PO2 Gradient Research Articles

Transcapillary PO2 Gradients in Contracting Muscles of Type I Diabetic Rats.

This study aimed to clarify the effect of Type I diabetes (DIA) on transcapillary PO2 gradients, which are oxygen-driving factors between the blood and the interstitium, in the contracting muscle of rats. Wistar male rats were divided into the diabetic (streptozocin i.p.) and sham groups. Microvascular and interstitial PO2 were measured in the extensor digitorum longus muscle during electrical stimulation-induced muscle contraction, using the phosphorescence quenching method. Transcapillary PO2 gradient, ΔPO2, was calculated as microvascular minus interstitial PO2. Resting microvascular PO2 was higher in the diabetic group than in the sham group (6.3 ± 1.7 vs. 4.7 ± 0.9 mmHg, p < 0.05) and remained for 180 s. Interstitial PO2 from rest to muscle contraction did not differ between the groups. The ΔPO2 was higher in the diabetic group than in the sham group at rest and during muscle contraction (4.03 ± 1.42 vs. 2.46 ± 0.90 mmHg at rest; 3.67 ± 1.51 vs. 2.22 ± 0.65 mmHg during muscle contraction, p < 0.05). Marked muscle atrophy was observed in the diabetic group. DIA increased microvascular and transcapillary PO2 gradients in the skeletal muscle. The enhanced PO2 gradients were maintained from rest to muscle contraction in diabetic muscle.

Spatial O2 Profile in Coix lacryma-jobi and Sorghum bicolor along the Gas Diffusion Pathway under Waterlogging Conditions.

While internal aeration in plants is critical for adaptation to waterlogging, there is a gap in understanding the differences in oxygen diffusion gradients from shoots to roots between hypoxia-tolerant and -sensitive species. This study aims to elucidate the differences in tissue oxygen concentration at various locations on the shoot and root between a hypoxia-tolerant species and a -sensitive species using a microneedle sensor that allows for spatial oxygen profiling. Job's tears, a hypoxia-tolerant species, and sorghum, a hypoxia-susceptible species, were tested. Plants aged 10 days were acclimated to a hypoxic agar solution for 12 days. Oxygen was profiled near the root tip, root base, root shoot junction, stem, and leaf. An anatomical analysis was also performed on the roots used for the O2 profile. The oxygen partial pressure (pO2) values at the root base and tip of sorghum were significantly lower than that of the root of Job's tears. At the base of the root of Job's tears, pO2 rapidly decreased from the root cortex to the surface, indicating a function to inhibit oxygen leakage. No significant differences in pO2 between the species were identified in the shoot part. The root cortex to stele ratio was significantly higher from the root tip to the base in Job's tears compared to sorghum. The pO2 gradient began to differ greatly at the root shoot junction and root base longitudinally, and between the cortex and stele radially, between Job's tears and sorghum. Differences in the root oxygen retention capacity and the cortex to stele ratio are considered to be related to differences in pO2.

Do Vascular and Extracellular Measurements Consistently Reflect Intracellular pO2?

Oxygen measurements are routinely made either in the vasculature or in the extracellular fluid surrounding the cells of tissues. Yet, metabolic oxygen availability depends on the pO2 within the cells, as does the enhancing effect of oxygen on radiotherapy outcomes. This article reports quantitative modeling work examining the effect of cellular plasma membrane composition on tissue permeability, as a window into tissue oxygen gradients. Previous application of the model indicates that lipid-mediated diffusion pathways accelerate oxygen transfer from capillaries to intracellular compartments and that the extent of acceleration is modulated by membrane lipid and protein composition. Here, the effects of broken intercellular junctions and increased gap size between cells in the model are addressed. The conclusion is reached that the pO2 gradient will likely be consistent among similar, healthy tissues but may increase with increased interstitial fluid fraction and broken intercellular junctions. Therefore, tissue structural changes in tumors and other diseased or damaged tissues may lead to aberrations in permeability that confound interpretation of extracellular oxygen measurements.

Direct electrochemical detection of trans-plasma membrane electron transfer: A possible alternative pathway for cell respiration

An electrochemical protocol was designed to enable Vero cells to transfer electrons to an electrode without any added redox mediator. The cells were cultured on the surface of electrodes polarized at the optimal potential of 400 mV/silver pseudo-reference. Gold, carbon, and CNT-coated carbon electrodes displayed similar current record patterns. Extracellular electron transfer was sustained for several days. Its intensity, up to 1.5 pA.cell−1, was in the range of the electron flows implemented by cell respiration. A large fraction of the current vanished as soon as anoxic conditions were established, which suggests a mitochondrial origin for a large proportion of the electrons. The current records always showed a two-phase pattern. The occurrence of the two phases was not due to an evolution of the cell mat structure, which was fully established during the first day of polarization and did not change significantly thereafter. Increasing the cell seeding density decreased the maximum current reached during the first phase and the duration of the phase. These observations put together lead us to propose a model, in which only the cells adhered on the electrode surface produced current by metabolizing glutamine during the first phase. The possible role of this extracellular electron transfer as an alternative cell respiration pathway is discussed. The key roles it could play in regulating pH and pO2 gradients are considered, specifically to explain the pH gradient reversal observed in cancer cells. These pioneering results pave the way for electrochemical sensors to directly address cellular metabolic pathways.

Computational Modeling and Imaging of the Intracellular Oxygen Gradient.

Computational modeling can provide a mechanistic and quantitative framework for describing intracellular spatial heterogeneity of solutes such as oxygen partial pressure (pO2). This study develops and evaluates a finite-element model of oxygen-consuming mitochondrial bioenergetics using the COMSOL Multiphysics program. The model derives steady-state oxygen (O2) distributions from Fickian diffusion and Michaelis–Menten consumption kinetics in the mitochondria and cytoplasm. Intrinsic model parameters such as diffusivity and maximum consumption rate were estimated from previously published values for isolated and intact mitochondria. The model was compared with experimental data collected for the intracellular and mitochondrial pO2 levels in human cervical cancer cells (HeLa) in different respiratory states and under different levels of imposed pO2. Experimental pO2 gradients were measured using lifetime imaging of a Förster resonance energy transfer (FRET)-based O2 sensor, Myoglobin-mCherry, which offers in situ real-time and noninvasive measurements of subcellular pO2 in living cells. On the basis of these results, the model qualitatively predicted (1) the integrated experimental data from mitochondria under diverse experimental conditions, and (2) the impact of changes in one or more mitochondrial processes on overall bioenergetics.

Isometric spiracular scaling in scarab beetles-implications for diffusive and advective oxygen transport.

The scaling of respiratory structures has been hypothesized to be a major driving factor in the evolution of many aspects of animal physiology. Here, we provide the first assessment of the scaling of the spiracles in insects using 10 scarab beetle species differing 180× in mass, including some of the most massive extant insect species. Using X-ray microtomography, we measured the cross-sectional area and depth of all eight spiracles, enabling the calculation of their diffusive and advective capacities. Each of these metrics scaled with geometric isometry. Because diffusive capacities scale with lower slopes than metabolic rates, the largest beetles measured require 10-fold higher PO2 gradients across the spiracles to sustain metabolism by diffusion compared to the smallest species. Large beetles can exchange sufficient oxygen for resting metabolism by diffusion across the spiracles, but not during flight. In contrast, spiracular advective capacities scale similarly or more steeply than metabolic rates, so spiracular advective capacities should match or exceed respiratory demands in the largest beetles. These data illustrate a general principle of gas exchange: scaling of respiratory transport structures with geometric isometry diminishes the potential for diffusive gas exchange but enhances advective capacities; combining such structural scaling with muscle-driven ventilation allows larger animals to achieve high metabolic rates when active.

Blood Supply and Oxygenation Status of the Liver: From Physiology to Malignancy.

To maintain a multitude of vital functions, blood flow to the normal liver and the hepatic oxygenation status has to be kept on a high level (1.0-1.2mL/g/min and 30-40mmHg, respectively). There is a longitudinal oxygen partial pressure (pO2) gradient within the liver sinusoids between periportal inflow and outflow into the central vein leading to a zonation of the O2 status, which is associated with a zoning of liver functions. Oxygenation of metastatic lesions of colorectal cancers in the liver is poor due to a dysfunctional vascularity and inadequate blood supply. Hepatocellular carcinomas (HCCs) are highly vascularised (arterialised), metabolically very active and present with a predominantly arterial blood supply. HCCs are generally believed to be very hypoxic. However,confirmation of severe hypoxia based on reliable, direct pO2 measurements in HCCs is still missing.

Blood Flow and Respiratory Gas Exchange in the Human Placenta at Term: A Data Update.

Reliable measurements using modern techniques and consensus in experimental design have enabled the assessment of novel data sets for normal maternal and foetal respiratory physiology at term. These data sets include (a) principal factors affecting placental gas transfer, e.g., maternal blood flow through the intervillous space (IVS) (500mL/min) and foeto-placental blood flow (480mL/min), and (b) O2, CO2 and pH levels in the materno-placental and foeto-placental circulation. According to these data, the foetus is adapted to hypoxaemic hypoxia. Despite flat oxygen partial pressure (pO2) gradients between the blood of the IVS and the umbilical arteries of the foetus, adequate O2 delivery to the foetus is maintained by the higher O2 affinity of the foetal blood, high foetal haemoglobin (HbF) concentrations, the Bohr effect, the double-Bohr effect, and high foeto-placental (=umbilical) blood flow. Again, despite flat gradients, adequate CO2 removal from the foetus is maintained by a high diffusion capacity, high foeto-placental blood flow, the Haldane effect, and the double-Haldane effect. Placental respiratory gas exchange is perfusion-limited, rather than diffusion-limited, i.e., O2 uptake depends on O2 delivery.

Investigation of thermo-chemical expansions in Pr and Gd doped ceria by a novel temperature modulated dilatometry approach

Many metal oxides exhibit thermo-chemical expansion due to change in the chemical potential of oxygen. The latter can result in change of oxidation state of the metal ions and/or loss of oxygen upon temperature and PO2 changes. These effects lead to mechanical failure in devices such as solid oxide fuel cells that operate at high temperatures and high PO2 gradients. It is difficult to study thermal and chemical effects separately in a qualitative manner, as both effects occur simultaneously. In this work, we demonstrate separation of the expansion caused by chemical effects from the pure thermal effects at different temperature ranges, using temperature modulated dilatometry. Such separation is possible if different processes occur on significantly different timescales. However, the case in our model materials - doped ceria and for comparison doped zirconia - is more complex, as different chemical effects are important at different temperatures. Values of coefficient of modulated temperature thermal expansion (MCTE) are compared with the coefficient of linear thermal expansion (CTE). The CTE remains independent of heating rate, whereas the MCTE generally depends on the modulation rate. The latter dependence of the MCTE is changed over temperature, as defect associates vanish, and cation valence change kicks in.

The thermal tolerance of a tropical population of blue crab (Callinectes sapidus) modulates aerobic metabolism during hypoxia.

The blue crab Callinectes sapidus is a widespread ectothermic species that supports large fisheries. Physiology of temperate and subtropical populations of blue crabs are well studied; however, a lack of information exists on tropical populations. Given the low locomotion capabilities of C. sapidus adult blue crabs, natural selection should favor traits that shape a particular thermal niche reflected through tolerance modulation to dissolved oxygen (DO). This study was designed to evaluate the thermal window and hypoxia sensitivity of the blue crab population in the southern Gulf of Mexico. The effect of acclimation temperatures from 20°C to 34°C on thermal preference (TP), critical thermal limits (CT), and thermal metabolic scope (TMS) was assessed in normoxia. Metabolic rate regulation over oxygen partial pressure (pO2) gradient was evaluated through oxygen consumption measurements at different degrees of acute hypoxia. Callinectes sapidus was observed tending to specialize towards higher temperatures, showing a mean TP from 26°C to 33°C. The lowest performance of aerobic pathways was observed at the coldest regimes and the highest at the warmest ones with mean TMS value being 35 % greater at 34°C than 20°C. Patterns for metabolic regulation were dependent on the interaction between environmental temperature and DO, in which the interval from 29°C to 34°C provoked a 50 % reduction in oxygen consumption when exposed to ∼20% air saturation levels. The results obtained showed that blue crabs distributed in the southern Gulf of Mexico could be close to their oxygen-temperature tolerance limits, which has important implications when climate change effects on species re-distribution is considered.

Tempol Reverses the Negative Effects of Morphine on Arterial Blood-Gas Chemistry and Tissue Oxygen Saturation in Freely-Moving Rats.

We have reported that pretreatment with the clinically approved superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), blunts the cardiorespiratory depressant responses elicited by a subsequent injection of fentanyl, in halothane-anesthetized rats. The objective of the present study was to determine whether Tempol is able to reverse the effects of morphine on arterial blood-gas (ABG) chemistry in freely-moving Sprague Dawley rats. The intravenous injection of morphine (10 mg/kg) elicited substantial decreases in pH, pO2 and sO2 that were accompanied by substantial increases in pCO2 and Alveolar-arterial gradient, which results in diminished gas-exchange within the lungs. Intravenous injection of a 60 mg/kg dose of Tempol 15 min after the injection of morphine caused minor improvements in pO2 and pCO2 but not in other ABG parameters. In contrast, the 100 mg/kg dose of Tempol caused an immediate and sustained reversal of the negative effects of morphine on arterial blood pH, pCO2, pO2, sO2 and Alveolar-arterial gradient. In other rats, we used pulse oximetry to determine that the 100 mg/kg dose of Tempol, but not the 60 mg/kg dose elicited a rapid and sustained reversal of the negative effects of morphine (10 mg/kg, IV) on tissue O2 saturation (SpO2). The injection of morphine caused a relatively minor fall in mean arterial blood pressure that was somewhat exacerbated by Tempol. These findings demonstrate that Tempol can reverse the negative effects of morphine on ABG chemistry in freely-moving rats paving the way of structure-activity and mechanisms of action studies with the host of Tempol analogues that are commercially available.

Surfactant Lung Lavage versus Standard Treatment for Meconium Aspiration Syndrome

Abstract Background: To evaluate diluted surfactant lung lavage as a therapy for severe meconium aspiration syndrome. Aim of Study: The aim of this study is to evaluate the efficacy and outcome of lung lavage using diluted surfactant compared to standard protocol for treatment of meconium aspiration syndrome. Patients and Methods: This was a prospective interven-tional study involved 24 patients with severe meconium aspiration syndrome divided into two equal groups one received the standard care in the form of high frequency ventilation and the second group received pulmonary lavage using diluted surfactant in addition to the standard care. Pulmonary lavage was done using of 15ml/kg of surfactant diluted to concentra-tion of 5mg of phospholipids/1ml of 0.9% NaCl divided into four equal aliquots. Results: On comparing both groups patients managed by pulmonary lavage using diluted surfactant showed significant improvement in PCO2 and mean airway pressure occurred 6 hours after lavage while improvement in PO2, oxygenation index and arterial-alveolar oxygen gradient occurred 24 hours after lavage. The duration of mechanical ventilation, oxygen therapy and hospital stay were shorter in the surfactant group. There was no difference between both groups in the incidence of complications, need for ECMO or death. Conclusion: Surfactant lung lavage is a safe and effective therapy for severe meconium aspiration syndrome.

Orthotopic Transplantation of Human Bioartificial Lung Grafts in a Porcine Model: A Feasibility Study

Lung transplantation is the only treatment for end-stage lung disease; however, donor organ shortage and intense immunosuppression limit its broad clinical impact. Bioengineering of lungs with patient-derived cells could overcome these problems. We created bioartificial lungs by seeding human-derived cells onto porcine lung matrices and performed orthotopic transplantation to assess feasibility and in vivo function. Porcine decellularized lung scaffolds were seeded with human airway epithelial cells and human umbilical vein endothelial cells. Following in vitro culture, the bioartificial lungs were orthotopically transplanted into porcine recipients with planned 1-day survival (n = 3). Lungs were assessed with histology and in vivo function. Orthotopic transplantation of cadaveric lungs was performed as control. Engraftment of endothelial and epithelial cells in the grafts were histologically demonstrated. Technically successful orthotopic anastomoses of the vasculatures and airway were achieved in all animals. Perfusion and ventilation of the lung grafts were confirmed intraoperatively. The gas exchange function was evident immediately after transplantation; PO2 gradient between pulmonary artery and vein were 178 ± 153 mm Hg in the bioartificial lung group and 183 ± 117 mm Hg in the control group. At time of evaluation 24 hours after reperfusion, the pulmonary arteries were found to be occluded with thrombus in all bioartificial lungs. Engineering and orthotopic transplantation of bioartificial lungs with human cells were technically feasible in a porcine model. Early gas exchange function was evident. Further progress in optimizing recellularization and maturation of the grafts will be necessary for sustained perfusability and function.

Noninvasive Cellular Oxygenation Measurement During Graded Hypoxia Using Visible-Near-Infrared Spectroscopy.

In critically ill patients, direct knowledge of intracellular pO2 would allow for identification of cellular hypoxia, which when prolonged leads to organ failure. We have developed a visible-near-infrared optical system that noninvasively measures myoglobin saturation, which is directly related to intracellular pO2, from the surface of the skin. We used an animal model of graded hypoxia from low levels of inspired oxygen (n = 5) and verified that low intracellular pO2 is correlated with high steady-state serum lactate values. In addition, the pO2 gradient between arterial blood and inside muscle cells was 83 mm Hg at 21% O2, but fell to 24 mm Hg at 8% O2. Continuous myoglobin saturation measurement in skeletal muscle displayed the same trends as cerebral oxygenation with no lag in changes over time, demonstrating its relevance as a measure of systemic oxygenation.

Transcapillary PO2 gradients in contracting muscles across the fibre type and oxidative continuum.

Within skeletal muscle the greatest resistance to oxygen transport is thought to reside across the short distance at the red blood cell-myocyte interface. These structures generate a significant transmural oxygen pressure (PO2 ) gradient in mixed fibre-type muscle. Increasing O2 flux across the capillary wall during exercise depends on: (i) the transmural O2 pressure gradient, which is maintained in mixed-fibre muscle, and/or (ii) elevating diffusing properties between microvascular and interstitial compartments resulting, in part, from microvascular haemodynamics and red blood cell distribution. We evaluated the PO2 within the microvascular and interstitial spaces of muscles spanning the slow- to fast-twitch fibre and high- to low-oxidative capacity spectrums, at rest and during contractions, to assess the magnitude of transcapillary PO2 gradients in rats. Our findings demonstrate that, across the metabolic rest-contraction transition, the transcapillary pressure gradient for O2 flux is: (i) maintained in all muscle types, and (ii) the lowest in contracting highly oxidative fast-twitch muscle. In mixed fibre-type skeletal muscle transcapillary PO2 gradients (PO2 mv-PO2 is; microvascular and interstitial, respectively) drive O2 flux across the blood-myocyte interface where the greatest resistance to that O2 flux resides. We assessed a broad spectrum of fibre-type and oxidative-capacity rat muscles across the rest-to-contraction (1Hz, 120s) transient to test the novel hypotheses that: (i) slow-twitch PO2 is would be greater than fast-twitch, (ii) muscles with greater oxidative capacity have greater PO2 is than glycolytic counterparts, and (iii) whether PO2 mv-PO2 is at rest is maintained during contractions across all muscle types. PO2 mv and PO2 is were determined via phosphorescence quenching in soleus (SOL; 91% type I+IIa fibres and CSa: ∼21μmol min-1 g-1 ), peroneal (PER; 33% and ∼20μmol min-1 g-1 ), mixed (MG; 9% and ∼26μmol min-1 g-1 ) and white gastrocnemius (WG; 0% and ∼8μmol min-1 g-1 ) across the rest-contraction transient. PO2 mv was higher than PO2 is in each muscle (∼6-13mmHg; P<0.05). SOL PO2 isarea was greater than in the fast-twitch muscles during contractions (P<0.05). Oxidative muscles had greater PO2 isnadir (9.4±0.8, 7.4±0.9 and 6.4±0.4; SOL, PER and MG, respectively) than WG (3.0±0.3mmHg, P<0.05). The magnitude of PO2 mv-PO2 is at rest decreased during contractions in MG only (∼11 to 7mmHg; time × (PO2 mv-PO2 is) interaction, P<0.05). These data support the hypothesis that, since transcapillary PO2 gradients during contractions are maintained in all muscle types, increased O2 flux must occur via enhanced intracapillary diffusing conductance, which is most extreme in highly oxidative fast-twitch muscle.

Degradation studies of ceria-based solid oxide fuel cells at intermediate temperature under various load conditions

Despite several disadvantages with the electronic conduction of ceria, researchers report the high performance of ceria-based solid oxide fuel cells (SOFCs) at intermediate temperatures with advanced cathode materials. However, it appears the long-term stability of ceria-based SOFCs in the anode-supported cell configuration have still not been proved experimentally at practical operating conditions. In particular, the chemical expansion of ceria electrolytes can cause potentially irreversible failure of SOFCs under large PO2 gradients. Hence, we investigate the degradation behavior of NiO-Nd0.1Ce0.9O2-δ anode-supported cells with Nd0.1Ce0.9O2-δ electrolyte in dynamic electrical modes, load trip (0.7–0 A cm−2), load cycle (0.2–0.12 A cm−2), and constant load operation (0.2 A cm−2), at 650 °C. We identify the specific degradation phenomenon of ceria-based cells by analyzing the electrochemical characteristics in post-mortem investigations after durability testing under various electrical load conditions. Additionally, we suggest a possible operation strategy to mitigate the performance degradation of cells under various electrical stresses through understanding of the main degradation mechanism.

Differences in alveolo-capillary equilibration in healthy subjects on facing O2 demand

Oxygen diffusion across the air-blood barrier in the lung is commensurate with metabolic needs and ideally allows full equilibration between alveolar and blood partial oxygen pressures. We estimated the alveolo-capillary O2 equilibration in 18 healthy subjects at sea level at rest and after exposure to increased O2 demand, including work at sea level and on hypobaric hypoxia exposure at 3840 m (PA ~ 50 mmHg). For each subject we estimated O2 diffusion capacity (DO2), pulmonary capillary blood volume (Vc) and cardiac output (dot{Q}). We derived blood capillary transit time {boldsymbol{(}}{boldsymbol{T}}{boldsymbol{t}}{boldsymbol{=}}frac{{boldsymbol{V}}{boldsymbol{c}}}{dot{{boldsymbol{Q}}}}{boldsymbol{)}} and the time constant of the equilibration process ({boldsymbol{tau }}{boldsymbol{=}}frac{{boldsymbol{beta }}{boldsymbol{V}}{boldsymbol{c}}}{{boldsymbol{D}}{{boldsymbol{O}}}_{{boldsymbol{2}}}}, β being the slope of the hemoglobin dissociation curve). O2 equilibration at the arterial end of the pulmonary capillary was defined as {{bf{L}}}_{{bf{e}}{bf{q}}}{boldsymbol{=}}{{bf{e}}}^{{boldsymbol{-}}frac{{bf{T}}t}{{boldsymbol{tau }}}}. Leq greately differed among subjects in the most demanding O2 condition (work in hypoxia): lack of full equilibration was found to range from 5 to 42% of the alveolo-capillary PO2 gradient at the venous end. The present analysis proves to be sensible enough to highlight inter-individual differences in alveolo-capillary equilibration among healthy subjects.

Breathing with fins: do the pectoral fins of larval fishes play a respiratory role?

Convective water flow across respiratory epithelia in water-breathing organisms maintains transcutaneous oxygen (O2) partial pressure (Po2) gradients that drive O2 uptake. Following hatch, larval fishes lack a developed gill and the skin is the dominant site of gas transfer, yet few studies have addressed the contribution of convective water flow to cutaneous O2 uptake in larvae. We hypothesized that the pectoral fins, which can generate water flow across the skin in larvae, promote transcutaneous O2 transfer and thus aid in O2 uptake. In zebrafish (Danio rerio), the frequency of pectoral fin movements increased in response to hypoxia at 4 days postfertilization (dpf), but the response was blunted by 15 dpf, when the gills become the dominant site of O2 uptake, and was absent by 21 dpf. In rainbow trout (Oncorhynchus mykiss), Po2 measured at the skin surface of ventilating larvae was lower when the pectoral fins had been surgically removed, directly demonstrating that fins contribute to convective flow that dissipates cutaneous Po2 boundary layers. Lack of pectoral fins compromised whole animal O2 consumption in trout during hypoxia, but this effect was absent in zebrafish. Overall, our findings support a respiratory role of the pectoral fins in rainbow trout, but their involvement in zebrafish remains equivocal.

Oxygen permeation through single-phase perovskite membrane: Modeling study and comparison with the dual-phase membrane

Dual-phase Ce0.85Sm0.15O1.925-Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) mixed ionic-electronic conducting (MIEC) membrane, which is highly stable in CO2-rich atmosphere, is a promising candidate for oxyfuel applications. Here, the oxygen permeation behavior of the single-phase perovskite Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SSAF) membrane is analyzed in comparison to that of SDC-SSAF. The oxygen permeation resistances and kinetic constants of a 0.5 mm-thick SSAF disk were regressed using the Zhu model. At 950 °C and under an oxygen partial pressure (PO2) gradient of 0.21 bar/0.02 bar, the characteristic thickness (Lc) was 0.443 mm. Oxygen permeation in SSAF is generally limited by a mixture of surface exchange reactions and bulk diffusion between 800 and 950 °C at 0.21 bar/0.02 bar (feed/permeate). Overall, temperature is more dominant than PO2 gradient to enhance the oxygen permeation flux. A surface exchange-bulk diffusion transition region that exists between 850 and 875 °C in SDC-SSAF case is absent in SSAF case since oxygen permeation through SSAF is governed by mixed bulk diffusion and surface exchange.

Skeletal muscle interstitial Po2 kinetics during recovery from contractions.

The oxygen partial pressure in the interstitial space (Po2 is) drives O2 into the myocyte via diffusion, thus supporting oxidative phosphorylation. Although crucial for metabolic recovery and the capacity to perform repetitive tasks, the time course of skeletal muscle Po2 is during recovery from contractions remains unknown. We tested the hypothesis that Po2 is would recover to resting values and display considerable on-off asymmetry (fast on-, slow off-kinetics), reflective of asymmetric capillary hemodynamics. Microvascular Po2 (Po2 mv) was also evaluated to test the hypothesis that a significant transcapillary gradient (ΔPo2 = Po2 mv - Po2 is) would be sustained during recovery. Po2 mv and Po2 is (expressed in mmHg) were determined via phosphorescence quenching in the exposed rat spinotrapezius muscle during and after submaximal twitch contractions (n = 12). Po2 is rose exponentially (P < 0.05) from end-contraction (11.1 ± 5.1), such that the end-recovery value (17.9 ± 7.9) was not different from resting Po2 is (18.5 ± 8.1; P > 0.05). Po2 is off-kinetics were slower than on-kinetics (mean response time: 53.1 ± 38.3 versus 18.5 ± 7.3 s; P < 0.05). A significant transcapillary ΔPo2 observed at end-contraction (16.6 ± 7.4) was maintained throughout recovery (end-recovery: 18.8 ± 9.6; P > 0.05). Consistent with our hypotheses, muscle Po2 is recovered to resting values with slower off-kinetics compared with the on-transient in line with the on-off asymmetry for capillary hemodynamics. Maintenance of a substantial transcapillary ΔPo2 during recovery supports that the microvascular-interstitium interface provides considerable resistance to O2 transport. As dictated by Fick's law (V̇o2 = Do2 × ΔPo2), modulation of O2 flux (V̇o2) during recovery must be achieved via corresponding changes in effective diffusing capacity (Do2; mainly capillary red blood cell hemodynamics and distribution) in the face of unaltered ΔPo2.NEW & NOTEWORTHY Capillary blood-myocyte O2 flux (V̇o2) is determined by effective diffusing capacity (Do2; mainly erythrocyte hemodynamics and distribution) and microvascular-interstitial Po2 gradients (ΔPo2 = Po2 mv - Po2 is). We show that Po2 is demonstrates on-off asymmetry consistent with Po2 mv and erythrocyte kinetics during metabolic transitions. A substantial transcapillary ΔPo2 was preserved during recovery from contractions, indicative of considerable resistance to O2 diffusion at the microvascular-interstitium interface. This reveals that effective Do2 declines in step with V̇o2 during recovery, as per Fick's law.