Low PO2 Research Articles

Combined resistive and thermoelectric oxygen sensor with almost temperature-independent characteristics

Abstract. The present study is focused in two directions. In the first part, BaFe(1-x)-0.01Al0.01TaxO3−δ (BFATx) thick films with a Ta content between 0.1 and 0.4 were manufactured using the novel room temperature coating method “aerosol deposition” (ADM), and its material properties were characterized to find the best composition of BFATx for temperature-independent oxygen sensors. The material properties “Seebeck coefficient” and “conductivity” were determined between 600 and 800 ∘C at different oxygen partial pressures. BaFe0.69Al0.01Ta0.3O3−δ (BFAT30) was found out to be very promising due to the almost temperature-independent behavior of both the conductivity and the Seebeck coefficient. In the second part of this study, films of BFAT30 were prepared on a special transducer that includes a heater, equipotential layers, and special electrode structures so that a combined direct thermoelectric/resistive oxygen sensor of BFAT30 with almost temperature-independent characteristics of both measurands, Seebeck coefficient and conductance could be realized. At high oxygen partial pressures (pO2 > 10−5 bar), the electrical conductance of the sensor shows an oxygen sensitivity of m = 0.24 (with m being the slope in the logσ vs. logpO2 representation according to the behavior of σαpO2m), while the Seebeck coefficient changes with a slope of −38 µV K−1 per decade of pO2 at 700 ∘C. However, at low pO2 (pO2 < 10−14 bar) the conductance and the Seebeck coefficient change with pO2, with a slope of m = −0.23 and −21.2 µV K−1 per decade pO2, respectively.

Contrasting P acquisition strategies of the bacterial communities associated with legume and grass in subtropical orchard soil.

Phosphorus (P) cycling is a fundamental process driven by microorganisms, and plants can regulate P cycling directly or via their influence on the soil microbial community. However, the differential P cycling patterns associated with legumes and grass are largely unknown. Therefore, we investigated the microbial community involved in P cycling in subtropical soil grown with stylo (Stylosanthes guianensis, legume) or bahiagrass (Paspalum notatum, grass) using metagenomic sequencing. P fractionation indicated that sparingly soluble inorganic P (Pi) accounted for approximately 75% of P pool. Bacteria involved in sparingly soluble Pi solubilization (pqq, gad, JEN) were more abundant in bahiagrass soil, with Candidatus Pelagibacter, Trichodesmium, Neorickettsia, Nitrobacter, Paraburkholderia, Candidatus Solibacter, Burkholderia as major contributors. In contrast, bacteria involved in organic P (Po) mineralization (php, glpQ, phn) were more abundant in stylo soil, consistent with phosphatase activity and Frankia, Kyrpidia, Thermobispora, Streptomyces, Rhodococcus were major contributors. Bacteria taking up low molecular-weight Po were more abundant in stylo soil than in bahiagrass soil, while those taking up Pi were less abundant. These data suggest that bacterial communities associated with legumes and grass develop contrasting P acquisition strategies, highlighting the possibility of intercropping with legumes and grass for better P cycling.

EPR-based oximetric imaging: a combination of single point-based spatial encoding and T1 weighting.

Spin-lattice relaxation rate (R1 )-based time-domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl-based Oxo71. The R1 dependence of the trityl probe Oxo71 on partial oxygen pressure (pO2 ) was assessed using single-point imaging mode of spatial encoding combined with rapid repetition, similar to T1 -weighted MRI, for which R1 was determined from 22 repetition times ranging from 2.1 to 40.0 μs at 300 MHz. The pO2 maps of a phantom with 3 tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2%, and 5% oxygen were determined by R1 and apparent spin-spin relaxation rate ( R2*) simultaneously. The pO2 maps derived from R1 and R2* agreed with the known pO2 levels in the tubes of Oxo71. However, the histograms of pO2 revealed that R1 offers better pO2 resolution than R2* in low pO2 regions. The SDs of pixels at 2% pO2 (15.2 mmHg) were about 5 times lower in R1 -based estimation than R2*-based estimation (mean ± SD: 13.9 ± 1.77 mmHg and 18.3 ± 8.70 mmHg, respectively). The in vivo pO2 map obtained from R1 -based assessment displayed a homogeneous profile in low pO2 regions in tumor xenografts, consistent with previous reports on R2*-based oximetric imaging. The scan time to obtain the R1 map can be significantly reduced using 3 repetition times ranging from 4.0 to 12.0 μs. Using the single-point imaging modality, R1 -based oximetry imaging with useful spatial and oxygen resolutions for small animals was demonstrated.

Urinary hypoxia: an intraoperative marker of risk of cardiac surgery-associated acute kidney injury.

Acute kidney injury (AKI) is common after cardiac surgery and profoundly affects postoperative mortality and morbidity. There are no validated methods to assess risk of AKI intraoperatively. We determined the association between postoperative AKI and intraoperative urinary oxygen tension (PO2), measured via a fiber optic probe in the tip of the urinary catheter, in 65 patients undergoing high-risk cardiac surgery requiring cardiopulmonary bypass (CPB). AKI was diagnosed by modified Kidney Disease: Improving Global Outcomes criteria. Urinary PO2 fell during the operation, often reaching its nadir during rewarming or after weaning from CPB. Nadir urinary PO2 was lower in the 26 patients who developed AKI (mean ± SD, 8.9 ± 5.6 mmHg) than in the 39 patients who did not (14.9 ± 10.2 mmHg, P = 0.008). Patients who developed AKI had longer periods of urinary PO2 ≤15 and 10 mmHg than patients who did not. Odds of AKI increased when urinary PO2 fell to ≤10 mmHg {3.60 [95% confidence interval (CI) 1.27-10.21]} or ≤5 mmHg [3.60 (95% CI 1.04-12.42), P = 0.04] during the operation. When urinary PO2 fell to ≤15 mmHg, for more than or equal to the median duration for all patients (4.8 min/h surgery), the odds of AKI were 4.85 (95% CI 1.64-14.40), P = 0.004. The area under the receiver-operator curve for this parameter alone was 0.69, and was 0.89 when other variables with P ≤ 0.10 in univariable analysis were included in the model. Low urinary PO2 during adult cardiac surgery requiring CPB predicts AKI, so may identify patients in which intervention to improve renal oxygenation might reduce the risk of AKI.

Role of glial-like type II cells as paracrine modulators of carotid body chemoreception.

Mammalian carotid bodies (CB) are chemosensory organs that mediate compensatory cardiorespiratory reflexes in response to low blood PO2 (hypoxemia) and elevated CO2/H+ (acid hypercapnia). The chemoreceptors are glomus or type I cells that occur in clusters enveloped by neighboring glial-like type II cells. During chemoexcitation type I cells depolarize, leading to Ca2+-dependent release of several neurotransmitters, some excitatory and others inhibitory, that help shape the afferent carotid sinus nerve (CSN) discharge. Among the predominantly excitatory neurotransmitters are the purines ATP and adenosine, whereas dopamine (DA) is inhibitory in most species. There is a consensus that ATP and adenosine, acting via postsynaptic ionotropic P2X2/3 receptors and pre- and/or postsynaptic A2 receptors respectively, are major contributors to the increased CSN discharge during chemoexcitation. However, it has been proposed that the CB sensory output is also tuned by paracrine signaling pathways, involving glial-like type II cells. Indeed, type II cells express functional receptors for several excitatory neurochemicals released by type I cells including ATP, 5-HT, ACh, angiotensin II, and endothelin-1. Stimulation of the corresponding G protein-coupled receptors increases intracellular Ca2+, leading to the further release of ATP through pannexin-1 channels. Recent evidence suggests that other CB neurochemicals, e.g., histamine and DA, may actually inhibit Ca2+ signaling in subpopulations of type II cells. Here, we review evidence supporting neurotransmitter-mediated crosstalk between type I and type II cells of the rat CB. We also consider the potential contribution of paracrine signaling and purinergic catabolic pathways to the integrated sensory output of the CB during chemotransduction.

Improvement of circumferential ductility by reducing discontinuities in a high-Mn TWIP steel weldment

Recently, high-frequency electrical resistance welded (HF-ERW) pipes have been introduced as an application of high-Mn twinning induced plasticity (TWIP) steels. However, the excellent ductility of the TWIP steels has been underutilized in expandable pipe applications due to discontinuities in the weldment. This work presents two key ways to improve the pipe expandability or circumferential ductility. In-depth microstructural analysis and flaring tests were conducted to identify bond line discontinuities and to evaluate the circumferential ductility. These results indicate that ductility formed to be strongly related to the welding atmosphere and post-weld heat treatment (PWHT) conditions. The welding atmosphere was related to oxide defects, while the PWHT conditions were related to intrinsic discontinuities. The distribution and amount of penetrator defects along the bond line are the main factors related to the deterioration of the circumferential ductility, which is affected by the sheet metal compositions and decreased remarkably at low PO2 content. We also suggest that PWHT is necessary for improving the ductility by inducing changes in the bond line texture and hardness distribution. The results were verified based on changes in the crack path propagation.

Strontium and carbon isotopic evidence for decoupling of pCO2 from continental weathering at the apex of the late Paleozoic glaciation

Earth's penultimate icehouse (ca. 340-285 Ma) was a time of low atmospheric pCO(2) and high pO(2), formation of the supercontinent Pangaea, dynamic glaciation in the Southern Hemisphere, and radiation of the oldest tropical rainforests. Although it has been long appreciated that these major tectonic, climatic, and biotic events left their signature on seawater Sr-87/Sr-86 through their influence on Sr fluxes to the ocean, the temporal resolution and precision of the late Paleozoic seawater Sr-87/Sr-86 record remain relatively low. Here we present a high-temporal-resolution and high-fidelity record of Carboniferous-early Permian seawater Sr-87/Sr-86 based on conodont bioapatite from an open-water carbonate slope succession in south China. The new data define a rate of long-term rise in Sr-87/Sr-86 (0.000035/m.y.) from ca. 334-318 Ma comparable to that of the middle to late Cenozoic. The onset of the rapid decline in Sr-87/Sr-86 (0.000043/m.y.), following a prolonged plateau (318-303 Ma), is constrained to ca. 303 Ma. A major decoupling of Sr-87/Sr-86 and pCO(2) during 303-297 Ma, coincident with the Paleozoic peak in pO(2), widespread low-latitude aridification, and demise of the pan-tropical wetland forests, suggests a major shift in the dominant influence on pCO(2) from continental weathering and organic carbon sequestration (as coals) on land to organic carbon burial in the ocean.

A mitochondrial-targeted antioxidant improves myofilament Ca2+ sensitivity during prolonged low frequency force depression at low PO2.

Skeletal muscle contractile activity is associated with an enhanced reactive oxygen species (ROS) generation. At very low PO2, ROS generation by mitochondria can be elevated in intact cells. An elevated intracellular oxidant activity may affect muscle force development and recovery from fatigue. We treated intact single muscle fibres with a mitochondrial antioxidant and stimulated the fibres to contract at a low extracellular PO2 that is similar to the intracellular PO2 that is observed during moderate to intense exercise in vivo. The mitochondrial antioxidant prevented a sustained decrease in the myofibrillar Ca2+ sensitivity and improved muscle submaximal force development after fatigue at low extracellular PO2. Skeletal muscle can develop a prolonged low frequency-stimulation force depression (PLFFD) following fatigue-inducing contractions. Increased levels of reactive oxygen species (ROS) have been implicated in the development of PLFFD. During exercise the skeletal muscle intracellular PO2 decreases to relatively low levels, and can be further decreased when there is an impairment in O2 diffusion or availability, such as in certain chronic diseases and during exercise at high altitude. Since ROS generation by mitochondria is elevated at very low PO2 in cells, we tested the hypothesis that treatment of muscle fibres with a mitochondrial-targeted antioxidant at a very low, near hypoxic, PO2 can attenuate PLFFD. We treated intact single fibres from mice with the mitochondrial-specific antioxidant SS31, and measured force development and intracellular [Ca2+ ] 30min after fatigue at an extracellular PO2 of ∼5Torr. After 30min following the end of the fatiguing contractions, fibres treated with SS31 showed significantly less impairment in force development compared to untreated fibres at submaximal frequencies of stimulation. The cytosolic peak [Ca2+ ] transients (peak [Ca2+ ]c ) were equally decreased in both groups compared to pre-fatigue values. The combined force and peak [Ca2+ ]c data demonstrated that myofibrillar Ca2+ sensitivity was diminished in the untreated fibres 30min after fatigue compared to pre-fatigue values, but Ca2+ sensitivity was unaltered in the SS31 treated fibres. These results demonstrate that at a very low PO2, treatment of skeletal muscle fibres with a mitochondrial antioxidant prevents a decrease in the myofibrillar Ca2+ sensitivity, which alleviates the fatigue induced PLFFD.

The quaternary state of polymerized human hemoglobin regulates oxygenation of breast cancer solid tumors: A theoretical and experimental study.

A major constraint in the treatment of cancer is inadequate oxygenation of the tumor mass, which can reduce chemotherapeutic efficacy. We hypothesize that polymerized human hemoglobin (PolyhHb) can be transfused into the systemic circulation to increase solid tumor oxygenation, and improve chemotherapeutic outcomes. By locking PolyhHb in the relaxed (R) quaternary state, oxygen (O2) offloading at low O2 tensions (<20 mm Hg) may be increased, while O2 offloading at high O2 tensions (>20 mm Hg) is facilitated with tense (T) state PolyhHb. Therefore, R-state PolyhHb may deliver significantly more O2 to hypoxic tissues. Biophysical parameters of T and R-state PolyhHb were used to populate a modified Krogh tissue cylinder model to assess O2 transport in a tumor. In general, we found that increasing the volume of transfused PolyhHb decreased the apparent viscosity of blood in the arteriole. In addition, we found that PolyhHb transfusion decreased the wall shear stress at large arteriole diameters (>20 μm), but increased wall shear stress for small arteriole diameters (<10 μm). Therefore, transfusion of PolyhHb may lead to elevated O2 delivery at low pO2. In addition, transfusion of R-state PolyhHb may be more effective than T-state PolyhHb for O2 delivery at similar transfusion volumes. Reduction in the apparent viscosity resulting from PolyhHb transfusion may result in significant changes in flow distributions throughout the tumor microcirculatory network. The difference in wall shear stress implies that PolyhHb may have a more significant effect in capillary beds through mechano-transduction. Periodic top-load transfusions of PolyhHb into mice bearing breast tumors confirmed the oxygenation potential of both PolyhHbs via reduced hypoxic volume, vascular density, tumor growth, and increased expression of hypoxia inducible genes. Tissue section analysis demonstrated primary PolyhHb clearance occurred in the liver and spleen indicating a minimal risk for renal damage.

Myoglobin: Oxygen Depot or Oxygen Transporter to Mitochondria? A Novel Mechanism of Myoglobin Deoxygenation in Cells (review).

In this review, we shortly summarize the data of our studies (and also corresponding studies of other authors) on the new mechanism of myoglobin (Mb) deoxygenation in a cell, according to which Mb acts as an oxygen transporter, and its affinity for the ligand, like in other transporting proteins, is regulated by the interaction with the target, in our case, mitochondria (Mch). We firstly found that contrary to previously formulated and commonly accepted concepts, oxymyoglobin (MbO2) deoxygenation occurs only via interaction of the protein with respiring mitochondria (low pO2 values are necessary but not sufficient for this process to proceed). Detailed studies of the mechanism of Mb-Mch interaction by various physicochemical methods using natural and artificial bilayer phospholipid membranes showed that: (i) the rate of MbO2 deoxygenation in the presence of respiring Mch fully coincides with the rate of O2 uptake by mitochondria from a solution irrespectively of their state (native coupled, freshly frozen, or FCCP-uncoupled), i.e. it is determined by the respiratory activity of Mch; (ii) Mb nonspecifically binds to membrane phospholipids of the outer mitochondrial membrane, while any Mb-specific protein or phospholipid sites on it are lacking; (iii) oxygen uptake by Mch from a solution and the uptake of Mb-bound oxygen are two different processes, as their rates are differently affected by proteins (e.g. lysozyme) that compete with MbO2 for binding to the mitochondrial membrane; (iv) electrostatic forces significantly contribute to the Mb-membrane interactions; the dependence of these interactions on ionic strength is provided by the local electrostatic interactions between anionic groups of phospholipids (the heads) and invariant Lys and Arg residues near the Mb heme pocket; (v) interactions of Mb with phospholipid membranes promote conformational changes in the protein, primarily in its heme pocket, without significant alterations in the protein secondary and tertiary structures; and (vi) Mb-membrane interactions lead to decrease in the affinity of myoglobin for O2, which could be monitored by the increase in the MbO2 autooxidation rate under aerobic conditions and under anaerobic ones, by the shift in the MbO2/Mb(2) equilibrium towards the ligand-free protein. The decrease in the affinity of Mb for the ligand should facilitate O2 dissociation from MbO2 at physiological pO2 values in cells.

Oxygen transport paths in screen-printed Pt-Al2O3 composite model electrodes on YSZ

In this work, Pt-Al2O3 composite electrodes without open porosity, screen-printed on polycrystalline YSZ, were analysed in order to identify relevant oxygen transport paths in thick-film electrodes. By using electrochemical impedance spectroscopy, the electrode processes were investigated at different oxygen partial pressures (pO2) and temperatures (T). Special sample layouts allowed the separation of three phase boundary (tpb) and electrode area-dependent transport processes. We found that the area-related transport path is dominating at low temperatures and high pO2, with a relatively low activation energy of 0.2 to 0.6eV and a pO2−0.7 dependence. In contrast, the tpb-related transport path dominates at high temperatures and low pO2, with activation energies between 0.8 and 1.4eV and a pO2−0.3 behaviour. A tracer experiment was performed additionally to visualize the location of oxygen incorporation below the electrode.

Oxygen Content and Thermodynamic Stability of YBaCo2O6−δ Double Perovskite

The thermodynamic stability of the double perovskite YBaCo2O6−δ was studied using the coulometric titration technique and verified by measurements of the overall conductivity depending on oxygen partial pressure at a given temperature. As a result, the stability diagram of YBaCo2O6−δ was plotted. YBaCo2O6−δ was found to be thermodynamically stable in air at 850°C and higher temperatures, whereas its thermodynamic stability at 900°C is limited by the range of oxygen partial pressures −3.56 ≤ log(pO2/atm) ≤ −0.14. Oxygen content in YBaCo2O6−δ slightly decreases at 900°C from 5.035 at log(pO2/atm) = −0.14 to 4.989 in the atmosphere with log(pO2/atm) = −3.565 indicating a crucial role which variation of Co+3/Co+2 ratio plays in its stability. YBaCo2O6−δ decomposes into the mixture of YCoO3 and BaCoO3−z at the high pO2 stability limit, whereas YBaCo4O7, BaCo1−xYxO3−γ, and Y2O3 were identified as the products of its decomposition at the low pO2 one.

Venous blood gas in free-living eastern box turtles (Terrapene carolina carolina) and effects of physiologic, demographic and environmental factors.

Sustainable wildlife populations depend on healthy individuals, and the approach to determine wellness of individuals is multifaceted. Blood gas analysis serves as a useful adjunctive diagnostic test for health assessment, but it is uncommonly applied to terrestrial reptiles. This study established reference intervals for venous blood gas panels in free-living eastern box turtles (Terrapene carolina carolina, N = 102) from Illinois and Tennessee, and modeled the effects of environmental and physiologic parameters on each blood gas analyte. Blood gas panels included pH, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), total carbon dioxide (TCO2), bicarbonate (HCO3-), base excess (BE) and lactate. Candidate sets of general linear models were constructed for each blood gas analyte and ranked using an information-theoretic approach (AIC). Season, packed cell volume (PCV) and activity level were the most important predictors for all blood gas analytes (P < 0.05). Elevations in PCV were associated with increases in pCO2 and lactate, and decreases in pH, pO2, HCO3-, TCO2 and BE. Turtles with quiet activity levels had lower pH and pO2 and higher pCO2 than bright individuals. pH, HCO3-, TCO2 and BE were lowest in the summer, while pCO2 and lactate were highest. Overall, blood pH was most acidic in quiet turtles with elevated PCVs during summer. Trends in the respiratory and metabolic components of the blood gas panel tended to be synergistic rather than antagonistic, demonstrating that either (1) mixed acid-base disturbances are common or (2) chelonian blood pH can reach extreme values prior to activation of compensatory mechanisms. This study shows that box turtle blood gas analytes depend on several physiologic and environmental parameters and the results serve as a baseline for future evaluation.

The Preference for Social Affiliation Renders Fish Willing to Accept Lower O2 Levels.

Animals are bombarded with information about their environment and must select and interpret the relevant cues to make behavioral adjustments critical to survival. How animals integrate and balance the many signals they receive about their environment is rarely assessed. We investigated how signals from the social and physical environment interact to influence environmental preferences in the endemic Tanganyikan cichlid Neolamprologus pulcher. Specifically, we explored how fish respond to the physiological challenge of declining O2 levels in light of embedded social preferences using a modified shuttle box apparatus to test O2 preferences. In the presence of a conspecific, the average (preferred) partial pressure of oxygen (Po2) and minimum Po2 experienced were significantly lower ([Formula: see text] and [Formula: see text] kPa, respectively) than in trials without a conspecific ([Formula: see text] and [Formula: see text] kPa, respectively). Fish with conspecifics also spent more time in the low Po2 zone of the shuttle box and moved between the high and low Po2 zones less frequently. Hence, O2 preferences were modified, and fish willingly remained in an area of continuously declining O2 availability to associate with a conspecific. The O2 preferences of an individual during social trials correlated with its excess postexercise O2 consumption following an exhaustive chase but not with its aerobic scope, routine O2 consumption rate, or body mass. These results suggest that some aspects of respiratory and metabolic physiology (such as the propensity to use anaerobic metabolism) but not others (such as O2 transport capacity) underpin some variation in social behavior under environmental stress.

Ferrous Iron Oxidation under Varying pO2 Levels: The Effect of Fe(III)/Al(III) Oxide Minerals and Organic Matter.

Abiotic Fe(II) oxidation by O2 commonly occurs in the presence of mineral sorbents and organic matter (OM) in soils and sediments; however, this tertiary system has rarely been studied. Therefore, we examined the impacts of mineral surfaces (goethite and γ-Al2O3) and organic matter [Suwannee River fulvic acid (SRFA)] on Fe(II) oxidation rates and the resulting Fe(III) (oxyhydr)oxides under 21 and 1% pO2 at pH 6. We tracked Fe dynamics by adding 57Fe(II) to 56Fe-labeled goethite and γ-Al2O3 and characterized the resulting solids using 57Fe Mössbauer spectroscopy. We found Fe(II) oxidation was slower at low pO2 and resulted in higher-crystallinity Fe(III) phases. Relative to oxidation of Fe(II)(aq) alone, both goethite and γ-Al2O3 surfaces increased Fe(II) oxidation rates regardless of pO2 levels, with goethite being the stronger catalyst. Goethite surfaces promoted the formation of crystalline goethite, while γ-Al2O3 favored nano/small particle or disordered goethite and some lepidocrocite; oxidation of Fe(II)aq alone favored lepidocrocite. SRFA reduced oxidation rates in all treatments except the mineral-free systems at 21% pO2, and SRFA decreased Fe(III) phase crystallinity, facilitating low-crystalline ferrihydrite in the absence of mineral sorbents, low-crystalline lepidocrocite in the presence of γ-Al2O3, but either crystalline goethite or ferrihydrite when goethite was present. This work highlights that the oxidation rate, the types of mineral surfaces, and OM control Fe(III) precipitate composition.

Hypoxia during VV ECMO

Venovenous extracorporeal membrane oxygenation (VV ECMO) is the preferred mode for any kind of acute respiratory failure. The desired PO2 is > 50 and SPO2 > 88% but the acceptable values can be PO2 > 45 and SPO2 > 80%. In case if we are accepting lower PO2, we have to keep a higher hematocrit and meticulously monitor neurological status, lactates, and urine output to maintain oxygen delivery. Saturation during ECMO run depends on ECMO circulation, native circulation, and ratio of ECMO flow to cardiac output ([Table 1]). Whenever the effective ECMO circulation decreases, saturation decreases. So, decrease in ECMO flow, ECMO FiO2, failing membrane oxygenator, and increase in recirculation will lead to hypoxia. Similarly, anything that decreases the contribution from native circulation will also lead to hypoxia. So, decrease in ventilator settings and worsening lung status lead to hypoxia. Anything that increases metabolism, such as fever and restlessness, will also cause hypoxia due to increased consumption.

Right ventricular dysfunction and Pre Implantation Vasopressors in Refractory ARDS Supported by VV-ECMO

Acute respiratory distress syndrome (ARDS) has been shown to be frequently associated with haemodynamic instability requiring the use of vasopressors. To date, there is still some uncertainty in the use of veno-venous Extracorporeal Membrane Oxygenation (VV-ECMO) in haemodynamically unstable ARDS patients. We therefore assessed whether patients receiving pre ECMO vasopressors had a worse prognosis and, furthermore, we reviewed the factors associated with the use of pre ECMO vasopressors in 92 consecutive patients with refractory ARDS treated with VV-ECMO. All patients were submitted to an echocardiogram before implantation. In our series, 55 patients (59.7%) were given a vasopressor. Septic shock is the main cause of vasopressor requirement (45.5%). When compared with patients without vasopressors, the subgroup under vasopressors showed a significantly higher sequential organ failure assessment (SOFA) score (p=0.040), a lower pH (p=0.013), lower pO2 values (p=0.030) and higher lactate levels (p=0.024). A higher incidence of right ventricular (RV) dysfunction and of biventricular dysfunction were observed in patients under vasopressors (p=0.018 and p=0.036, respectively). The intensive care unit (ICU) mortality rate was 43.4% (40/92) with no difference between the two subgroups. In refractory ARDS requiring VV-ECMO, infusion of vasopressors is needed in a high proportion of patients, who did not exhibit a worse prognosis when compared to haemodynamically stable patients. Pre ECMO echocardiography helps in characterising these patients since they showed a higher incidence of RV (and biventricular) dysfunction. According to our data, in ARDS patients refractory to conventional treatment, haemodynamic instability should not be considered a contraindication to VV-ECMO support.

Temperature dependence of partial conductivities of the BaZr0.7Ce0.2Y0.1O3-δ proton conductor

Partial conductivities are presented for BaZr0.7Ce0.2Y0.1O3-δ, an important proton conductor for protonic-ceramic fuel cells and membrane reactors. Atmospheric dependencies of impedance performed in humidified and dry O2, air, N2 and H2(10%)/N2(90%) in the temperature range 300–900 °C, supported by the modified emf method, confirm significant electron-hole and protonic contributions to transport. For very reducing and wet atmospheres, the conductivity is predominantly ionic, with a higher participation of protons with decreasing temperature and increasing water-vapour partial pressure (pH2O). From moderately reducing conditions of wet N2 to wet O2, however, the conductivity is considerably influenced by electron holes as revealed by a significant dependence of total conductivity on oxygen partial pressure (pO2). With higher pH2O, proton transport increases, with a concomitant decrease of holes and oxygen vacancies. However, the effect of pH2O is also influenced by temperature, with a greater protonic contribution at both lower temperature and pO2. Values of proton transport number tH ≈ 0.63 and electronic transport number th ≈ 0.37 are obtained at 600 °C for pH2O = 0.022 atm and pO2 = 0.2 atm, whereas tH ≈ 0.95 and th ≈ 0.05 for pO2 = 10−5 atm. A hydration enthalpy of −109 kJ mol−1 is obtained in the range 600–900 °C.

Influence of oxygen availability on the metabolism and morphology of Yarrowia lipolytica: insights into the impact of glucose levels on dimorphism.

Dynamic behavior of Yarrowia lipolytica W29 strain under conditions of fluctuating, low, and limited oxygen supply was characterized in batch and glucose-limited chemostat cultures. In batch cultures, transient oscillations between oxygen-rich and -deprived environments induced a slight citric acid accumulation (lower than 29mgL-1). By contrast, no citric acid was detected in continuous fermentations for all stress conditions: full anoxia (zero pO2 value, 100% N2), limited (zero pO2 value, 75% of cell needs), and low (pO2 close to 2%) dissolved oxygen (DO) levels. The macroscopic behavior (kinetic parameters, yields, viability) of Y. lipolytica was not significantly affected by the exposure to DO fluctuations under both modes of culture. Nevertheless, conditions of oxygen limitation resulted in the destabilization of the glucose-limited growth during the continuous cultivations. Morphological responses of Y. lipolytica to DO oscillations were different between batch and chemostat runs. Indeed, a yeast-to-mycelium transition was induced and progressively intensified during the batch fermentations (filamentous subpopulation reaching 74% (v/v)). While, in chemostat bioreactors, the culture consisted mainly of yeast-like cells (mean diameter not exceeding 5.7μm) with a normal size distribution. During the continuous cultures, growth at low DO concentration did not induce any changes in Y. lipolytica morphology. Dimorphism (up to 80.5% (v/v) of filaments) was only detected under conditions of oxygen limitation in the presence of a residual glucose excess (more than 0.75gL-1). These data suggest an impact of glucose levels on the signaling pathways regulating dimorphic responses in Y. lipolytica.

Electrochemical Study of (La0.6Sr0.4)0.99CoO3-δ Thin Film Microelectrodes

Solid Oxide Fuel/Electrolysis Cells (SOFC/SOEC, collectively termed SOC) are one of the most promising reversible energy conversion/storage technologies. Long term durability is required for such devices to become economically feasible. One approach to make SOCs more durable and at a lower cost is to decrease the operation temperature. However, lowering the operation temperature of SOCs has shown to be challenging due to the difficulty in finding suitable oxygen electrodes which have high catalytic activity for oxygen reduction and fast ionic transport. (La,Sr)CoO3-δ (LSC) is one of the promising cathode materials due to its high electronic and ionic conductivity as well as good catalytic activity for oxygen reduction at intermediate temperatures (500-700 °C)1. However, LSC is characterized by low chemical stability. Multiple degradation mechanisms are reported for LSC such as zirconate formation due to reactivity with YSZ (electrolyte) at operating temperature, decomposition at low pO2, SrO enrichment of and precipitation at the surface2 and Cr poisoning3 , 4. Several studies on the electrochemical properties of oxygen electrode materials are reported in the literature. Most of the studies are performed on porous electrodes with the purpose of having a realistic scenario; however we still lack fundamental understanding of the underlying degradation mechanism. Even though porous electrode studies have provided invaluable information about the degradation of the oxygen electrode, the deconvolution of geometrical effects from the intrinsic properties of the material is very difficult. Therefore, the presented work aims to study the oxygen reduction mechanism using geometrically well-defined dense model electrodes. Gd doped CeO2 (CGO) was deposited on polished single crystals YSZ (100) and on top of the CGO layer was deposited a (La0.6Sr0.4)0.99CoO3-δ(LSC40) using pulsed laser deposition (PLD). The thin CGO film (~100 nm) was deposited to avoid any reaction between the YSZ and LSC40 (250 nm). Subsequently, using photolithography and ion beam etching the microelectrode arrays with varying diameters (from 100 µm to 5 µm) were produced. Each sample has 4 macro-electrodes which were used as counter-electrode while performing electrochemical measurements. To observe the effect of temperature on the film microstructure and chemistry one sample was heat treated for 16 hours. SEM images, AFM and ToF-SIMS reveal similar behavior for both heat treated and as-deposited films. ToF-SIMS depth profiling reveals a Sr and Co rich surface compared to the bulk of the LSC40 for both samples. The difference between the two samples are in the distribution of common impurities, such as silica. After the heat treatment, the Si signal is higher in the LSC/CGO and CGO/YSZ interfaces (See Figure 1 a-b)). The electrochemical measurements were recorded in a Controlled Atmosphere High Temperature Scanning Probe Microscope (CAHT-SPM)5which can reach temperatures up to 850 °C. The impedance spectra reveal a high frequency intercept which is related to the conductivity of the electrolyte, a small arc at high/middle frequencies originating from the electrode electrolyte interface, and finally a low frequency arc which is related to the air electrode interface. The evolution of the impedance spectra with changing temperature, atmosphere, polarization and microelectrode size combined with surface chemical analysis and imaging techniques reveals information about the underlying degradation mechanism of LSC electrodes. 1. Adler, S. B. Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes. Chem. Rev. 104,4791–4843 (2004). 2. Lee, W., Han, J. W., Chen, Y., Cai, Z. & Yildiz, B. Cation Size Mismatch and Charge Interactions Drive Dopant Segregation at the Surfaces of Manganite Perovskites. J. Am. Chem. Soc. 135,7909–7925 (2013). 3. Zhao, L., Drennan, J., Kong, C., Amarasinghe, S. & Jiang, S. P. Insight into Surface Segregation and Chromium Deposition on La0.6Sr0.4Co0.2Fe0.8O3-δ Cathodes of Solid Oxide Fuel Cells. J. Mater. Chem. A 2,11114–11123 (2014). 4. Fergus, J. W. Effect of Cathode and Electrolyte Transport Properties on Chromium Poisoning in Solid Oxide Fuel Cells. Int. J. Hydrogen Energy 32,3664–3671 (2007). 5. Hansen, K. V., Wu, Y., Jacobsen, T., Mogensen, M. B. & Theil Kuhn, L. Improved Controlled Atmosphere High Temperature Scanning Probe Microscope. Rev. Sci. Instrum. 84, 73701 (2013). Figure 1