O2 Exchange Research Articles

METABOLIC MYOPATHIES I: P.272No effect of triheptanoin on exercise performance in patients with McArdle disease - a double blind placebo-controlled crossover study

Patients with McArdle disease have blocked muscle glycogen breakdown due to an inherited defect myophosphorylase. This causes exercise intolerance with muscle pain, contractures and rhabdomyolysis. McArdle patients cannot increase fat oxidation to fully compensate for the energy deficiency due to a slow turnover in the tricarboxylic acid cycle (TCA). Metabolism of the 7-carbon fatty acid, triheptanoin, generates acetyl-CoA and propionyl-CoA, which enter the TCA and can therefore potentially boost fat oxidation in McArdle patients. In this double blind, placebo-controlled, crossover study we included 22 patients. Participants completed two 2-week treatment periods with a diet on triheptanoin or placebo oil (1g × kg-1 × day-1) separated by 1-2 weeks of washout. At baseline and at the end of the treatment periods, patients performed 20 minutes of submaximal exercise on a cycle ergometer followed by increments until exhaustion. Blood metabolites were measured every 10 minutes and exchange of O2. and CO2 was measured breath-by-breath. Nineteen patients completed the trial and qualified for data analysis. The patients had similar mean heart rates during submaximal exercise with triheptanoin (120±SD16 bpm) and with placebo treatment (121±SD16 bpm). Submaximal respiratory quotients were the same with triheptanoin (0.82±SD0.05) and placebo (0.84±SD0.03). They reached the same maximal workloads with treatment vs. placebo (105±SD38 vs. 102±SD31 Watts) and maximal oxygen uptake (1938±SD499 vs. 1977±SD380 mL × kg-1 × day-1). Blood glucose dropped with exercise to 4.6±SD0.8 vs. 4.4±SD1.0 mM and there was no difference in the production of ammonia with exercise (167±SD88 vs. 202±SD111 µM). Biochemical analyses of plasma TCA intermediates and fatty acids are ongoing. These preliminary data show no effect of triheptanoin treatment on exercise capacity and tolerance or muscle energy metabolism in McArdle patients.

A Computational Model of Heat Loss and Water Condensation on the Gas-Side of Blood Oxygenators.

Clinical observation of condensation at the gas flow exit of blood oxygenators is a recurrent event during cardiopulmonary bypass. These devices consist of a bundle of hollow fibers made of a microporous membrane that allows the exchange of O2 and CO2. The fibers carry a gas mixture inside (intraluminal flow), while blood flows externally around them (extraluminal flow). Although different studies described this effect in the past, the specific role of the different sections of the device requires further analysis, and the total condensation rate remains unquantified. In this study, a closer look is taken at the transition of gas between the oxygenation bundle and the external room air. A method is proposed to estimate the total condensate output, combining computational fluid dynamics (CFD) of thermal distribution and a simplified 1D model of water vapor saturation of gas. The influence of a number of different parameters is analyzed, regarding material properties, environmental conditions, and clinical use. Results show that condensation rate could vary in a 30‐fold range within reasonably small variations of the different variables considered.

A mathematical model of CO2, O2 and N2 exchange during venovenous extracorporeal membrane oxygenation

BackgroundVenovenous extracorporeal membrane oxygenation (vv-ECMO) is an effective treatment for severe respiratory failure. The interaction between the cardiorespiratory system and the oxygenator can be explored with mathematical models. Understanding the physiology will help the clinician optimise therapy. As others have examined O2 exchange, the main focus of this study was on CO2 exchange.MethodsA model of the cardiorespiratory system during vv-ECMO was developed, incorporating O2, CO2 and N2 exchange in both the lung and the oxygenator. We modelled lungs with shunt fractions varying from 0 to 1, covering the plausible range from normal lung to severe acute respiratory distress syndrome. The effects on PaCO2 of varying the input parameters for the cardiorespiratory system and for the oxygenator were examined.ResultsPaCO2 increased as the shunt fraction in the lung and metabolic CO2 production rose. Changes in haemoglobin and FIO2 had minimal effect on PaCO2. The effect of cardiac output on PaCO2 was variable, depending on the shunt fraction in the lung.PaCO2 decreased as extracorporeal circuit blood flow was increased, but the changes were relatively small in the range used clinically for vv-ECMO of > 2 l/min. PaCO2 decreased as gas flow to the oxygenator rose and increased with recirculation. The oxygen fraction of gas flow to the oxygenator had minimal effect on PaCO2.ConclusionsThis mathematical model of gas exchange during vv-ECMO found that the main determinants of PaCO2 during vv-ECMO were pulmonary shunt fraction, metabolic CO2 production, gas flow to the oxygenator and extracorporeal circuit recirculation.

Exercise Training Improves Ventilatory Efficiency in Patients With a Small Abdominal Aortic Aneurysm: A RANDOMIZED CONTROLLED STUDY.

To investigate the effects of exercise training on ventilatory efficiency and physiological responses to submaximal exercise in subjects with small abdominal aortic aneurysm (AAA). Sixty-five male patients (72.3 ± 7.0 years) were randomized to exercise training (n = 33) or usual care group (n = 32). Exercise subjects participated in a training groups for 3 mo. Cardiopulmonary exercise testing was performed before and after the study period and peak (Equation is included in full-text article.)O2, the ventilatory threshold (VT), the oxygen uptake efficiency slope (OUES), and the (Equation is included in full-text article.)E2/(Equation is included in full-text article.)CO2 slope were identified. Baseline work rates at VT were matched to examine cardiopulmonary responses after training. Significant interactions indicating improvements before and after training in the exercise group were noted for time (P < .01), (Equation is included in full-text article.)O2 (P < .01), and work rate (P < .01) at the VT. At peak effort, significant interactions were noted for time (P < .01) and work rate (P < .01), while borderline significance was noted for absolute (P = .07) and relative (P = .04) (Equation is included in full-text article.)O2. Significant interactions were observed for the OUES both when using all exercise data (P = .04) and when calculated up to the VT (P < .01). For the (Equation is included in full-text article.)E2/(Equation is included in full-text article.)CO2 slope, significance was noted only when calculated up to the VT (P = .04). After training, heart rate, (Equation is included in full-text article.)E, (Equation is included in full-text article.)O2 and respiratory exchange ratio were significantly attenuated for the same baseline work rate only in the exercise group (all P < .01). Exercise training improves ventilatory efficiency in patients with small AAA. In addition, patients who exercised exhibited less demanding cardiorespiratory responses to submaximal effort.

Chronic atorvastatin and exercise can partially reverse established skeletal muscle microvasculopathy in metabolic syndrome.

It has long been known that chronic metabolic disease is associated with a parallel increase in the risk for developing peripheral vascular disease. Although more clinically relevant, our understanding about reversing established vasculopathy is limited compared with our understanding of the mechanisms and development of impaired vascular structure/function under these conditions. Using the 13-wk-old obese Zucker rat (OZR) model of metabolic syndrome, where microvascular dysfunction is sufficiently established to contribute to impaired skeletal muscle function, we imposed a 7-wk intervention of chronic atorvastatin treatment, chronic treadmill exercise, or both. By 20 wk of age, untreated OZRs manifested a diverse vasculopathy that was a central contributor to poor muscle performance, perfusion, and impaired O2 exchange. Atorvastatin or exercise, with the combination being most effective, improved skeletal muscle vascular metabolite profiles (i.e., nitric oxide, PGI2, and thromboxane A2 bioavailability), reactivity, and perfusion distribution at both individual bifurcations and within the entire microvascular network versus responses in untreated OZRs. However, improvements to microvascular structure (i.e., wall mechanics and microvascular density) were less robust. The combination of the above improvements to vascular function with interventions resulted in an improved muscle performance and O2 transport and exchange versus untreated OZRs, especially at moderate metabolic rates (3-Hz twitch contraction). These results suggest that specific interventions can improve specific indexes of function from established vasculopathy, but either this process was incomplete after 7-wk duration or measures of vascular structure are either resistant to reversal or require better-targeted interventions. NEW & NOTEWORTHY We used atorvastatin and/or chronic exercise to reverse established microvasculopathy in skeletal muscle of rats with metabolic syndrome. With established vasculopathy, atorvastatin and exercise had moderate abilities to reverse dysfunction, and the combined application of both was more effective at restoring function. However, increased vascular wall stiffness and reduced microvessel density were more resistant to reversal. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/reversal-of-microvascular-dysfunction/ .

Use of argon to measure gas exchange in turbulent mountain streams

Abstract. Gas exchange is a parameter needed in stream metabolism and trace gas emissions models. One way to estimate gas exchange is via measuring the decline of added tracer gases such as sulfur hexafluoride (SF6). Estimates of oxygen (O2) gas exchange derived from SF6 additions require scaling via Schmidt number (Sc) ratio, but this scaling is uncertain under conditions of high gas exchange via bubbles because scaling depends on gas solubility as well as Sc. Because argon (Ar) and O2 have nearly identical Schmidt numbers and solubility, Ar may be a useful tracer gas for estimating stream O2 exchange. Here we compared rates of gas exchange measured via Ar and SF6 for turbulent mountain streams in Wyoming, USA. We measured Ar as the ratio of Ar : N2 using a membrane inlet mass spectrometer (MIMS). Normalizing to N2 confers higher precision than simply measuring [Ar] alone. We consistently enriched streams with Ar from 1 to 18 % of ambient Ar concentration and could estimate gas exchange rate using an exponential decline model. The mean ratio of gas exchange of Ar relative to SF6 was 1.8 (credible interval 1.1 to 2.5) compared to the theoretical estimate 1.35, showing that using SF6 would have underestimated exchange of Ar. Steep streams (slopes 11–12 %) had high rates of gas exchange velocity normalized to Sc=600 (k600, 57–210 m d−1), and slope strongly predicted variation in k600 among all streams. We suggest that Ar is a useful tracer because it is easily measured, requires no scaling assumptions to estimate rates of O2 exchange, and is not an intense greenhouse gas as is SF6. We caution that scaling from rates of either Ar or SF6 gas exchange to CO2 is uncertain due to solubility effects in conditions of bubble-mediated gas transfer.

Influence of Background H2O on the Collision-Induced Dissociation Products Generated from [UO2NO3].

Developing a comprehensive understanding of the reactivity of uranium-containing species remains an important goal in areas ranging from the development of nuclear fuel processing methods to studies of the migration and fate of the element in the environment. Electrospray ionization (ESI) is an effective way to generate gas-phase complexes containing uranium for subsequent studies of intrinsic structure and reactivity. Recent experiments by our group have demonstrated that the relatively low levels of residual H2O in a 2-D, linear ion trap (LIT) make it possible to examine fragmentation pathways and reactions not observed in earlier studies conducted with 3-D ion traps (Van Stipdonk et al. J. Am. Soc. Mass Spectrom. 14, 1205-1214, 2003). In the present study, we revisited the dissociation of complexes composed of uranyl nitrate cation [UVIO2(NO3)]+ coordinated by alcohol ligands (methanol and ethanol) using the 2-D LIT. With relatively low levels of background H2O, collision-induced dissociation (CID) of [UVIO2(NO3)]+ primarily creates [UO2(O2)]+ by the ejection of NO. However, CID (using He as collision gas) of [UVIO2(NO3)]+ creates [UO2(H2O)]+ and UO2+ when the 2-D LIT is used with higher levels of background H2O. Based on the results presented here, we propose that product ion spectrum in the previous experiments was the result of a two-step process: initial formation of [UVIO2(O2)]+ followed by rapid exchange of O2 for H2O by ion-molecule reaction. Our experiments illustrate the impact of residual H2O in ion trap instruments on the product ions generated by CID and provide a more accurate description of the intrinsic dissociation pathway for [UVIO2(NO3)]+. Graphical Abstract ᅟ.

The physiological cost of diazotrophy for Trichodesmium erythraeum IMS101.

Trichodesmium plays a significant role in the oligotrophic oceans, fixing nitrogen in an area corresponding to half of the Earth’s surface, representing up to 50% of new production in some oligotrophic tropical and subtropical oceans. Whilst Trichodesmium blooms at the surface exhibit a strong dependence on diazotrophy, colonies at depth or at the surface after a mixing event could be utilising additional N-sources. We conducted experiments to establish how acclimation to varying N-sources affects the growth, elemental composition, light absorption coefficient, N2 fixation, PSII electron transport rate and the relationship between net and gross photosynthetic O2 exchange in T. erythraeum IMS101. To do this, cultures were acclimated to growth medium containing NH4+ and NO3- (replete concentrations) or N2 only (diazotrophic control). The light dependencies of O2 evolution and O2 uptake were measured using membrane inlet mass spectrometry (MIMS), while PSII electron transport rates were measured from fluorescence light curves (FLCs). We found that at a saturating light intensity, Trichodesmium growth was ~ 10% and 13% lower when grown on N2 than with NH4+ and NO3-, respectively. Oxygen uptake increased linearly with net photosynthesis across all light intensities ranging from darkness to 1100 μmol photons m-2 s-1. The maximum rates and initial slopes of light response curves for C-specific gross and net photosynthesis and the slope of the relationship between gross and net photosynthesis increased significantly under non-diazotrophic conditions. We attribute these observations to a reduced expenditure of reductant and ATP for nitrogenase activity under non-diazotrophic conditions which allows NADPH and ATP to be re-directed to CO2 fixation and/or biosynthesis. The energy and reductant conserved through utilising additional N-sources could enhance Trichodesmium’s productivity and growth and have major implications for its role in ocean C and N cycles.

Changes in the PO2‐dependence of oxygen consumption in the skeletal muscle of developing rats

A continuous supply of O2 to cells in a mammalian organism is necessary to maintain normal physiological function and the microcirculation is especially important in this matter as it is the site of O2 exchange. Under conditions of active/functional hyperemia following muscle contraction, the O2 transport system in older subjects does not appear to respond as rapidly and to the same degree as in younger subjects. With aging, elements of the O2 transport and regulatory system are changed in such a way that matching O2 supply to O2 demand does not work as well in older as in younger subjects. With regard to the O2 demand component of the overall system, in vitro studies have shown that oxygen consumption (VO2) remains constant until a critical partial pressure (Pcrit) of O2 (&lt;1 mmHg) is reached. This knowledge was predicated on the assumption that the in vitro studies mimicked conditions in living tissue. More recently, however, in vivo studies have shown that VO2 varies over a much wider range of O2 partial pressure in the interstitial fluid (PISFO2). An intravital microscopic approach is being used to show that developmental changes in the O2 transport system begin earlier than previously thought. Significant and rapid changes in the microvascular network of skeletal muscle have been observed during the first few weeks of postnatal development. Three different developmental groups of male Sprague‐Dawley rats (2, 4, and 6 months) were used to investigate early changes in the O2 demand component of the transport system by measuring VO2 and the PISFO2 dependence of VO2 under resting conditions. VO2 of the spinotrapezius muscle was measured with a quasi‐continuous, flash‐synchronized, rapidly pressurized airbag system to briefly arrest blood flow and determine the rate of decrease of oxygen tension (dPO2/dt) in the ISF bathing the skeletal muscle fibers. Changes in PISFO2 of the skeletal muscle were measured using phosphorescence quenching microscopy. To understand the PO2 dependence of VO2, VO2 data were plotted versus PO2 and the results analyzed using a generalization of Michaelis‐Menten kinetics. This yielded information about both maximum VO2 (Vmax) and the PO2 at half Vmax (P50). Experiments were carried out on 16 animals with average weights (mean ± SEM) from 280 ± 10, 408 ± 17, to 454 ± 6 grams at 2 mo, 4 mo, and 6 mo, respectively. Average Vmax (mean ± SEM) was 138 ± 9, 148 ± 15, to 122 ± 6 nL O2/cm3·s for 2 mo, 4 mo, and 6 mo, respectively. Between 2 mo and 6 mo, there was a downward trend with Vmax which was not significant. Average P50 (mean ± SEM) was 11 ± 1, 15 ± 1, to 21 ± 1 mmHg for 2 mo, 4 mo, and 6 mo, respectively. There was a significant (p &lt; 0.05) increase in P50 from 2 mo to 6 mo which indicates that as the developmental age of the animal increases, there is an increased sensitivity of O2 consumption to changes in PISFO2. The findings are consistent with published data indicating that VO2 depends on PISFO2 over a much wider physiological range than previously thought. It is clear that as the rat develops, it consumes less O2 which may be ascribed to some combination of changes in the O2 delivery system and mitochondrial function.Support or Funding InformationSupport from Department of Physiology and BiophysicsThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The effect of use of edutainment on changes in hemoglobin levels in adolescents (Case study of SMPN 4 banjarbaru)

Anemia is a body condition characterized by deficiency in size and number of erythrocytes or in insufficient hemoglobin levels for the function of O2 and CO2 exchange between blood tissues. The prevalence of anemia in adolescents in Indonesia is quite high, namely 21.7% with anemia sufferers aged 5–14 years by 26.4% and 18.4% of patients aged 15–24 years. Banjarabaru City is the highest area of ​​anemia in adolescents in South Kalimantan Province at 58.75%. Efforts that can be made to improve the application of balanced nutrition in adolescents in preventing anemia have not been optimal either direct efforts such as giving tablets blood or not directly through counseling and socialization. another effort to provide information related to nutrition according to their needs, one of which is to provide nutritional education in the form of counseling edutainment. Edutainment is a form of counseling or education that is packaged in the form of fun entertainment. The purpose of the study is to analyze the effect of using edutainment on changes in hemoglobin levels in young women.

Continuous measurement of air–water gas exchange by underwater eddy covariance

Abstract. Exchange of gases, such as O2, CO2, and CH4, over the air–water interface is an important component in aquatic ecosystem studies, but exchange rates are typically measured or estimated with substantial uncertainties. This diminishes the precision of common ecosystem assessments associated with gas exchanges such as primary production, respiration, and greenhouse gas emission. Here, we used the aquatic eddy covariance technique – originally developed for benthic O2 flux measurements – right below the air–water interface (∼ 4 cm) to determine gas exchange rates and coefficients. Using an acoustic Doppler velocimeter and a fast-responding dual O2–temperature sensor mounted on a floating platform the 3-D water velocity, O2 concentration, and temperature were measured at high-speed (64 Hz). By combining these data, concurrent vertical fluxes of O2 and heat across the air–water interface were derived, and gas exchange coefficients were calculated from the former. Proof-of-concept deployments at different river sites gave standard gas exchange coefficients (k600) in the range of published values. A 40 h long deployment revealed a distinct diurnal pattern in air–water exchange of O2 that was controlled largely by physical processes (e.g., diurnal variations in air temperature and associated air–water heat fluxes) and not by biological activity (primary production and respiration). This physical control of gas exchange can be prevalent in lotic systems and adds uncertainty to assessments of biological activity that are based on measured water column O2 concentration changes. For example, in the 40 h deployment, there was near-constant river flow and insignificant winds – two main drivers of lotic gas exchange – but we found gas exchange coefficients that varied by several fold. This was presumably caused by the formation and erosion of vertical temperature–density gradients in the surface water driven by the heat flux into or out of the river that affected the turbulent mixing. This effect is unaccounted for in widely used empirical correlations for gas exchange coefficients and is another source of uncertainty in gas exchange estimates. The aquatic eddy covariance technique allows studies of air–water gas exchange processes and their controls at an unparalleled level of detail. A finding related to the new approach is that heat fluxes at the air–water interface can, contrary to those typically found in the benthic environment, be substantial and require correction of O2 sensor readings using high-speed parallel temperature measurements. Fast-responding O2 sensors are inherently sensitive to temperature changes, and if this correction is omitted, temperature fluctuations associated with the turbulent heat flux will mistakenly be recorded as O2 fluctuations and bias the O2 eddy flux calculation.

Processes and Effects of Oxygen and Moisture in Resistively Switching TaOx and HfOx

AbstractForeign components such as dopants and impurities in molecular or ionic form may significantly influence forming/switching processes in redox‐based memories. This work presents a systematic study and discussion on effects of oxygen and moisture in Ta2O5 and HfO2 thin films, being two of the most used materials for redox‐based resistively switching random access memories. Whereas oxygen is found to not affect the device behavior, the presence of moisture profoundly influences it. It plays a crucial role for the counter electrode reaction, providing additional charged species and enabling the formation of oxygen vacancies, thus determining the forming voltage and the kinetics of this process. Here, methods for incorporation of moisture within the oxide films and its defect chemistry are discussed. Based on the standard electrode potentials and analysis of the electrochemical processes at both electrodes, it is possible to predict their sequence during switching. The difference using symmetric cells with inert electrodes Pt/MeOx/Pt and asymmetric devices with ohmic electrodes Me/MeOx/Pt is explained by the electrochemical reaction sequence and ability of the ohmic electrode to undergo redox reactions. Upon oxidation the Me electrode can either exchange O2− with the oxide or can be a source for cations within the MeOx, keeping the balance between oxygen rich/deficient matrix.

Metabolic Flexibility Underpins Growth Capabilities of the Fastest Growing Alga

The factors rate-limiting growth of photosynthetic organisms under optimal conditions are controversial [1-8]. Adaptation to extreme environments is usually accompanied by reduced performance under optimal conditions [9, 10]. However, the green alga Chlorella ohadii, isolated from a harsh desert biological soil crust [11-17], does not obey this rule. In addition to resistance to photodamage [17, 18], it performs the fastest growth ever reported for photosynthetic eukaryotes. A multiphasic growth pattern (very fast growth [phase I], followed by growth retardation [phase II] and additional fast growth [phase III]) observed under constant illumination and temperature indicates synchronization of the algal population. Large physiological changes at transitions between growth phases suggest metabolic shifts. Indeed, metabolome analyses at points along the growth phases revealed large changes in the levels of many metabolites during growth with an overall rise during phase I and decline in phase II. Multivariate analysis of the metabolome data highlighted growth phase as the main factor contributing to observed metabolite variance. The analyses identified putrescine as the strongest predictive metabolite for growth phase and a putative growth regulator.Indeed, extracellular additions of polyamines strongly affected the growth rate in phase I and the growth arrest in phase II, with a marked effect on O2 exchange. Our data implicate polyamines as the signals harmonizing metabolic shifts and suggest that metabolic flexibility enables the immense growth capabilities of C.ohadii. The data provide anew dimension to current models focusing on growth-limiting processes in photosynthetic organisms where the anabolic and catabolic metabolisms must be strictly regulated.

Investigation of Cr Poisoning on the LSCF Cathode Under Different Temperatures for Solid Oxide Fuel Cell

The Cr poisoning effect on cathode is identified as a considerable negative factor for the long-term performance of Solid Oxide Fuel Cells(SOFCs). With the lowering of the operating temperature of SOFCs, more high performance cathode materials could be used. In this study, the relation between testing temperature of SOFC and the Cr poisoning effect on La0.6Sr0.4Fe0.8Co0.2O3-δ - Ce0.9Gd0.1O2-δ symmetric cells is investigated . Combined with the SEM and XRD , a secondary phase, identified as SrCrO4 is found formed on the surface of cathode to cause serious cathode degradation. The EIS shows that as the increasing of performance temperature from 550°C to 750°C, the Cr poisoning effect firstly increases to the maximal poisoning effect on 650°C and then decreases as the increasing of testing temperature. The evaporation of Cr from metallic interconnect could increase with the rising of testing temperature, However , the surface incorporation and exchange of Cr or O2 may not obey the tendency of temperature. With the DRT calculation, the Cr is more easily to occupy the Co sites on the LSCF but O is more tend to occupy the Sr sites, which may lead to the existence of the peak performance temperature for the remarkable Cr poisoning effect on LSCF.

Diet density during the first week of life: Effects on energy and nitrogen balance characteristics of broiler chickens

This study aimed to determine effects of diet density on growth performance, energy balance, and nitrogen (N) balance characteristics of broiler chickens during the first wk of life. Effects of diet density were studied using a dose-response design consisting of 5 dietary fat levels (3.5, 7.0, 10.5, 14.0, and 17.5%). The relative difference in dietary energy level was used to increase amino acid levels, mineral levels, and the premix inclusion level at the same ratio. Chickens were housed in open-circuit climate respiration chambers from d 0 to 7 after hatch. Body weight was measured on d 0 and 7, whereas feed intake was determined daily. For calculation of energy balances, O2 and CO2 exchange were measured continuously and all excreta from d 0 to 7 was collected and analyzed at d 7. Average daily gain (ADG) and average daily feed intake (ADFI) decreased linearly (P = 0.047 and P < 0.001, respectively), whereas gain to feed ratio increased (P < 0.001) with increasing diet density. Gross energy (GE) intake and metabolizable energy (ME) intake were not affected by diet density, but the ratio between ME and GE intake decreased linearly with increasing diet density (P = 0.006). Fat, N, and GE efficiencies (expressed as gain per unit of nutrient intake), heat production, and respiratory exchange ratio (CO2 to O2 ratio) decreased linearly (P < 0.001) as diet density increased. Energy retention, N intake, and N retention were not affected by diet density. We conclude that a higher diet density in the first wk of life of broiler chickens did not affect protein and fat retention, whereas the ME to GE ratio decreased linearly with increased diet density. This suggests that diet density appears to affect digestibility rather than utilization of nutrients.

Molecular Design of Mesoporous NiCo2O4 and NiCo2S4 with Sub‐Micrometer‐Polyhedron Architectures for Efficient Pseudocapacitive Energy Storage

Spinel‐type NiCo2O4 (NCO) and NiCo2S4 (NCS) polyhedron architectures with sizes of 500–600 nm and rich mesopores with diameters of 1–2 nm are prepared facilely by the molecular design of Ni and Co into polyhedron‐shaped zeolitic imidazolate frameworks as solid precursors. Both as‐prepared NCO and NCS nanostructures exhibit excellent pseudocapacitance and stability as electrodes in supercapacitors. In particular, the exchange of O2− in the lattice of NCO with S2− obviously improves the electrochemical performance. NCS shows a highly attractive capacitance of 1296 F g−1 at a current density of 1 A g−1, ultrahigh rate capability with 93.2% capacitance retention at 10 A g−1, and excellent cycling stability with a capacitance retention of 94.5% after cycling at 1 A g−1 for 6000 times. The asymmetric supercapacitor with an NCS negative electrode and an active carbon positive electrode delivers a very attractive energy density of 44.8 Wh kg−1 at power density 794.5 W kg−1, and a favorable energy density of 37.7 Wh kg−1 is still achieved at a high power density of 7981.1 W kg−1. The specific mesoporous polyhedron architecture contributes significantly to the outstanding electrochemical performances of both NCO and NCS for capacitive energy storage.

Impacts of ENSO on air‐sea oxygen exchange: Observations and mechanisms

AbstractModels and observations of atmospheric potential oxygen (APO ≃ O2 + 1.1 * CO2) are used to investigate the influence of El Niño–Southern Oscillation (ENSO) on air‐sea O2 exchange. An atmospheric transport inversion of APO data from the Scripps flask network shows significant interannual variability in tropical APO fluxes that is positively correlated with the Niño3.4 index, indicating anomalous ocean outgassing of APO during El Niño. Hindcast simulations of the Community Earth System Model (CESM) and the Institut Pierre‐Simon Laplace model show similar APO sensitivity to ENSO, differing from the Geophysical Fluid Dynamics Laboratory model, which shows an opposite APO response. In all models, O2 accounts for most APO flux variations. Detailed analysis in CESM shows that the O2 response is driven primarily by ENSO modulation of the source and rate of equatorial upwelling, which moderates the intensity of O2 uptake due to vertical transport of low‐O2 waters. These upwelling changes dominate over counteracting effects of biological productivity and thermally driven O2 exchange. During El Niño, shallower and weaker upwelling leads to anomalous O2 outgassing, whereas deeper and intensified upwelling during La Niña drives enhanced O2 uptake. This response is strongly localized along the central and eastern equatorial Pacific, leading to an equatorial zonal dipole in atmospheric anomalies of APO. This dipole is further intensified by ENSO‐related changes in winds, reconciling apparently conflicting APO observations in the tropical Pacific. These findings suggest a substantial and complex response of the oceanic O2 cycle to climate variability that is significantly (&gt;50%) underestimated in magnitude by ocean models.

Neurogenic hypertension and the secrets of respiration.

Despite recent advances in the knowledge of the neural control of cardiovascular function, the cause of sympathetic overactivity in neurogenic hypertension remains unknown. Studies from our laboratory point out that rats submitted to chronic intermittent hypoxia (CIH), an experimental model of neurogenic hypertension, present changes in the central respiratory network that impact the pattern of sympathetic discharge and the levels of arterial pressure. In addition to the fine coordination of respiratory muscle contraction and relaxation, which is essential for O2 and CO2 pulmonary exchanges, neurons of the respiratory network are connected precisely to the neurons controlling the sympathetic activity in the brain stem. This respiratory-sympathetic neuronal interaction provides adjustments in the sympathetic outflow to the heart and vasculature during each respiratory phase according to the metabolic demands. Herein, we report that CIH-induced sympathetic over activity and mild hypertension are associated with increased frequency discharge of ventral medullary presympathetic neurons. We also describe that their increased frequency discharge is dependent on synaptic inputs, mostly from neurons of the brain stem respiratory network, rather than changes in their intrinsic electrophysiological properties. In perspective, we are taking into consideration the possibility that changes in the central respiratory rhythm/pattern generator contribute to increased sympathetic outflow and the development of neurogenic hypertension. Our experimental evidence provides support for the hypothesis that changes in the coupling of respiratory and sympathetic networks might be one of the unrevealed secrets of neurogenic hypertension in rats.

Inflammatory Responses Regulating Alveolar Ion Transport during Pulmonary Infections

The respiratory epithelium is lined by a tightly balanced fluid layer that allows normal O2 and CO2 exchange and maintains surface tension and host defense. To maintain alveolar fluid homeostasis, both the integrity of the alveolar–capillary barrier and the expression of epithelial ion channels and pumps are necessary to establish a vectorial ion gradient. However, during pulmonary infection, auto- and/or paracrine-acting mediators induce pathophysiological changes of the alveolar–capillary barrier, altered expression of epithelial Na,K-ATPase and of epithelial ion channels including epithelial sodium channel and cystic fibrosis membrane conductance regulator, leading to the accumulation of edema and impaired alveolar fluid clearance. These mediators include classical pro-inflammatory cytokines such as TGF-β, TNF-α, interferons, or IL-1β that are released upon bacterial challenge with Streptococcus pneumoniae, Klebsiella pneumoniae, or Mycoplasma pneumoniae as well as in viral infection with influenza A virus, pathogenic coronaviruses, or respiratory syncytial virus. Moreover, the pro-apoptotic mediator TNF-related apoptosis-inducing ligand, extracellular nucleotides, or reactive oxygen species impair epithelial ion channel expression and function. Interestingly, during bacterial infection, alterations of ion transport function may serve as an additional feedback loop on the respiratory inflammatory profile, further aggravating disease progression. These changes lead to edema formation and impair edema clearance which results in suboptimal gas exchange causing hypoxemia and hypercapnia. Recent preclinical studies suggest that modulation of the alveolar–capillary fluid homeostasis could represent novel therapeutic approaches to improve outcomes in infection-induced lung injury.

Dynamics of Skeletal Muscle Microvascular and Interstitial PO2 from Rest to Contractions

Oxygen pressure (PO2) gradients within the microcirculation are required for diffusive O2 transport and, thus, to support oxidative metabolism. The greatest resistance to O2 flux into the skeletal muscle is considered to reside in the short distance between the red blood cell and the adjacent sarcolemma. Given the high flux density and absence of an O2 carrier within this diffusion path, we tested the hypothesis that PO2 gradients between muscle microvascular and interstitial spaces (PO2mv and PO2is; respectively) would be present at rest and maintained or increased during contractions. Oxyphor probes G2 (Pd‐meso‐tetra‐(4‐carboxyphenyl)‐porphyrin; i.a.) and G4 (Pd‐meso‐tetra‐(3,5‐dicarboxyphenyl)‐tetrabenzoporphyrin; tissue microinjection) were used to determine PO2mv and PO2is, respectively, via phosphorescence quenching in the exposed rat spinotrapezius muscle at rest and during submaximal twitch contractions (1 Hz, 6 V, 3 min). Due to overlapping spectral features of G2 and G4, separate measurements of PO2mv (right spinotrapezius; second protocol) and PO2is (left spinotrapezius; first protocol) were performed in the same animals (Sprague‐Dawley; n=7). There were no differences in mean arterial pressure or heart rate during the rest‐contraction transient between protocols (P&gt;0.05 for all). PO2mv was higher than PO2is in all instances from rest to contractions (baseline: 34.3±2.3 vs. 13.8±1.4; steady‐state: 27.4±1.8 vs. 9.3±1.6 mmHg, respectively; P&lt;0.05 for both) such that the mean PO2 gradient throughout the entire protocol was 18.3±2.2 mmHg (z‐test P&lt;0.05). No differences in the magnitude of the PO2 fall induced by contractions were observed between the microvascular and interstitial spaces (amplitude: 9.3±1.4 vs. 11.1±0.9 mmHg, respectively; P&gt;0.05). The speed of the PO2is fall during contractions was slower than that of PO2mv (time constant: 13.0±1.9 vs. 9.6±2.0 s, respectively; P&lt;0.05). Consistent with our hypothesis, a significant gradient between PO2mv and PO2is was sustained (but not increased) from rest to contractions in skeletal muscle. These data support that the carrier‐free region is the site of a substantial PO2 gradient driving blood‐myocyte O2 flux. Therefore, Oxyphor G2 and G4 probes allow discrete investigation of O2 exchange in the microvascular and interstitial spaces. Differences in PO2mv and PO2is kinetics illustrate the potential for muscle microcirculatory O2 exchange dynamics at sites closer to the mitochondria to provide novel insights into the control of muscle oxidative function in health and dysfunction in disease.Support or Funding InformationNIH HL‐2‐108328