONCLUSIONS: fibrin glue application is associated with a significant reduction in lymphatic complications.

Adult↗
PubMed2001

Determination of paralytic shellfish poisoning toxins by high-performance ion-exchange chromatography.

An efficient LC method has been developed for the determination of paralytic shellfish poisoning (PSP) toxins based on ion-exchange chromatographic separation of the toxins followed by electrochemical post-column oxidation and fluorescence detection as well as mass spectrometric (MS) detection. The method can be applied to the determination of PSP toxins in phytoplankton and to control seafood for PSP content.

Chromatography, High Pressure Liquid↗
PubMed2001

Reduction of groin lymphatic complications by application of fibrin glue: preliminary results of a randomized study.

Lymphoceles and lymph fistulas are common complications after exposure of the common femoral artery in the Scarpa triangle because of operative transsection of overlying lymphatics. The purpose of this prospective randomized study was to determine the incidence of groin lymphatic complications and to assess the impact of routine application of fibrin glue on lymphatic structures and subcutaneous tissue prior to closure. All patients undergoing exposure of the common femoral artery in the Scarpa triangle were included in this study. They were divided into two groups according to closure technique. In group A, closure was performed without fibrin glue. In Group B, fibrin glue was applied to lymphatic structures prior to closure. The efficacy of fibrin glue application was estimated on the basis of two criteria: incidence of local complications and amount of lymphatic fluid in the Redon drain. The preliminary findings suggest that application of fibrin glue leads to a significant reduction in the incidence of lymphatic complications after femoral artery exposure in the Scarpa triangle.

Adult↗
PubMed2001

Microsatellite instability is an independent indicator of recurrence in sporadic stage I-II endometrial adenocarcinoma.

PURPOSE: The aim of this study was to define the prognostic role of microsatellite status in 65 stage I-II primary sporadic endometrioid endometrial adenocarcinoma (EEA) patients. PATIENTS AND METHODS: Familiarity for neoplasia was ascertained in all patients on the basis of a questionnaire. Microsatellite status was assessed by matching normal and tumoral DNA probed for five dinucleotide repeats and one mononucleotide repeat marker. Microsatellite status was analyzed in relation to clinicopathologic characteristics of the patients and length of disease-free survival (DFS). RESULTS: Eleven tumors (17%) of 65 had instability at two or more loci and were considered as unstable or microsatellite instability (MI). Tumors with no instability or instability at one locus were classified as microsatellite stable (MS). The percentage of MI was significantly higher in poorly than in well to moderately differentiated tumors (50% v 9%; P =.003). The 5-year DFS rate of MI patients was 63% (95% confidence interval [CI], 35% to 91%) versus 96% (95% CI, 91% to 101%) of MS patients (P =.0004). In multivariate analysis, only the presence of MI, stage II of disease, and depth of myometrial invasion greater than 50% retained independent prognostic roles. CONCLUSION: The assessment of microsatellite status may provide useful information for preoperative prognostic characterization of stage I-II primary sporadic EEA patients in which more individualized treatment options can be attempted.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Evaluation of dialysis as a technique for the removal of lipids prior to the GC determination of ortho- and non-ortho-chlorobiphenyls, using 14C-labelled congeners.

Dialysis was evaluated as a non-destructive clean-up technique to isolate chlorobiphenyls (CBs) from fish-oil prior to further analysis. 14C-CBs were used to study the transfer processes of the CBs across polyethylene membranes. Single step processes using equilibrium dialysis were compared to a dynamic method of refluxing solvent. The dynamic method reduced the duration of the separation to 8 h. The transfer of CBs and the lipids was dependent on temperature and nature of the analyte with smaller molecules being dialysed substantially faster than larger molecules. An optimised dynamic method was used to compare the dialytic clean-up with a traditional method using sulfuric acid-impregnated silica for the determination of CBs in a laboratory reference material. Labelled recovery standards for each individual congener are recommended in combination with dialysis as a method for clean-up.

Journal Article↗
PubMed2001

Endothelin mediates the altered renal hemodynamics associated with experimental congestive heart failure.

Congestive heart failure (CHF) is commonly associated with renal dysfunction. The goal of the current study was to evaluate the role of endothelin in the renal dysfunction of experimental CHF by using tezosentan, a potent dual endothelin receptor antagonist. Rats were subjected to coronary artery ligation. Cardiac and renal hemodynamics were assessed after 3-5 weeks, when CHF had developed. Compared with control rats, CHF rats had significantly higher left ventricular end-diastolic pressure (LVEDP), lower mean arterial pressure, and reduced dP/dt(max). CHF rats had severe renal vasoconstriction, as assessed by increased renal vascular resistance (RVR, p < 0.001), decreased renal plasma flow (RPF, p < 0.001), and glomerular filtration rate (GFR, p < 0.001). Filtration fraction rose (p < 0.001). Urine flow rate and sodium excretion were markedly lower. Acute administration of tezosentan induced a marked decrease in LVEDP without change of dP/dt(max) and heart rate. Tezosentan decreased RVR (-43%, p < 0.001) and increased RPF and GFR. Filtration fraction decreased slightly. Tezosentan also increased urine flow rate and sodium excretion. These findings demonstrate that endothelin at least partly mediates the altered renal hemodynamics associated with experimental CHF. Dual endothelin receptor blockade could be useful for the improvement of both cardiac and renal function in CHF.

Animals↗
PubMed2001

Additional effects of endothelin receptor blockade and angiotensin converting enzyme inhibition in rats with chronic heart failure.

AIM: To evaluate the acute effects of tezosentan, a new dual parenteral endothelin receptor antagonist, on hemodynamics in a rat model of chronic heart failure (CHF), and further investigated if the combination of tezosentan with the angiotensin converting enzyme (ACE) inhibitor, enalapril, had additive hemodynamic effect. METHODS: Hemodynamics was measured in rats with CHF, induced by ligation of the left coronary artery. RESULTS: At 3 to 5 weeks after myocardial infarction, rats developed CHF. This was evidenced by a marked increase in left ventricular end-diastolic pressure (LVEDP) with mean values of 23 to 26 mmHg, by a 30 % to 40 % reduction in left ventricular dp/dt(max) and by a more than 10 % decrease in mean arterial pressure (MAP) as compared to sham-operated rats. In CHF rats, acute intravenous administration of either tezosentan (10 mg . kg) or enalapril (1 mg . kg) markedly decreased MAP and LVEDP, without affecting heart rate or dp/dtmax. Tezosentan had additive effects on MAP and LVEDP when given with enalapril compared with tezosentan (P < 0.05) or enalapril (P < 0.05) alone. There were no significant changes in heart rate and dp/dtmax with the combination treatment compared with tezosentan- or enalapril-treated CHF rats. CONCLUSION: Acute intravenous tezosentan improves cardiac hemodynamics and decreases LVEDP and afterload (MAP) without changes in heart rate and cardiac contractility dp/dtmax) in CHF rats. These favorable effects of tezosentan are similar to those of enalapril. Furthermore, the benefits of tezosentan are apparent in addition to ACE inhibition. Thus, tezosentan could be a useful therapeutic agent in the acute treatment of heart failure.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2000

Requirement of JNK for stress-induced activation of the cytochrome c-mediated death pathway.

The c-Jun NH2-terminal kinase (JNK) is activated when cells are exposed to ultraviolet (UV) radiation. However, the functional consequence of JNK activation in UV-irradiated cells has not been established. It is shown here that JNK is required for UV-induced apoptosis in primary murine embryonic fibroblasts. Fibroblasts with simultaneous targeted disruptions of all the functional Jnk genes were protected against UV-stimulated apoptosis. The absence of JNK caused a defect in the mitochondrial death signaling pathway, including the failure to release cytochrome c. These data indicate that mitochondria are influenced by proapoptotic signal transduction through the JNK pathway.

Animals↗