Diffusive Oxygen Supply Research Articles

An attachment oxygen supply method for improving the sleep space environment in the Tibetan Plateau

The hypoxic environment results in common sleep problems for the local inhabitants of the Tibetan Plateau. Based on attachment ventilation, this study proposed an attachment oxygen supply device (AOSD) to improve the sleep space environment. The field tests were conducted in Lhasa to verify the oxygen supply effect of the AOSD and compared it with the traditional diffusive oxygen supply device (T-DOSD). The field tests were divided into two segments: the test of environmental parameters within the bedroom and the physiological parameters of the subjects. The results showed that the AOSD could create a comfortable oxygen-enriched environment for sleep space. At an oxygen flow of 10 L/min, compared to the initial oxygen concentration in the breathing zone, the oxygen concentration in the breathing zone is increased to 26.1% with the AOSD and 22.0% with the T-DOSD. When the oxygen flow is the same at 10 L/min, the AOSD increases oxygen concentration in the breathing zone by 4.1% compared to utilizing the T-DOSD. In addition, there was a decrease in heart rate and an increase in arterial oxygen saturation of subjects utilizing the AOSD. Therefore, the AOSD oxygen supply effect was further verified. The research contributes to improving both the sleep space environment and the sleep quality for inhabitants in an effective and energy-saving approach.

Polar gigantism and the oxygen-temperature hypothesis: a test of upper thermal limits to body size in Antarctic pycnogonids.

The extreme and constant cold of the Southern Ocean has led to many unusual features of the Antarctic fauna. One of these, polar gigantism, is thought to have arisen from a combination of cold-driven low metabolic rates and high oxygen availability in the polar oceans (the 'oxygen-temperature hypothesis'). If the oxygen-temperature hypothesis indeed underlies polar gigantism, then polar giants may be particularly susceptible to warming temperatures. We tested the effects of temperature on performance using two genera of giant Antarctic sea spiders (Pycnogonida), Colossendeis and Ammothea, across a range of body sizes. We tested performance at four temperatures spanning ambient (-1.8°C) to 9°C. Individuals from both genera were highly sensitive to elevated temperature, but we found no evidence that large-bodied pycnogonids were more affected by elevated temperatures than small individuals; thus, these results do not support the predictions of the oxygen-temperature hypothesis. When we compared two species, Colossendeis megalonyx and Ammothea glacialis, C. megalonyx maintained performance at considerably higher temperatures. Analysis of the cuticle showed that as body size increases, porosity increases as well, especially in C. megalonyx, which may compensate for the increasing metabolic demand and longer diffusion distances of larger animals by facilitating diffusive oxygen supply.

Impact of Isahaya dike construction on DO concentration in the Ariake Sea

In the Ariake Sea, dike construction in Isahaya Bay in 1997 for reclamation and disaster prevention was thought to cause big anthropogenic impacts on the marine ecosystem. Currently, hypoxia or anoxia occurs every summer in Isahaya Bay and the inner Ariake Sea. However, the effects of the dike construction on the DO concentration are unclarified. The present study evaluated the impact of the dike construction on the DO concentration by applying a numerical ecosystem model. The present calculation showed that the dike construction could affect the DO concentration in summer in a wider area than reported before in the steady state with a neap-spring tidal cycle. In Isahaya Bay, the dike construction caused a decrease of DO concentration greater than 2.0 mg l−1 , due to the decrease in DO supply from the vertical diffusion process with reduction of tidal current and the intensification of the density stratification. The dike construction also affected the DO concentration in the inner Ariake Sea by decreasing the DO concentration of the water transported by the estuarine circulation and the reduction of the diffusive supply of oxygen vertically with stratification enhanced by the dike construction. For the first time, this study showed with numerical simulation that the dike construction could affect the DO concentration in a wide area of the Ariake Sea.

Transport, anoxia and end-product accumulation control carbon dioxide and methane production and release in peat soils

Anaerobic respiration and methanogenesis have been found to slow-down in water saturated peat soils with accumulation of metabolic end-products, i.e. dissolved inorganic carbon (DIC) and methane (CH4), due to a lack of solute and gas transport. So far it is not well understood how solute and gas transport may control this effect. We conducted a column experiment with homogenized ombrotrophic peat over a period of 300 days at 20 °C. We specifically evaluated the effects of diffusive flux as control, downward advective water flux, intensified ebullition by conduit gas transport and diffusive oxygen supply on controlling anaerobic decomposition rates and carbon (C) turnover. To simulate advective flux, water and solutes were recirculated downward through the column after stripping of dissolved gases. We analyzed DIC and CH4 concentrations, production rates and fluxes, gas filled porosity, oxygen profiles (O2) and microbial C biomass over time. DIC residence time thereby served as proxy to characterize transport. A slowdown of anaerobic respiration and methanogenesis evolved with the accumulation of the end-products DIC and CH4 and set in after 150 days. This slow-down was accompanied by a decrease in the distribution of microbial biomass C with depths. Anaerobic DIC and CH4 production rates were fastest close to the water table and sharply slowed with depth. Accumulation of DIC and CH4 in the homogeneous peat material throughout the column decreased decomposition constants from about 10−5 near the surface to 10−9 year−1 deeper in the profile. Advective water transport extended the zone of active methanogenesis compared to a diffusive system; experimental enhancement of ebullition had little or no effect as well as strictly anoxic conditions. DIC residence time was negatively correlated to anaerobic respiration suggesting this parameter to be a predictor of anaerobic peat decomposition in peatlands. Overall, this study suggests that burial of peat and accumulation of metabolic end-products effectively slows decomposition and that this effect needs to be considered to explain peat accumulation and the response of peat mineralization rates to changes in environmental conditions.

Radius-dependent decline of performance in isolated cardiac muscle does not reflect inadequacy of diffusive oxygen supply

The study of cardiac energetics commonly involves the use of isolated muscle preparations (papillary muscles or trabeculae carneae). Their contractile performance has been observed to vary inversely with thickness. This inverse dependence has been attributed, almost without exception, to inadequate diffusion of oxygen into the centers of muscles of large diameter. It is thus commonly hypothesized that the radius-dependent diminution of performance reflects the development of an anoxic core. We tested this hypothesis theoretically by solving a modification of the diffusion equation, in which the rate of oxygen consumption is a sigmoidal function of the partial pressure of oxygen. The model demonstrates that sufficiently thick muscles, operating at sufficiently high rates of oxygen demand or sufficiently low ambient partial pressures of oxygen, will indeed show diminished energetic performance, whether indirectly indexed as stress (force per cross-sectional area) development or as the rate of heat production. However, such simulated behavior requires the adoption of extreme parameter values, often differing by an order of magnitude from their experimental equivalents. We thus conclude that the radius-dependent diminution of muscle performance in vitro cannot be attributed entirely to an insufficient supply of oxygen via diffusion.

On the origin of the substrate-induced oxidation of Ni/NiO(001) studied by X-ray Photoelectron Spectroscopy and Molecular Dynamics Simulations

Metallic Ni, vapor-deposited on NiO(001) near room temperature, could be gradually oxidised upon annealing between 800 K and 940 K in Ultra High Vacuum (UHV), as evidenced by X-ray Photoelectron Spectroscopy for initial Ni coverage of 1.6, 3.8 and 7.5 equivalent monolayers (ML). The time dependence of the oxidation process was consistent with a diffusion mechanism, supplying oxygen via the NiO crystal to a coalesced particulate deposit and resulting in an oxide shell, which grew over the entire surface and enclosed a shrinking metallic core. Similar to the well known behaviour upon gas phase oxidation, the process was fast within a depth of two atomic layers of Ni, limited by the diffusive supply of oxygen from the substrate. Molecular Dynamics Simulations for 0.06, 0.11 and 0.22 ML of Ni ions deposited on a model NiO(001) substrate indicated the formation of NiO islands via oxygen ions transferred from the surface and near-surface layers of the crystal. A significant atomic concentration of oxygen vacancies of the order of 10 to 20% could be created in each underneath layer, before the next one started donating lattice anions. This suggests a possible explanation for the aforementioned NiO-substrate-induced oxidation of deposited Ni, whereby the formation of oxygen vacancies inside the crystal supplies the necessary oxygen.

Analysis of methanotrophic communities in landfill biofilters using diagnostic microarray

Biofilters operated for the microbial oxidation of landfill methane at two sites in Northern Germany were analysed for the composition of their methanotrophic community by means of diagnostic microarray targeting the pmoA gene of methanotrophs. The gas emitted from site Francop (FR) contained the typical principal components (CH4, CO2, N2) only, while the gas at the second site Müggenburger Strasse (MU) was additionally charged with non-methane volatile organic compounds (NMVOCs). Methane oxidation activity measured at 22 degrees C varied between 7 and 103 microg CH4 (g dw)(-1) h(-1) at site FR and between 0.9 and 21 microg CH4 (g dw)(-1) h(-1) at site MU, depending on the depth considered. The calculated size of the active methanotrophic population varied between 3 x 10(9) and 5 x 10(11) cells (g dw)(-1) for biofilter FR and 4 x 10(8) to 1 x 10(10) cells (g dw)(-1) for biofilter MU. The methanotrophic community in both biofilters as well as the methanotrophs present in the landfill gas at site FR was strongly dominated by type II organisms, presumably as a result of high methane loads, low copper concentration and low nitrogen availability. Within each biofilter, community composition differed markedly with depth, reflecting either the different conditions of diffusive oxygen supply or the properties of the two layers of materials used in the filters or both. The two biofilter communities differed significantly. Type I methanotrophs were detected in biofilter FR but not in biofilter MU. The type II community in biofilter FR was dominated by Methylocystis species, whereas the biofilter at site MU hosted a high abundance of Methylosinus species while showing less overall methanotroph diversity. It is speculated that the differing composition of the type II population at site MU is driven by the presence of NMVOCs in the landfill gas fed to the biofilter, selecting for organisms capable of co-oxidative degradation of these compounds.

Molecular characterisation and expression of Atlantic cod ( Gadus morhua) myoglobin from two populations held at two different acclimation temperatures

Much previous research has demonstrated the plasticity of myoglobin concentrations in both cardiac and skeletal myocytes in response to hypoxia and training. No study has yet looked at the effect of thermal acclimation on myoglobin in fish. Atlantic cod ( Gadus morhua) from two different populations, i.e. the North Sea and the North East Arctic, were acclimated to 10 and 4 °C. Both the myoglobin mRNA and myoglobin protein in cod hearts increased significantly by up to 3.7 and 2.3 fold respectively as a result of acclimation to 4 °C. These increments were largest in the Arctic population, which in earlier studies have been shown to possess cold compensated metabolic demands at low temperatures. These metabolic demands associated with higher mitochondrial capacities may have driven the increase in cardiac myoglobin concentrations, in order to support diffusive oxygen supply. At the same time the increase in myoglobin levels may serve further functions during cold acclimation, for example, protection of the cell against reactive oxygen species, and scavenging nitric oxide, thereby contributing to the regulation of mitochondrial volume density.

Cardiac development in crayfish: ontogeny of cardiac physiology and aerobic metabolism in the red swamp crayfish Procambarus Clarkii

The cardiovascular system performs key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval development in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25 degrees C, 20 kPa O2). Prior to eclosion, heart rate (fH) decreases significantly. Previous data suggests that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation of the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption primarily increased while egg surface area remains constant. The limited area for gas exchange of the egg membrane, in combination with the increasing oxygen demand of the embryo could result in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late stage embryos were exposed to hyperoxic water (PO2 = 40 kPa O2). The fH in late stage embryos increased significantly over control values when exposed to hyperoxic water suggesting that the suppression in cardiac function observed in late stage embryos is likely due to a limited oxygen supply.

Resting metabolism of mouse papillary muscle

The aims of this study were to measure the resting metabolic rate of isolated mouse papillary muscles and to determine whether diffusive O2 supply is adequate to support the resting metabolism. Resting metabolism of left ventricular papillary muscles was measured in vitro (27 degrees C) using the myothermic technique. The rate of resting metabolism declined exponentially with time towards a steady value, with a time constant of 18+/-2 min (n=13). There was no alteration in isometric force output during this time. The magnitude of the resting metabolism, which depended inversely on muscle mass, more than doubled following a change in substrate from glucose to pyruvate and was increased 2.5-fold when the osmolarity of the bathing solution was increased by addition of 300 mM sucrose. Addition of 30 mM 2, 3-butanedione monoxime affected neither the time course of the decline in metabolic rate nor the eventual steady value. Analysis of the diffusive oxygen supply to the isolated preparation indicated that small papillary muscles (mass <1 mg), which have a very high resting metabolic rate early in an experiment, are unlikely to be adequately oxygenated.

Effect of low external flow on flame spread over polyethylene-insulated wire in microgravity

An experimental study of flame spread phenomena over polyethylene-insulated wires has been performed in opposed flow under microgravity. The experiments were performed at the Japan Microgravity Center (JAMIC) 10 s drop shaft. Two samples with different insulation thicknesses, 0.075 and 0.15 mm, and with the same inner core diameter, 0.5 mm, were used. Experiments were performed with O 2 concentrations of 21%–50% and external flow velocities 0 (quiescent) to 30 cm/s. The results show that the rate of flame spread is affected by the flow velocity and that the effect is much stronger at high oxygen concentrations. According to the results, flame spread phenomena of wire insulation can be classified into four different regimes based on the flow velocity: (1) an oxygen transport control regimes, (2) a geometrical effect regime, (3) a thermal regime, and (4) a chemical kinetic control regime. A special feature of the flame spread over wire insulation is the existence of the geometrical effect regime and a maximum spread rate between the oxygen transport control and geometrical effect regimes. The mechanism that gives rise to the unique features is discussed based on changes in preheat length, standoff distance, and flame temperature. The importance of the three effects and their relation to sample geometry, enhancement of diffusive oxygen supply, reduction of standoff distance, and logarithmic effect for the heat transfer are discussed.

Effects of sessile Protozoa on intracapsular oxygen tension and embryonic shell calcification in the muricid Chorus giganteus

Clusters of egg capsules deposited by some common marine Mollusca may suffer problems of a low diffusive oxygen supply to the embryos they contain, especially if the capsules are exposed to hypoxic seawater or attachment and growth of marine biofouling organisms. The present study was undertaken to determine the effects of severe biofouling by sessile Protozoa on intracapsular oxygen tension (IPO 2 ) and the development of embryos contained in the egg capsules of the muricid snail Chorus giganteus. We also investigated the effects of ambient oxygen tension (EPO2) on IPO 2 . The presence of sessile Protozoa attached to the outer wall of the egg capsules significantly reduced the IPO 2 compared to capsules not fouled by Protozoa. Clean capsules containing embryos showed an IPO 2 of about 105 mm Hg, compared with about 92 mm Hg for protozoan-fouled capsules when both were immersed in air-saturated seawater at 12°C. The embryos in capsules without Protozoa grew normally, hatching in about 70 d as veliconch larvae, whereas the development of larvae in protozoan-fouled capsules showed impairment of shell formation and delay in hatching for up to 5 mo. Pre-hatch embryos at 60 d measured about 922 μm and had an ash content near 18 μg embryo -1 embryos in capsules covered by micro-organisms measured only about 783 pm, with an ash content of about 3 μg embryo -1 over the same time period. Our study suggested that the lack of larval calcification observed in the presence of sessile Protozoa on the outer wall of the egg capsules was probably related to reduced IPO 2 . Similarly, any factor reducing oxygen supply to encapsulated embryos (i.e. exposure to water masses with low oxygen content, biofouling, reduced water movement) could impair embryonic development, a significant phenomenon thus far not reported in C. giganteus.

Calculation of effective diffusivities and reactivities in immobilized cell systems using finite difference methods

Immobilized cell systems typically consist of a single cell type encased in a semi-rigid polymer support. The rates at which nutrient molecules diffuse and react in these materials determine the feasible longevity and the amount of desirable product generated by the cells. Finite difference techniques were developed to calculate effective diffusivities and rates of reaction of small molecules in such immobilized cell systems. The structures analyzed consist of multiple cellular inclusions distributed in a continuous phase where molecules diffuse more slowly in the cells than in the continuous phase. Diffusivities are in excellent agreement with available theoretical bounds. Under typical reactive conditions, the depth to which oxygen can penetrate ranges from 24–200 μm, depending on the cell volume fraction, oxygen supply, and cellular uptake kinetics. Increases in the cell fraction beyond 0.55 yield minimal increases in the oxygen consumption rate, suggesting that such materials are limited by the diffusive supply of oxygen.

Impact of boundary layer flow velocity on oxygen utilisation in coastal sediments

Small pressure gradients generated by boundary flow-topography interactions cause advective pore water flows in permeable sediments. Advective pore water exchange enhances the flux of solutes between the sediment and the overlying water, thus generating conditions for an increased utilisation of oxygen. We compared a less permeable (k = 5 X 10-l2 m2) with a permeable sediment (k = 5 X 10- m') typical for coastal and shelf sediments. Total oxygen utilisation (TOU) in incubated sediment cores was measured in 10 laboratory experiments using recirculating flow tanks (33 runs). TOU was a function of flow velocity in permeable sediment where advective pore water flow occurred. TOU increased with the increasing volume of sediment flushed with oxygenated water. We found that TOU increased by 91 2 23% in coarse sand when flow increased from 3 to 14 cm S-' (38 mounds m-', height 10 to 30 mm, flow measured 8 cm above the sediment). Additlon of fresh algal material caused a stronger stimulation of TOU in the coarse sand than in the fine sand (4 additional flume runs). After the addition, intensive oxygen consumption reduced the oxygen penetration depth in the advectively flushed zone of the coarse sediment. However, counteracting this process, advectlve flow maintained an oxic sediment volume still larger than that in the less permeable sediment. Flow-enhanced oxygen utilisation is potentially effective in permeable beds of coastal and shelf regions, in contrast to the situation in cohesive sediments limited by predominantly diffusive oxygen supply.

Oxygen Supply and Limits on Aggregation of Embryos

Effects of oxygen supply on development rates of embryos in gelatinous masses were tested with natural masses of three species of opisthobranch gastropods and artificial masses made with embryos of a sea urchin and agarose gel. When diffusive exchange was restricted for embryos in such masses, increased oxygen alone was sufficient to maintain development rates of embryos. Diffusive supply of oxygen is therefore a limiting factor for embryos clustered in gelatinous masses. Development rates were constant over a wide range of experimentally altered oxygen concentrations but retarded with oxygen below about 10% of air saturation. Some opisthobranch embryos exposed to low oxygen concentrations hatched with shorter shells. Delayed hatching and shorter shells at hatching were both associated with a central position in the globose gelatinous mass of one of the opisthobranch species, even in air-saturated and vigorously stirred water. The pH near the centres of the masses was lower when embryos were at more advanced stages; thus the intracapsular stirring caused by cilia of embryos at later stages does not compensate for their greater metabolic rates. The pH in some egg masses was about seven or lower, and this pH affected development in separate experiments. The masses approach limits for removal of wastes, although oxygen becomes limiting for rates of development before accumulation of wastes becomes limiting. Embryos of opisthobranchs that are normally aggregated and embryos of sea urchins that are normally dispersed were similarly tolerant of low oxygen concentrations and low pH. In respect to tolerance of hypoxia and accumulating wastes, embryos in many clades are preadapted for aggregation into masses, but there are limits on the size of the aggregation. Egg masses are commonly at those limits.

Studies on blood substitutes based on hemoglobin and perfluorocarbon.

Unmodified, and to a lesser extent, modified stroma-free hemoglobin preparations have been reported to exhibit coronary and renal vasoconstrictor activity in isolated perfused hearts and kidneys. The physiological significance in vivo of such ex vivo demonstrated vasoconstriction has not yet been established. We have conducted a number of in vivo dog experiments designed to elucidate (a) whether free hemoglobin in the plasma phase contributes to diffusive oxygen supply to the tissues and (b) whether excessive vasoconstriction results in functional impairment. Our findings indicate that (a) the infusion of unmodified SFHS does not cause a significant disturbance of central hemodynamics, although it causes an elevation of the arterial blood pressure; the latter is accompanied by vasoconstriction in the skeletal muscle vascular bed and in the renal cortex; (b) there is no significant improvement of diffusive oxygen supply to the tissue at rest; and (c) that glutaraldehyde cross-linked SFHS administered to hypotensive dogs causes a brief further aggravation of hypotension as well as renal vasoconstriction accompanied by renal functional impairment. The findings suggest that coronary autoregulatory mechanisms in vivo can override the vasoconstrictor potency demonstrated in vitro, but the renal effects of SFHS containing unmodified hemoglobin can give rise to significant concern.

Arterioles supply oxygen to capillaries by diffusion as well as by convection

In the early part of this century, August Krogh proposed a model of oxygen transport in capillaries that assumes that all oxygen is delivered to the capillaries by convection from small terminal arterioles and lost from these capillaries by diffusion. This model and its consequences have been used extensively to interpret whole organ oxygen transport data in terms of diffusion between capillaries and tissues and to relate changes in microvascular hemodynamics to alterations in oxygen transport. We evaluated the appropriateness of such extrapolation by measuring oxygen saturation at discrete locations along the lengths of individual capillaries in the hamster cheek pouch retractor muscle. Our results indicate that the amount of oxygen lost from individual capillaries can be markedly affected by the presence of larger microvessels that frequently cross the capillary path. These larger vessels act either as a diffusive supply of oxygen for the red blood cells within the capillary or as an additional sink for the oxygen depending on the direction of the oxygen tension gradient. This transfer of oxygen between larger microvessels and capillaries attenuates the importance of capillary hemodynamics in oxygen exchange. Therefore, conclusions about local oxygen exchange that utilize only hemodynamic data from whole organ or microvascular experiments and the Krogh model will generally be invalid and should be viewed with caution.