Oxygen Transport Measurements Research Articles

Tuning defect nonequilibrium of brownmillerite Sr1+xY2-xO4+δ for rich-oxygen-vacancy direct ammonia solid oxide fuel cells cathode

We prepared brownmillerite SrR2O4+δ (SRO, R = Y, Yb, Gd, Sm) with n-type semiconductors, where SYO is the most negative in conduction band and the smallest in band gap. And it is easy for the electrons to overcome energy barrier. As a result, SYO-based solid oxide fuel cells (SOFC) can offer a maximum power density (MPD) of 1.03 W/cm−2 at 800 °C, which is higher than that based on other three SRO oxides. Due to the enlargement of SYO unit cells and reduction of bond energy, the introduction of Sr2+ at B sites of Sr1+xY2-xO4+δ [SYO(x)] causes decrease of band gap, resulting in a 4-fold increase of electronic conductivity. The foreign Sr2+ tunes oxygen non-stoichiometry and creates surface oxygen vacancies to boost interfacial transport. The measurement of oxygen transport reveals that SYO(0.10) exhibits a bulk diffusion coefficient 500 folds higher than that of La0.7Sr0.3MnO3 (LSM). An anode supported Ni-YSZ|YSZ|SYO(0.10)-60YSZ direct ammonia solid oxide fuel cells (DA-SOFC) yields an MPD of 0.24 W/cm2 at 600 °C and 1.21 W/cm2 at 800 °C, about 1.73- and 1.29-folds higher than that of LSM-based SOFC, respectively. SYO(0.10)-based DA-SOFC can continuously operate at 800 °C for 100 h without significant degradation, displaying high thermal and operation stability.

Measurement of Oxygen Transport through Separators in Flooded Batteries

An in-depth understanding of oxygen transport in flooded lead acid batteries is necessary to better understand and mitigate water loss in the next generation of batteries for start-stop vehicle applications. The presence of the oxygen cycle leads to a lower rate of water loss observed during intermittent drive cycle testing compared to the gassing that would be calculated from the integrated overcharge current into the battery [1]. A model of the oxygen cycle in flooded lead acid batteries has been proposed [2] but until recently the oxygen transport through the separator-electrolyte system hasn’t been measured.A method for measuring oxygen transport through the separator-electrolyte system has been developed which uses electrodes harvested from commercial batteries. In this method, the separator is sealed between two chambers of a test cell, one containing the positive electrode and the other containing the negative electrode plus a reference. A constant stream of oxygen is delivered to the positive side of the cell using an air pump and diffuser. The negative side is purged, sealed and constantly stirred. The cell is charged and allowed to rest at OCV. Oxygen diffuses from the constant source on the positive side to the negative side where it oxidizes some of the negative active mass. This creates a measurable capacity change at the negative electrode which can be measured during a potentiostatically-controlled recharge cycle.We will report on measurements of oxygen transport through the separator-electrolyte system for different separator materials in a flooded cell using commercial lead acid electrodes. Results are compared with modeling of the oxygen cycle and related to factors in the separator which influence the oxygen transport rate, such as porosity, pore size distribution and tortuosity,.[1] Wirth, 16ELBC, 07 September 2018, Vienna Austria[2] Meissner, Scientific Workshop: High-Temperature Durability Tests for Advanced Lead 12-V Batteries, 30 January 2017, Kloster Eberbach, Germany

Effect of Catalyst Loading on the Degradation of d-PtCo/C Cathode Catalyst

The Consortium for Fuel Cell Performance and Durability (FC-PAD) was formed by the U.S. Department of Energy Fuel Cell Technologies office (FCTO) in 2015 to improve the understanding of performance and durability issues in polymer electrolyte membrane fuel cells (PEMFCs) and to help meet the DOE 2020 targets. This talk will summarize some of the durability work performed within the consortium on commercial dealloyed-PtCo/C catalyst-based membrane electrode assemblies (MEAs). Commercial MEAs using Nafion®HP membranes, ElystPt300670 (30wt.%PtCo/high surface area C) cathode catalyst, and ElystPt200380 (20wt.%Pt/Graphitized carbon) anode catalyst were obtained from Umicore. The MEAs were assembled in a 5cm2differential cell reported by D. R. Baker et al.1and conditioned extensively before performing beginning of life (BOL) characterization. The conditioning protocol included a recovery step where the cell was operated at high RH and low temperatures and voltages to flush out impurities and maximize the performance.2,3The samples were then subjected to the DOE-recommended square wave catalyst accelerated stress test (AST) which is a 3 sec hold at 0.6V and 3 sec hold at 0.95V at 80oC and 100%RH.4Characterizations were performed after 15,000 and 30,000 cycles of the AST with the recovery protocol applied to the MEA before characterization. Electrochemical characterization included mass activity, electrochemical surface area, polarization curves, Electrochemical Impedance Spectroscopy (EIS), and oxygen transport measurements. The BOL and end-of-test catalysts were also characterized by electron microscopy, energy dispersive X-ray spectroscopy, X-ray absorption spectroscopy, and small-angle X-ray scattering to determine particle size and Pt to Co content. The oxygen reduction reaction mass activity, electrochemical surface area, and performance in the kinetic region of the catalysts degrade with AST cycling. This loss can be attributed to both Co leaching from the catalyst and catalyst particle size increase. The effect of this degradation was most pronounced in the high current region for the MEA with low Pt loading. For example, in Figure 1, the voltage loss at 1A/cm2after 30,000 AST cycles is ~50mV for the 0.15mgPt/cm2MEA and ~200mV for the 0.05mgPt/cm2MEA. This is primarily due to increases in the pressure-independent oxygen transport resistance. The non-Fickian oxygen transport resistance of low-loaded (0.05 mgPt/cm2) MEAs is significantly larger than those of the high-loaded MEAs even at BOL and worsens significantly with ageing of the catalyst. EIS experiments in HelOx (21% O2, balance He) also revealed that there was an increase in the pressure-dependent gas transport during the AST cycling. However, little or no change was observed in the ionomer sheet resistance over the course of the durability testing, independent of the catalyst loading. These results will be compared with recent results reported for pure Pt catalyst-based MEAs subjected to similar tests.5In this talk, the analysis of the cathode catalyst composition and morphology before and after the testing will be presented in detail and correlated to the observed performance losses. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos and Technical Development Manager: Greg Kleen). References D. R. Baker, D. A. Caulk, K. C. Neyerlin, and M. W. Murphy, J. Electrochem. Soc.,V156(9), B991-B1003 (2009). https://doi.org/10.1149/1.3152226.Zhang, B. A. Litteer, F. D. Coms, and R. Makharia,. J. Electrochem. Soc., V159(7),F287-F293 (2012). https://doi.org/10.1149/2.063207jes.Zhang et al, U.S Patent Application Publication US 2011/0195324 A1, August 11 (2001).United States Department of Energy Fuel Cells Technologies Office Multi-Year Research, Development, and Demonstration Plan. https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf.G. S. Harzer, J. N. Schwammiein, A. M. Damjanovic, S. Ghosh, and H. A. Gasteiger, J. Electrochem. Soc.,V165(6), F3118-F3131 (2018). https://doi.org/10.1149/2.0161806jes Figure 1

Development and oxygen scavenging performance of three‐layer active PET films for food packaging

ABSTRACTPolymeric active materials represent an innovative food packaging concept that has been introduced to improve the quality of foods and to enhance their shelf life. In this article, the effect of the inclusion of an oxygen scavenger in a polymeric matrix, realizing multilayer active polyester films by coextrusion process, is analyzed. In particular, three layer active films, at different mass ratios of the layers, were produced to form symmetrical "ABA" structures comprising polyethylene terephthalate (PET) with a polymeric oxygen scavenger (OS) as core layer and pure PET as external layers. Oxygen scavenging tests conducted on the multilayer active structures have pointed out the role of the relative layer thickness in controlling the scavenging capacity, the activity time and the oxygen absorption rate. A modeling of the scavenging phenomena, which combines a quasi steady‐state distribution in the skin layers with a flat profile of O2content in the active core layer, can explain the experimentally observed oxygen absorption rate at short times. Moreover, steady state oxygen transport measurements, performed when the scavenger reactive capacity is exhausted, have shown that the presence of the active phase slightly reduces the O2permeability, compared with the neat PET. The effect, which progressively increases with the amount of active phase in the film formulation, was related to the different morphological state developed on processing. Finally, preliminary shelf life tests on fresh‐cut untreated apples suggest that the developed three layer active films have a significant potential in the shelf‐life extension of oxygen sensitive food products. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 41465.

Clinical Hemodynamic Parameters Do Not Accurately Reflect Systemic Oxygen Transport in Neonates after the Norwood Procedure.

Clinical hemodynamic parameters (heart rate, systolic arterial pressure [SAP], and arterial and venous oxygen saturation saturations [SaO2 and SvO2 ]) are commonly used to guide management to optimize oxygen transport after the Norwood procedure. The adequacy of this practice has not been demonstrated. We examined the correlations between these clinical parameters and direct measurements of oxygen transport in these patients. Oxygen consumption (VO2 ) was measured using respiratory mass spectrometry for 72 hours in 17 neonates after the Norwood procedure. Arterial, superior vena caval, and pulmonary venous blood gases and pressures were measured at intervals of 2-4 hours to calculate cardiac output (CO), systemic and pulmonary blood flows (Qs , Qp), systemic vascular resistance (SVR), total pulmonary vascular resistance including the Blalock-Taussig shunt (tPVR), oxygen delivery (DO2), and extraction ratio (ERO2 ). Heart rate and SAP were also recorded. Heart rate was positively correlated with VO2 (P = .004) and ERO2 (P = .005). SAP was positively correlated with CO (P = .006), VO2 (P = .02), ERO2 (P = .01), and SVR (P = .08). SaO2 was negatively correlated with tPVR, Qs, and DO2 but positively with Qp and SVR (P < .05 for all). SvO2 was positively correlated with CO, Qs , and DO2 (P < .0001 for all) and negatively correlated with SVR, VO2, and ERO2 (P < .05 for all). Routine clinical hemodynamic parameters do not accurately reflect oxygen transport after the Norwood procedure, except for SvO2, which does not differentiate between VO2 and DO2. Higher heart rate and SAP are correlated with a worse balance of oxygen transport. The results of clinical hemodynamic monitoring should be interpreted with caution. Direct measurements of oxygen transport parameters are important in the care of neonates after the Norwood procedure.

Determination of Oxygen Permeability in Acrylic‐Based Hydrogels by Proton NMR Spectroscopy and Imaging

Polymer network membranes with a high capacity for water absorption are obtained by radical polymerization ofN‐[2‐(2‐hydroxyethoxy)ethyl]methacrylamide (HEEMAM). The permeability, solubility, and diffusion coefficients of oxygen in hydrogels are determined using nuclear magnetic resonance (NMR) methods based on the paramagnetic effect of dissolved oxygen gas on the proton spin‐lattice relaxation times of water, and the results are compared with those obtained with electrochemical procedures. The results of NMR measurements of oxygen transport coefficients in distilled water show excellent agreement with corresponding literature values. The results of the potentiostatic and NMR oxygen transport measurements in hydrogels are in reasonable agreement and support the viability of the NMR method.image

Measurement of oxygen transport in La0.8Sr0.2MnO3 perovskite grains

In this work values for the diffusion coefficient, D*, and surface exchange coefficient, k*, have been obtained from individual La0.8Sr0.2MnO3 perovskite grains. Oxygen tracer diffusion profiles were created via the well established isotope exchange techniques. The tracer diffusion profiles were then measured using a FIB-SIMS workstation. Several measurements were taken over randomly selected grains including un-faceted and faceted grains. The values for D* and k* obtained compared very well with previous measurements made on bulk La0.8Sr0.2MnO3 samples i.e. over many grains. The results therefore indicate that D* and k* are independent of orientation. Furthermore the diffusion profiles indicated that only one single grain had been SIMS depth profiled and did not cross a grain boundary. Also by analysing in the centre of large grains, and not analysing up to the edge of the grains, no grain boundary diffusion was observed. Finally, the work also confirms that previous measurements of k* on this material have been correctly measured and not under estimated due to experimental errors.

Perioperative cerebral and somatic oxygenation in neonates with hypoplastic left heart syndrome or transposition of the great arteries

Significant depression in cerebral oxygen saturation has been observed in patients with hypoplastic left heart syndrome (HLHS) undergoing Norwood operations. We monitored cerebral oxygen saturation with near-infrared spectroscopy before and after this procedure. Patients with transposition of great arteries (TGA) before and after arterial switch operation were also studied to elucidate whether post-cardiopulmonary bypass (CPB) changes in cerebral oxygen saturation are related to CPB or hemodynamic alterations inherent in single-ventricle physiology. We monitored 33 patients with HLHS and 20 with TGA 24 hours before and 48 hours after CPB. In addition to cerebral oxygen saturation, routine measurements of oxygen transport and delivery were performed. Preoperatively, cerebral oxygen saturation was higher in patients with HLHS than with TGA (61% ± 7% vs 56% ± 8%, P = .04). After CPB, cerebral oxygen saturation was markedly depressed in both groups but increased toward end of monitoring (HLHS vs TGA minimal value 42% ± 12% vs 54% ± 11%, P < .001, value 48 hours after CPB 62% ± 7% vs 80% ± 8%, P < .0001). Routine measures of oxygen delivery, such as arterial and central venous oxygen saturations, were similar at minimal cerebral oxygen saturation and 48 hours after CPB. Depression of cerebral oxygen saturation is prevalent among neonates with congenital heart disease regardless of whether univentricular or biventricular circulation is present, suggesting that cerebral desaturation is mainly induced by CPB's effect on cerebral blood flow. Routine measures of oxygen delivery fail to indicate cerebral desaturation.

Real-time measurement of oxygen transport across an oil–water emulsion interface

A method for real-time, in situ measurement of oxygen transport across oil-in-water emulsion interface was developed. This method is based on reversible fluorescence quenching of tris ruthenium (II) bis (hexafluorophosphate) complex dye encapsulated in the oil phase of an emulsion upon interaction with oxygen. Oxygen transport across the oil–water interface for four different emulsions (whey protein isolate (WPI), sodium-dodecyl sulphate (SDS), cross-linked WPI and SDS–chitosan emulsions) was measured and effective diffusion coefficients were calculated. Results show that cross-linking of WPI did not alter the oxygen transport rate ( p > 0.01), while addition of a chitosan layer to the SDS emulsion significantly reduced the oxygen transport rate ( p < 0.01). An increase in temperature from 25 to 40 °C reduced the oxygen transport rate in WPI and cross-linked WPI emulsions ( p < 0.01). Effective diffusion coefficient values for transport of oxygen based on fluorescence data were 0.14–1.15 × 10 −12 cm 2/s for the tested emulsions. Regardless of relatively low effective diffusion coefficients, the selected emulsions exhibited poor barrier properties in limiting oxygen transport across an emulsion interface. In summary, this rapid method is sensitive to detect changes in rate of oxygen transport due to changes in temperature and chemical composition of emulsion interface. This method can be used to screen and evaluate the barrier properties of encapsulation matrices leading to rational design of encapsulated structures.

Erythrocytes: surveyors as well as purveyors of oxygen?

for more than a century a large body of evidence has accumulated in the physiological and pathophysiological literature to support the close relationship between the demand of oxygen by the tissues and the supply of oxygen by the cardiorespiratory system. When the demand for oxygen changes, how is

Systemic central venous oxygen saturation is associated with clot strength during traumatic hemorrhagic shock: A preclinical observational model

BackgroundClot strength by Thrombelastography (TEG) is associated with mortality during trauma and has been linked to severity of tissue hypoperfusion. However, the optimal method for monitoring this important relationship remains undefined. We hypothesize that oxygen transport measurements will be associated with clot strength during traumatic shock, and test this hypothesis using a swine model of controlled traumatic shock.MethodsN = 33 swine were subjected to femur fracture and hemorrhagic shock by controlled arterial bleeding to a predetermined level of oxygen debt measured by continuous indirect calorimetry. Hemodynamics, oxygen consumption, systemic central venous oxygenation (ScvO2), base excess, lactate, and clot maximal amplitude by TEG (TEG-MA) as clot strength were measured at baseline and again when oxygen debt = 80 ml/kg during shock. Oxygen transport and metabolic markers of tissue perfusion were then evaluated for significant associations with TEG-MA. Forward stepwise selection was then used to create regression models identifying the strongest associations between oxygen transport and TEG-MA independent of other known determinants of clot strength.ResultsMultiple markers of tissue perfusion, oxygen transport, and TEG-MA were all significantly altered during shock compared to baseline measurements (p < 0.05). However, only ScvO2 demonstrated a strong bivariate association with TEG-MA measured during shock (R = 0.7, p < 0.001). ScvO2 measured during shock was also selected by forward stepwise selection as an important covariate in linear regression models of TEG-MA after adjusting for the covariates fibrinogen, pH, platelet count, and hematocrit (Whole model R2 = 0.99, p ≤ 0.032).ConclusionsAmong multiple measurements of oxygen transport, only ScvO2 was found to retain a significant association with TEG-MA during shock after adjusting for multiple covariates. ScvO2 should be further studied for its utility as a clinical marker of both tissue hypoxia and clot formation during traumatic shock.

Effects of levosimendan in normodynamic endotoxaemia: a controlled experimental study

Levosimendan is an inotropic and vasodilator drug that has proved to be useful in cardiogenic shock. Pretreatment with levosimendan in experimental hypodynamic septic shock in pigs has shown valuable effects in oxygen transport. Our goal was to assess the effects of levosimendan in a normodynamic model of endotoxaemia. Twelve sheep were anaesthetized and mechanically ventilated. After taking basal haemodynamic and oxygen transport measurements, sheep were assigned to two groups during 120 min: (1) endotoxin (5 microg/kg endotoxin); (2) levosimendan (5 microg/kg endotoxin plus levosimendan 200 microg/kg followed by 200 microg/kg/h). Both groups received hydration of 20 ml/kg/h of saline solution. In the endotoxin group, cardiac output, intestinal blood flow and systemic and intestinal oxygen transports and consumptions (DO(2) and VO(2)) remained unchanged. In the levosimendan group, systemic and intestinal DO(2) were significantly higher than in the endotoxin group. Because stroke volume did not change (basal versus 120': 0.9+/-0.1 ml/kg versus 0.9+/-0.2 ml/kg, p=0.3749), the elevation in cardiac output by levosimendan (145+/-17 ml/min/kg versus 198+/-16 ml/min/kg, p=0.0096) was related to an increased heart rate (159+/-32 beats l/min versus 216+/-19 beats l/min, p=0.0037). Levosimendan precluded the development of gut intramucosal acidosis at 120' (endotoxin versus levosimendan, ileal intramucosal-arterial PCO(2) difference: 19+/-4 Torr versus 10+/-4 Torr, p=0.0025). However, levosimendan decreased mean arterial blood pressure (99+/-20 Torr versus 63+/-13 Torr, p=0.0235) and increased blood lactate levels (2.4+/-0.9 mmol/l versus 4.8+/-1.5 mmol/l, p=0.0479). All p-values are differences in specific points (paired or unpaired t-test with Bonferroni correction) after two-way repeated measures ANOVA. A p-value<0.05 was considered significant. Levosimendan improved oxygen transport and prevented the development of intramucosal acidosis in this experimental model of endotoxaemia. However, systemic hypotension and lactic acidosis occurred. Additional studies are needed to show if different doses and timing of levosimendan administration in septic shock might improve gut perfusion without adverse effects.

A New Video Image Analysis System to Study Red Blood Cell Dynamics and Oxygenation in Capillary Networks

The authors present a Measurement and Analysis System for Capillary Oxygen Transport (MASCOT) to study red blood cell (RBC) dynamics and oxygenation in capillary networks. The system enables analysis of capillaries to study geometry and morphology and provides values for capillary parameters such as diameter and segment length. It also serves as an analysis tool for capillary RBC flow characteristics, including RBC velocity, lineal density, and supply rate. Furthermore, the system provides a means of determining the oxygen saturation of hemoglobin contained within RBCs, by analysis of synchronized videotapes containing images at two wavelengths, enabling the quantification of the oxygen content of individual RBCs. Video recordings of RBC flow at two wavelengths, 420 nm (isosbestic) and 436 nm (oxygen sensitive), are made using a dual camera video microscopy system. The 420-nm recording is used to generate images based on the variance of light intensity fluctuations that help to identify capillaries in a given field of view that are in sharp focus and exhibit flow of individual RBCs separated by plasma gaps. A region of interest enclosing the desired capillary is defined and a fixed number of successive video frames at the two wavelengths are captured. Next a difference image is created, which delineates the RBC column, whose width is used to estimate the internal diameter of the capillary. The 420-nm images are also used to identify the location and centroid of each RBC within the capillary. A space-time image is generated to compute the average RBC velocity. Lineal density is calculated as the number of RBCs per unit length of a capillary segment. The mean optical density (OD) of each RBC is calculated at both wavelengths, and the average SO(2) for each cell is determined from OD(436)/OD(420). MASCOT is a robust and flexible system that requires simple hardware, including a SGI workstation fitted with an audio-visual module, a VCR, and an oscilloscope. Since the new system provides information on an individual cell basis from entire capillary segments, the authors believe that results obtained using MASCOT will be more accurate than those obtained from previous systems. Due to its flexibility and ease of extension to other applications, MASCOT has the potential to be applied widely as an analysis tool for capillary oxygen transport measurements.

Improving transparency of stretched PET/MXD6 blends by modifying PET with isophthalate

Compatibilized blends of PET and MXD6 have good transparency because their refractive indices match closely. However, haziness is observed when the blends are stretched because stretching imparts greater refractive index anisotropy to PET than to MXD6. Analysis of the strain-dependent birefringence reveals that different molecular deformation models describe the intrinsic birefringence of PET and MXD6. This study focuses on reducing the intrinsic birefringence of PET by partially replacing terephthalate with isophthalate. Statistical copolymers are prepared by conventional copolymerization of the monomers. Alternatively, blocky copolymers are obtained by melt blending PET with poly(ethylene isophthalate) (PEI). A close refractive index match with stretched MXD6 is achieved with copolymers containing 15–20% isophthalate. Statistical copolymers in this composition range are not satisfactory for blending because they have low molecular weight and are difficult to stretch. However, blocky copolymers containing 15–20% isophthalate form blends that stretch readily. After biaxial stretching, transparency of blends with 10 wt% MXD6 approaches that of PET. Good transparency of the blends is validated with stretch-blown bottle walls. Oxygen transport measurements confirm that partial replacement of terephthalate with isophthalate does not affect the good gas barrier properties of biaxially stretched PET blends.

Determination of Chemical Diffusion and Surface Exchange Coefficients of Oxygen by Electrochemical Impedance Spectroscopy

A rigorous mathematical model is developed for the complex impedance of a solid-state electrochemical cell, which is commonly used for the measurement of oxygen transport, oxygen exchange kinetics, and thermodynamic properties of nonstoichiometric mixed conducting oxides. The model leads to a simple equivalent circuit for the cell with unambiguous definition of the physical significance of its components. A method is proposed for the analysis of experimental data. The methodology thus developed is validated by comparing the experimental data measured for a well-studied perovskite with the results obtained from the completely equivalent potential-step technique. In addition, various electrochemical properties of the other cell components, such as Pt electrodes and yttria-stabilized zirconia electrolyte, also obtainable from measurements, show good agreement with the available literature data. The cell design, which significantly minimizes the gas space in contact with the sample, has a clear advantage over similar relaxation cells in terms of reducing the dominating effect of the gas-phase capacitance in numerical data analysis. A possible disadvantage, however, is the large impedance of the oxygen pump at low oxygen partial pressures, which may in a similar manner obstruct deconvolution of the sample properties from the measured data. © 2002 The Electrochemical Society. All rights reserved.

Measuring oxygen diffusion and oxygen surface exchange by conductivity relaxation

Abstract For materials that are predominantly electronic conductors and possess a materials property that changes with oxygen partial pressure then a ‘relaxation’ technique may be used to measure oxygen transport behaviour. Perhaps the simplest to implement is electrical conductivity relaxation. For many mixed conducting materials a change in the oxygen partial pressure will result in a corresponding change in the electrical conductivity of the material due to, primarily, a change in the concentration of charge carriers. If the ionic conductivity of a material is significantly less than its electronic conductivity then the time for this change to propagate throughout the material is almost exclusively controlled by the movement of ionic species. This change or ‘relaxation’ can be modelled and oxygen diffusion coefficients and surface exchange coefficients can be extracted from the data. This paper will discuss the measurement of oxygen transport in mixed-conducting ceramic oxides using the conductivity relaxation technique. Emphasis will be placed on the analysis of the ‘relaxation’ profile and the problems associated with determining oxygen diffusion coefficients and oxygen surface exchange coefficients simultaneously.

Hypoxic hepatitis caused by acute exacerbation of chronic respiratory failure: a case-controlled, hemodynamic study of 17 consecutive cases.

Out of a prospective series of 142 consecutive episodes of hypoxic (ischemic) hepatitis (HH), we identified 17 episodes associated with an acute exacerbation of chronic respiratory failure (CRF) without left cardiac failure. In the aim to evaluate the role of arterial hypoxemia in the pathogenesis of HH associated with respiratory failure, these 17 episodes of HH (study group) were hemodynamically compared with a control group of 17 episodes of HH associated with congestive heart failure (CHF) (control group 1) and a group of 16 episodes of acute respiratory failure (ARF) not complicated by HH (control group 2). Arterial hypoxemia was significantly more severe in the study group (arterial blood tension in O2 [PaO2], 34 mm Hg) than in control group 1 (PaO2, 70 mm Hg; P <.0001) and control group 2 (PaO2, 45.5 mm Hg; P =.002). The role of arterial hypoxemia, however, appeared weakened by comparable degrees of systemic hypotension and liver passive congestion in episodes of HH associated with CRF and episodes of HH associated with CHF. Finally, the causative role of arterial hypoxemia emerged from hemodynamic measurements of cardiac index (CI), systemic vascular resistances (SVR), and oxygen transport: systemic hypotension in HH associated with CHF (control group 1) was the result of a fall in CI (median, 2. 33 L/min. m2; range, 1.21-3.14 L/min. m2) associated with high SVR (median, 2,492 dyn. s/cm5. m2; range, 1,382-4,053 dyn. s/cm5. m2), whereas in HH associated with respiratory failure (study group), systemic hypotension was the result of a fall in SVR (median, 1,053 dyn. s/cm5. m2; range, 646-3,148 dyn. s/cm5. m2), resulting in high CI (median, 4.23 L/min. m2; range, 1.9-5.32 L/min. m2) (P =.0087 and. 0038 for cardiac index and SVR, respectively). Moreover, measurements of oxygen transport in patients with HH associated with respiratory failure showed low values of O2 delivery (DO2) (median, 376 mL/min. m2; range, 253-427 mL/min. m2) as a result of extreme arterial hypoxemia despite high CI. In conclusion, these hemodynamic results and additional measurements of hepatic blood flow (HBF) by the method of galactose clearance at a low concentration suggest that in the setting of HH associated with respiratory failure, the liver is not "ischemic," despite hypotension, but rather "hypoxic" as a result of the combination of severe arterial hypoxemia and elevated central venous pressure (CVP).

Oxygen Transport by Erythrocyte/Hemoglobin Solution Mixtures in anin VitroCapillary as a Model of Hemoglobin-Based Oxygen Carrier Performance

Oxygen transport behavior of erythrocyte/extracellular hemoglobin mixtures flowing in microvessels was studied as a model of hemoglobin-based oxygen carrier (HBOC) performance. An experimentalin vitro25-μm-diameter capillary model was used to provide detailed oxygen flux measurements for hemoglobin solutions, erythrocyte suspensions, and erythrocyte/hemoglobin solution mixtures. The experimental apparatus includes computerized data acquisition and control coupled to a dual wavelength microspectrophotomer. This apparatus had been previously validated by good agreement of experimental measurements with predictive mathematical models of oxygen transport for either erythrocyte suspensions or hemoglobin solutions. The experimental methodology was extended to measurement of oxygen transport in erythrocyte/hemoglobin solutions. The hemoglobin solutions consisted of either purified or gluteraldehyde polymerized bovine hemoglobin. Dose–response plots were generated by varying the extracellular to intracellular hemoglobin ratio while holding the overall hemoglobin concentration constant. Measurements were also made on unmixed erythrocyte suspensions and hemoglobin solutions to generate limiting cases for comparison. Direct comparison of experimental results showed that both types of hemoglobin solutions were substantially more efficient than erythrocyte suspension in uptake and release of oxygen. Increased extracellular hemoglobin concentration increased oxygen transport efficiency for both uptake and release, even when total hemoglobin concentration was held constant. When only 10% of the total hemoglobin was extracellular, approximately half of the increased efficiency of pure hemoglobin solutions was reached. When 50% of the total hemoglobin was extracellular, the increased efficiency was virtually equal to that of pure hemoglobin solutions.

Clinical assessment and measurement of oxygen transport in the critical care setting

Adequate delivery of oxygen to the tissues is an important factor both in the initial resuscitation of the shocked patient and subsequently in the development of multiple organ failure. The advent of the pulmonary artery catheter has facilitated the calculation of global measurements of oxygen transport at the bedside. Calculated oxygen delivery in fact represents arterial oxygen dispatch rather than actual oxygen delivery to the respiring tissues. Considerable controversy still surrounds the issue of resuscitation of critically ill patients to predetermined goals for oxygen delivery and consumption. More recently interest has arisen in other measures of oxygen transport, in particular regional techniques such as the gastric tonometer.

The Effect of Oxygen Delivery-Directed Resuscitation on Splanchnic and Hepatic Oxygen Transport after Hemorrhagic Shock

Background: Gut and hepatic dysfunction, during and after hypovolemic shock, have been implicated as causative mechanisms in the development of multiple system organ failure in the trauma patient. Current techniques of assessment of perfusion only detect changes in systemic oxygen transport. We designed an animal model that can measure changes in oxygen transport in the liver and gut during hypovolemic shock and resuscitation. Materials and methods: Animals were hemorrhaged to a mean arterial pressure (MAP) of 60 mm Hg and maintained at 60 mm Hg for 60 min. Animals were then assigned to one of three groups. Group I served as nontreatment controls. Group II received shed blood and saline in sufficient volumes to restore MAP to baseline. Group III animals were resuscitated with shed blood, saline, and donor blood to restore systemic oxygen delivery to the preshock value. Results: The animals resuscitated to their baseline systemic oxygen delivery, Group III, had significantly higher systemic, hepatic, and splanchnic oxygen delivery than the remaining groups. In addition, Group III had higher oxygen consumption, portal flow, and hepatic artery flow than the blood pressure-directed group, Group II. The decrease in oxygen extraction ratio in the gut and liver was significantly greater in Group III than in Group II. Conclusions: These data show that hepatic and gut vascular beds are better perfused when resuscitation from hemorrhage is guided by systemic oxygen transport measurements compared to resuscitation guided by blood pressure.