Role of oxygen in limiting respiration in the in situ myocardium

1H NMR has now detected the proximal histidyl N delta H myoglobin (Mb) signal from the myocardium in situ. Upon ligation of the left anterior descending coronary artery in the rat myocardium, the deoxy Mb signal appears at 78 ppm During dopamine infusion at up to 80 micrograms/kg/min, the heart rate pressure product (RPP) increases by a factor of 2, the phosphocreatine (PCr) decreases by 17%, and the ratio of the change in inorganic phosphate over PCr (delta Pi/PCr) increases by 0.2. However, no deoxy myoglobin signal is detected. Oxygen availability does not appear to limit oxygen consumption nor oxidative phosphorylation under dopamine enhanced work state in myocardium.     

Hemodynamics, cerebral circulation, and oxygen saturation in Cheyne-Stokes respiration

Because cardiovascular disorders and stroke may induce Cheyne-Stokes respiration, our purpose was to study the interaction among cerebral activity, cerebral circulation, blood pressure, and blood gases during Cheyne-Stokes respiration. Ten patients with heart failure or a previous stroke were investigated during Cheyne-Stokes respiration with recordings of daytime polysomnography, cerebral blood flow velocity, intra-arterial blood pressure, and intra-arterial oxygen saturation with and without oxygen administration. There were simultaneous changes in wakefulness, cerebral blood flow velocity, and respiration with accompanying changes in blood pressure and heart rate approximately 10 s later. Cerebral blood flow velocity, blood pressure, and heart rate had a minimum occurrence in apnea and a maximum occurrence during hyperpnea. The apnea-induced oxygen desaturations were diminished during oxygen administration, but the hemodynamic alterations persisted. Oxygen desaturations were more severe and occurred earlier according to intra-arterial measurements than with finger oximetry. It is not possible to explain Cheyne-Stokes respiration by alterations in blood gases and circulatory time alone. Cheyne-Stokes respiration may be characterized as a state of phase-linked cyclic changes in cerebral, respiratory, and cardiovascular functions probably generated by variations in central nervous activity.     

Application of the McNabb-Foster trapping equations to the diffusion of oxygen in dilute niobium alloys

The McNabb-Foster equations, solved using a finite difference approach, have been applied to the data reported earlier by Lauf and Altstetter for the diffusion of oxygen in dilute niobium alloys. It was assumed that the substitutional alloy atoms acted as traps for the oxygen. Ratios of the release coefficient to the trapping coefficient,p/k, were calculated at various temperatures by computer-assisted curve fitting. Trapping energies obtained from plots ofp/k vs 1/T agree fairly well with those reported earlier using the Oriani model, but differ somewhat from those obtained using a recent model proposed by McLellan. The merits and limitations of the models with respect to the treatment of experimental data are discussed. Initial fractional trap occupancies were also calculated for these alloys and plotted against 1/T, and the results are also discussed.     

The indices of external respiration and oxygen homeostasis in human subjects with different types of blood circulation

The cardiac output and other parameters of central hemodynamics in human were evaluated by means of tetrapolar rheography. Three types of circulation (hypo-, eu- and hyperkinetic) were picked out according to value of their cardiac index. Quantity of persons in groups of hypo-, eu- and hyperkinetics was as 25:35:40, 85 healthy people of both sex 18-27 years old were examined. There is no statistically significant difference in values of respiration rate, the tidal volume, a minute volume, the oxygen consumption, the concentration of O2 and CO2 in the alveolar air between groups with different types of circulation. The respiration rate, the tidal volume, a minute volume and the oxygen consumption have been studied spirographically. The concentration of O2 and CO2 in the alveolar air have been studied by means of mass-spectrometry. Comparison of the CO defined by means of impedance cardiography (COic) and the CO calculated by oxygen consumption data (COox) demonstrated that COox in group of the hypokinetics is more than COic, the eukinetics have them almost equal, and the hyperkinetics have COic which is more than COox. There is positive correlation between the COic/COox ratio and CI (r = 0.85, P < 0.01). In spite of almost equal oxygen consumption in all groups of human, hypokinetics use less blood volume for providing their body by oxygen.     

Hydrogen trapping in precipitation-hardened alloys

The ingress of hydrogen in three precipitation-hardened alloys (Inconel 718, Incoloy 925, and 18 Ni maraging steel) exposed to an acetate electrolyte (1 mol L⁻¹ HAc/1 mol L⁻¹ NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants (k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 718 and Incoloy 925 was calculated from k and found to be in excellent agreement with the concentration of NbTi(CN) and TiC particles, respectively. The maraging steel was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps thought to be TiC/Ti(CN) particles. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement. Moreover, a comparison of the trapping constants with those for AISI 4340 steel and two other nickel-base alloys (Monel K-500 and MP35N) indicates that a strong correlation exists between hydrogen embrittlement susceptibility and trapping capability over all the alloys.     

Hydrogen trapping models in steel

This article describes the role of hydrogen trapping in steel. Trapping increases the solubility of hydrogen and decreases the diffusivity. Traps are characterized by their nature, i.e., reversible or irreversible, saturable or unsaturable. A dislocation core is a saturable, reversible trap, while voids and crack are unsaturable, reversible traps. A trap model based on saturable, reversible traps is developed, which is slightly different from the trap model of McNabb and Foster. In equilibrium, the trap model corresponds to Oriani’s trap model. Kumnick and Johnson found experimentally that the trap density increases as the plastic strain increases. Using their trap data, it is shown that equilibrium between hydrogen in lattice sites and trap sites can be assumed when strain rates are used as in standard tensile tests.     

Hydrogen trapping in thoria-dispersed nickel

Trapping of hydrogen in thoria-dispersed nickel has been investigated by the hydrogen thermal desorption technique. It has been found that voids are formed at the particle-matrix interface during cold-working. Annealing at high temperature removes these extra trapping sites, allowing an intrinsic trapping effect due to the thoria particle-matrix interface to be measured. The trapbinding energy and trap-activation energy of hydrogen at the ThO₂-nickel matrix interface are estimated as 35 kJ mole^-1 and 48.7 kJ mole^-1, respectively, using the mathematical models derived from the existing trap theory. The energy level of hydrogen around the ThO₂-lattice interface is derived from the above values. The saddle-point energy of hydrogen at the ThO₂-lattice interface, 13.7 kJ mole^-1, is lower than the activation energy for hydrogen diffusion through a normal lattice, 40.2 kJ mole^-1. It is suggested that during thermal desorption from thoria-dispersed nickel, some of the hydrogen atoms in normal lattice interstitial sites are retrapped at ThO₂-matrix lattice interfaces which are not occupied with hydrogen at the charging temperature. Trap sites at ThO₂-matrix interfaces are dilutely occupied under 1-atm hydrogen pressure in the temperature range of 598 to 773 K. The fractional occupancy of traps ranged from 0.14 to 0.05. SUNG-MAN LEE, formerly with the Korea Advanced Institute of Science and Technology     

Hydrogen trapping in work-hardened alloys

The ingress of hydrogen in two work-hardened nickel-base alloys (Inconel 625 and Hastelloy C-276) exposed to an acetate electrolyte (1 mol L⁻¹HAc/1 mol L⁻¹ NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants (k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 625 was calculated from k and found to be in excellent agreement with concentration of NbTi(C) particles. Hastelloy C-276 was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps. The density of irreversible traps was shown to agree with the concentration of phosphorus segregated at grain boundaries. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement.     

Nitrogenase activity and respiration of cultures of Rhizobium spp. with special reference to concentrations of dissolved oxygen

Studies of nitrogenase in cultures of the cowpea rhizobia (Rhizobium spp.) strains 32H1 and CB756 are reported. Preliminary experiments established that, even when agar cultures were grown in air, suspensions of bacteria prepared anaerobically from them were most active at low concentrations of free dissolved O2. Consequently, assays for activity used low concentrations of O2, stabilized by adding the nodule pigment leghaemoglobin. In continuous, glutamine-limited cultures of 32H1, nitrogenase activity appeared only when the concentration of dissolved O2 in the cultures approached 1 muM. Lowering the glutamine concentration in the medium supplied to the culture from 2 to 1 mM halved the cell yield and nitrogenase activity was also diminished. Omitting succinate from the medium caused the concentration of dissolved O2 to rise and nitrogenase activity was lost. Upon restoration of the succinate supply, the O2 concentration immediately fell and nitrogenase was restored. The activity doubled in about 8 h, whereas the doubling time of this culture was 14 h. Sonic extracts of 32H1 cells from continuous cultures with active nitrogenase contained components reacting with antiserum against nitrogenase Mo-Fe protein from soybean bacteroids. Continuous cultures grown at higher O2 concentration, with only a trace of active nitrogenase, contained less of these antigens and they were not detected in highly aerobic cultures. Nitrogenase activity of a continuous culture was repressed by NH+4; the apparent half-life was about 90 min. Cells of 32H1 from a continuous culture growing at between 30 and 100 muM dissolved O2 possessed a protective mechanism which permitted respiration to increase following exposure to a rapid increase in O2 concentration from low levels (O2 shock). This effect disappeared as the O2 concentration for growth was reduced towards 1 muM.     

The mechanism of red cell (dis)aggregation investigated by means of direct cell manipulation using multiple optical trapping

Red cell exchange is important in the care of acutely ill sickle-cell patients, and may be life-saving. An automated red cell exchange technique has been developed using a Baxter blood cell separator, enabling an isovolaemic exchange to be performed within 2.5 h. A total of 20 procedures have been performed in 15 patients, including one woman in the third trimester of pregnancy, with a mean decrease of 72% in the circulating sickle haemoglobin (HbS) level. This method enables almost all adult patients with sickle cell anaemia to have their HbS reduced to safe levels by only one procedure. The procedure was well tolerated by all patients, including those who were acutely ill. This technique provides an effective procedure for reducing the percentage of circulating HbS rapidly in acutely ill patients with complications of sickle cell anaemia.     

Kinetic analysis of tetraethylammonium transport in the kidney epithelial cell line, LLC-PK1

PURPOSE: The aims of this study were to establish a kinetic means of analyzing the membrane transport of organic cations in renal epithelial cells, and to simultaneously evaluate drug interactions in apical and basolateral membranes. METHODS: Tetraethylammonium (TEA) transport was measured using LLC-PK1 cell monolayers grown on microporous membrane filters. After incubating the cells with unlabeled TEA or other drugs, apical or basolateral medium was changed to that containing labeled TEA, and transcellular transport and cellular accumulation were measured. Clearance from apical medium to cells (CL12), cells to apical medium (CL21), cells to basolateral medium (CL23) and basolateral medium to cells (CL32) were calculated based on a three compartment model. RESULTS: TEA was accumulated progressively in the monolayers from the basolateral side and was transported unidirectionally to the apical side. CL32 was greater than CL12 and CL23 was greater than CL21. Therefore, the rate limiting step of TEA transport from the basolateral to the apical medium was the cell-to-apical step. Co-incubation of TEA with procainamide decreased the transport parameters of TEA, CL12, CL21 and CL32, whereas that with levofloxacin decreased only CL12 and CL21, not affecting the parameters in basolateral membranes. CONCLUSIONS: Using a simple model, we analyzed the transport of organic cation in kidney epithelial cell line, LLC-PK1. This method can be useful for the analysis of cation transport and drug interactions in the apical and basolateral membranes of renal tubules.