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Net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) and water vapor (H 2 O) fluxes from irrigated grain sorghum ( Sorghum bicolor L. Moench) and maize ( Zea mays L.) fields in the Texas High Plains were quantified using the eddy covariance (EC) technique during 2014–2016 growing seasons and examined in terms of relevant controlling climatic variables. Eddy covariance measured evapotranspiration (ET EC ) was also compared against lysimeter measured ET (ET Lys ). Daily peak (7-day averages) NEE reached approximately −12 g C m −2 for sorghum and −14.78 g C m −2 for maize. Daily peak (7-day averages) ET EC reached approximately 6.5 mm for sorghum and 7.3 mm for maize. Higher leaf area index (5.7 vs 4–4.5 m 2  m −2 ) and grain yield (14 vs 8–9 t ha −1 ) of maize compared to sorghum caused larger magnitudes of NEE and ET EC in maize. Comparisons of ET EC and ET Lys showed a strong agreement (R 2  = 0.93–0.96), while the EC system underestimated ET by 15–24% as compared to lysimeter without any corrections or energy balance adjustments. Both NEE and ET EC were not inhibited by climatic variables during peak photosynthetic period even though diurnal peak values (~2-weeks average) of photosynthetic photon flux density (PPFD), air temperature (T a ), and vapor pressure deficit (VPD) had reached over 2000 μmol m −2  s −1 , 30 °C, and 2.5 kPa, respectively, indicating well adaptation of both C 4 crops in the Texas High Plains under irrigation. However, more sensitivity of NEE and H 2 O fluxes beyond threshold T a and VPD for maize than for sorghum indicated higher adaptability of sorghum for the region. These findings provide baseline information on CO 2 fluxes and ET for a minimally studied grain sorghum and offer a robust geographic comparison for maize outside the United States Corn Belt. However, longer-term measurements are required for assessing carbon and water dynamics of these globally important agro-ecosystems. [ABSTRACT FROM AUTHOR]

Hemoglobins are a group of respiratory proteins principally functioning in transport of oxygen and carbon dioxide in red blood cells of all vertebrates and some invertebrates. The blood clam T. granosa is one of the few invertebrates that have hemoglobin-containing red hemocytes. In the present research, the peroxidase activity of T. granosa hemoglobins (Tg-Hbs) was characterized and the associated mechanism of action was deciphered via structural comparison with other known peroxidases. We detected that purified Tg-Hbs catalyzed the oxidation of phenolic compounds in the presence of exogenous H2O2. Tg-Hbs peroxidase activity reached the maximum at pH 5 and 35°C and was inhibited by Fe2+, Cu2+, SDS, urea, and sodium azide. Tg-Hbs shared few similarities in amino acid sequence and overall structural characteristics with known peroxidases. However, the predicted structure at their heme pocket was highly similar to that of horseradish peroxidase (HRP) and myeloperoxidase (MPO). This research represented the first systemic characterization of hemoglobin as a peroxidase. [ABSTRACT FROM AUTHOR]

One way to increase potential crop yield could be increasing mesophyll conductance g m . This variable determines the difference between the CO 2 partial pressure in the intercellular air spaces ( C i ) and that near Rubisco ( C c ). Various methods can determine g m from gas exchange measurements, often combined with measurements of chlorophyll fluorescence or carbon isotope discrimination. g m lumps all biochemical and physical factors that cause the difference between C c and C i . g m appears to vary with C i . This variability indicates that g m does not satisfy the physical definition of a conductance according to Fick’s first law and is thus an apparent parameter. Uncertainty about the mechanisms that determine g m can be limited to some extent by using analytical models that partition g m into separate conductances. Such models are still only capable of describing the CO 2 diffusion pathway to a limited extent, as they make implicit assumptions about the position of mitochondria in the cells, which affect the re-assimilation of (photo)respired CO 2 . Alternatively, reaction-diffusion models may be used. Rather than quantifying g m , these models explicitly account for factors that affect the efficiency of CO 2 transport in the mesophyll. These models provide a better mechanistic description of the CO 2 diffusion pathways than mesophyll conductance models. Therefore, we argue that reaction-diffusion models should be used as an alternative to mesophyll conductance models, in case the aim of such a study is to identify traits that can be improved to increase g m . [ABSTRACT FROM AUTHOR]

In New Caledonia, a world-renowned mangrove, the “Coeur de Voh”, grows in a semi-arid climate and at a high elevation in the intertidal zone. Net CO 2 exchange (NEE) between the Avicennia marina shrub mangrove and the atmosphere was studied using an eddy-covariance system. The NEE and its biophysical controls were investigated, and net ecosystem production (NEP) was determined for one year. The daytime NEE ranged from −10.7 μmol m −2 s −1 to +6.9 μmol m −2 s −1 and the nighttime NEE ranged from +0.38 μmol m −2 s −1 to +8.80 μmol m −2 s −1 . Both minimum values of daytime NEE and maximum values of nighttime NEE were measured during the wet, and warm season. Solar radiation, temperature and vapor pressure deficit were the controlling factors of NEE variations on both diel and seasonal scales. Water availability from tides and rainfall appeared to be key factors driving mangrove productivity. The tidal cycle also had pronounced effects on the mangrove NEE. Our results suggest that submerged conditions during high tide decreased the ecosystem respiration contribution and may increase the rate of tree photosynthesis. The absence of flooding spanning a few days rapidly decreased the NEE, suggesting that the trees experience water stress. The NEP was significantly and negatively correlated with rainfall and showed high seasonal variation. During the wet season, the NEP was very low and even negative, whereas the ecosystem photosynthesis was the greatest of the year. Indeed, the low NEP during the wet season was related to a significant increase in ecosystem respiration, whereas the low NEP during the dry season was linked to a decrease in ecosystem photosynthesis due primarily to an absence of freshwater from rainfall and seawater from tides. We estimate that the annual NEP was 73.8 gC m −2 and may be lower if carbon tidal exports are significant. Consequently, the NEP of this dwarf mangrove in a semi-arid climate was much lower than that of mangroves in humid climates. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to visualizing regional lung function, through quantitative three-dimensional maps of O 2 and CO 2 transfer rates. These maps describe the contribution of anatomical regions to overall gas exchange and demonstrate how transfer rates of the two gas species’ differ regionally. An algorithm for generating such maps is presented, and for illustration, regional gas transfer maps were generated using values of ventilation and perfusion imaged by PET/CT for a healthy subject and an asthmatic patient after bronchoprovocation. In a sensitivity analysis, compartment values of gas transfer showed minor sensitivity to imaging noise in the ventilation and perfusion data, and moderate sensitivity to estimation errors in global lung input values, chiefly global alveolar ventilation, followed by cardiac output and arterial-venous O 2 content difference. Gas transfer maps offer an intuitive display of physiologically relevant lung function at a regional level, the potential for an improved understanding of pulmonary gas exchange in health and disease, and potentially a presurgical evaluation tool. [ABSTRACT FROM AUTHOR]

Maintaining a proper pH level is crucial for successful cell culturing. Mammalian cells are commonly cultured in incubators, where the cell culture medium is saturated with a mixture of air and 5% carbon dioxide (CO 2 ). Therefore, to keep cell culture medium pH in an acceptable level outside these incubators, a suitable CO 2 concentration must be dissolved in the medium. However, it can be very difficult to control and measure precisely local concentration levels. Furthermore, possible undesired concentration gradients generated during long-term cell culturing are almost impossible to detect. Therefore, we have developed a computational model to estimate CO 2 transport in silicone-based microfluidic devices. An extensive set of experiments was used to validate the finite element model. The model parameters were obtained using suitable measurement set-ups and the model was validated using a fully functional cell cultivation device. The predictions obtained by the simulations show very good responses to experiments. It is shown in this paper how the model helps to understand the dynamics of CO 2 transport in silicone-based cell culturing devices possessing different geometries, thus providing cost-effective means for studying different device designs under a variety of experimental conditions without the need of actual testing. Finally, based on the results from the computational model, an alternative strategy for feeding CO 2 is proposed to accelerate the system performance such that a faster and more uniform CO 2 concentration response is achieved in the area of interest. [ABSTRACT FROM AUTHOR]

Blood oxygenation level dependent (BOLD) functional MRI signal is known to be modulated by the CO 2 level. Typically only end-tidal CO 2 , rather than the arterial partial pressure of CO 2 (paCO 2 ), was measured while the arterial partial pressure of O 2 (paO 2 ) level was not controlled due to free breathing, making their contribution not separable. Especially, the influences of paO 2 and paCO 2 on resting-state functional connectivity are not well studied. In this study, we investigated the relationship between paCO 2 and resting as well as stimulus-evoked BOLD signals under hyperoxic and hypercapnic manipulation with tight control of arterial paO 2 . Rats under isoflurane anesthesia were subjected to six inspired gas conditions: 47% O 2 in air (Normal), adding 1%, 2% or 5% CO 2 , carbogen (95% O 2 /5% CO 2 ), and 100% O 2 . Somatosensory BOLD activation was significantly increased under 100% O 2 , while reduced with increased paCO 2 levels. However, while resting BOLD connectivity pattern expanded and bilateral correlation increased under 100% O 2 , the correlation coefficient between the left and right somatosensory cortex was generally not dependent on paCO 2 or paO 2 . Interestingly, the correlation in 0.04–0.07 Hz range significantly increased with CO 2 levels. Intracortical electrophysiological recordings showed a similar trend as the BOLD but the neurovascular coupling varied. The results suggest that paO 2 and paCO 2 together rather than paCO 2 alone alter the BOLD signal. The response is not purely vascular in nature but has strong neuronal origins. This should be taken into consideration when designing calibrated BOLD experiment and interpreting functional connectivity data especially in aging, under drug, or neurological disorders. [ABSTRACT FROM AUTHOR]

Aimed: The main aim of this study is to improve the mechanistic understanding of soil CO efflux (F), especially its temporal variation at short-time scales, by investigating, through modeling, which underlying process among CO production and its transport up to the atmosphere is responsible for observed intra-day variation of F and soil CO concentration [CO]. Methods: In this study, a measurement campaign of F and vertical soil [CO] profiles was conducted in a Scots Pine Forest soil in Hartheim (Germany) and used to develop a model testing several hypotheses. A reference model taking into account a purely diffusive CO transport and a temperature-dependent CO production is compared to models with a more complex description of either CO production or CO transport. For transport, the introduction of advection and the dispersion is investigated. For the production, the emergent hypothesis of the phloem pressure concentration wave (PPCW) influence is tested. Results: We show that intra-day variation of F and [CO] is better represented when the more complex CO production expression is taken into account compared to the more detailed description of CO transport. Conclusion: We conclude that focus should be placed on the potential factors affecting the CO production, rather than on the transport process description [ABSTRACT FROM AUTHOR]

Abstract: Background: Determination of CO2 diffusion rates in living cells revealed inconsistencies with existing models about the mechanisms of membrane gas transport. Mainly, these discrepancies exist in the determined CO2 diffusion rates of bio-membranes, which were orders of magnitudes below those for pure lipid bilayers or theoretical considerations as well as in the observation that membrane insertion of specific aquaporins was rescuing high CO2 transport rates. This effect was confirmed by functional aquaporin protein analysis in heterologous expression systems as well as in bacteria, plants and partly in mammals. Scope of Review: This review summarizes the arguments in favor of and against aquaporin facilitated membrane diffusion of CO2 and reports about its importance for the physiology of living organisms. Major Conclusions: Most likely, the aquaporin tetramer forming an additional fifth pore is required for CO2 diffusion facilitation. Aquaporin tetramer formation, membrane integration and disintegration could provide a mechanism for regulation of cellular CO2 exchange. The physiological importance of aquaporin mediated CO2 membrane diffusion could be shown for plants and cyanobacteria and partly for mammals. General Significance: Taking the mentioned results into account, consequences for our current picture of cell membrane transport emerge. It appears that in some or many instances, membranes might not be as permeable as it was suggested by current bio-membrane models, opening an additional way of controlling the cellular influx or efflux of volatile substances like CO2. This article is part of a Special Issue entitled Aquaporins. [Copyright &y& Elsevier]

Aquaporins and Rh proteins can function as gas (CO2 and NH3) channels. The present study explores the urea, H2O, CO2, and NH3 permeability of the human urea transporter B (UT-B) (SLC14A1), expressed in Xenopus oocytes. We monitored urea uptake using [14C]urea and measured osmotic water permeability (Pf) using video microscopy. To obtain a semiquantitative measure of gas permeability, we used microelectrodes to record the maximum transient change in surface pH (ΔpHS) caused by exposing oocytes to 5% CO2/33 mM HCO3- (pHS increase) or 0.5 mM NH3/NH4+ (pHS decrease). UT-B expression increased oocyte permeability to urea by >20-fold, and Pf by 8-fold vs. H2O-injected control oocytes. UT-B expression had no effect on the CO2-induced ΔpHS but doubled the NH3-induced ΔpHS. Phloretin reduced UT-B-dependent urea uptake (Jurea*) by 45%, Pf* by 50%, and (- ΔpHS* )NH3 by 70%. p-Chloromercuribenzene sulfonate reduced Jurea* by 25%, Pf* by 30%, and (ΔpHS* )NH3 by 100%. Molecular dynamics (MD) simulations of membrane-embedded models of UT-B identified the monomeric UT-B pores as the main conduction pathway for both H2O and NH3 and characterized the energetics associated with permeation of these species through the channel. Mutating each of two conserved threonines lining the monomeric urea pores reduced H2O and NH3 permeability. Our data confirm that UT-B has significant H2O permeability and for the first time demonstrate significant NH3 permeability. Thus the UTs become the third family of gas channels. Inhibitor and mutagenesis studies and results of MD simulations suggest that NH3 and H2O pass through the three monomeric urea channels in UT-B. [ABSTRACT FROM AUTHOR]

Abstract: The mammalian Rh glycoproteins belong to the solute transporter family SLC42 and include RhAG, present in red blood cells, and two non-erythroid members RhBG and RhCG that are expressed in various tissues, including kidney, liver, skin and the GI tract. The Rh proteins in the red blood cell form an “Rh complex” made up of one D-subunit, one CE-subunit and two RhAG subunits. The Rh complex has a well-known antigenic effect but also contributes to the stability of the red cell membrane. RhBG and RhCG are related to the transporters of the yeast and bacteria but their exact function is yet to be determined. This review describes the expression and molecular properties of these membrane proteins and their potential role as NH3/ and CO2 transporters. The likelihood that these proteins transport gases such as CO2 or NH3 is novel and significant. The review also describes the physiological importance of these proteins and their relevance to human disease. [Copyright &y& Elsevier]

Abstract: The Brown Norway (BN; BN/NHsdMcwi) rat exhibits a deficit in ventilatory CO2 sensitivity and a modest serotonin (5-HT) deficiency. Here, we tested the hypothesis that the selective serotonin reuptake inhibitor fluoxetine would augment CO2 sensitivity in BN but not Sprague Dawley (SD) rats. Ventilation during room air or 7% CO2 exposure was measured before, during and after 3 weeks of daily injections of saline or fluoxetine (10mg/(kgday)) in adult male BN and SD rats. Fluoxetine had minimal effects on room air breathing in BN and SD rats (p >0.05), although tidal volume (V T) was reduced in BN rats (p <0.05). There were also minimal effects of fluoxetine on CO2 sensitivity in SD rats, but fluoxetine increased minute ventilation, breathing frequency and V T during hypercapnia in BN rats (p <0.05). The augmented CO2 response was reversible upon withdrawal of fluoxetine. Brain levels of biogenic amines were largely unaffected, but 5-HIAA and the ratio of 5-HIAA/5-HT were reduced (p <0.05) consistent with selective and effective 5-HT reuptake inhibition. Thus, fluoxetine increases ventilatory CO2 sensitivity in BN but not SD rats, further suggesting altered 5-HT system function may contribute to the inherently low CO2 sensitivity in the BN rat. [Copyright &y& Elsevier]

Abstract: Evidence from in vivo and in vitro experiments conclude that serotonin (5-HT) neurons are involved in and play an important role in central respiratory CO2/H+ chemosensitivity. This study was designed to assess the importance of 5-HT neurons and 5-HT receptor activation in the frequency and amplitude components of the hypercapnic response of the respiratory network in the unanesthetized perfused in situ juvenile rat brainstem preparation that exhibits patterns of phrenic nerve discharge similar to breathing in vivo. Exposure to a hypercapnic perfusate increased phrenic burst frequency and/or amplitude, the neural correlates of breathing frequency and tidal volume in vivo. Hypercapnic responses were also assessed during exposure to ketanserin (5-HT2 receptor antagonist), and 8-OH-DPAT (inhibiting 5-HT neurons via 5-HT1A autoreceptors). Neither of these drugs substantially altered baseline activity, however, both abolished hypercapnic responses of the respiratory network. These data illustrate that 5-HT neurons and 5-HT receptor activation are not required for respiratory rhythm generation per se, but are critical for CO2 responses in situ, supporting the hypothesis that 5-HT neurons play an important role in central ventilatory chemosensitivity in vivo. [Copyright &y& Elsevier]

ABSTRACT The membrane CO2 flux into Arabidopsis mesophyll cells was studied using a scanning pH microelectrode. Arabidopsis thaliana mesophyll cells were exposed to photosynthesis-triggering light intensities, which induced cellular CO2 uptake. Data obtained on a AtPIP1;2 T-DNA insertion line indicated that under these conditions, cellular CO2 transport was not limited by unstirred layer effects but was dependent on the expression of the aquaporin AtPIP1;2. Complementation of the AtPIP1;2 knockout restored membrane CO2 transport levels to that of controls. The results provide new arguments for the ongoing debate about the validity of the lipid bilayer model system and the Meyer - Overton rule for cellular gas transport. In conclusion, we suggest a modified model of molecular gas transport mechanisms in living cells. [ABSTRACT FROM AUTHOR]

Biotin is a cofactor responsible for carbon dioxide transfer in several carboxylase enzymes, which play a significant role in various metabolic reactions such as fatty acid synthesis, branched chain amino acid catabolism, and gluconeogenesis. Biotin is also involved in citric acid cycle, which is the process of biochemical energy generation during aerobic respiration. Though the function of biotin in the growth of algae has been extensively investigated, little is known about the biosynthetic routes of biotin in the algal kingdom. In the present study, 44 biotin biosynthesis-related genes were identified from 14 eukaryotic photosynthetic algal genomes by BLASTP and TBLASN programs. A comprehensive analysis was performed to characterize distribution, phylogeny, structure domains, and coevolution patterns of those genes. Forty-four biotin biosynthesis-related enzymes (BBREs) were found to be distributed in three groups: 7-keto-8-aminopelargonic acid synthase, diaminopelargonic acid synthase/dethiobiotin synthetase, and biotin synthase. Structure domains were considerably conserved among the subfamilies of BBREs. The intramolecular coevolutionary sites are widely distributed in biotin synthase. The present study provides new insights into the origin and evolution of biotin biosynthetic pathways in eukaryotic photosynthetic algae. Furthermore, the characterization of biotin biosynthesis-related genes from algae will promote the identification and functional studies of BBREs. [ABSTRACT FROM AUTHOR]

Polyhemoglobin-superoxide dismutase-catalase-carbonic anhydrase (PolyHb-SOD-CAT-CA) is a therapeutic antioxidant that also transports both oxygen and carbon dioxide. This is formed by crosslinking Hb with SOD, CAT, and CA using glutaraldehyde. Crosslinking stroma-free Hb from red blood cell (RBC) reduces CA activity to 55%. Addition of more CA resulted in a preparation with the same CA activity as RBC. PolyHb in the complex acts as a buffer to prevent large pH changes as carbon dioxide is converted to carbonic acid. We then prepare and optimize a novel PolyHb-SOD-CAT-CA, a therapeutic antioxidant that also transports both oxygen and carbon dioxide. [ABSTRACT FROM AUTHOR]

ABSTRACT Conductance to CO2 inside leaves, known as mesophyll conductance ( gm), imposes large limitations on photosynthesis. Because gm is difficult to quantify, it is often neglected in calculations of 13C photosynthetic discrimination. The 'soluble sugar method' estimates gm via differences between observed photosynthetic discrimination, calculated from the δ13C of soluble sugars, and discrimination when gm is infinite. We expand upon this approach and calculate a photosynthesis-weighted average for canopy mesophyll conductance (c gm) using δ13C of stem phloem contents. We measured gas exchange at three canopy positions and collected stem phloem contents in mature trees of three conifer species ( Pseudotsuga menziesii, Thuja plicata and Larix occidentalis). We generated species-specific and seasonally variable estimates of c gm. We found that c gm was significantly different among species (0.41, 0.22 and 0.09 mol m−2 s−1 for Larix, Pseudotsuga and Thuja, respectively), but was similar throughout the season. Ignoring respiratory and photorespiratory fractionations (cΔef) resulted in ≈30% underestimation of c gm in Larix and Pseudotsuga, but was innocuous in Thuja. Substantial errors (∼1-4‰) in photosynthetic discrimination calculations were introduced by neglecting c gm and cΔef. Our method is easy to apply and cost-effective, captures species variation and would have captured seasonal variation had it existed. The method provides an average canopy value, which makes it suitable for parameterization of canopy-scale models of photosynthesis, even in tall trees. [ABSTRACT FROM AUTHOR]

Summary Cellular exchange of carbon dioxide (CO2) is of extraordinary importance for life. Despite this significance, its molecular mechanisms are still unclear and a matter of controversy. In contrast to other living organisms, plants are physiologically limited by the availability of CO2. In most plants, net photosynthesis is directly dependent on CO2 diffusion from the atmosphere to the chloroplast. Thus, it is important to analyze CO2 transport with regards to its effect on photosynthesis. A mutation of the Arabidopsis thaliana AtPIP1;2 gene, which was characterized as a non-water transporting but CO2 transport-facilitating aquaporin in heterologous expression systems, correlated with a reduction in photosynthesis under a wide range of atmospheric CO2 concentrations. Here, we could demonstrate that the effect was caused by reduced CO2 conductivity in leaf tissue. It is concluded that the AtPIP1;2 gene product limits CO2 diffusion and photosynthesis in leaves. [ABSTRACT FROM AUTHOR]

Nanohybrid membranes comprising organic and inorganic components with high CO2affinity are ideal substitutes for traditional high footprint gas separation technologies. The CO2permeability of these membranes resembles those of polydimethylsiloxane (PDMS), the most permeable rubbery material, while possessing CO2/H2separation factors that supersede PDMS. Such membranes are synthesized using a simple acid-catalyzed sol–gel process. In this work, we investigate the relationship between the CO2permeation properties of these nanohybrid membranes and membrane and siloxane network morphology by attuning the reaction kinetics of the sol–gel process. The CO2permeability of these nanohybrid membranes can reach 1810 barrer, an improvement of 7.5 folds; while H2permeability increase by 5.7 fold, from 30 to 170 barrer. The mechanism behind gas transport enhancements observed in these nanohybrid membranes is elucidated using positron annihilation lifetime spectroscopy and sorption measurements. Relative fractional free volume (FFV) content and CO2sorption behaviors in these membranes are augmented as a function of inorganic phase morphology. The CO2sorption behavior of the inorganic phase is regulated by the organic/inorganic ratio and water/silicon ratio in the sol–gel synthesis process. Harnessing the advantages of a unique combination of organic and inorganic materials, these nanohybrid membranes outperform most other CO2-philic polymeric membranes. [ABSTRACT FROM AUTHOR]

Carbohydrate stores within muscle are considered essential as a fuel for prolonged endurance exercise, and regimes for enhancing such stores have proved successful in aiding performance. This study explored the effects of a hyperglycaemic-hyperinsulinemic clamp performed 18 h previously on subsequent prolonged endurance performance in cycling. Seven male subjects, accustomed to prolonged endurance cycling, performed 90 min of cycling at ~65% VO(2max) followed by a 16-km time trial 18 h after a 2-h hyperglycemic-hyperinsulinemic clamp (HCC). Hyperglycemia (10 mM) with insulin infused at 300 mU/m(2)/min over a 2-h period resulted in a total glucose uptake of 275 g (assessed by the area under the curve) of which glucose storage accounted for about 73% (i.e. 198 g). Patterns of substrate oxidation during 90-min exercise at 65% VO(2max) were not altered by HCC. Blood glucose and plasma insulin concentrations were higher during exercise after HCC compared with control (p < 0.05) while plasma NEFA was similar. Exercise performance was improved by 49 s and power output was 10-11% higher during the time trial (p < 0.05) after HCC. These data suggest that carbohydrate loading 18 h previously by means of a 2-h HCC improves cycling performance by 3.3% without any change in pattern of substrate oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Polyhemoglobin-superoxide dismutase-catalase-carbonic anhydrase (PolyHb-SOD-CAT-CA) is a therapeutic antioxidant that also transports both oxygen and carbon dioxide. This is formed by crosslinking Hb with SOD, CAT, and CA using glutaraldehyde. Crosslinking stroma free Hb from red blood cell (rbc) reduces CA activity to 55%. Addition of more CA resulted in a preparation with the same CA activity as RBC. PolyHb in the complex acts as a buffer to prevent large pH changes as carbon dioxide is converted to carbonic acid. We then prepare and optimize a novel PolyHb-SOD-CAT-CA, a therapeutic antioxidant that also transports both oxygen and carbon dioxide. [ABSTRACT FROM AUTHOR]

Abstract: During large-scale column tests at BHP Billiton''s Johannesburg Technology Centre (JTC) on a low-grade copper ore during 2005/6, the concentrations of both oxygen and CO2 were continuously monitored in feed and exit gas as well as at various intermediate positions over the height of the column. This paper describes results from a test run at 40°C fed with an air stream enriched to between 1000 and 2000ppm CO2. Oxygen consumption very closely tracks iron and copper leaching. CO2 is consumed rapidly from the bottom up, resulting in significant depletion midway through the column, even though an enriched feed was used. Oxidation rates decline in CO2 depleted zones, but were not observed to cease completely. This decline is postulated to be linked to a slowly decaying population unable to regenerate itself, and a relative rate of decay in the absence of oxygen has been estimated to be around 3%/day. A comparison between O2 and CO2 consumption rates shows a linear correlation beyond a minimum oxidation rate. This minimum rate corresponds to a non-growth maintenance energy requirement, and the slope of the linear correlation to the growth yield. Both are functions of available CO2 in the range 50 to 1000ppm, with maintenance declining and yield increasing. The findings of this study imply that CO2 supplementation in bioheaps will stimulate microbial growth and CO2 consumption, but not necessarily increase the rate of oxygen uptake and hence leaching. Absence of CO2 is expected to result in gradual population decline, but a degree of oxidation continues on the basis of maintenance. In tall heaps, CO2 depletion with height is likely and may therefore result in impaired leaching in the upper zones. [Copyright &y& Elsevier]

We estimated the net flux of inorganic phosphorus (kg P d-1) due to geostrophic transport in the upper 100 m of a control volume (CV) off Baja California (Mexico) during 2003 and 2004. The influence of this flux on integrated primary production (IPP) in the photic zone (<100 m depth) was estimated comparing the net P flux into the CV against the P requirements for IPP. The greatest P fluxes occurred during spring and summer 2004; the northern side of the CV was the main recipient of P. The most persistent P outflow occurred along the southern side of the CV, except in winter 2003, when there was an input of P fluxes related to cyclonic and anticyclonic eddies off Ensenada. The net geostrophic transport during 2003 and 2004 contributed enough P to support the IPP requirements during winter and spring, indicating that P was not limiting for phytoplankton organic carbon production during these seasons. [ABSTRACT FROM AUTHOR]

The Southern Ocean, with its large surface area and vigorous overturning circulation, is potentially a substantial sink of anthropogenic CO2 (refs 1–4). Despite its importance, the mechanism and pathways of anthropogenic CO2 uptake and transport are poorly understood. Regulation of the Southern Ocean carbon sink by the wind-driven Ekman flow, mesoscale eddies and their interaction is under debate. Here we use a high-resolution ocean circulation and carbon cycle model to address the mechanisms controlling the Southern Ocean sink of anthropogenic CO2. The focus of our study is on the intra-annual variability in anthropogenic CO2 over a two-year time period. We show that the pattern of carbon uptake is correlated with the oceanic vertical exchange. Zonally integrated carbon uptake peaks at the Antarctic polar front. The carbon is then advected away from the uptake regions by the circulation of the Southern Ocean, which is controlled by the interplay among Ekman flow, ocean eddies and subduction of water masses. Although lateral carbon fluxes are locally dominated by the imprint of mesoscale eddies, the Ekman transport is the primary mechanism for the zonally integrated, cross-frontal transport of anthropogenic CO2. Intra-annual variability of the cross-frontal transport is dominated by the Ekman flow with little compensation from eddies. A budget analysis in the density coordinate highlights the importance of wind-driven transport across the polar front and subduction at the subtropical front. Our results suggest intimate connections between oceanic carbon uptake and climate variability through the temporal variability of Ekman transport. [ABSTRACT FROM AUTHOR]

OBJECTIVES: To determine the optimal clinical reading time for the transcutaneous measurement of oxygen saturation (SpO2) and transcutaneous CO2 (TcPCO2) in awake spontaneously breathing individuals, considering the overshoot phenomenon (transient overestimation of arterial PaCO2). EXPERIMENTAL SECTION: Observational study of 91 (75 men) individuals undergoing forced spirometry, measurement of SpO2 and TcPCO2 with the SenTec monitor every two minutes until minute 20 and arterial blood gas (ABG) analysis. Overshoot severity: (a) mild (0.1-1.9 mm Hg); (b) moderate (2-4.9 mm Hg); (c) severe: (>5 mm Hg). The mean difference was calculated for SpO2 and TcPCO2 and arterial values of PaCO2 and SpO2. The intraclass correlation coefficient (ICC) between monitor readings and blood values was calculated as a measure of agreement. RESULTS: The mean age was 63.1 ± 11.8 years. Spirometric values: FVC: 75.4 ± 6.2%; FEV1: 72.9 ± 23.9%; FEV1/FVC: 70 ± 15.5%. ABG: PaO2: 82.6 ± 13.2; PaCO2: 39.9.1 ± 4.8 mmHg; SaO2: 95.3 ± 4.4%. Overshoot analysis: overshoot was mild in 33 (36.3%) patients, moderate in 20 (22%) and severe in nine (10%); no overshoot was observed in 29 (31%) patients. The lowest mean differences between arterial blood gas and TcPCO2 was -0.57 mmHg at minute 10, although the highest ICC was obtained at minutes 12 and 14 (>0.8). The overshoot lost its influence after minute 12. For SpO2, measurements were reliable at minute 2. CONCLUSIONS: The optimal clinical reading measurement recommended for the ear lobe TcPCO2 measurement ranges between minute 12 and 14. The SpO2 measurement can be performed at minute 2. [ABSTRACT FROM AUTHOR]

Abstract: This study was designed to determine whether awareness of change in load alters ventilatory response during moderate exercise. Subjects performed two incremental exercise protocols on a cycle ergometer. The load was increased from 1.0 to 1.5kp in steps of 0.1kp every 3min. Subjects were provided true information about the load in the control protocol and untrue information that the load would remain constant in the deception protocol. Slope of ventilation against CO2 output was significantly lower in the deception protocol than control protocol. Integrated EMG (iEMG) and ratings of perceived exertion (RPE) were similar between the two protocols, but awareness of change in load was significantly attenuated by the deception protocol. However, there was no temporal coincidence between awareness and actual change in load. These results suggest that ventilatory response during moderate exercise depends not so much on RPE but mainly on awareness or attention that is closely connected to information detection. [Copyright &y& Elsevier]

Previous reports have shown that CO2 dissolved in xylem sap in tree stems can move upward in the transpiration stream. To determine the fate of this dissolved CO2, the internal transport of respired CO2 at high concentration from the bole of the tree was simulated by allowing detached young branches of sycamore (Platanus occidentalis L.) to transpire water enriched with a known quantity of 13CO2 in sunlight. Simultaneously, leaf net photosynthesis and CO2 efflux from woody tissue were measured. Branch and leaf tissues were subsequently analysed for 13C content to determine the quantity of transported 13CO2 label that was fixed. Treatment branches assimilated an average of 35% (SE=2.4) of the 13CO2 label taken up in the treatment water. The majority was fixed in the woody tissue of the branches, with smaller amounts fixed in the leaves and petioles. Overall, the fixation of internally transported 13CO2 label by woody tissues averaged 6% of the assimilation of CO2 from the atmosphere by the leaves. Woody tissue assimilation rates calculated from measurements of 13C differed from rates calculated from measurements of CO2 efflux in the lower branch but not in the upper branch. The results of this study showed unequivocally that CO2 transported in xylem sap can be fixed in photosynthetic cells in the leaves and branches of sycamore trees and provided evidence that recycling of xylem-transported CO2 may be an important means by which trees reduce the carbon cost of respiration. [ABSTRACT FROM PUBLISHER]

Erythrocytes evolved to carry out the crucial function of transportation of oxygen from lungs to various tissues in the body and to carry back carbon dioxide. Absence of a nucleus in erythrocytes facilitates their easy movement in blood capillaries and make space for large quantities of haemoglobin, the oxygen carrier molecule, but renders the cells ill equipped to effectively repair themselves from oxidative and other damages. Turnover rate of erythrocytes is fast and the average life span of murine erythrocytes in blood is only 50 days. What age related changes occur in circulating erythrocytes and which of these changes are crucial determining factors in triggering the destruction of old erythrocytes, are not well understood. The main reason for a lack of information in this area is the fact that there were not available any good and easy to perform technique to identify circulating erythrocytes of different age groups. We have recently developed a technique that involved in vivo biotinylation of erythrocytes in two steps that has allowed us for the first time to objectively assess age-related changes in blood erythrocytes. We have utilized this technique to study various aspects of aging of murine erythrocytes. On the basis of these results, our current thinking about the process of erythrocyte aging in vivo is summarized in the this article. [ABSTRACT FROM AUTHOR]

This study estimated changes in whole body oxygen stores (O2s) and carbon dioxide stores (CO2s) during steady state exercise with leg ischemia induced by leg cuff inflation. Six physically fit subjects performed 75 W steady state exercise for 15 min on a cycle ergometer. After 5 min of exercise, cuffs on the upper and lower legs were inflated to 140 mmHg. Cuffs were deflated after 5 min and exercise continued for another 5 min. O2 uptake (V˙O2) and CO2 output (V˙CO2 significantly increased during the first 30 s after inflation, significantly decreased between 60 and 90 s, and then rose linearly until deflation. V˙O2 and V˙CO2 significantly increased further after cuff deflation, peaking between 30 and 60 s and then returned to near baseline exercise levels. Modelestimated changes in total O2s and CO2s were compared with time-integrated store changes from V˙O2 and V˙CO2. During 5 min after cuff deflation, V˙O2 and V˙CO2 exceeded the model-estimated change in stores by 273 and 697 mL, respectively. These results reflect the O2 cost repayment of the anaerobic component and lactate buffering to neutralize circulating metabolites caused by the preceding ischemia. [ABSTRACT FROM AUTHOR]

We examined whether additional helmet flow obtained by a single-circuit and a modified plateau valve applied at the helmet expiratory port (open-circuit ventilators) improves CO2 wash-out by increasing helmet airflow. Randomized physiological study in a university research laboratory. Ten healthy volunteers. Helmet continuous positive airway pressure and pressure support ventilation delivered by an ICU ventilator (closed-circuit ventilator) and two open-circuit ventilators equipped with a plateau valve placed either at the inspiratory or at the helmet expiratory port. We measured helmet air leaks, breathing pattern, helmet minute ventilation ( $$ \dot{\text{V}} $$ Eh), minute ventilation washing the helmet ( $$ \dot{\text{V}} $$ Ewh), CO2 wash-out, and ventilator inspiratory assistance. Air leaks were small and similar in all conditions. Breathing pattern was similar among the different ventilators. Inspiratory and end-tidal CO2 were lower, while $$ \dot{\text{V}} $$ Eh and $$ \dot{\text{V}} $$ Ewh were higher only using open-circuit ventilators with the plateau valve placed at the helmet expiratory port. This occurred notwithstanding these ventilators delivered a lower inspiratory assistance. Additional helmet flow provided by open-circuit ventilators can lower helmet CO2 rebreathing. However, inspiratory pressure assistance significantly decreases using open-circuit ventilators, still casting doubts on the choice of the optimal helmet ventilation setup. [ABSTRACT FROM AUTHOR]

Abstract: Modelling of soil respiration plays an important role in the prediction of climate change. Soil respiration is usually divided in a fraction originating from root respiration and a heterotrophic fraction originating from microbial decomposition of soil organic carbon. This paper reports on the coupling of an one-dimensional water, heat and CO2 flux model (SOILCO2) with a pool concept of carbon turnover (RothC) for the prediction of soil heterotrophic respiration. In order to test this coupled model, it was applied to a bare soil experimental plot located in Bornim, Germany. Soil temperature and soil water content measurements were used for comparison with the respective model predictions. An 8 years data set of CO2 efflux measurements, covering a broad range of atmospheric conditions, was used to evaluate the model. In a first step we quantified the improvement of the CO2 efflux prediction due to the coupling of the flux model with a pool concept of carbon turnover. The humus pool decomposition rate constant and its soil water content dependent reduction were derived from the first 5 years of CO2 efflux measurements using inverse modelling. The following 3 years of measurements were used to validate the model. The overall model performance of CO2 efflux predictions was acceptable with the measured and simulated mean daily respiration being 0.861 and 0.868gCm−2 d−1, respectively, and a mean absolute difference between modelled and measured rates of 0.21gCm−2 d−1. The inverse estimation of the humus decomposition rate constant resulted in a value of 0.04year−1, which is higher than the default value in RothC. This is attributed to the agricultural practice during the experiment. [Copyright &y& Elsevier]

Abstract: A multi-organ systems model of O2 and CO2 transport is developed to analyze the control of ventilation and blood flow during hypoxia. Among the aspects of the control processes that this model addressed are possible mechanisms responsible for the second phase of the ventilatory hypoxic response to mild hypoxia, i.e., hypoxic ventilatory decline (HVD). Species mass transport processes are described by compartmental mass balances in brain, heart, skeletal muscle, and “other tissues” connected in parallel via the circulation. In pulmonary and systemic capillaries and in the vasculature connecting the systemic tissues, species transport processes are represented by a one-dimensional, convection-dispersion model. The effects of bicarbonate acid-base buffering, hemoglobin, and myoglobin on the transport processes are included. The model incorporates feedback control mechanisms through a cardiorespiratory control system in which peripheral and central chemoreceptors sense O2 and CO2 partial pressures. Model simulations of the ventilatory responses to isocapnic and poikilocapnic hypoxia show two phases with distinct dynamics. A fast phase is discernable immediately after switching from normoxic to hypoxic conditions, while a delayed slow phase (HVD) typically becomes manifested after several minutes. Model simulations allow quantitative evaluation of several proposed mechanisms to account for HVD. Under isocapnic hypoxia, simulations indicate that an increase in brain blood flow has no effect on HVD, but that HVD can be entirely described by central ventilatory depression (CVD). Under poikilocapnic hypoxia, the hypocapnia caused by hypoxic hyperventilation has no effect on HVD. [Copyright &y& Elsevier]

Abstract: Forest gaps may provide conduits that preferentially vent moist, CO2-rich subcanopy air to the atmosphere. We measured the above-canopy fluxes of momentum, sensible heat (H), CO2, and water vapor (Et), and the vertical profiles of CO2 and water vapor, from two 67-m meteorological towers in a selectively logged Brazilian rainforest. The logging removed ∼3.5treesha−1, and increased the incidence of gaps by a factor of 3 over nearby undisturbed forest. One tower was located in an intact patch of forest within the selectively logged area; the other was 400m upwind in a large gap created by the logging. During daytime the subcanopy air in the intact patch of forest had more CO2, more water vapor, and was cooler than the air at comparable altitudes in the gap. Meanwhile, the daytime CO2 flux was less negative (reduced CO2 uptake) above the gap than above the intact forest, the daytime Et was greater above the gap than the intact forest, and the daytime H was lower above the gap than the intact forest. These patterns cannot be explained fully by the local loss of canopy gas exchange in the gap, but are consistent with the horizontal transport into the gap, and subsequent vertical transport out of the gap, of high-CO2, humid, cool air from the forest understory. The understory was drier and warmer during daytime after the logging, which would be expected to increase flammability. Further measurement and modeling efforts are needed to better understand the effect of canopy gaps on the local CO2 and energy exchange, as well as the flux footprint. [Copyright &y& Elsevier]

We aimed to quantify the separate effects of photosynthetic and postphotosynthetic carbon isotope discrimination on δ13C of the fast-turn-over carbon pool (water soluble organic carbon and CO2 emitted from heterotrophic tissues), including their diel variation, along the pathway of carbon transport from the foliage to the base of the stem. For that purpose, we determined δ13C in total and water-soluble organic matter of the foliage plus δ13C and δ18O in phloem organic matter of twigs and at three heights along the stem of Pinus sylvestris over a nine-day period, including four measurements per day. These data were related to meteorological and photosynthesis parameters and to the δ13C of stem-emitted CO2. In the canopy (foliage and twigs), the δ13C of soluble organic matter varied diurnally with amplitudes of up to 1.9‰. The greatest 13C enrichment was recorded during the night/early morning, indicating a strong influence of starch storage and remobilization on the carbon isotope signatures of sugars exported from the leaves. 13C enrichment of soluble organic matter from the leaves to the twig phloem and further on to the phloem of the stem was supposed to be a result of carbon isotope fractionation associated with metabolic processes in the source and sink tissues. CO2 emitted from the stem was enriched by 2.3–5.2‰ compared with phloem organic matter. When day-to-day variation was addressed, water-soluble leaf δ13C and twig phloem δ18O were strongly influenced by ci/ ca and stomatal conductance ( Gs), respectively. These results show that both photosynthetic and postphotosynthetic carbon isotope fractionation influence δ13C of organic matter over time, and over the length of the basipetal transport pathway. Clearly, these influences on the δ13C of respired CO2 must be considered when using the latter for partitioning of ecosystem CO2 fluxes or when the assessment of δ13C in organic matter is applied to estimate environmental effects in ci/ ca. [ABSTRACT FROM AUTHOR]

Several vital systemic functions are controlled by the brainstem, which has been studied in a variety of experimental preparations and by various techniques, including in-vitro electrophysiological preparations. Although these in-vitro approaches have greatly advanced the understanding of brainstem neurons, most recording methods with microelectrodes and patch pipettes are invasive. To take advantage of in-vitro approaches but avoid their potential problems, we have studied brainstem neurons in microelectrode arrays (MEA). Neurons were isolated from the medulla oblongata and cultured in DMEM. Extracellular recordings were performed with no evident perturbations to the cellular environment. Neurons started firing after 24–48 h in culture, reached stable activity in 3–4 weeks, and retained this activity for at least 3 months. From their firing patterns, these neurons could be divided into tonic and bursting units. The latter could be further divided into regular and irregular bursters based on their burst intervals. Cells were stimulated or inhibited by exposure to 10% CO2. The stimulatory effect of CO2, though smaller, was still seen after selective ablation of serotonergic neurons or with low Ca++ and high Mg++ in the extracellular medium. Similar treatments had no significant effect on CO2-inhibited units. The abundance of units with respect to their firing patterns and CO2 responses, together with the long-term stable non-invasive recordings with no evident perturbation to cellular environments, suggests that MEA represent another promising in-vitro approach for studying brainstem neurons. [ABSTRACT FROM AUTHOR]

A new 3D global coupled carbon–climate model is presented in the framework of the Community Climate System Model (CSM-1.4). The biogeochemical module includes explicit land water–carbon coupling, dynamic carbon allocation to leaf, root, and wood, prognostic leaf phenology, multiple soil and detrital carbon pools, oceanic iron limitation, a full ocean iron cycle, and 3D atmospheric CO2 transport. A sequential spinup strategy is utilized to minimize the coupling shock and drifts in land and ocean carbon inventories. A stable, 1000-yr control simulation [global annual mean surface temperature ±0.10 K and atmospheric CO2 ± 1.2 ppm (1σ)] is presented with no flux adjustment in either physics or biogeochemistry. The control simulation compares reasonably well against observations for key annual mean and seasonal carbon cycle metrics; regional biases in coupled model physics, however, propagate clearly into biogeochemical error patterns. Simulated interannual-to-centennial variability in atmospheric CO2 is dominated by terrestrial carbon flux variability, ±0.69 Pg C yr-1 (1σ global net annual mean), which in turn reflects primarily regional changes in net primary production modulated by moisture stress. Power spectra of global CO2 fluxes are white on time scales beyond a few years, and thus most of the variance is concentrated at high frequencies (time scale <4 yr). Model variability in air–sea CO2 fluxes, ±0.10 Pg C yr-1 (1σ global annual mean), is generated by variability in sea surface temperature, wind speed, export production, and mixing/upwelling. At low frequencies (time scale >20 yr), global net ocean CO2 flux is strongly anticorrelated (0.7–0.95) with the net CO2 flux from land; the ocean tends to damp (20%–25%) slow variations in atmospheric CO2 generated by the terrestrial biosphere. The intrinsic, unforced natural variability in land and ocean carbon storage is the “noise” that complicates the detection and mechanistic attribution of contemporary anthropogenic carbon sinks. [ABSTRACT FROM AUTHOR]

This work describes a comprehensive mathematical model of the human respiratory control system which incorporates the central mechanisms for predicting sleep-induced changes in chemical regulation of ventilation. The model integrates four individual compartments for gas storage and exchange, namely alveolar air, pulmonary blood, tissue capillary blood, body tissues, and gas transport between them. An essential mechanism in the carbon dioxide transport is its dissociation into bicarbonate and acid, where a buffering mechanism through hemoglobin is used to prevent harmfully low pH levels. In the current model, we assume high oxygen levels and consider intracellular hydrogen ion concentration as the principal respiratory control variable. The resulting system of delayed differential equations is solved numerically. With an appropriate choice of key parameters, such as velocity of blood flow and gain of a non-linear controller function, the model provides steady-state results consistent with our experimental observations measured in subjects across sleep onset. Dynamic predictions from the model give new insights into the behaviour of the system in subjects with different buffering capacities and suggest novel hypotheses for future experimental and clinical studies. [ABSTRACT FROM AUTHOR]

The article explores the mechanisms of carbon dioxide transportation, its effects on tissues, lungs, red blood cells and acid elimination and the impact of apnoea. The three ways in which carbon dioxide is transported in the blood according to the authors are dissolved solution, buffered with water to create carbonic acid and binding with proteins and haemoglobin. It says that the presence of carbonic anhydrase increases the transportation of carbon dioxide in red blood cells. Hydrogen-ion concentration in the blood rises when haemoglobin decreases.

The article provides information on a study that evaluates the effects of various levels of pressure support (PS) during noninvasive ventilation delivered through a helmet on breathing pattern, inspiratory effort, carbon-dioxide rebreathing, and comfort. Volunteers received ventilation through a helmet with four different PS/positive end-expiratory pressure combinations applied in random order. In volunteers, the helmet is efficient in ventilation, allowing a tidal volume increase and esophageal respiratory rate reduction. A significant discomfort was present only at the highest level of assistance; however, it did not affect patient/ventilator interaction.

Inorganic carbon acquisition has been investigated in the marine prymnesiophytes Dicrateria inornata and Ochrosphaera neapolitana . The presence of external and internal carbonic anhydrase (CA) was detected in air-grown cells of D. inornata by potentiometric assay and corroborated by mass spectrometry. Growth on 3% CO 2 repressed external CA activity. Extracts of air-grown cells of O. neapolitana showed considerable internal CA activity, but no external CA activity was detected by mass spectrometry. Illumination of air-grown cells of D. inornata incubated with 100 μM H 13 CO 3 - and treated with the CA inhibitor acetazolamide caused a rapid drop in the extracellular CO 2 concentration to a level below its equilibrium concentration indicating that cells were actively taking up CO 2 from the medium. The rate of O 2 evolution at the CO 2 compensation concentration was higher than could be supported by the uncatalysed formation of CO 2 from HCO 3 - , demonstrating that the cells were taking up HCO 3 - directly. Similar results were obtained with air-grown cells of O. neapolitana. Active CO 2 transport in both species was not repressed by growth under high levels of CO 2 . The photosynthetic electron transport inhibitor 3-(3′, 4′-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibited CO 2 uptake in air-grown cells of both species, demonstrating that the energy to support active CO 2 transport was derived from photosynthetic linear electron transport. These results show that the physiological characteristics of the CO 2 concentrating mechanism in related species do not appear to be correlated with the availability of CO 2 in the surrounding medium. [ABSTRACT FROM AUTHOR]

Abstract: To study gas exchange in the filter during continuous venovenous hemodiafiltration (CVVHDF), an air-tight heated mixing chamber with adjustable CO2 supply was constructed and connected to a CVVHDF monitor. Bicarbonate-free crystalloid (Part 1) and packed red blood cell (Part 2) solutions were circulated at 150 ml · min-1. Gas exchange expressed as pre-postfilter difference in CO2 and O2 contents was measured at different CVVHDF settings and temperatures of circulating and dialysis solutions. Ultrafiltration was most efficacious for CO2 removal (at 1,000 ml · h-1 ultrafiltration CO2 losses reached 13% of prefilter CO2 content). Addition of dialysis (1,000 ml · h-1) increased CO2 loss to 17% and at maximal parameters (filtration 3,000 ml · h-1, dialysis 2,500 ml · h-1), the loss of CO2 amounted to 35% of prefilter content. Temperature changes of circulating and/or dialysis fluids had no significant impact on CO2 losses. The O2 exchange during CVVHDF was negligible. Currently used CVVHDF is only marginally effective in CO2 removal. Higher volume ultrafiltration combined with dialysis can be expected to reach clinical significance. [ABSTRACT FROM AUTHOR]

Examines the respiratory physiology of captive harbor porpoises in a strandings rehabilitation facility for marine mammals in Harderwijk, Netherlands. Effects of differential rates of store adjustment on the ratio of carbon dioxide output and oxygen intake; Gas exchange ratio of the stores; Mean lung values during postapneic breathing bouts.

Presents a study which evaluated the changes in the carbon dioxide carrying power of blood during and after cardiopulmonary bypass. Correlation of the impaired carbon dioxide transport with the increase in mixed venous blood; Materials and methods; Results and discussion.

Background: We sought to evaluate the parameters of CO[sub 2] transport during the administration of acetazolamide in order to assess the role of carbonic anhydrase in CO[sub 2] transport. Materials and methods: The partial pressure of carbon dioxide in tissue (Ptco[sub 2]), arterial blood (Paco[sub 2]) and end-tidal gas (PETco[sub 2]) were monitored to study the correlation between Paco[sub 2], Ptco[sub 2] and PETco[sub 2] in spontaneously breathing healthy volunteers after the intravenous administration of acetazolamide 6 mg kg[sup -1]. Results: At 60 min after the administration of acetazolamide, the Ptco[sub 2] peaked at more than 60 mmHg, and although it decreased by 90 min, it then remained stable above the baseline value. The Paco[sub 2] did not change and the PETco[sub 2] decreased significantly. The changes in Ptco[sub 2] were greater than those of either Paco[sub 2] or PETco[sub 2]. The minute ventilation increased progressively throughout the study. Conclusions: We concluded that gastrotonometry represents a new method for monitoring the dramatic increase in Ptco[sub 2] induced by drugs such as acetazolamide clinically, and that it could be a warning against acetazolamide administration in severe patients without keeping a ventilation and circulation reserve. [ABSTRACT FROM AUTHOR]

The occurrence of an active CO2 transport system and of carbonic anhydrase (CA) has been investigated by mass spectrometry in the marine, unicellular rhodophyte Porphyridium cruentum (S.F. Gray) Naegeli and two marine chlorophytes Nannochloris atomus Butcher and Nannochloris maculata Butcher. Illumination of darkened cells incubated with 100 μM H13CO3- caused a rapid initial drop, followed by a slower decline in the extracellular CO2 concentration. Addition of bovine CA to the medium raised the CO2 concentration by restoring the HCO3-–CO2 equilibrium, indicating that cells were taking up CO2 and were maintaining the CO2 concentration in the medium below its equilibrium value during photosynthesis. Darkening the cell suspensions caused a rapid increase in the extracellular CO2 concentration in all three species, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. CA activity was detected by monitoring the rate of exchange of 18O from 13C18O2 into water. Exchange of 18O was rapid in darkened cell suspensions, but was not inhibited by 500 μM acetazolamide, a membrane-impermeable inhibitor of CA, indicating that external CA activity was not present in any of these species. In all three species, the rate of exchange was completely inhibited by 500 μM ethoxyzolamide, a membrane-permeable CA-inhibitor, showing that an intracellular CA was present. These results demonstrate that the three species are capable of CO2 uptake by active transport for use as a carbon source for photosynthesis. [ABSTRACT FROM AUTHOR]

Examines carbon dioxide transport and carbonic anhydrase in blood and muscle. Forms of carbon dioxide (CO2) in the body; Role of carbonic anhydrase in the hydration/dehydration reaction of CO2, bicarbonate and hydrogen ion; Theoretical model of CO2 and lactic acid exchange in muscle; Permeability of the capillary wall to lactate.

Ventilation with decelerating inspiratory flow is known to reduce the dead space fraction and to decrease PaCO[sub 2]. Constant inspiratory flow with an end-inspiratory pause (EIP) is also known to increase the removal of CO[sub 2]. The aim of the study was to elucidate the effect of the pause/no-flow period while both the pattern and rate of inspiratory flow was unchanged, and when the lung was ventilated with sufficient PEEP to prevent end-expiratory collapse. Surfactant depleted piglets were assigned to decelerating or constant respiratory flow with 24 breaths per minute (bpm) or 12 bpm, or to constant flow, without and with an end-inspiratory pause of 25%. By adding an EIP the total time without active inspiratory flow of the respiratory cycle was kept unchanged. Gas exchange, airway pressures, functional residual capacity (using sulfurhexafuoride) and haemodynamics (thermo-dye indicator dilution technique) were measured Irrespective of ventilatory frequency, PaCO[sub 2] was lower and serial dead space reduced with decelerating flow, compared with constant inspiratory flow. With an end-respiratory pause added to constant inspiratory flow, serial dead space was reduced but did not decrease PaCO[sub 2]. The results of this study corroborate the assumption that total time without active inspiratory flow is important for arterial CO[sub 2]-tension. [ABSTRACT FROM AUTHOR]

Investigates whether voltage-gated hydrogen channels in alveolar epithelial cells contribute to carbon dioxide elimination by the lung. Carbon dioxide permeability of cell membranes; Role of human carbon anhydrase II in carbon dioxide extrusion by the lungs; Properties of hydrogen channels.

The effect of different fractions of inspired oxygen on subcutaneous oxygen tension, carbon dioxide tension and pH in relation to arterial and mixed venous blood gases and pH and hemodynamic variables was evaluated in 13 domestic pigs. Subcutaneous, arterial and mixed venous oxygen tensions were closely correlated (r = 0.94). A minor significant increase in subcutaneous carbon dioxide tension was noted during hyperoxia (p < 0.05). A major increase (33%) was noted during the last step of hypoxia, when arterial and mixed venous carbon dioxide tensions increased only 12 and 17%, respectively. A minor decrease in subcutaneous pH was noted during hyperoxia (p < 0.05) and a major decrease during hypoxia (p < 0.05). Measurements of subcutaneous tissue gases and pH are indicators of oxygen utilization during hyper- and hypoxia. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the postcapillary carbon dioxide partial pressure disequilibrium between arterial blood and arterial gas in turtles. Materials and methods; Results and discussion.