Gas Exchange Components Research Articles

Medium-Term Disability and Long-Term Functional Impairment Persistence in Survivors of Severe COVID-19 ARDS: Clinical and Physiological Insights

BackgroundAlthough the medium- and long-term sequelae of survivor of acute respiratory distress syndrome (ARDS) of any cause have been documented, little is known about the way in which COVID-19-induced ARDS affects functional disability and exercise components. Our aims were to examine the medium-term disability in severe COVID-19-associated ARDS survivors, delineate pathophysiological changes contributing to their exercise intolerance, and explore its utility in predicting long-term functional impairment persistence. MethodsWe studied 108 consecutive subjects with severe COVID-19 ARDS who remained alive 6 months after intensive care unit (ICU) discharge. Lung morphology was assessed with chest non-contrast CT scans and CT angiography. Functional evaluation included spirometry, plethysmography, muscle strength, and diffusion capacity, with assessment of gas exchange components through diffusing capacity of nitric oxide. Disability was assessed through an incremental exercise test, and measurements were repeated 12 and 24 months later in patients with functional impairments. ResultsAt 6 months after ICU discharge, a notable dissociation between morphological and clinical-functional sequelae was identified. Moderate-severe disability was present in 47% of patients and these subjects had greater limitation of ventilatory mechanics and gas exchange, as well as greater symptomatic perception during exercise and a probable associated cardiac limitation. Female sex, hypothyroidism, reduced membrane diffusion component, lower functional residual capacity, and high-attenuation lung volume were independently associated with the presence of moderate-severe functional disability, which in turn was related to higher frequency and greater intensity of dyspnea and worse quality of life. Out of the 71 patients with reduced lung volumes or diffusion capacity at 6 months post-ICU discharge, only 19 maintained a restrictive disorder associated with gas exchange impairment at 24 months post-discharge. In these patients, 6-month values for diffusion membrane component, maximal oxygen uptake, ventilatory equivalent for CO2, and dead space to tidal volume ratio were identified as independent risk factors for persistence of long-term functional sequelae. ConclusionsLess than half of survivors of COVID-19 ARDS have moderate-severe disability in the medium term, identifying several risk factors. In turn, diffusion membrane component and exercise tolerance at 6-month ICU discharge are independently associated with the persistence of long-term functional sequelae.

Organic Nitrogen Fertilizer Selection Influences Water Use Efficiency in Drip-Irrigated Sweet Corn

Organic farmers often rely on off-farm nitrogen (N) sources for mid-season N. Farmers can also produce cyano-fertilizer on-farm by growing N-fixing cyanobacteria (Anabaena spp.) in raceways and applying the cyanobacteria through irrigation systems. A two-year field study was conducted, and blood meal, feather meal, fish emulsion, and cyano-fertilizer were evaluated to determine whether the water use efficiency (WUE) of sweet corn (Zea mays) was affected by fertilizer type. Fish emulsion and cyano-fertilizer were supplied in four split applications through drip irrigation, while the blood meal and feather meal were subsurface banded pre-plant. Leaf gas exchange measurements were taken during tasseling. The amounts of phytohormone and Fe applied in organic N fertilizers were correlated with field water use efficiency (fWUE), instantaneous water use efficiency (iWUE), and leaf gas exchange components of sweet corn. A positive relationship was observed between the amount of salicylic acid (SA) applied with both iWUE (r = 0.71, p < 0.05) and fWUE (r = 0.68, p < 0.01). The amount of Fe applied was positively correlated with the leaf vapor pressure deficit (r = 0.54, p < 0.01) and transpiration rate (r = 0.53, p < 0.01). Cyano-fertilizer had the highest yield and WUE, likely due to the high amount of SA applied, although fish emulsion was comparable in year one. These relationships require further exploration to elucidate the mechanisms impacting WUE.

The end-tidal alveolar dead space fraction for risk stratification during the first week of invasive mechanical ventilation: an observational cohort study

BackgroundThe end-tidal alveolar dead space fraction (AVDSf = [PaCO2−PETCO2]/PaCO2) is a metric used to estimate alveolar dead space. Higher AVDSf on the first day of mechanical ventilation is associated with mortality and fewer ventilator-free days. It is not clear if AVDSf is associated with length of ventilation in survivors, how AVDSf performs for risk stratification beyond the first day of ventilation, or whether AVDSf adds predictive value to oxygenation (oxygenation index [OI]) or severity of illness (Pediatric Risk of Mortality [PRISM III]) markers.MethodsRetrospective single-center observational cohort study of children and young adults receiving invasive mechanical ventilation. In those with arterial or capillary blood gases, AVDSf was calculated at the time of every blood gas for the first week of mechanical ventilation.ResultsThere were 2335 children and young adults (median age 5.8 years [IQR 1.2, 13.2]) enrolled with 8004 analyzed AVDSf values. Higher AVDSf was associated with mortality and longer length of ventilation in survivors throughout the first week of ventilation after controlling for OI and PRISM III. Higher OI was not associated with increased mortality until ≥ 48 h of ventilation after controlling for AVDSf and PRISM III. When using standardized variables, AVDSf effect estimates were generally higher than OI for mortality, whereas OI effect estimates were generally higher than AVDSf for the length of ventilation in survivors. An AVDSf > 0.3 was associated with a higher mortality than an AVDSf < 0.2 within each pediatric acute respiratory distress syndrome severity category.The maximum AVDSf within 12 h of intensive care unit admission demonstrated good risk stratification for mortality (AUC 0.768 [95% CI 0.732, 0.803]). AVDSf did not improve mortality risk stratification when added to PRISM III but did improve mortality risk stratification when added to the gas exchange components of PRISM III (minimum 12-h PaO2 and maximum 12-h PCO2) (p < 0.00001).ConclusionsAVDSf is associated with mortality and length of ventilation in survivors throughout the first week of invasive mechanical ventilation. Some analyses suggest AVDSf may better stratify mortality risk than OI, whereas OI may better stratify risk for prolonged ventilation in survivors than AVDSf.

Improving thermotolerance in Gossypium hirsutum by using signalling and non-signalling molecules under glass house and field conditions

The climate change and global warming driven rise in temperature and unpredictable occurrence of heat waves impede cotton plants growth and development. Therefore, environmental friendly thermotolerance strategies are required to sustain optimum crop yield under stressful conditions. Reports on heat stress impacts on plant water relations, gas exchange attributes and physiological parameters, at different reproductive stages of cotton, under controlled and natural conditions are lacking. To investigate the impact of temperature and exogenous application of elicitors, a medium heat tolerant cotton genotype was exposed to control/optimal (30/20 °C), medium (38/24 °C) and high (45/30 °C) temperature stress at squaring, flowering and boll formation stages. Plants were staggered to April (early), May (normal) and June (late) sowing dates under field conditions. Growth regulators, salicylic acid (SA-50 ppm), bio-stimulant moringa leaf extract (MLE-30 times diluted) and signaling molecules, i.e. hydrogen peroxide (H2O2 -30 ppm) and ascorbic acid (ASA-70 ppm), were applied foliarly one day prior to temperature stress treatments. Several physio-biochemical parameters, such as leaf non-enzymatic antioxidant, gas exchange attributes and water relations were measured seven-days after exposure to medium and high temperature regimes. Elevated temperature (45/30 °C) increased the content of total soluble proteins (TSP), activity of glutathione reductase (GR), radical scavenging capacity (DPPH%) and H2O2 generation by 64 %, 26 %, 39 % and 57 %, respectively, compared with optimal temperature plants (control). Similarly, the stomatal conductance (GS), seed index and ginning out turn (GOT%) were reduced by 49 %, 47 % and 44 %, respectively under the high temperature regime compared with control temperature regime. Gas exchange components, water relations, seed index and GOT were also reduced under medium and high temperature regimes. Among the exogenous applications, H2O2 showed profound alleviation of temperature stress, followed by ASA and MLE. Foliar application of H2O2 increased TSP, GR and DPPH% by 1.16 folds, 70 % and 82 % (averaged across during three reproductive stages); while, GS, seed index and GOT were increased by 45 %, 20 %, 22 % under high temperature stress over the control plants of the same thermal regime. In conclusion, oxidative burst and antioxidant activities were increased, whereas stomatal conductance, seed index and GOT were reduced with increasing temperature from 30/20 °C to 38/24 °C and from 38/24 °C to 45/30 °C. On the other hand, H2O2 improved thermotolerance of cotton plants via maintaining cellular redox balance, gas exchange attributes, and further enhanced seed weight and ginning out turn under medium and high temperature regimes.

Анализ показателей газообмена организма в высотном полете на основе статической модели респираторной системы

The purpose of the research was to analyze the dynamics of indicators of human gas exchange in high-altitude flight on the basis of a static model of the respiratory system of the body. First, we developed the structure of this model and an algorithm for calculating the gas exchange of the body. Next, we analyzed changes in indicators of the function of external respiration and gas exchange, and clarified the quantitative parameters that determine the nature of the relationships between the components of gas exchange. Finally, we carried out a computational experiment to simulate ascent to a height. The results of the analysis of the calculations showed that when a person rises to a height with a drop in pressure, tidal volumes change the volume of the alveolar space decreases and the dead space increases in the ratio from 4.7 to 0.7. An uncompensated respiratory alkalosis develops, leading to a violation of the acid-base reactions of the body.

Oceanic Uptake of Oxygen During Deep Convection Events Through Diffusive and Bubble‐Mediated Gas Exchange

The concentration of dissolved oxygen (O2) plays fundamental roles in diverse chemical and biological processes throughout the oceans. The balance between the physical supply and the biological consumption controls the O2 level of the interior ocean, and the O2 supply to the deep waters can only occur through deep convection in the polar oceans. We develop a theoretical framework describing the oceanic O2 uptake during open‐ocean deep convection events and test it against a suite of numerical sensitivity experiments. Our framework allows for two predictions, confirmed by the numerical simulations. First, both the duration and the intensity of the wintertime cooling contribute to the total O2 uptake for a given buoyancy loss. Stronger cooling leads to deeper convection and the oxygenation can reach down to deeper depths. Longer duration of the cooling period increases the total amount of O2 uptake over the convective season. Second, the bubble‐mediated influx of O2 tends to weaken the diffusive influx by shifting the air‐sea disequilibrium of O2 toward supersaturation. The degree of compensation between the diffusive and bubble‐mediated gas exchange depends on the dimensionless number measuring the relative strength of oceanic vertical mixing and the gas transfer velocity. Strong convective mixing, which may occur under strong cooling, reduces the degree of compensation so that the two components of gas exchange together drive exceptionally strong oceanic O2 uptake.

In situ study of deep roots of Capparis spinosa L. during the dry season: Evidence from a natural “rhizotron” in the ancient catacombs of Milos Island (Greece)

The growing period of the deep-rooted, winter-deciduous Capparis spinosa (caper) coincides with the dry season, in the Mediterranean Basin. Roots of wild shrubs of C. spinosa penetrated cracks of a pumice substrate and lengthened in the subterranean environment of the ancient catacombs of Milos Island (Greece); therein, they reached depths of up to 20 m and exploited water present in deep soil layers. Elevated water potential (Ψ) was measured in root segments (Ψr = −0.35 ± 0.06 MPa), a few centimetres from the root apices of C. spinosa found in the catacombs during the dry season. Also, estimates of foliar predawn water potential and gas exchange components, as well as of nocturnal floral water potential of C. spinosa grown on slopes above the subterranean monument were high and reflected the efficiency of roots in retaining acquisition of water from deep soil layers, during the dry season.

Photosynthetic characterization of Australian pitcher plant Cephalotus follicularis

Australian carnivorous pitcher plant Cephalotus follicularis Labill. produces two types of leaves. During the spring time, the plant produces a foliage type of noncarnivorous leaf called lamina. Later, the second type of leaf is produced — carnivorous pitcher. Using simultaneous measurements of gas exchange and chlorophyll (Chl) fluorescence photosynthetic efficiency of these two distinct forms of leaves were compared. In addition stomatal density, an important component of gas exchange, and Chl concentration were also determined. Pitcher trap had lower net photosynthetic rate (P N) in comparison to noncarnivorous lamina, whereas the rate of respiration (R D) was not significantly different. This was in accordance with lower stomatal density and Chl concentration in the pitcher trap. On the other hand maximum quantum yield of PSII (Fv/Fm) and effective quantum yield of photochemical energy conversion in PSII (ΦPSII) was not significantly different. Nonphotochemical quenching (NPQ) was significantly higher in the lamina at higher irradiance. These data are in accordance with hypothesis that changing the leaf shape in carnivorous plants to make it a better trap generally makes it less efficient at photosynthesis. However, the pitcher of Cephalotus had much higher P N than it was expected from the data set of the genus Nepenthes. Because it is not possible to optimize for contrasting function such as photosynthesis and carnivory, it is hypothesized that Cephalotus pitchers are less elaborated for carnivorous function than the pitchers of Nepenthes.

AN IMPROVED MODEL FOR THE DIFFUSION OF OXYGEN INTO RESPIRING WOOD

Diffusion is an essential component of gas exchange at the cellular and tissue level, and a mathematical analysis of diffusion is therefore important to model biological processes in many systems. When several factors affect diffusion, finding an explicit non-steady-state equation can be difficult or impossible. In an earlier work (J Biol Systems15:63–72), we described such a function for a system where oxygen diffuses from the air into a body that consumes oxygen, assuming that the exchange surface is flat. Here, an explicit solution is limited to the case where tissue oxygen consumption decreases linearly with oxygen concentration and reaches 0 only when all oxygen has been consumed. The objective of this article is the analysis of gas diffusion into a respiring tissue that is cylindrical, which applies to tree stems and is a more realistic approximation for many other organs. This approach differs from diffusion along a flat surface, resulting in formally completely different explicit solutions, and is more flexible allowing for different relationships between oxygen concentration and tissue oxygen consumption.

Methane emission from living tree wood

The time courses of CO2, CH4, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O2 absorption and CO2 evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH4 and H2 from the wood depended on temperature. The temperature dependence of CH4 emission was similar to the temperature dependence of wood respiration. The high correlation between CO2, CH4, and H2 release and O2 absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH4 emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH4 and CO2 volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.

Determination of mesophyll diffusion resistance in Chamaerion angustifolium by the method of three-dimensional reconstruction of the leaf cell packing

A detailed quantitative analysis of the three-dimensional organization of the mesophyll was performed, and mesophyll diffusion resistance to CO2 in the leaves of Chamaerion angustifolium formed under different irradiance was calculated using an original method of stereometric cellular packing. For each type of leaves (sun and shade), we determined structural components of gas exchange: the volume of mesophyll per unit leaf area (Vmes), the volume of the intercellular space in the mesophyll (Vis), the area of the total mesophyll surface (S), the area of the free mesophyll surface facing the intercellular spaces (Smes), and the ratios of the total and the free mesophyll surfaces to its volume (S/V and Smes/V). As compared with sun leaves, in the shade leaves of Ch. angustifolium, S and Vmes decreased twofold, tissue density was reduced twofold, and the share of the intercellular space in the mesophyll rose from 49 to 72%. In shade, the diffusion resistance of the mesophyll increased by 1.8 times because of changes in the leaf structure. At the same time, the ratio Smes/V was found to increase by 1.4 times, which facilitated the diffusion of CO2. In the shade leaves of Ch. angustifolium, the diffusion resistance of the intercellular air spaces was reduced twofold as a result of an increase in their share in the leaf mesophyll and simplification of their geometry. Thus, the method of three-dimensional reconstruction of sun and shade leaves of Ch. angustifolium showed a comprehensive rearrangement of the mesophyll spatial organization in shade and revealed the structural mechanisms of changes in the resistance to CO2 diffusion within the leaf.

Study of the spatial organization of the gas exchange components of a snake lung – the sandboa Eryx colubrinus (Reptilia: Ophidia: Colubridae) – by latex casting

AbstractThe vasculature and the air ways of the lung of the sandboa Eryx colubrinus were cast using latex rubber, corroded, and studied with a scanning electron microscope to determine the shape, topographic configurations, and relative sizes of the gas exchange components. The sandboa had a right lung and a vestigeal left one. The lung, which terminated close to the anus, consisted of two distinctive anatomical regions. The exchange tissue was located in the cranial half of the lung while the caudal one consisted of a transparent avascular ‘air sac’. The right pulmonary artery, which was found on the laterodorsal aspect of the lung, gave rise to branches which supplied blood to the pleura and the faveolar septal walls. The geometric relationship between the flow of the venous blood (from the pulmonary artery) into the parenchymal zone of the lung and the convective/diffusive outwards air flow from the central air duct into the parenchyma is essentially counter‐current: the air moves centrifugally and the blood centripetally. However, the arrangement between the air flow in central air duct and that of the venous blood is cross‐current (i.e. the two media run in directions perpendicular to each other). These architectural schemes are similar to those that have developed in the avian lung. In fact, in its simplest form, the parenchymal region of the snake's lung corresponds with a single tertiary bronchus (parabronchus) of a bird lung. Further investigations are necessary to identify the factors that enforced this morphological convergence and to verify whether these congruent features are analogous, as they would seem to be, or from a phylogenetic perspective possibly homologous.

Study of the spatial organization of the gas exchange components of a snake lung – the sandboa Eryx colubrinus (Reptilia: Ophidia: Colubridae) – by latex casting

Study of the spatial organization of the gas exchange components of a snake lung – the sandboa Eryx colubrinus (Reptilia: Ophidia: Colubridae) – by latex casting

Computer-Assisted Analysis of the Impact of Respiratory Quotient on Blood CO2Tension and pH Changes

A computer model for the accurate quantification of blood gas exchange components was used to assess the impact of respiratory quotient (RQ) on venoarterial CO2tension and pH differences over a large group of patient measurements. The combined use of measured and computer-generated data has shown that, for any given increase in blood CO2concentration (i.e., when the arterial blood becomes venous), the associated increase in CO2tension and decrease in pH are inversely related to the RQ, and that this relationship is mediated by the Haldane effect. These results are useful for a thorough understanding of blood gas and metabolic interactions in normal and abnormal states, and for improving the interpretation of changes in venoarterial CO2tension gradient in clinical monitoring.

Relationships Between Nitrogen Content and Net Gas Exchange Components of a Cotton Leaf During Ontogeny

Relationships between leaf nitrogen (N) content and leaf gas exchange components of a single cotton (Gossypium hirsutum L.) leaf subtending the fruit during ontogeny were investigated under field conditions. A 20-d old leaf exhibited the highest physiological activity characterized by net photosynthetic (PN) and transpiration (E) rates, stomatal conductances to CO2 exchange (gsCO2) and water vapor transfer (gsH2O), and nitrogen (N) content. With the advent of leaf senescence, the gas exchange rates declined as exhibited by the 30-, 40-, and 60-d old leaves. Regression analysis indicated close relationships between gsCO2 and PN, and gsH2O and E as the leaves advanced towards senescence. Both PN and gsCO2 were related to N as they declined with leaf age. Thus, the declines in PN were associated with stomatal closure and removal of N during leaf ontogeny.

Analysis of the gas exchange components in chilled tomato plants

A positive linear relationship between the net CO2 exchange rate (P N) and the leaf stomatal conductance (gs) under an optimal temperature, and even more distinct one after a short-term chilling (CH, 15-17 h, 2 °C in darkness), that was found in two tomato cultivars (sensitive to a low temperature cv. Robin and tolerant cv. New Yorker) suggested a partial stomatal limitation of photosynthesis. The CH treatment of cv. Robin resulted in an intercellular CO2 concentration (C i) increase because of which a negative correlation between C i and P N was observed. In cv. New Yorker a positive correlation was observed. Detrimental effect of the low temperature in cv. Robin was more evident in plants with a relatively small root system (SR), but drought-hardening positively affected the response to CH only in the plants with bigger roots (BR). On the contrary, in cv. New Yorker the favourable effect of such pre-treatment was more evident in SR than in BR plants.

A Method for Separating Cuticular and Stomatal Components of Gas Exchange by Amphistomatous Leaves

A new technique for estimating the cuticular component of epidermal gas exchange by a stomatous leaf side is proposed. It is based on the process of elimination of stomatal diffusion by mass flow of air applying an air pressure gradient across the leaf. This technique was designed to enable a reliable estimation of the cuticular component irrespective of stomatal opening. A model solution of diffusive and mass flow counteraction in terms of general substance fluxes is presented

A Method for Separating Cuticular and Stomatal Components of Gas Exchange by Amphistomatous Leaves

The apparent cuticular component of transpiration of stomata bearing leaf epidermis was estimated by restricting stomatal diffusion by mass flow of air in the opposite direction. This was achieved by applying an air pressure gradient across the amphistomatous leaf. Some assumptions of the previously suggested method (Šantrůcek and Slavík, 1990) were experimentally verified using maize leaves. The technique makes possible a quantitative estimation of cuticular water loss including that of the external peristomatal (i.e. vapour not passing through the pores) and the respective conductance when the stomata are partially open. In addition to the fact that the cuticular portion of the total leaf vapour loss (i.e. relative cuticular transpiration) depends on stomatal opening, even the absolute value of apparent cuticular transpiration was (1) increased by lower vapour pressure deficit and (2) decreased with closing stomata. These changes, induced by variations in a vapour pressure deficit of 2.45±0.35 kPa, ranged between 0.66±0.14μg cm −2 s−1. The absolute value of apparent cuticular transpiration changed on average by a factor of 2.3 due to stomata opening or closing which was induced by turning the light on or by exogenous ABA application. Possible interference by residual vapour diffusing through the stomatal pore was evaluated by the model application. An attempt was also made to assess the cuticular component of CO2-uptake rate. Experimental results are discussed in context with the feedforward response of stomata to air humidity.

Contribution of continuing gas exchange to phase III exhaled PCO2 and PO2 profiles.

Changes in PCO2 and PO2 during expiration have been ascribed to simultaneous gas exchange, but other factors such as ventilation-perfusion inhomogeneity in combination with sequential emptying may also contribute. An experimental and model approach was used to study the relationship between gas exchange and changes in expired PCO2 and PO2 in anesthetized dogs during prolonged high tidal volume expirations. Changes in PCO2 and PO2 were quantified by taking the area bounded by the sloping exhalation curve and a line drawn horizontally from a point where the Fowler dead space plus 250 ml had been expired. This procedure is similar to using the slope of the exhalation curve but it circumvents problems caused by nonlinearity of the PCO2 and PO2 curves. The gas exchange components of the CO2 and O2 areas were calculated using a single-alveolus lung model whose input parameters were measured in connection with each prolonged expiration. The relationship between changes in experimental CO2 areas caused by sudden reductions in mixed venous PCO2 (produced by right atrial infusions of NaOH) and those calculated by the model was also studied. In seven dogs, calculated CO2 and O2 areas were 13% higher and 25% lower than the respective experimental areas, but interindividual variations were large. Changes in experimental CO2 areas caused by step changes in mixed venous PCO2 were almost identical to changes in the calculated areas. We conclude that the changes in PCO2 and PO2 during expiration cannot be explained solely by gas exchange. However, the single-alveolus lung model accurately predicts changes in the CO2 exhalation curve caused by alterations in the alveolar CO2 flow.