Showing papers on "Oxygen published in 1977"

The oxygen transport system in trout (salmo gairdneri) during sustained exercise

Abstract: 1. The capabilities of the oxygen transport system of rainbow trout in supplying the increased oxygen demands in exercise, in a water tunnel at 9–10.5 °C, have been investigated by increasing the velocity of water flow, with a 1 h period between increments, up to the maximum swimming speed (critical velocity, U crit ). 2. At U crit , N O2 was elevated above the resting level by 7.5 times. The logarithm of N O O2 was linearly related to the swimming speed expressed as a proportion of U crit . V g increased in almost direct proportion to the increase in N O O2 . 3. Heart rate rose slightly at half U crit and reached a maximum, 1.6 times the resting rate, as U crit was approached. Ventral and dorsal aortic mean blood pressures rose by 60% and 20% respectively at U crit while their pulse pressures doubled. Central venous pressure was virtually unchanged. 4. P a, O a, O2 fell slightly during exercise but C a, O a, O2 was unaffected. On the other hand P v, O v, O2 halved and C v, O v, O2 fell from 3.17 (S.E. = 0.3) to 0.6(S.E. = 0.7) mmol/1. Cardiac output increased by about 3 times resting values. 5. The results are discussed and an attempt is made to estimate the maximum capabilities of the components of the oxygen transport system in sustained exercise.

Singlet oxygen in natural waters

Abstract: MANY studies have shown that singlet molecular oxygen can oxidise a variety of organic substances1–7. These studies have included biologically important compounds present in the aquatic environment such as amino acids4,7 and pollutants like polycyclic aromatic hydrocarbons5 and pesticides6. No data, however, have been obtained to demonstrate that reactions involving singlet oxygen (often called oxygenations) are sufficiently rapid to be significant in natural waters. The most likely mechanism for oxygenation in the environment was originally proposed by Kautsky8 by which light energy absorbed by a sensitiser is transferred to ground-state oxygen to form singlet oxygen, which in turn reacts with the organic substance, or ‘acceptor’ (A), to form a peroxide. Here we present evidence that rapid photochemical generation of singlet oxygen occurs in inland and coastal water bodies of the south-eastern United States.

Utilization of blood‐borne and intramuscular substrates during continuous and intermittent exercise in man.

Abstract: 1. Substrate utilization in the legs during bicycle exercise was studied in five subjects when performing intermittent intense exercise (15 sec work--15 sec rest) as well as continuous exercise during 60 min, with an almost identical average power output and oxygen uptake in both situations. 2. Muscle biopsies were obtained from vastus lateralis at rest, during, and after exercise in order to determine intramuscular lipid and carbohydrate utilization. The contribution from blood-borne substrates to total oxidative metabolism was determined by arterial-femoral venous (a-fv) differences for oxygen, FFA, glucose, and lactate and leg blood flow. 3. Intermittent and continuous exercise revealed a similar glycogen depletion and the intramuscular lactate accumulation was rather small. A similar uptake of blood-borne substrate (FFA, glucose) was found in both situations whereas a release of lactate only was observed in intermittent exercise. 4. ATP and CP levels oscillated between work and rest periods in intermittent exercise but were not resynthesized to resting levels at the end of the rest periods. The mainly aerobic energy release during each work period in intermittent exercise is partly caused by myoglobin functioning as an oxygen store; this factor was calculated to be more important than ATP and CP or lactate level oscillations. 5. The metabolic response to intermittent exercise was found to be similar to that found in continuous exercise with approximately the same average power output and oxygen uptake. This indicates that some factor in the intermediary metabolism, for instance citrate, functions as a regulator retarding glycolysis and favouring lipid utilization and an aerobic energy release in intermittent exercise.

Effect of oxygen tension on cellular energetics

Abstract: Simultaneous measurements of the mitochondrial [NAD+]/[NADH], the cytoplasmic [ATP]/[ADP] x [Pi], and the respiratory rate were carried out in suspensions of cultured kidney cells in a range of defined oxygen tensions. The results show that as the extracellular oxygen concentration falls there is a decrease in the respiratory rate, which is accompanied by a decrease in the [ATP]/[ADP] and a progressive reduction of cytochrome c. Even at low O2 tensions the mitochondrial respiratory chain between the NAD couple and cytochrome c remains at near equilibrium with the ATP synthesizing reactions. It is concluded that limited oxygen supply affects cellular metabolism at much higher concentrations than the P50 value for the oxygen dependence of respiration, but the respiratory rate remains relatively unchanged due to compensatory changes in the [ATP]/[ADP] X [Pi] and progressive reduction of cytochrome c. These metabolic changes may form a basis for the phenomenon of tissue oxygen sensing at near physiological oxygen tensions.

Heterogeneity of the hypoxic state in perfused rat heart.

Abstract: Tissue oxygen gradients were examined in the saline-perfused rat heart by NADH fluorescence photography. In high flow hypoxia, where the coronary flow was maintained and the arterial oxygen tension was gradually reduced, oxygen extraction was virtually complete before oxygen consumption was significantly diminished. Inadequate oxygen delivery resulted in a well defined pattern of anoxic zones. The anoxic zones were several hundred microns in width, an order of magnitude greater than intercapillary distances. In low flow hypoxia (ischemia), where the arterial oxygen tension remained at its control value and the coronary flow was diminished, anoxic zones also developed, following the same pattern as in high flow hypoxia. However, in ischemia, the anoxic areas developed while the effluent oxygen tesion was significantly greater than zero. Whereas respiratory acidosis between pH 7.3 and 6.9 resulted in vasodilation, below PH 6.8 there was a marked increase in vascular resistance. Anoxic zones appeared despite only a slight change in effluent oxygen tension from the control. In high flow hypoxia, ischemia, and acidosis-induced ischemia, the anoxic zones disappeared when control perfusion conditions were restored. The data demonstrate that tissue oxygen gradients are very steep in the hypoxic state, so that ischemia and hypoxia result in discrete heterogeneous areas of anoxic tissue bounded by sharp areas where the oxygen supply is sufficient to maintain normal mitochondrial oxidative function. In these states in which oxygen delivery is less than oxygen demand, coronary perfusion appears to be regulated at the level of the arterioles rather than the capillaries.

ESCA Study of Polymer Surfaces Treated by Plasma

Abstract: Surfaces of polymers [polyethylene, polystyrene, poly(ethylene terephthalate), poly(oxymethylene), cellulose acetate, polyacrylonitrile, nylon 6, and polytetrafluoroethylene] treated with argon (inert) and nitrogen (reactive) plasma were examined by ESCA (electron spectroscopy for chemical analysis). Argon plasma treatment generally introduces oxygen functionalities into the polymer surface. Nitrogen treatment generally incorporates nitrogen and oxygen functionalities into the treated surface. The extent of oxygen incorporation is typically less than that produced by argon plasma. When nitrogen and oxygen functional groups are already in a polymer structure, the extent of additional incorporation of these two elements as a result of plasma treatment is very much less than with other polymers. Polymers which contain only one of the elements tend to incorporate the other element to much the same degree as polymers without either element initially present.

Geothermometry and Oxygen Barometry Using Coexisting Iron-Titanium Oxides: A Reappraisal

Abstract: Equilibrium thermodynamic methods are used to develop an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964). The geothermometer and oxygen barometer are presented graphically for coexisting ilmenite solid solution and magnetite solid solution in the system FeO-Fe2O3-TiO2. Equations are also given for calculating temperature and oxygen activity for natural coexisting iron-titanium oxides containing other components. Large departures in composition from the system FeO-Fe2O3-TiO3 result in large uncertainties in the calculated temperature and activity of oxygen.

Causes of high blood O2 affinity of animals living at high altitude.

Abstract: We have measured the partial pressure of O2 at 50% saturation (P50) and the concentration of various phosphate compounds in the erythrocytes of the bar-headed goose and the guanaco to establish the cause of the high blood O2 affinity in animals who normally reside at high altitude. The same data were obtained in the blood of two goose species, that live at sea level, and in human blood. At standard conditions (pH 7.4, PCO2 40 Torr, 37 degrees C), P50 was 29.7 Torr in the blood of the bar-headed goose and was about 10 Torr higher in the goose species living at sea level. Since the concentration of organic phosphates was not markedly different in the erythrocytes of either goose species we conclude that the hemoglobin of the bar-headed goose reacts more weakly with organic phosphates, which can also be inferred from studies on purified hemoglobin solutions. Likewise, the low P50 of guanaco blood in comparison with human blood can be explained by a reduced interaction of 2,3-bisphosphoglycerate of guanaco hemoglobin compared to the human pigment.

Aerobic and anaerobic bacterial respiration monitored by electrodes.

Abstract: SUMMARY: A technique is described by which both oxygen and nitrate (or nitrite or chlorate) levels were continuously monitored during bacterial respiration. Paracoccus (Micrococcus) denitrificans and Escherichia coli oxidizing succinate rapidly ceased to reduce nitrate when oxygen was available, and equally rapidly commenced nitrate reduction when all the oxygen had been consumed. By contrast, membrane vesicles isolated from P. denitrificans reduced oxygen and nitrate simultaneously. The respiratory nitrate reductase in intact cells of P. denitrificans appeared to be inaccessible to chlorate present in the reaction medium, and it is suggested that the nitrate reductase is orientated on the plasma membrane so that nitrate gains access from the inner (cytosolic) face.

Trapping and removal of oxygen in Tokamaks

Abstract: Various discharge cleaning techniques have been studied in Microtor. It was found that high temperature discharges are not only ineffective in reducing the oxygen on the wall, and hence in the plasma, but may even induce trapping. Oxygen can be removed from the wall by a low-temperature, partially ionized hydrogen plasma by conversion to water vapour. The amount of loosely bound oxygen on the surface is thus reduced below 1% of a monolayer. The residual amount of the oxygen in the plasma is near 1010 atom cm−3, and represents a significant improvement over previous tokamak results.

The oxygen electrode. Part 8.—Oxygen evolution at ruthenium dioxide anodes

Abstract: The electrocatalytic behaviour of Ti-supported RuO2, prepared by thermal decomposition of RuCl3, as substrate for oxygen evolution was investigated by a variety of techniques. B.E.T. adsorption experiments showed that the RuO2 layers are highly porous with large surface area values which, however, decrease rapidly as the annealing temperature increases above ∼ 300°C. Both the charge involved in the cyclic voltammograms and the oxygen evolution rates are dependent on the true (rather than apparent) area of these electrode surfaces, and also on the pH of the solution. The results for oxygen evolution are discussed in terms of electrochemically generated unstable surface oxides whose decomposition is catalysed by protons in acid, and hydroxide ions in base. The lower reactivity of the oxide at intermediate pH value is attributed on the one hand to loss of protons by OH groups, resulting in oxygen bridging, and on the other to lack of enhanced coordination of surface ruthenium species by OH– ions, which in this pH region are present only at low activity. The charge associated with voltammetric sweeps is accounted for in terms of surface redox processes rather than bulk penetration of protons into the oxide. The need for surface area measurements as a guide to the interpretation of the electrochemical data in the case of these oxide systems is stressed.

Ultraviolet photoemission and flash‐desorption studies of the chemisorption and decomposition of methanol on Ni(111)

Abstract: The chemisorption and decomposition of methanol (CH3OH) on Ni(111) has been studied by ultraviolet photoemission spectroscopy (UPS) and flash‐deposition mass spectroscopy. The UPS spectra suggest that exposure at ∠80 K produces chemisorbed CH3OH in which the chemisorption interaction affects two molecular orbitals, the oxygen lone‐pair oriented perpendicular to the COH plane and an in‐plane orbital having mixed lone‐pair and σ‐bonding character. Upon warming to ∠160 K, some CH3OH desorption occurs and the UPS spectrum changes markedly. Further warming to ∠300 K produces H2 desorption and leaves chemisorbed CO as the final decomposition product on the surface.

Relative contributions of large and small airways to flow limitation in normal subjects before and after atropine and isoproterenol.

Abstract: Bronchodilatation was produced in normal subjects by the inhalation of atropine, a parasympatholytic agent, and isoproterenol, a beta adrenergic stimulator. Density dependence of maximal expiratory flow (Vmax), expressed as a ratio of Vmax with an 80% helium-20% oxygen gas mixture to Vmax with air at isolung volumes, indicated that the predominant flow regimes across upstream airways changed differently after each agent was given separately. After atropine Vmax increased, elastic recoil pressure did not change, and density dependence decreased. Utilizing the equal pressure points analysis which defines upstream and downstream segments of the intrathoracic airways at flow limitation, these results suggest a greater relative dilatation of the larger upstream airways such that more of the driving pressure is dissipated across the smaller airways in which flow is less dependent upon gas density. After isoproterenol Vmax increased, elastic recoil pressure did not change, and density dependence increased. This suggests a preferential dilatation of the smaller and more peripheral airways with less density-dependent flow regimes such that more of the driving pressure would be dissipated in the larger airways in which flow is more dependent upon gas density. Systematic decreases after isoproterenol lead independently to the same conclusion. After both agents together, Vmax increased and density dependence and critical alveolar pressures did not change from control, suggesting a relatively uniform dilatation of all the airways comprising the upstream segment.

Thermal oxidation of silicon in various oxygen partial pressures diluted by nitrogen

Abstract: Oxide growth kinetics of SiO2 films grown on silicon at 950 to 1100 °C in an O2/N2 mixture is empirically studied. It is found that a linear‐parabolic law is in excellent agreement with the oxidation data under the oxygen partial pressure PO2 of 1 or 10−1 atm. However, a parabolic law is obtained at 10−2 atm, and an inverse‐logarithmic law at 10−3 atm. The Mott‐Cabrera oxidation rate equation is adapted to the thermal oxidation of silicon in the case of PO2≲10−2 atm. Finally, 43.9 kcal/mole is derived as the activation energy value of silicon atoms entering into the oxide.

Oxygen Is Toxic

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