The effect of the width of the ventilation-perfusion distribution on arterial blood oxygen content

We investigate the effect of the width of ventilation-perfusion distributions on arterial blood oxygen content. We assume that the perfusion within the alveolar volume is a continuous function of ventilation-perfusion ratio, known as the continuous ventilation-perfusion distribution, and then write down the conservation of mass equations in the lung incorporating the nonlinear relationship between oxygen concentration in the gas phase and blood oxygen content. We solve these equations for various unimodal and bimodal ventilation-perfusion distributions believed to occur in practice and calculate the arterial blood oxygen content in each case. When a subject has a unimodal ventilation-perfusion distribution we show that the fraction of cardiac output to that mode (i.e. the fraction of non-shunted blood) has a large effect on arterial oxygen blood content. However, the width of the distribution has only a negligible effect on arterial oxygen blood content. For a bimodal ventilation-perfusion distribution the location and fraction of cardiac output to each mode has a large effect on arterial oxygen blood content. Again, the width of each mode of the distribution has little effect on arterial oxygen blood content. As a result there is little point, from a clinical perspective, in developing techniques for investigating the width of modes of these distributions since all relevant clinical information is contained in the nature (i.e. unimodal or bimodal) and in the location of the modes.     

On-line biomass estimation using a modified oxygen utilization rate

A procedure for estimating biomass during batch fermentation from on-line gas analysis is presented. First, the respiratory quotient was used to determine the fraction of the total oxygen utilization rate required for cell maintenance and growth versus product synthesis. The modified oxygen utilization rate was then used to estimate biomass on-line by integrating the oxygen balance for cell synthesis-maintenance. The method is illustrated for the case of L-lysine synthesis by Corynebacterium glutamicum.List of Symbols CER mmol CO₂/l · h carbon dioxide evolution rate - M _{O 2}/x mmol O₂/h · g cells maintenance coefficient - OUR mmol O₂/l · h oxygen utilization rate - OUR _X mmol O₂/l · h OUR fraction for cell maintenance and growth - RQ mmol CO₂/mmol O₂ respiratory quotient(CER/OUR) - X g cells/l biomass concentration - Y _X/O₂ yield coefficients     

Generation of recombinant Orf virus using an enhanced green fluorescent protein reporter gene as a selectable marker

Background

The purpose of this study was to compare the effects of 0.5 fraction of inspired oxygen (FiO₂) and >0.95 FiO₂ on pulmonary gas exchange, shunt fraction and oxygen delivery (DO₂) in dorsally recumbent horses during inhalant anesthesia. The use of 0.5 FiO₂ has the potential to reduce absorption atelectasis (compared to maximal FiO₂) and augment alveolar oxygen (O₂) tensions (compared to ambient air) thereby improving gas exchange and DO₂. Our hypothesis was that 0.5 FiO₂ would reduce ventilation-perfusion mismatching and increase the fraction of pulmonary blood flow that is oxygenated, thus improving arterial oxygen content and DO₂.

Results

Arterial partial pressures of O₂ were significantly higher than preanesthetic levels at all times during anesthesia in the >0.95 FiO₂ group. Arterial partial pressures of O₂ did not change from preanesthetic levels in the 0.5 FiO₂ group but were significantly lower than in the >0.95 FiO₂ group from 15 to 90 min of anesthesia. Alveolar to arterial O₂ tension difference was increased significantly in both groups during anesthesia compared to preanesthetic values. The alveolar to arterial O₂ tension difference was significantly higher at all times in the >0.95 FiO₂ group compared to the 0.5 FiO₂ group. Oxygen delivery did not change from preanesthetic values in either group during anesthesia but was significantly lower than preanesthetic values 10 min after anesthesia in the 0.5 FiO₂ group. Shunt fraction increased in both groups during anesthesia attaining statistical significance at varying times. Shunt fraction was significantly increased in both groups 10 min after anesthesia but was not different between groups. Alveolar dead space ventilation increased after 3 hr of anesthesia in both groups.

Conclusions

Reducing FiO₂ did not change alveolar dead space ventilation or shunt fraction in dorsally recumbent, mechanically ventilated horses during 3 hr of isoflurane anesthesia. Reducing FiO₂ in dorsally recumbent isoflurane anesthetized horses does not improve oxygenation or oxygen delivery.     

Biochemical markers for clinical monitoring of tissue perfusion

The assessment and monitoring of the tissue perfusion is extremely important in critical conditions involving circulatory shock. There is a wide range of established methods for the assessment of cardiac output as a surrogate of oxygen delivery to the peripheral tissues. However, the evaluation of whether particular oxygen delivery is sufficient to ensure cellular metabolic demands is more challenging. In recent years, specific biochemical parameters have been described to indicate the status between tissue oxygen demands and supply. In this review, the authors summarize the application of some of these biochemical markers, including mixed venous oxygen saturation (S_vO₂), lactate, central venous–arterial carbon dioxide difference (PCO₂ gap), and PCO₂ gap/central arterial-to-venous oxygen difference (C_a–vO₂) for hemodynamic assessment of tissue perfusion. The thorough monitoring of the adequacy of tissue perfusion and oxygen supply in critical conditions is essential for the selection of the most appropriate therapeutic strategy and it is associated with improved clinical outcomes.

     

Effects of exercise-stress on ventilation,cardiac output and blood respiratory parameters in the carp,Cyprinus carpio

• 1.1. Carp (Cyprinus carpio) were stressed to exercise by rolling in a respiration chamber. Ventilatory water flow rate, cardiac output and blood respiratory parameters were determined.
• 2.2. During exercise, oxygen uptake increased about 3.5-fold and returned to pre-exercise level within 15 min.
• 3.3. This exercise-stress resulted in no plasma acidosis and in no swelling of the erythrocytes.
• 4.4. Ventilatory water flow rate increased 6-fold, whereas cardiac output increased 2-fold. Hence the ventilation-perfusion ratio increased during exercise.
• 5.5. During exercise, arterial O₂ content (CaO₂) increased due to increases in O₂ tension (PaO₂), O₂ saturation of hemoglobin (SaO₂) and hemoglobin concentration (Hb). On the other hand, Pv̄O₂ and Sv̄O₂ remained at the resting levels but Cv̄O₂ slightly increased due to an increase in Hb.
• 6.6. Arterial-venous O₂ difference (CaO₂-Cv̄O₂) increased by 38%, which was met by a much greater increase in CaO₂ than Cv̄O₂.

     

Oxygen consumption by Campylobacter sputorum subspecies Bubulus with formate as substrate

The kinetics of oxygen utilization by the microaerophile Campylobacter sputorum subspecies bubulus was studied. With formate as substrate two enzyme systems were found to be responsible for electron transfer between formate and oxygen. In the case of lactate oxidation one enzyme system could account for the activity measured. One of the formateoxidizing systems possessed a high affinity for oxygen [K _m(O₂)=approx. 4M O₂]. From inhibitor studies it was concluded that a respiratory chain was involved in its activity. Respiration by this system must be responsible for proton translocation and electron transport-linked phosphorylation at formate oxidation. The other enzyme system had an extremely low affinity for oxygen [K _m (O₂)=approx. 1 mM O₂]. It was tentatively identified as the H₂O₂-producing formate oxidase previously found in C. sputorum. The H₂O₂ production by this enzyme is implicated in an explanation of the microaerophilic nature of C. sputorum. Sensitivity of formate dehydrogenase to H₂O₂ was demonstrated. The influence of the formate concentration on aerobic formate oxidation was determined. The pH- and temperature dependencies of oxygen uptake with formate as substrate were examined at airsaturation and at a low dissolved oxygen tension.Abbreviations TL medium tryptose-lactate medium - TF medium tryptose-formate medium - HQNO 2-n-heptyl-4-hydroxyquinoline N-oxide - SHAM salicylhydroxamic acid - DCPIP 2,6-dichlorophenolindophenol     

Toward Promising Cathode Catalysts for Nonlithium Metal–Oxygen Batteries

The success of Li–air/O₂ batteries has brought extensive attention to the development of various promising non‐Li metal–O₂ batteries, such as Zn–O₂, Al–O₂, Mg–O₂ batteries, etc., which have exhibited unique advantages, such as low production cost, high energy density, and much enhanced safety. The versatile non‐Li metal–O₂ batteries provide a better opportunity for meeting the practical requirements for sustainable energy supplies in various applications. A high‐performance cathode in non‐Li metal–O₂ batteries that can effectively trigger both oxygen reduction and evolution reactions and thus boost the overall battery performance is of great research interest. In this article, a comprehensive review on the development of Li‐free metal–O₂ batteries and particularly focusing on the oxygen catalytic cathodes for both primary and secondary non‐Li metal–O₂ batteries is carefully performed. The current challenges and potential solutions are also outlined and proposed. Through carefully selecting and rationally designing promising catalytic cathodes, a series of non‐Li metal–oxygen batteries toward practical energy storage applications are highly anticipated.     

Kinetics of Energetic O<Superscript>−</Superscript> Ions in the Discharge Plasmas of Water Vapor and H<Subscript>2</Subscript>O-Containing Mixtures

The process of relaxation of energetic O^– ions formed via dissociative attachment of electrons to molecules in the discharge plasmas of water vapor and H₂O: O₂ mixtures in a strong electric field is studied by the Monte Carlo method. The probability of energetic ions being involved in threshold ion–molecular processes is calculated. It is shown that several percent of energetic O^– ions formed via electron attachment to H₂O molecules in the course of plasma thermalization transform into OH^– ions via charge exchange or are destroyed with the formation of free electrons. The probabilities of charge exchange of O^– ions and electron detachment from them increase significantly (up to 90%) when O^– ions are formed via electron attachment to O₂ molecules in water vapor with an oxygen additive. This effect decreases with increasing oxygen fraction in the mixture but remains appreciable even when the fraction of H₂O molecules in the H₂O: O₂ mixture does not exceed several percent.     

Film models for multicomponent mass transfer: Diffusion in physiological gas mixtures

The exact solution of the Maxwell-Stefan equations for steady state diffusion in a stagnant film due to Krishna and Standart (1976) is compared to the approximate solutions of Toor (1964) and Stewart and Prober (1964) for osmotic diffusion of oxygen in the three physiological gas mixtures He−N₂−O₂, He−SF₆−O₂, N₂−SF₆−O₂. It is found that the predicted fluxes of He, N₂ and SF₆ are usually in excellent agreement but that the two methods could predict differing directions of transfer of oxygen. Concentration profiles obtained from the linearized equations may be significantly different from the profiles calculated from an exact solution of the film model.     

Evidence for improved myocardial oxygen delivery and function during hypoxia in the mole rat

Summary The high capillary density of the hypoxic adapted mole rat may provide an efficient oxygen extraction system that permits the maintenance of a normal metabolic rate during hypoxia. We compared myocardial function and energetics in the isolated working heart of the mole rat with that of the white rat during oxygenation (567 torr O₂) and 3 hypoxic periods of 319, 232 and 155 torr O₂, each followed by a reoxygenation period. Control hearts were perfused for a similar time but with oxygenated buffer. The control oxygenated mole rat heart had higher coronary flow (CF), systolic pressure and myocardial O₂ consumption and lower coronary resistance compared with the heart of the white rat. The hypoxic heart of the mole rat had higher CF, aortic flow, stroke volume, , mechanical power and efficiency, and lower coronary resistance compared with the hypoxic heart of the white rat. The better performance of the hypoxic mole rat heart was not due to a more efficient O₂ extraction but was associated with a lower coronary resistance. The findings correlate with the known cardiac physiology of the intact mole rat.     

Critical oxygen pressure for growth and respiration of excised and intact roots

A method based on the measurement of ATP/ADP ratios is described. It permits the determination of the critical respiratory oxygen pressure of any organ, or part of any organ, of an intact plant. The data obtained by this method with intact maize (Zea mays L. INRA 508) root tips are compared with polarographic determinations on similar excised tissues.

When internal O₂ transport from the aerial part was prevented, the critical oxygen pressure found for the respiration of intact tips was similar to that found with excised tips. It was close to 10 kilopascals in a humid atmosphere and about 30 kilopascals in a liquid medium. Flooding of the gas spaces by vacuum infiltration did not modify these results. When internal O₂ transport from the aerial parts of the plant occurred, significantly lower values were obtained in liquid medium for the critical oxygen pressure, which shifted from more than 21 to 6 kilopascals. The higher values observed with excised root tips, compared to those obtained with intact tissues, can be explained by the lack of internal O₂ transport, rather than by the flooding of gas spaces.

Data are presented which show that root growth started to be limited at a significantly higher pressure than the respiration. These results are attributed to nonrespiratory oxidative processes with a low affinity for O₂ involved in root elongation.

     

Interfacial Super‐Assembled Porous CeO2/C Frameworks Featuring Efficient and Sensitive Decomposing Li2O2 for Smart Li–O2 Batteries

The Li–O₂ battery (LOB) represents a promising candidate for future electric vehicles owing to its outstanding energy density. However, the practical application of LOB cells is largely blocked by the poor cycling performance of cathode materials. Herein, an ultralong 440‐cycle life of an LOB cell is achieved using CeO₂ nanocubes super‐assembled on an inverse opal carbon matrix as the cathode material without any additives. CeO₂ is proved to be effective for the complete and sensitive decomposition of loosely stacked Li₂O₂ films during the oxygen evolution reaction process and full accommodation of volume changes caused by the fast growth of Li₂O₂ films during the oxygen reduction reaction process. The super‐assembled porous CeO₂/C frameworks satisfy critical requirements including controlled size, morphology, high Ce³⁺/Ce⁴⁺ ratio, and efficient volume change accommodation, which dramatically increase the cycle life of LOB cell to 440 cycles. This study reveals the design strategy for high performance CeO₂ catalyst cathodes for LOB cells and the generation mechanisms of Li₂O₂ films during the discharge process by using density functional theory calculations, showing new avenues for improving the future smart design of CeO₂‐based cathode catalysts for Li–O₂ batteries.     

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°C, 20 kPa O₂). Prior to eclosion, heart rate (ƒH) 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 ƒH 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.     

Radiorespirometer for continuous monitoring of chick embryo development.

A radiorespirometer is described that is capable of continuous monitoring of O₂ utilization, CO₂ and/or ¹⁴CO₂ production per minute, heart rate, and body activity of an embryonated egg while it develops for several days in a closed chamber with near normal pO₂ or other desired pO₂. Oxygen is supplied to the embryo by an electrolytic cell, and CO₂ is removed by a KOH solution flowing through a diffusion cell separated from the embryo chamber by a CO₂ permeable rubber membrane. The instrument permits selecting embryos for viability and developmental stage, according to their O₂ utilization per minute and respiratory quotient, without breaking the eggshell. Inoculation of the embryonated egg with ¹⁴C-labeled substrates, drugs, or toxins can occur without interfering with continuous recording of metabolic activity.     

Über den Einfluß niedriger und hoher O2-Partialdrucke auf den Sauerstoff- und Kohlendioxidumsatz von Amaranthus und Phaseolus während der Lichtphase

Summary Carbon dioxide and oxygen gas exchange of illuminated Amaranthus and Phaseolus leaves was measured from 0–600 ppm of CO₂ in an open system.At low oxygen concentration (2% O₂) the ratio of CO₂ uptake to O₂ evolution came close to 1.At high oxygen partial pressure (42% O₂) the O₂ compensation point of an Amaranthus leaf was increased and oxygen evolution was depressed. Accordingly the CO₂/O₂ quotients were variable; the lowest value of 1,9 differed significantly from 1,0.The oxygen and carbon dioxide compensation points of a Phaseolus leaf were increased at high oxygen concentration (42% O₂) and oxygen evolution as well as carbon dioxide uptake were reduced. Therefore the ratios CO₂ over O₂ varied and differed greatly from 1,0.It was concluded that the nature of photosynthates is regulated by the gas composition around the leaves.     

A Mathematical Model of the Controlled Plant of the Réspiratory System

Ability to predict the dynamic response of oxygen, carbon dioxide tensions, and pH in blood and tissues to abrupt changes in ventilation is important in the mathematical modeling of the respiratory system. In this study, the controlled plant (the amount and distribution of O₂ and CO₂) of the respiratory system is modeled. Although the body tissues are divided into a finite number of “compartments” (three tissue groups), in contrast to earlier models, the blood and tissue gas tensions within each compartment are considered to be continuously distributed in time and in one spatial coordinate. The mass conservation equations for oxygen and carbon dioxide involved in the blood-tissue gas exchange are described by a set of partial differential equations which take into account convection of O₂ and CO₂ caused by the flow of blood as well as diffusion due to local tension gradients. Nonlinear algebraic equations for the dissociation curves, which take into account the Haldane and Bohr effects in blood, are used to obtain the relationships between concentrations and partial pressures. Time-variable delays caused by the arterial and venous transport of the respiratory gases are also included. The model so constructed successfully reproduced actual O₂ and CO₂ tensions in arterial blood, and in muscle venous and mixed venous blood when ventilation was abruptly changed.     

Defect Engineering of Oxygen‐Deficient Manganese Oxide to Achieve High‐Performing Aqueous Zinc Ion Battery

A major limitation of MnO₂ in aqueous Zn/MnO₂ ion battery applications is the poor utilization of its electrochemical active surface area. Herein, it is shown that by generating oxygen vacancies (V_O) in the MnO₂ lattice, Gibbs free energy of Zn²⁺ adsorption in the vicinity of V_O can be reduced to thermoneutral value (≈0.05 eV). This suggests that Zn²⁺ adsorption/desorption process on oxygen‐deficient MnO₂ is more reversible as compared to pristine MnO₂. In addition, because of the fact that fewer electrons are needed for Zn? O bonding in oxygen‐deficient MnO₂, more valence electrons can be contributed into the delocalized electron cloud of the material, which aids in enhancing the attainable capacity. As a result, the stable Zn/oxygen‐deficient MnO₂ battery is able to deliver one of the highest capacities of 345 mAh g^?1 reported for a birnessite MnO₂ system. This excellent electrochemical performance suggests that generating oxygen vacancies in MnO₂ may aid in the future development of advanced cathodes for aqueous Zn ion batteries.     

Transport of O2 along a model pathway through the respiratory region of the lung

A pathway through the system of branching in the respiratory region of the lung is modelled by a circular cylinder, closed at one end, with partitions which define the component respiratory units. In this model the transport of O₂ during inspiration, generated by diffusion is compared with that produced by diffusion together with convection and the importance of convection in the respiratory region in promoting oxygen uptake at the alveolar wall is discussed. For this discussion it is only necessary to consider inspiration. The equations are solved numerically for flow rates of 10, 85 and 200 liters/min. O₂ uptake at the wall and curves of constant O₂ concentration are shown to illustrate the influence of convection. It is found that after a 2 sec inspiration from an O₂ tension of 98 mm Hg and a lung volume of 2300 ml, convection is about 12 per cent as important as diffusion at a flow rate of 85 liters/min, whereas at 10 liters/min convection is only about 0.4 per cent as important as diffusion.     

Noninvasive estimation of human tissue respiration with wavelet-analysis of oxygen saturation and blood flow oscillations in skin microvessels

Laser Doppler flowmetry, laser spectrophotometry of oxygen saturation, and the fluorescence determination of the NADH/FAD ratio were carried out in 30 subjects in the upper limb skin zones with and without arteriolovenular anastomoses (AVAs). It was demonstrated that the wavelet-analysis of oxygen saturation and blood flow oscillations in microvessels was an efficient approach to noninvasive estimation of the skin oxygen extraction (OE) and oxygen consumption (OC) rates. OE = (SaO₂ ? SvO₂)/SaO₂, where SaO₂ (%) and SvO₂ (%) are the oxygen saturations of arterial and venular blood, respectively. If the cardiac (A_c, perfusion units, p.u.) to respiratory rhythm amplitude (A_r, p.u.) ratio A_c/A_r ?? 1, SvO₂ = SO₂. If A_c/A_r > 1, SvO₂ = SO₂/(A_c/A_r). OC = M _nutr (SaO₂ ?? SvO₂) in p.u. · %O₂, where M _nutr is the nutritive blood flow value in p.u. M _nutr = M/SI, where SI is the shunting index of blood flow in microvessels. The perfusion, OE, and OC values were higher in the skin with AVAs than in the skin without AVAs. The perfusion and oxygen saturation values were more variable in the skin with AVAs. The oxygen diffusing from the tiniest arterioles and capillaries is the most important for tissue metabolism. The contribution of the total perfusion and the oxygen diffusion from arterioles to tissue metabolism increased under the tissue ischemia conditions.     

The importance of physiological oxygen concentrations in the sandwich cultures of rat hepatocytes on gas‐permeable membranes

Oxygen supply is a critical issue in the optimization of in vitro hepatocyte microenvironments. Although several strategies have been developed to balance complex oxygen requirements, these techniques are not able to accurately meet the cellular oxygen demand. Indeed, neither the actual oxygen concentration encountered by cells nor the cellular oxygen consumption rates (OCR) was assessed. The aim of this study is to define appropriate oxygen conditions at the cell level that could accurately match the OCR and allow hepatocytes to maintain liver specific functions in a normoxic environment. Matrigel overlaid rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes under either atmospheric oxygen concentration [20%‐O₂ (+)] or physiological oxygen concentrations [10%‐O₂ (+), 5%‐O₂ (+)], respectively, to investigate the effects of various oxygen concentrations on the efficient functioning of hepatocytes. In parallel, the gas‐impermeable cultures (polystyrene) with PDMS membrane inserts were used as the control groups [PS‐O₂ (?)]. The results indicated that the hepatocytes under 10%‐O₂ (+) exhibited improved survival and maintenance of metabolic activities and functional polarization. The dramatic elevation of cellular OCR up to the in vivo liver rate proposed a normoxic environment for hepatocytes, especially when comparing with PS‐O₂ (?) cultures, in which the cells generally tolerated hypoxia. Additionally, the expression levels of 84 drug‐metabolism genes were the closest to physiological levels. In conclusion, this study clearly shows the benefit of long‐term culture of hepatocytes at physiological oxygen concentration, and indicates on an oxygen‐permeable membrane system to provide a simple method for in vitro studies. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1401–1410, 2014