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Oxygen Pressure (oxygen + pressure)
Kinds of Oxygen Pressure Selected AbstractsAcute Hypervolaemia Improves Arterial Oxygen Pressure in Athletes with Exercise-Induced HypoxaemiaEXPERIMENTAL PHYSIOLOGY, Issue 4 2003Gerald S. Zavorsky The aim of this study was to determine the effect of acute plasma volume expansion on arterial blood-gas status during 6.5 min strenuous cycling exercise comparing six athletes with and six athletes without exercise-induced arterial hypoxaemia (EIAH). We hypothesized that plasma volume expansion could improve arterial oxygen pressure in a homogeneous sample of athletes - those with EIAH. In this paper we have extended the analysis and results of our recently published surprising findings that lengthening cardiopulmonary transit time did not improve arterial blood-gas status in a heterogeneous sample of endurance cyclists. One 500 ml bag of 10% Pentastarch (infusion condition) or 60 ml 0.9% saline (placebo) was infused prior to exercise in a randomized, double-blind fashion on two different days. Power output, cardiac output, oxygen consumption and arterial blood gases were measured during strenuous exercise. Cardiac output and oxygen consumption were not affected by acute hypervolaemia. There were group × condition interaction effects for arterial oxygen pressure and alveolar-arterial oxygen pressure difference, suggesting that those with hypoxaemia experienced improved arterial oxygen pressure (+4 mmHg) and lower alveolar-arterial oxygen pressure difference (-2 mmHg) with infusion. In conclusion, acute hypervolaemia improves blood-gas status in athletes with EIAH. The impairment of gas exchange occurs within the first minute of exercise, and is not impaired further throughout the remaining duration of exercise. This suggests that arterial oxygen pressure is only minimally mediated by cardiac output. [source] Capillary Hemodynamics and Oxygen Pressures in the Aging MicrocirculationMICROCIRCULATION, Issue 4 2006DAVID C. POOLE ABSTRACT Healthy aging acts to redistribute blood flow (Q,) and thus O2 delivery (Q,O2) among and within the exercising muscles such that Q,O2 to highly oxidative muscle fibers may be compromised. Within the microcirculation of old muscles capillary hemodynamics are altered and the matching of Q,O2 to oxidative requirements (V,O2) is impaired such that at exercise onset the microvascular O2 pressure falls below that seen in their younger counterparts. This is important because the microvascular O2 pressure denotes the sole driving force for blood-myocyte O2 transfer and any compromise may slow V,O2 kinetics and reduce exercise tolerance. This review considers the microcirculatory evidence for a reduced perfusive (Q,O2) and diffusive O2 flux within aged muscle and highlights the pressing need for intravital microscopy studies of the muscle microcirculation during exercise. [source] Measurement of Muscle Microvascular Oxygen Pressures: Compartmentalization of Phosphorescent ProbeMICROCIRCULATION, Issue 4 2004DAVID C. POOLE Objective: To determine whether the phosphorescent probe Oxyphor R2 (a palladium porphyrin dendrimer) becomes extravasated within normotensive skeletal muscle, R2 perfusion and washout studies were performed using a perfused rat hindlimb preparation. Methods: Phosphorescence signals were monitored in tibialis anterior muscles after 35 min of R2 blood perfusion and across a subsequent washout period that included vasodilation (sodium nitroprusside, SNP, ,3 × 10,2 M). Results: Two responses were evident: Group 1 (n = 4),Inflowing blood pressure and vascular conductance remained stable close to initial values and subsequently a marked vasodilation was evident with SNP (vascular conductance; R2 blood perfusion, 0.096 ± 0.005; washout, pre-SNP, 0.085 ± 0.005, post-SNP, 0.110 ± 0.005 mL/min/mmHg, p < .05, for pre- vs. post-SNP). Baseline phosphorescence signals could be monitored up to 99 ± 36 s post-SNP when the phosphorescence signal disappeared. For these muscles, palladium content was undetectable. Group 2 (n = 3),Inflowing blood pressure increased 112% and vascular conductance fell , 50%. These hindlimbs were unresponsive to SNP, phosphorescence signal was undiminished by washout and SNP, and muscles became edematous. Conclusions: These results suggest that in normotensive muscle (i.e., Group 1 above), extravasation of phosphorescent probe R2 over 35 min of perfusion is insufficient to yield a detectable phosphorescence signal in skeletal muscle. [source] Floating zone growth of CuO under elevated oxygen pressure and its relevance for the crystal growth of cupratesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005G. Behr Abstract CuO single crystals have been grown from the melt by a floating zone method with optical heating at elevated oxygen pressures 3.5 to 5.5 MPa and growth rates as high as 10 mm/h. Melting experiments and recalculated Cu-O phase diagram data show that CuO melts incongruently. The melting temperature increases and the concentration difference between the melt and the CuO phase decreases for rising oxygen partial pressure. Accordingly, increasing the oxygen partial pressure improves the growth process by reducing both the significant oxygen loss during melting as well as the composition difference at the growth interface. The results on CuO provide important information for the crystal growth of more complex cuprates. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhanced external counterpulsation improves skin oxygenation and perfusionEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 6 2004M. J. Hilz Abstract Background, Enhanced external counterpulsation (EECP) augments diastolic and reduces systolic blood pressures. Enhanced external counterpulsation has been shown to improve blood flow in various organ systems. Beneficial effects on skin perfusion might allow EECP to be used in patients with skin malperfusion problems. This study was performed to assess acute effects of EECP on superficial skin blood flow, transdermal oxygen and carbon dioxide pressures. Materials and methods, We monitored heart rate, blood pressure, transdermal blood flow as well as oxygen and carbon dioxide pressures in 23 young, healthy persons (28 ± 4 years) and 15 older patients (64 ± 7 years) with coronary artery disease before, during and 3 min after 5 min EECP. Friedman test was used to compare the results of 90-s epochs before, during and after EECP. Significance was set at P < 0·05. Results, Enhanced external counterpulsation increased heart rate and mean blood pressure. During EECP, transdermal oxygen pressure and concentration of moving blood cells increased while transdermal carbon dioxide pressure and velocity of moving blood cells decreased significantly in both groups. After EECP, transdermal carbon dioxide pressure was still reduced while the other parameters returned to baseline values. Conclusions, Improved skin oxygenation and carbon dioxide clearance during EECP seem to result from the increased concentration and reduced flow velocity, i.e. prolonged contact time, of erythrocytes. The increased concentration of moving blood cells and the decreased velocity of moving blood cells at both tested skin sites indicate peripheral vasodilatation. [source] Human melanocytes can be isolated, propagated and expanded from plucked anagen hair folliclesEXPERIMENTAL DERMATOLOGY, Issue 6 2010Christina Dieckmann Please cite this paper as: Human melanocytes can be isolated, propagated and expanded from plucked anagen hair follicles. Experimental Dermatology 2010; 19: 543,545. Abstract:, Herein, we report a technically simple method for isolation and culture of human follicular melanocytes based on explant cultures of epilated hair follicles. This technique does not require any surgical intervention and allows the isolation and cultivation of follicular melanocytes from a comparatively small amount of raw material. Generally, 30,60 human anagen hair follicles have been plucked from the scalp of healthy donors and cultivated under low oxygen pressure (5%). After a short period of time cells of various types were growing out from the outer root sheath (ORS) of the hair follicles. Under the selected culture conditions, most of the cells other than melanocytes have been eliminated and a nearly 100% pure population of melanocytes has been achieved, as confirmed by immunohistochemical analyses for melanocyte-specific markers, for example, Tyrosinase-1, S-100 and premelanosomal antigens. These melanocytes derived from the ORS were proliferating for up to 2 months. [source] Acute Hypervolaemia Improves Arterial Oxygen Pressure in Athletes with Exercise-Induced HypoxaemiaEXPERIMENTAL PHYSIOLOGY, Issue 4 2003Gerald S. Zavorsky The aim of this study was to determine the effect of acute plasma volume expansion on arterial blood-gas status during 6.5 min strenuous cycling exercise comparing six athletes with and six athletes without exercise-induced arterial hypoxaemia (EIAH). We hypothesized that plasma volume expansion could improve arterial oxygen pressure in a homogeneous sample of athletes - those with EIAH. In this paper we have extended the analysis and results of our recently published surprising findings that lengthening cardiopulmonary transit time did not improve arterial blood-gas status in a heterogeneous sample of endurance cyclists. One 500 ml bag of 10% Pentastarch (infusion condition) or 60 ml 0.9% saline (placebo) was infused prior to exercise in a randomized, double-blind fashion on two different days. Power output, cardiac output, oxygen consumption and arterial blood gases were measured during strenuous exercise. Cardiac output and oxygen consumption were not affected by acute hypervolaemia. There were group × condition interaction effects for arterial oxygen pressure and alveolar-arterial oxygen pressure difference, suggesting that those with hypoxaemia experienced improved arterial oxygen pressure (+4 mmHg) and lower alveolar-arterial oxygen pressure difference (-2 mmHg) with infusion. In conclusion, acute hypervolaemia improves blood-gas status in athletes with EIAH. The impairment of gas exchange occurs within the first minute of exercise, and is not impaired further throughout the remaining duration of exercise. This suggests that arterial oxygen pressure is only minimally mediated by cardiac output. [source] Chronic Hypoxia Delays Myocardial Lactate Dehydrogenase Maturation in Young RatsEXPERIMENTAL PHYSIOLOGY, Issue 3 2003Z. Daneshrad The effect of exposure to hypobaric hypoxia for 4 weeks (oxygen pressure = 106 hPa), equivalent to 5500 m in altitude) on myocardial total lactate dehydrogenase (tLDH) activity and isoform (H and M) composition was comparatively studied in growing (4.5 weeks old) and in adult (4.5 months old) male rats. The consequences of the hypoxia-induced anorexia were checked in growing rats using a pair-fed group. Exposure to hypoxia induced a significant decrease in the H/tLDH ratio in the left (LV) and right ventricle (RV) of growing and adult rats. In adult rats this alteration was mainly a consequence of the significant increase in the specific activity of the M isomer, which resulted in an increase in the overall LDH activity. In contrast, in the LV of young rats exposed to hypoxia, the specific activity of the M isomer was similar to that of normoxic animals while the H isomer activity was significantly lower than in normoxic rats, and the overall LDH activity remained unchanged. These effects were specifically due to hypoxia per se since no significant alterations were observed in pair-fed animals. In the hypertrophied RV, the alteration of H and M isomers following hypoxia was similar to that observed in adults (i.e. no change in H and an increase in M isoform). We conclude that the well-known hypoxia-induced decrease in the H/tLDH ratio is governed by different age-dependent mechanisms. In adult rats, hypoxia may induce in both ventricles a stimulating effect on M isomer expression. In the LV of growing rats this stress could inhibit the H isomer maturation without any effect on the M isomer. In the RV of growing rats this effect could have been counteracted by the growth effect of the hypertrophying process. [source] Arterial blood gases in extraperitoneal laparoscopic urethrocystopexyINTERNATIONAL JOURNAL OF UROLOGY, Issue 8 2002Hasan Kocoglu Abstract Background: The aim of this study was to investigate the effects of extraperitoneal laparoscopy and carbon dioxide insufflation on hemodynamic parameters, arterial blood gases and complications in urethrocystopexy operations. Methods: Twenty-five female patients who underwent extraperitoneal laparoscopic mesh urethrocystopexy operation for the correction of urinary incontinence were allocated to the study. Hemodynamic parameters were noted and blood gas analyzes were performed before the induction of anesthesia, 10 min after induction, 5 and 10 min after the beginning of carbon dioxide insufflation, at the end of carbon dioxide insufflation and 30 min after exsufflation. Results: There was no significant change in mean arterial pressure, peripheral oxygen saturation, arterial carbon dioxide pressure, and arterial oxygen saturation compared to preinsufflation and preinduction values. End-tidal carbon dioxide pressure did not increase above 45 mm/Hg during carbon dioxide insufflation. Arterial oxygen saturation and partial oxygen pressure did not decrease. Subcutaneous emphysema, pneumothorax, pneumomediastinum and pleural effusion were not noted in any patient. Conclusion: We conclude that, extraperitoneal laparoscopic urethrocystopexy is not associated with hemodynamic and respiratory impairment. [source] Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Emmanuel Richaud Abstract Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80°C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 × 10,3 mol L,1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 × 10,3 mol L,1. The results indicate the existence of a direct phenol-oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build-up and stabilizer consumption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Oxidative degradation of 4-nitrophenol in UV-illuminated titania suspensionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2001Jimmy Lea Abstract An internally-irradiated annular photoreactor has been used to investigate the oxidative degradation of aqueous 4-nitrophenol with titania as the photocatalyst. Reaction runs were performed over a 3-h period and in practically all cases, complete degradation was possible within about 2,h. The kinetics was determined as a function of nitrophenol concentration, oxygen partial pressure, catalyst loading, pH, temperature and light intensity. The reaction was characterised by a relatively low activation energy of 7.83,kJ,mol,1 although transport intrusions were negligible. Rate decreased almost exponentially with pH while a quadratic (maximum) behaviour with respect to both oxygen pressure and nitrophenol concentration is symptomatic of self-inhibition possibly due to the formation of intermediates which competitively adsorb on similar sites to the reactants. Increased catalyst dosage also improved the reaction rate although the possible effects of light scattering and solution opacity caused a drop at loadings higher than about 1.20,g,dm,3. Rate, however, has a linear dependency on light intensity, suggesting that hole,electron recombination processes were negligible at the conditions investigated. © 2001 Society of Chemical Industry [source] Catalytic wet air oxidation of phenol using active carbon: performance of discontinuous and continuous reactorsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2001Frank Stüber Abstract Catalytic wet air oxidation (CWAO) of an aqueous phenol solution using active carbon (AC) as catalytic material was compared for a slurry and trickle bed reactor. Semi-batchwise experiments were carried out in a slurry reactor in the absence of external and internal mass transfer. Trickle-bed runs were conducted under the same conditions of temperature and pressure. Experimental results from the slurry reactor study showed that the phenol removal rate significantly increased with temperature and phenol concentration, whereas partial oxygen pressure had little effect. Thus, at conditions of 160,°C and 0.71,MPa of oxygen partial pressure, almost complete phenol elimination was achieved within 2,h for an initial phenol concentration of 2.5,g,dm,3. Under the same conditions of temperature and pressure, the slurry reactor performed at much higher initial rates with respect to phenol removal than the trickle bed reactor, both for a fresh active carbon and an aged active carbon, previously used for 50,h in the trickle bed reactor, but mineralisation was found to be much lower in the slurry reactor. Mass transfer limitations, ineffective catalyst wetting or preferential flow in the trickle bed alone cannot explain the drastic difference in the phenol removal rate. It is likely that the slurry system also greatly favours the formation of condensation polymers followed by their irreversible adsorption onto the AC surface, thereby progressively preventing the phenol molecules to be oxidised. Thus, the application of this type of reactor in CWAO has to be seriously questioned when aiming at complete mineralisation of phenol. Furthermore, any kinetic study of phenol oxidation conducted in a batch slurry reactor may not be useful for the design and scale-up of a continuous trickle bed reactor. © 2001 Society of Chemical Industry [source] Oxygen delignification kinetics: CSTR and batch reactor comparisonAICHE JOURNAL, Issue 10 2007Yun Ji Abstract In the past, oxygen delignification studies were mostly performed in batch reactors, whereby the caustic and dissolved oxygen concentrations are changing during the reaction. Also the lignin content and cellulose degradation of the pulp are only established at the end of an experiment when the sample is removed from the reactor. To overcome these deficiencies, a differential reactor system (called Berty reactor) has been adopted. In this continuous stirred-tank reactor (CSTR), the dissolved oxygen concentration and the alkali concentration in the feed are kept constant, and the rate of lignin removal is determined from the dissolved lignin concentration in the outflow stream measured by UV,vis spectroscopy. The delignification rate is found to be first-order in HexA-free residual lignin content. The delignification rate reaction order in [NaOH] and oxygen pressure are 0.412 ± 0.060 and 0.305 ± 0.260 respectively. The activation energy is 54.5 ± 6.8 kJ/mol. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Involvement of thromboxane A2 (TXA2) in the early stages of oleic acid-induced lung injury and the preventive effect of ozagrel, a TXA2 synthase inhibitor, in guinea-pigsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2004Yoichi Ishitsuka ABSTRACT An intravenous injection of oleic acid into animals can produce a lung injury with hypoxaemia and pulmonary vascular hyper-permeability. Although oleic acid lung injury is used as a model of acute respiratory distress syndrome (ARDS), the precise mechanisms of the lung injury are still unclear. We have investigated whether thromboxane A2 (TXA2) participated in the lung injury and have evaluated the efficacy of ozagrel, a TXA2 synthase inhibitor, on the lung injury in guinea-pigs. Oleic acid injection increased the plasma level of TXB2, a stable metabolite of TXA2, and the time-course of plasma TXB2 was similar to that of the decreased partial oxygen pressure of arterial blood (Pao2) induced with oleic acid. Ozagrel administered intravenously 30 min before oleic acid injection prevented the decrease in Pao2 and pulmonary vascular hyper-permeability. It also prevented increases in lactate dehydrogenase activity, a measure of lung cell injury, TXB2 and its weight ratio to 6-keto prostaglandin F1 , in bronchoalveolar lavage fluid. Although ozagrel administered simultaneously with oleic acid ameliorated the decrease in Pao2, post treatment showed little effect. We suggest that TXA2 participated in the oleic acid lung injury, as an "early phase" mediator, and rapidly-acting TXA2 synthase inhibitors were effective in the prevention of acute lung injury. [source] Relationship between bronchial hyperresponsiveness and development of asthma in children with chronic coughPEDIATRIC PULMONOLOGY, Issue 6 2001Hideko Nishimura MD Abstract To evaluate the relationship between bronchial hyperresponsiveness (BHR) and the development of asthma in children with chronic cough, we performed methacholine inhalation challenges and transcutaneous oxygen pressure (tcPO2) measurements in 92 children with chronic cough aged from 1,13 years (55 boys and 37 girls; mean, 5.3 years) and followed them for ,,,10 years. Forty-four age-matched children with asthma (24 males and 20 females; mean, 6.5 years) and 44 age-matched children without cough or asthma served as controls (18 males and 26 females; mean, 4.6 years). Consecutive doubling doses of methacholine were inhaled until a 10% decrease in tcPO2 from baseline was observed. The cumulative dose of methacholine at the inflection point of the tcPO2 record (Dmin-PO2) was considered to represent hyperresponsiveness to inhaled methacholine. After 10 years or more of follow-up, 60 of the 92 subjects with cough answered our questionnaire, and 27/60 had been diagnosed with asthma. There was a statistical difference in Dmin-PO2 between the children who presented with chronic cough originally and who developed asthma (asthma-developed group) and those who did not develop asthma (asthma-free group). There was no difference in the value of Dmin-PO2 between the asthma-developed group and the asthma group, or between the asthma-free group and the age-matched control group. Among the children with chronic cough, there was no difference in Dmin-PO2 between girls and boys, either in the asthma-developed group or in the asthma-group. We conclude that 45% of the children with a chronic cough in early life developed asthma, and that BHR in children with chronic cough during the childhood period is a strong risk factor for the development of asthma. Pediatr Pulmonol. 2001; 31:412,418. © 2001 Wiley-Liss, Inc. [source] Blood samples collected under venous oxygen pressure from patients with sickle cell disease contain a significant number of a new type of reversibly sickled cells: Constancy of the percentage of sickled cells in individual patients during steady stateAMERICAN JOURNAL OF HEMATOLOGY, Issue 4 2005Toshio Asakura Abstract We found various levels of a new type of reversibly sickled cell (RSC) with blunt edges in 44 blood samples obtained from 32 steady-state patients with sickle cell disease (SCD) without exposure to air (UnExp-blood). Because these RSCs could be generated in vitro by partial oxygenation of once-deoxygenated SS cells to venous oxygen pressure, we named them "partially oxygenated sickled cells" (POSCs). These RSCs were classified into elongated and non-elongated RSCs, depending on the ratio of the short axis to long axis. The presence of these cells was previously unknown because the standard blood collection method oxygenates most of the POSCs to discocytes due to oxygen in the air space in the needle, syringe, and blood collection tube (Exp-blood). Although the shape of elongated POSCs is similar to that of irreversibly sickled cells (ISCs), POSCs revert to discocytes upon exposure to air. We found the following: (1) the percentage of total sickled cells (total POSCs + ISCs) in UnExp-blood (29.0 ± 14.5%) was significantly higher than the percentage of sickled cells (mainly ISCs) in Exp-blood (7.3 ± 5.7%); (2) the percentage of sickled cells in UnExp-blood was specific to individual patients during steady state, while it decreased at the onset of a vaso-occlusive event; and (3) the percentage of sickled cells in UnExp-blood varied widely among steady-state patients (4,56%). This new type of RSC may be used as an internal biomarker to evaluate the disease state of individual patients. Am. J. Hematol. 80:249,256, 2005. © 2005 Wiley-Liss, Inc. [source] Effect of oxygen partial pressure on optical and electrical properties of co-sputtered amorphous zinc indium tin oxide thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008K. J. Saji Abstract Transparent thin films of amorphous zinc indium tin oxide were prepared at room temperature by co-sputtering of zinc oxide and indium tin oxide. Effect of oxygen partial pressure on the optical and electrical properties of amorphous zinc indium tin oxide thin films were investigated. Conductivity, carrier concentration and Hall mobility showed strong dependence on the oxygen partial pressure and these parameters decreased with the increase of oxygen pressure. The effect of subgap states caused a sharp difference in measured optical band gap values between the films deposited with and without oxygen partial pressure. Carrier transport studies were carried out by temperature dependent conductivity measurements. At low electron density, the conductivity showed thermally activated behaviour and at higher carrier concentrations it changed to almost degenerate band conduction. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of Sn doped ZnO thin films by pulsed laser depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006E. López-Ponce Abstract Sn:ZnO thin films with different Sn concentrations were grown by pulsed laser deposition (PLD) onto single-crystal Si(001) substrates at an oxygen pressure of 2 × 10,2 mbar and substrate temperature of 600 °C. The targets used were high density Sn:ZnO pellets with different Sn concentrations produced by mixing ZnO and SnO2 by conventional ceramic routes. A deep structural and electrical characterization was carried out in order to determine the role of an increasing Sn nominal concentration on the ZnO film transport properties. Only films with a nominal 0.1 at% Sn show an improvement of the transport properties, lower resistivity and higher donor concentration, with respect to pure ZnO thin films. For films with larger Sn nominal concentrations segregated SnZnO phases appear that lead to larger film resistivities and no increase in donor concentration. The 0.1 at% Sn film is accordingly a good candidate to study the possible room temperature ferromagnetism when co doping with Mn. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Catalytic role of manganese in autoclave oxidation of germanium-rich sphalerite concentratesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Liang Duoqiang Abstract An attempt was made to investigate the catalytic role of manganese in enhancing the reaction rate with respect to autoclave oxidation of germanium-rich sphalerite concentrates. A series of batch experiments was performed in different conditions to investigate the variables such as temperature and oxygen pressure. Experimental results obtained show that as a catalyst, aqueous divalent manganese can accelerate the leaching of sphalerite concentrates significantly. On a tenté d'étudier le rôle catalytique du manganèse pour améliorer la vitesse de réaction de l'oxydation en autoclave de concentrés de sphalérite riche en germanium. Une série d'expériences discontinues ont été menées dans différentes conditions afin d'étudier les variables telles que la température et la pression d'oxygène. Les résultats expérimentaux obtenus montrent qu'en tant que catalyseur, le manganèse divalent aqueux peut significativement accélérer la lixiviation des concentrés de sphalérite. [source] Recurrent spreading depolarizations after subarachnoid hemorrhage decreases oxygen availability in human cerebral cortexANNALS OF NEUROLOGY, Issue 5 2010Bert Bosche MD Objective Delayed ischemic neurological deficit (DIND) contributes to poor outcome in subarachnoid hemorrhage (SAH) patients. Because there is continuing uncertainty as to whether proximal cerebral artery vasospasm is the only cause of DIND, other processes should be considered. A potential candidate is cortical spreading depolarization (CSD)-induced hypoxia. We hypothesized that recurrent CSDs influence cortical oxygen availability. Methods Centers in the Cooperative Study of Brain Injury Depolarizations (COSBID) recruited 9 patients with severe SAH, who underwent open neurosurgery. We used simultaneous, colocalized recordings of electrocorticography and tissue oxygen pressure (ptiO2) in human cerebral cortex. We screened for delayed cortical infarcts by using sequential brain imaging and investigated cerebral vasospasm by angiography or time-of-flight magnetic resonance imaging. Results In a total recording time of 850 hours, 120 CSDs were found in 8 of 9 patients. Fifty-five CSDs (,46%) were found in only 2 of 9 patients, who later developed DIND. Eighty-nine (,75%) of all CSDs occurred between the 5th and 7th day after SAH, and 96 (80%) arose within temporal clusters of recurrent CSD. Clusters of CSD occurred simultaneously, with mainly biphasic CSD-associated ptiO2 responses comprising a primary hypoxic and a secondary hyperoxic phase. The frequency of CSD correlated positively with the duration of the hypoxic phase and negatively with that of the hyperoxic phase. Hypoxic phases significantly increased stepwise within CSD clusters; particularly in DIND patients, biphasic ptiO2 responses changed to monophasic ptiO2 decreases within these clusters. Monophasic hypoxic ptiO2 responses to CSD were found predominantly in DIND patients. Interpretation We attribute these clinical ptiO2 findings mainly to changes in local blood flow in the cortical microcirculation but also to augmented metabolism. Besides classical contributors like proximal cerebral vasospasm, CSD clusters may reduce O2 supply and increase O2 consumption, and thereby promote DIND. ANN NEUROL 2010;67:607,617 [source] Hydrogen production by photoautotrophic sulfur-deprived Chlamydomonas reinhardtii pre-grown and incubated under high lightBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Irina V. Tolstygina Abstract We have previously demonstrated that Chlamydomonas reinhardtii can produce hydrogen under strictly photoautotrophic conditions during sulfur deprivation [Tsygankov et al. (2006); Int J Hydrogen Energy 3:1574,1584]. The maximum hydrogen photoproduction was achieved by photoautotrophic cultures pre-grown under a low light regime (25 µE,m,2,s,1). We failed to establish sustained hydrogen production from cultures pre-grown under high light (100 µE,m,2,s,1). A new approach for sustained hydrogen production by these cultures is presented here. Assuming that stable and reproducible transition to anerobiosis as well as high starch accumulation are important for hydrogen production, the influence of light intensity and dissolved oxygen concentration during the oxygen evolving stage of sulfur deprivation were investigated in cultures pre-grown under high light. Results showed that light higher than 175 µE,m,2,s,1 during sulfur deprivation induced reproducible transition to anerobiosis, although the total amount of starch accumulation and hydrogen production were insignificant. The potential PSII activity measured in the presence of an artificial electron acceptor (DCBQ) and an inhibitor of electron transport (DBMIB) did not change in cultures pre-grown under 20 µE,m,2,s,1 and incubated under 150 µE,m,2,s,1 during sulfur deprivation. In contrast, the potential PSII activity decreased in cultures pre-grown under 100 µE,m,2,s,1 and incubated under 420 µE,m,2,s,1. This indicates that cultures grown under higher light experience irreversible inhibition of PSII in addition to reversible down regulation. High dissolved O2 content during the oxygen evolving stage of sulfur deprivation has a negative regulatory role on PSII activity. To increase hydrogen production by C. reinhardtii pre-grown under 100 µE,m,2,s,1, cultures were incubated under elevated PFD and decreased oxygen pressure during the oxygen evolving stage. These cultures reproducibly reached anaerobic stage, accumulated significant quantities of starch and produced significant quantities of H2. It was found that elevation of pH from 7.4 to 7.7 during the oxygen producing stage of sulfur deprivation led to a significant increase of accumulated starch. Thus, control of pH during sulfur deprivation is a possible way to further optimize hydrogen production by photoautotrophic cultures. Biotechnol. Bioeng. 2009;102: 1055,1061. © 2008 Wiley Periodicals, Inc. [source] Intrinsic Oxygen Use Kinetics of Transformed Plant Root CultureBIOTECHNOLOGY PROGRESS, Issue 3 2001Patrick T. Asplund Root meristem oxygen uptake, root tip extension rate, and specific growth rate are assessed as a function of dissolved oxygen level for three transformed root cultures. The influence of hydrodynamic boundary layer was considered for all measurements to permit correlation of oxygen-dependent kinetics with the concentration of oxygen at the surface of the root meristem. Oxygen uptake rate is shown to be saturated at ambient conditions, and a saturation level of approximately 300 ,mole O2/(cm3 tissue·hr) was observed for all three of these morphologically diverse root types. In nearly all cases, the observation of a minimum oxygen pressure, below which respiration, extension, or root growth would not occur, could be accounted for as a boundary layer mass transfer resistance. The critical oxygen pressure below which respiration declines is below saturated ambient oxygen conditions. In contrast, critical oxygen pressures for root tip extension were much higher; extension was nearly linear for the two thicker root types (Hyoscyamus muticus, henbain; Solanum tuberosum, potato) above ambient oxygen levels. The performance of the thinnest root, Brassica juncea (Indian mustard) was consistent with reduced internal limitations for oxygen transport. Extension rates did not correlate with biomass accumulation. The fastest growing henbain culture (, = 0.44 day,1) displayed the slowest extension rate (0.16 mm/hr), and the slowest growing mustard culture (, = 0.22 day,1) had the fastest tip extension rate (0.3 mm/hr). This apparent paradox is explained in terms of root branching patterns, where the root branching ratio is shown to be dependent upon the oxygen-limited mersitem extension rate. The implications of these observations on the performance of root culture in bioreactors is discussed. [source] 3353: Response of the human eye against oxidative stress at high altitudesACTA OPHTHALMOLOGICA, Issue 2010S KARAKUCUK Purpose To evaluate the response of the anterior segment of the eye against oxidative stress during acute exposure to high altitudes. Methods Forty volunteers were examined and measurements performed at Erciyes University Medical Faculty,Ophthalmology Clinic, Kayseri,Turkey(1080m). On the following day, participants were transported to Mt. Erciyes Ski Center by bus(2200m); thereafter they climbed to an altitude of 2800m.with a moderate pace. Central corneal thickness, intraocular pressure,spheric equivalent of refraction, arterial oxygen pressure,blood pressure, pulse rate and body temperature were measured at both altitudes. Venous blood samples were taken from volunteers at both altitudes;total oxidant status (TOS),total antioxidant status(TAS),advanced oxidation protein products (AOPP), xanthine oxidase (XO), thiol, adenosine deaminase(ADA)levels were investigated at 1080m and 2800m. Results TOS(7.02µmol H2O2 equiv/L, range:0.49-22.07) and AOPP(220.74µmol/L,range:103.81-667.35)significantly increased at high altitude, compared to low altitude levels (3.32µmol H2O2 equiv/L range:0.92-18.41,and 195.58µmol/L,range:84.77-663.16, resp; p<0.05).IOP significantly elevated at high altitude (14.45±3.54mmHg vs 13.22±2.74mmHg; p<0.05). There was a significant positive correlation between IOP and TAS levels(p<0.05). No significant correlation was found between spherical equivalent or central corneal thickness with the investigated oxidation parameters at both altitudes Conclusion We conclude that oxidative stress markers, TOS and AOPP are increased along with IOP during acute exposure to hypoxic environment at high altitudes and that antioxidant system may have a limited capacity to counter balance this effect because of acute unacclimatized ascent. [source] Floating zone growth of CuO under elevated oxygen pressure and its relevance for the crystal growth of cupratesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005G. Behr Abstract CuO single crystals have been grown from the melt by a floating zone method with optical heating at elevated oxygen pressures 3.5 to 5.5 MPa and growth rates as high as 10 mm/h. Melting experiments and recalculated Cu-O phase diagram data show that CuO melts incongruently. The melting temperature increases and the concentration difference between the melt and the CuO phase decreases for rising oxygen partial pressure. Accordingly, increasing the oxygen partial pressure improves the growth process by reducing both the significant oxygen loss during melting as well as the composition difference at the growth interface. The results on CuO provide important information for the crystal growth of more complex cuprates. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An integrated care pathway to save the critically ischaemic diabetic footINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 6 2006K. El Sakka Summary This prospective study describes and evaluates the efficacy of an integrated care pathway for the management of the critically ischaemic diabetic foot patients by a multidisciplinary team. A weekly joint diabetes/vascular/podiatry ward round and outpatient clinic was established where patients were assessed within 7 days of referral by clinical examination, ankle-brachial-index-pressures, duplex angiogram and transcutaneous oxygen pressures. An angiogram ± angioplasty or alternatively a magnetic resonance angiography prior to surgical revascularisation was performed in patients deemed not suitable for angioplasty based on the above vascular assessment. Between January 2002 and June 2003(18 months), 128 diabetic patients with lower limb ischaemia were seen. Thirty-four (26.6%) patients received medical treatment alone, and 18 (14.1%) were deemed ,palliative' due to their significant co-morbidities. The remaining 76 (59.4%) patients underwent either angioplasty (n = 56), surgical reconstruction (n = 18), primary major amputation (n = 2) or secondary amputation after surgical revascularisation (n = 1). Minor toe amputations were required in 35 patients. The mortality in the intervention group was 14% (11/76). This integrated multidisciplinary approach offers a consistent and equitable service to diabetic patients with critically ischaemic feet and appears to have a beneficial major/minor amputation ratio. [source] Effects of sevoflurane on collagen production and growth factor expression in rats with an excision woundACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 7 2010H.-J. LEE Background: Sevoflurane is a widely used inhalation anesthetic, but there are no studies on its effect on the wound-healing process. This study was undertaken to evaluate the effect of exposure time to sevoflurane on wound healing. Method: Male Sprague,Dawley rats were used. Two circular full-thickness skin defects 8 mm in diameter were made on the dorsum of the rats. The animals were divided into six groups according to exposed gas type and time: S1 (sevoflurane, 1 h), S4 (sevoflurane, 4 h), S8 (sevoflurane, 8 h), O1 (oxygen, 1 h), O4 (oxygen, 4 h), and O8 (oxygen, 8 h). The surface area of the wounds was measured 0, 1, 3, and 7 days after surgery. Separately, the mean blood pressures (MBP) and arterial oxygen pressures (PaO2) were monitored during the sevoflurane exposure. Collagen type I production and transforming growth factor-,1 (TGF-,1) and basic fibroblast growth factor (bFGF) expression on the wound surface were analyzed. Routine histological analysis was also performed. Result: Exposure duration to sevoflurane had no influence on MBP and PaO2. The reduction in wound size and collagen type I production was delayed in S8. The expression of TGF-,1 and bFGF on the wound surface in S8 was significantly attenuated in S8. The histology of the S8 demonstrated a delayed healing status. Conclusions: Prolonged exposure to sevoflurane might alter the inflammatory phase of the wound-healing process by attenuation of growth factor expression such as TGF-,1 and bFGF and subsequently by reduced collagen production. [source] Stress-Corrosion Cracking of Silicon Carbide Fiber/Silicon Carbide CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Russell H. Jones Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiCf/SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiCf/SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ,700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber,matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value (d > dc) and the temperature below a critical value (T < Tg), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < dc and may occur at T > Tg for d > dc. This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation. [source] Preliminary Observations on Phase Relations in the "V2O3,FeO" and V2O3,TiO2 Systems from 1400°C to 1600°C in Reducing AtmospheresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Theresa Coetsee Phase relations within the "V2O3,FeO" and V2O3,TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10,10, 2.99 × 10,9, and 2.31 × 10,8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (MnO2n,1, where M = V, Ti) were identified in the V2O3,TiO2 system. In the "V2O3,FeO" system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified. [source] Vacancy-mediated room-temperature ferromagnetism in Zn1,xMnxO thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010N. Gopalakrishnan Abstract The effect of oxygen vacancies on ferromagnetism (FM) in Zn1,xMnxO thin films grown by radio frequency (RF) sputtering has been investigated. The grown films at different oxygen pressures have been characterized by X-ray diffraction (XRD), Hall effect, photoluminescence (PL) and vibrating sample magnetometry (VSM). The observed ferromagnetism/diamagnetism by the VSM measurement due to the variation of oxygen vacancies has been confirmed by XRD, PL, and Hall results. The vacancy-mediated FM has been explained by the formation of magnetic polarons. [source] EPR and photoluminescence diagnostics of singlet oxygen generation on porous silicon surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009E. A. Konstantinova Abstract Electron paramagnetic resonance and photoluminescence spectroscopy are used to investigate photosensitized generation of singlet oxygen in the porous silicon layers. The singlet oxygen concentration in the samples was estimated at various oxygen pressures. The time of energy transfer from excitons confined in Si nanocrystals to adsorbed O2 molecules on silicon nanocrystal surface and photosensitization efficiency are found to depend on the porosity of the samples. The singlet oxygen generation efficiency increases strongly for porous silicon with high (>80%) porosity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||