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Background and purpose: Oxygen dynamics may be important for the tissue-sparing effect observed at ultra-high dose rates (FLASH sparing effect). This study investigated the correlation between local instantaneous dose rate and radiation-induced oxygen pressure reduction during proton pencil beam scanning (PBS) irradiations of a sample and quantified the oxygen consumption g-value. Materials and methods: A 0.2 ml phosphorescent sample (1 µM PtG4 Oxyphor probe in saline) was irradiated with a 244 MeV proton PBS beam. Four irradiations were performed with variations of a PBS spot pattern with 5 × 7 spots. During irradiation, the partial oxygen pressure (pO2) was measured with 4.5 Hz temporal resolution with a phosphorometer (Oxyled) that optically excited the probe and recorded the subsequently emitted light. A calibration was performed to calculate the pO2 level from the measured phosphorescence lifetime. A fiber-coupled scintillator simultaneously measured the instantaneous dose rate in the sample with 50 kHz sampling rate. The oxygen consumption g-value was determined on a spot-by-spot level and using the total pO2 change for full spot pattern irradiation. Results: A high correlation was found between the local instantaneous dose rate and pO2 reduction rate, with a correlation coefficient of 0.96-0.99. The g-vales were 0.18 ± 0.01 mmHg/Gy on a spot-by-spot level and 0.17 ± 0.01 mmHg/Gy for full spot pattern irradiation. Conclusions: The pO2 reduction rate was directly related to the local instantaneous dose rate per delivered spot in PBS deliveries. The methodology presented here can be applied to irradiation at ultra-high dose rates with modifications in the experimental setup.

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In pursuing advanced neuromorphic applications, this study introduces the successful engineering of a flexible electronic synapse based on WO3-x, structured as W/WO3-x/Pt/Muscovite-Mica. This artificial synapse is designed to emulate crucial learning behaviors fundamental to in-memory computing. We systematically explore synaptic plasticity dynamics by implementing pulse measurements capturing potentiation and depression traits akin to biological synapses under flat and different bending conditions, thereby highlighting its potential suitability for flexible electronic applications. The findings demonstrate that the memristor accurately replicates essential properties of biological synapses, including short-term plasticity (STP), long-term plasticity (LTP), and the intriguing transition from STP to LTP. Furthermore, other variables are investigated, such as paired-pulse facilitation, spike rate-dependent plasticity, spike time-dependent plasticity, pulse duration-dependent plasticity, and pulse amplitude-dependent plasticity. Utilizing data from flat and differently bent synapses, neural network simulations for pattern recognition tasks using the Modified National Institute of Standards and Technology dataset reveal a high recognition accuracy of ∼95% with a fast learning speed that requires only 15 epochs to reach saturation.

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BACKGROUND: Phosphocreatine dynamics provide the gold standard evaluation of in-vivo mitochondrial function and is tightly coupled with oxygen availability. Low mitochondrial oxidative capacity has been associated with health issues and low exercise performance. METHODS: To evaluate the relationship between near-infrared spectroscopy-based muscle oxygen dynamics and magnetic resonance spectroscopy-based energy-rich phosphates, a systematic review of the literature related to muscle oxygen dynamics and energy-rich phosphates was conducted. PRISMA guidelines were followed to perform a comprehensive and systematic search of four databases on 02-11-2021 (PubMed, MEDLINE, Scopus and Web of Science). Beforehand pre-registration with the Open Science Framework was performed. Studies had to include healthy humans aged 18-55, measures related to NIRS-based muscle oxygen measures in combination with energy-rich phosphates. Exclusion criteria were clinical populations, laboratory animals, acutely injured subjects, data that only assessed oxygen dynamics or energy-rich phosphates, or grey literature. The Effective Public Health Practice Project Quality Assessment Tool was used to assess methodological quality, and data extraction was presented in a table. RESULTS: Out of 1483 records, 28 were eligible. All included studies were rated moderate. The studies suggest muscle oxygen dynamics could indicate energy-rich phosphates under appropriate protocol settings. CONCLUSION: Arterial occlusion and exercise intensity might be important factors to control if NIRS application should be used to examine energetics. However, more research needs to be conducted without arterial occlusion and with high-intensity exercises to support the applicability of NIRS and provide an agreement level in the concurrent course of muscle oxygen kinetics and muscle energetics. TRIAL REGISTRATION: https://osf.io/py32n/ . KEY POINTS: 1. NIRS derived measures of muscle oxygenation agree with gold-standard measures of high energy phosphates when assessed in an appropriate protocol setting. 2. At rest when applying the AO protocol, in the absence of muscle activity, an initial disjunction between the NIRS signal and high energy phosphates can been seen, suggesting a cascading relationship. 3. During exercise and recovery a disruption of oxygen delivery is required to provide the appropriate setting for evaluation through either an AO protocol or high intensity contractions.

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Increasing evidence demonstrates that mammals have different reactions to hypoxia with varied oxygen dynamic patterns. It takes ∼24 h for tri-gas incubator to achieve steady cell hypoxia, which fails to recapitulate ultrafast oxygen dynamics of intestinal ischemia/reperfusion (IR) injury. Inspired from the structure of native intestinal villi, we engineered an intestinal organoid chip embedded with engineered artificial microvessels based on co-axial microfluidic technology by using pH-responsive ZIF-8/sodium alginate scaffold. The chip was featured on: (i) eight times the oxygen exchange efficiency compared with the conventional device, tri-gas incubator, (ii) implantation of intestinal organoid reproducing all types of intestinal epithelial cells, and (iii) bio-responsiveness to hypoxia and reoxygenation (HR) by presenting metabolism disorder, inflammatory reaction, and cell apoptosis. Strikingly, it was found for the first time that Olfactomedin 4 (Olfm4) was the most significantly down-regulated gene under a rapid HR condition by sequencing the RNA from the organoids. Mechanistically, OLFM4 played protective functions on HR-induced cell inflammation and tissue damage by inhibiting the NF-kappa B signaling activation, thus it could be used as a therapeutic target. Altogether, this study overcomes the issue of mismatched oxygen dynamics between in vitro and in vivo, and sets an example of next-generation multisystem-interactive organoid chip for finding precise therapeutic targets of IR injury.

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The expression of plant cysteine oxidase (PCO) enzyme in Saccharomyces cerevisiae enables the Arg/Cys N-degron pathway (Cys-NDP) for selective protein degradation that, in plants, functions as direct oxygen perception mechanism. A synthetic construct based on the plant Cys-NDP substrate related to apetala 2.12 (RAP2.12), the dual luciferase oxygen reporter (DLOR), exploits the N-terminal Cys of RAP2.12, and its oxygen-dependent degradation through the Cys-NDP. The luminescent output of DLOR can be used as a proxy for intracellular oxygen dynamics in budding yeast. Replacement of the luciferase reporter of the DLOR with fluorescent proteins would furthermore facilitate the imaging of reporter dynamics in living cells. In this chapter, we describe the methods for delivering the DLOR synthetic construct to yeast and calibrating its output by means of oxygen quantification in the culture with a physical oxygen sensor. We explain the setup needed to carry out hypoxic treatments with several colonies as replicates. We also describe the method to measure oxygen concentration in the culture, the closest indication of intracellular oxygen levels, as a way that would serve to calibrate the DLOR output. Finally, we propose a strategy to replace the luminescent reporters in the DLOR with fluorescent proteins to visualize oxygen dynamics in vivo.

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Understanding how microbial communities of aquatic ecosystems respond to environmental change remains a critical challenge in microbial ecology. In this study, we used light-dependent oxic-anoxic micro-ecosystems to understand how the functioning and diversity of aerobic and anaerobic lake analog communities are affected by a pulse light deprivation. Continuous measurements of oxygen concentration were made and a time series of full-length 16S rRNA sequencing was used to quantify changes in alpha- and beta diversity. In the upper oxic layer, oxygen concentration decreased significantly under light reduction, but showed resilience in daily mean, minimum, and maximum after light conditions were restored to control level. Only the amplitude of diurnal fluctuations in oxygen concentrations did not recover fully, and instead tended to remain lower in treated ecosystems. Alpha diversity of the upper oxic layer communities showed a delayed increase after light conditions were restored, and was not resilient in the longer term. In contrast, alpha diversity of the anoxic lower layer communities increased during the light reduction, but was resilient in the longer term. Community composition changed significantly during light reduction, and showed resilience in the oxic layer and lack of resilience in the anoxic layer. Alpha diversity and the amplitude of daily oxygen fluctuations within and among treatments were strongly correlated, suggesting that higher diversity could lead to less variable oxygen concentrations, or vice versa. Our experiment showed that light deprivation induces multifaceted responses of community function (oxygen respiration) and structure, hence focusing on a single stability component could potentially be misleading.

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Aquatic eddy covariance (AEC) is increasingly being used to study benthic oxygen (O2) flux dynamics, organic carbon cycling, and ecosystem health in marine and freshwater environments. Because it is a noninvasive technique, has a high temporal resolution (∼15 min), and integrates over a large area of the seafloor (typically 10-100 m2), it has provided new insights on the functioning of aquatic ecosystems under naturally varying in situ conditions and has given us more accurate assessments of their metabolism. In this review, we summarize biogeochemical, ecological, and biological insightsgained from AEC studies of marine ecosystems. A general finding for all substrates is that benthic O2 exchange is far more dynamic than earlier recognized, and thus accurate mean values can only be obtained from measurements that integrate over all timescales that affect the local O2 exchange. Finally, we highlight new developments of the technique, including measurements of air-water gas exchange and long-term deployments.

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We sampled the Klang estuary during the inter-monsoon and northeast monsoon period (July-Nov 2011, Oct-Nov 2012), which coincided with higher rainfall and elevated Klang River flow. The increased freshwater inflow into the estuary resulted in water column stratification that was observed during both sampling periods. Dissolved oxygen (DO) dropped below 63 µM, and hypoxia was observed. Elevated river flow also transported dissolved inorganic nutrients, chlorophyll a and bacteria to the estuary. However, bacterial production did not correlate with DO concentration in this study. As hypoxia was probably not due to in situ heterotrophic processes, deoxygenated waters were probably from upstream. We surmised this as DO correlated with salinity (R2 = 0.664, df = 86, p < 0.001). DO also decreased with increasing flushing time (R2 = 0.556, df = 11, p < 0.01), suggesting that when flushing time (> 6.7 h), hypoxia could occur at the Klang estuary. Here, we presented a model that related riverine flow rate to the post-heavy rainfall hypoxia that explicated the episodic hypoxia at Klang estuary. As Klang estuary supports aquaculture and cockle culture, our results could help protect the aquaculture and cockle culture industry here.

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Objective: To preliminarily investigate the effect of intraoperative goal-directed fluid management (GDFM) on pulmonary function and oxygen dynamics in patients with severe burns. Methods: From February 2017 to May 2018, 30 patients admitted to Burn Department of our hospital with severe burns who met the criteria for inclusion and needed escharectomy and skin grafting were enrolled in this prospective randomized controlled trial. The patients were divided into group GDFM of 15 cases [14 males and 1 female, (45±14) years old] and conventional liquid management group of 15 cases [12 males and 3 females, (42±10) years old] according to the random number table. During escharectomy and skin grafting, volume of patients in group GDFM was managed according to the GDFM scheme, based on cardiac output index, stroke volume variation, stroke volume index, hemoglobin, central venous oxygen saturation (ScvO(2)), and other parameters; volume of patients in conventional liquid management group was managed according to clinical experience and conventional liquid management scheme, based on mean arterial pressure, central venous pressure, urine output, hemoglobin, and other parameters. At post operation hour (POH) 1, 6, 12, and 24, arterial and venous blood was collected from patients of the two groups to determine the levels of extravascular lung water index (ELWI), global end-diastolic volume index (GEDI), oxygenation index, ScvO(2), central venous-to-arterial blood carbon dioxide partial pressure difference (Pcv-aCO(2)), lactic acid, pH value, bicarbonate ion, and base excess routinely. Data were processed with Fisher's exact probability test, t test, analysis of variance for repeated measurement, and least significant difference test. Results: (1) The ELWI of patients in group GDFM was (4.3±1.1) mL/kg at POH 1, which was significantly lower than (6.5±3.6) mL/kg in conventional liquid management group (t=2.26, P<0.05). The ELWI levels of patients in group GDFM at POH 6, 12, and 24 were (6.8±2.2), (6.6±2.0), and (6.9±1.6) mL/kg, respectively, significantly higher than the level at POH 1 within the same group (P<0.01), and similar to (8.5±3.1), (7.8±2.3), and (8.0±3.5) mL/kg in conventional liquid management group (t=1.73, 1.53, 1.10, P>0.05). The GEDI levels between patients of the two groups were similar, and there was no significantly statistical difference between the two groups as a whole (treatment factor main effect F=2.35, time factor main effect F=0.44, interaction F=0.07, P>0.05). (2) The oxygenation index of patients in group GDFM was (350±78) mL/kg at POH 1, which was significantly higher than (259±109) mL/kg in conventional liquid management group (t=2.63, P<0.05). In conventional liquid management group, the oxygenation index of patients at POH 6 was significantly higher than that at POH 1, 12, or 24 (P<0.01). The ScvO(2) levels of patients in group GDFM at POH 1, 6, and 12 were 0.516±0.105, 0.679±0.121, and 0.713±0.104, respectively, which were significantly higher than 0.382±0.194, 0.545±0.194, and 0.595±0.191 in conventional liquid management group (t=2.35, 2.27, 2.10, P<0.05). The ScvO(2) levels of patients in the two groups at POH 6, 12, and 24 were significantly higher than those levels at POH 1 within the same group (P<0.01), and the ScvO(2) of patients in conventional liquid management group at POH 24 was significantly higher than that at POH 6 or 12 within the same group (P<0.05 or P<0.01). The Pcv-aCO(2) levels of patients in group GDFM were significantly lower than those in conventional liquid management group at POH 1 and 6 (t=2.55, 2.71, P<0.05). The Pcv-aCO(2) of patients in group GDFM at POH 12 was significantly lower than that at POH 6 or 24 within the same group (P<0.05). (3) The blood lactic acid levels and pH values between patients of the two groups were similar at POH 1, 6, 12, and 24 (t=0.89, 0.19, 0.26, 0.23; 1.55, 0.71, 0.77, 0.77, P>0.05). In conventional liquid management group, the blood lactic acid levels of patients at POH 6, 12, and 24 were significantly lower than the level at POH 1 within the same group (P<0.05), and the pH values of patients at POH 6, 12, and 24 were significantly higher than the value at POH 1 within the same group (P<0.05). The levels of bicarbonate ion and base excess between patients of the two groups were similar, and there were no significantly statistical differences between the two groups as a whole (treatment factor main effect F=0.06, 0.11, time factor main effect F=2.07, 1.59, interaction F=1.45, 0.91, P>0.05). Conclusions: GDFM is helpful to improve the pulmonary function and oxygen dynamics in patients with severe burns in the short term after escharectomy and skin grafting. It has certain significance in preventing and reducing pulmonary edema and pulmonary complications in patients with severe burn after operation.

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Objective@#To preliminarily investigate the effect of intraoperative goal-directed fluid management (GDFM) on pulmonary function and oxygen dynamics in patients with severe burns.@*Methods@#From February 2017 to May 2018, 30 patients admitted to Burn Department of our hospital with severe burns who met the criteria for inclusion and needed escharectomy and skin grafting were enrolled in this prospective randomized controlled trial. The patients were divided into group GDFM of 15 cases [14 males and 1 female, (45±14) years old] and conventional liquid management group of 15 cases [12 males and 3 females, (42±10) years old] according to the random number table. During escharectomy and skin grafting, volume of patients in group GDFM was managed according to the GDFM scheme, based on cardiac output index, stroke volume variation, stroke volume index, hemoglobin, central venous oxygen saturation (ScvO2), and other parameters; volume of patients in conventional liquid management group was managed according to clinical experience and conventional liquid management scheme, based on mean arterial pressure, central venous pressure, urine output, hemoglobin, and other parameters. At post operation hour (POH) 1, 6, 12, and 24, arterial and venous blood was collected from patients of the two groups to determine the levels of extravascular lung water index (ELWI), global end-diastolic volume index (GEDI), oxygenation index, ScvO2, central venous-to-arterial blood carbon dioxide partial pressure difference (Pcv-aCO2), lactic acid, pH value, bicarbonate ion, and base excess routinely. Data were processed with Fisher′s exact probability test, t test, analysis of variance for repeated measurement, and least significant difference test.@*Results@#(1) The ELWI of patients in group GDFM was (4.3±1.1) mL/kg at POH 1, which was significantly lower than (6.5±3.6) mL/kg in conventional liquid management group (t=2.26, P<0.05). The ELWI levels of patients in group GDFM at POH 6, 12, and 24 were (6.8±2.2), (6.6±2.0), and (6.9±1.6) mL/kg, respectively, significantly higher than the level at POH 1 within the same group (P<0.01), and similar to (8.5±3.1), (7.8±2.3), and (8.0±3.5) mL/kg in conventional liquid management group (t=1.73, 1.53, 1.10, P>0.05). The GEDI levels between patients of the two groups were similar, and there was no significantly statistical difference between the two groups as a whole (treatment factor main effect F=2.35, time factor main effect F=0.44, interaction F=0.07, P>0.05). (2) The oxygenation index of patients in group GDFM was (350±78) mL/kg at POH 1, which was significantly higher than (259±109) mL/kg in conventional liquid management group (t=2.63, P<0.05). In conventional liquid management group, the oxygenation index of patients at POH 6 was significantly higher than that at POH 1, 12, or 24 (P<0.01). The ScvO2 levels of patients in group GDFM at POH 1, 6, and 12 were 0.516±0.105, 0.679±0.121, and 0.713±0.104, respectively, which were significantly higher than 0.382±0.194, 0.545±0.194, and 0.595±0.191 in conventional liquid management group (t=2.35, 2.27, 2.10, P<0.05). The ScvO2 levels of patients in the two groups at POH 6, 12, and 24 were significantly higher than those levels at POH 1 within the same group (P<0.01), and the ScvO2 of patients in conventional liquid management group at POH 24 was significantly higher than that at POH 6 or 12 within the same group (P<0.05 or P<0.01). The Pcv-aCO2 levels of patients in group GDFM were significantly lower than those in conventional liquid management group at POH 1 and 6 (t=2.55, 2.71, P<0.05). The Pcv-aCO2 of patients in group GDFM at POH 12 was significantly lower than that at POH 6 or 24 within the same group (P<0.05). (3) The blood lactic acid levels and pH values between patients of the two groups were similar at POH 1, 6, 12, and 24 (t=0.89, 0.19, 0.26, 0.23; 1.55, 0.71, 0.77, 0.77, P>0.05). In conventional liquid management group, the blood lactic acid levels of patients at POH 6, 12, and 24 were significantly lower than the level at POH 1 within the same group (P<0.05), and the pH values of patients at POH 6, 12, and 24 were significantly higher than the value at POH 1 within the same group (P<0.05). The levels of bicarbonate ion and base excess between patients of the two groups were similar, and there were no significantly statistical differences between the two groups as a whole (treatment factor main effect F=0.06, 0.11, time factor main effect F=2.07, 1.59, interaction F=1.45, 0.91, P>0.05).@*Conclusions@#GDFM is helpful to improve the pulmonary function and oxygen dynamics in patients with severe burns in the short term after escharectomy and skin grafting. It has certain significance in preventing and reducing pulmonary edema and pulmonary complications in patients with severe burn after operation.

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Due to cultural eutrophication and global climate change, an exponential increase in the number and extent of hypoxic zones in marine and freshwater ecosystems has been observed in the last few decades. Hypoxia, or low dissolved oxygen (DO) concentrations, can produce strong negative ecological impacts and, therefore, is a management concern. We measured biomass and densities of Dreissena in Lake Erie, as well as bottom DO in 2014 using 19 high frequency data loggers distributed throughout the central basin to validate a three-dimensional hydrodynamic-ecological lake model. We found that a deep, offshore hypoxic zone was formed by early August, restricting the Dreissena population to shallow areas of the central basin. Deeper than 20 m, where bottom hypoxia routinely develops, only young of the year mussels were found in small numbers, indicating restricted recruitment and survival of young Dreissena. We suggest that monitoring Dreissena distribution can be an effective tool for mapping the extent and frequency of hypoxia in freshwater. In addition, our results suggest that an anticipated decrease in the spatial extent of hypoxia resulting from nutrient management has the potential to increase the spatial extent of profundal habitat in the central basin available for Dreissena expansion.

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Measurements of oxygen uptake are central to methods for the assessment of physical fitness and endurance capabilities in athletes. Two important parameters extracted from such data of incremental exercise tests are the maximal oxygen uptake and the critical power. A commonly accepted model of the dynamics of oxygen uptake during exercise at a constant work rate comprises a constant baseline oxygen uptake, an exponential fast component, and another exponential slow component for heavy and severe work rates. We have generalized this model to variable load protocols with differential equations that naturally correspond to the standard model for a constant work rate. This provides the means for predicting the oxygen uptake response to variable load profiles including phases of recovery. The model parameters have been fitted for individual subjects from a cycle ergometer test, including the maximal oxygen uptake and critical power. The model predictions have been validated by data collected in separate tests. Our findings indicate that the oxygen kinetics for a variable exercise load can be predicted using the generalized mathematical standard model. Such models can be applied in the field where the constant work rate assumption generally is not valid.

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An increase in the incidence rate of cardiovascular disease is attributed to high daily sitting time, while a drop in risk of cardiovascular disease comes from a decrease in daily sitting time, rather than an increase in physical activity levels. Although short-duration passive exercise increases energy expenditure and blood flow, few studies have reported on the responses of cardiorespiratory dynamics to long-duration passive exercise. The purpose of this study was to consider the effect of long-duration passive exercise for 20 min on cardiorespiratory and muscle oxygen dynamics. Eight healthy men continuously performed passive exercise using a cycle ergometer for 20 min at 50 rpm. Changes in oxygen uptake, cardiac output and muscle oxygenation were measured during passive cycling exercise. The oxygen uptake at 1 min after the start of passive exercise was significantly increased, compared to resting level, but subsequently returned to the same as resting level. Cardiac output showed no change during passive cycling exercise. Tissue oxygen saturation increased after the start of passive exercise and subsequently maintained steady state. These results suggest that the effect of increases in energy expenditure was not maintained by passive exercise for 20 min. In addition, it is likely that passive cycling exercise for 20 min has an effect on peripheral circulation, although the exercise seems to have no effect on central circulation.

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The function of the brain neural circuit is highly dependent on oxygen supply. Imaging the precise oxygen distribution and dynamics are critical for understanding the relationship between neuronal activity and oxygen dynamics of the nearby capillaries. Here, we develop fast acousto-optic scanning two-photon microscopy. Combined with oxygen probes, such as PtP-C343, we can monitor oxygen dynamics at the submicron level by this real-time microscopy. In this fast acousto-optic scanning microscopy, an acousto-optic deflector (AOD), an inertia-less scanner, is used to scan the femtosecond laser. A cylindrical lens is used to compensate the 'cylindrical lens effect' of AOD and a prism is used to compensate the chromatic dispersion of AOD. An electro-optical modulator (EOM) and a sCMOS camera are gated to measure the phosphorescence lifetime. With a 40× water objective lens, this set-up can image a 100 µm × 100 µm field of view at a speed of 20 frames per second and a 25 µm × 8 µm field of view at a speed of 500 frames per second. This real-time two-photon microscopy is expected to be a good tool for observing and recording the precise rapid oxygen dynamics in the cerebral cortex, which will facilitate studies of oxygen metabolism in neurosciences.

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Wetland plants actively provide oxygen for aerobic processes in submerged tissues and the rhizosphere. The novel concomitant assessment of diurnal dynamics of oxygen and carbon dioxide concentrations under field conditions tests the whole-system interactions in plant-internal gas exchange and regulation. Oxygen concentrations ([O2]) were monitored in-situ in central culm and rhizome pith cavities of common reed (Phragmites australis) using optical oxygen sensors. The corresponding carbon dioxide concentrations ([CO2]) were assessed via gas samples from the culms. Highly dynamic diurnal courses of [O2] were recorded, which started at 6.5-13 % in the morning, increased rapidly up to 22 % during midday and declined exponentially during the night. Internal [CO2] were high in the morning (1.55-17.5 %) and decreased (0.04-0.94 %) during the rapid increase of [O2] in the culms. The observed negative correlations between [O2] and [CO2] particularly describe the below ground relationship between plant-mediated oxygen supply and oxygen use by respiration and biogeochemical processes in the rhizosphere. Furthermore, the nocturnal declining slopes of [O2] in culms and rhizomes indicated a down-regulation of the demand for oxygen in the complete below ground plant-associated system. These findings emphasize the need for measurements of plant-internal gas exchange processes under field conditions because it considers the complex interactions in the oxic-anoxic interface.

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Muscle O2 dynamics during ramp cycling exercise were compared between aerobic capacity-matched elderly men (n=8, age 65±2 years) and women (n=8, age 66±3 years). Muscle O2 saturation (SmO2) and relative change in deoxygenated (Δdeoxy-Hb) and total hemoglobin concentration (Δtotal-Hb) were monitored continuously during exercise in the vastus lateralis (VL) and gastrocnemius medialis (GM) by near infrared spatial resolved spectroscopy. SmO2 was significantly higher during exercise in women than in men in VL, but not in GM. In VL, Δdeoxy-Hb and Δtotal-Hb were significantly higher in men than in women, especially during high intensity exercise. However, no significant difference was observed in Δdeoxy-Hb or Δtotal-Hb in GM. Sex-related differences in muscle deoxygenation response may be heterogeneous among leg muscles in elderly subjects.

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The cerebral microvasculature plays a vital role in adequately supplying blood to the brain. Determining the health of the cerebral microvasculature is important during pathological conditions, such as stroke and dementia. Recent studies have shown the complex relationship between cerebral metabolic rate and transit time distribution, the transit times of all the possible pathways available dependent on network topology. In this paper, we extend a recently developed technique to solve for residue function, the amount of tracer left in the vasculature at any time, and transit time distribution in an existing model of the cerebral microvasculature to calculate cerebral metabolism. We present the mathematical theory needed to solve for oxygen concentration followed by results of the simulations. It is found that oxygen extraction fraction, the fraction of oxygen removed from the blood in the capillary network by the tissue, and cerebral metabolic rate are dependent on both mean and heterogeneity of the transit time distribution. For changes in cerebral blood flow, a positive correlation can be observed between mean transit time and oxygen extraction fraction, and a negative correlation between mean transit time and metabolic rate of oxygen. A negative correlation can also be observed between transit time heterogeneity and the metabolic rate of oxygen for a constant cerebral blood flow. A sensitivity analysis on the mean and heterogeneity of the transit time distribution was able to quantify their respective contributions to oxygen extraction fraction and metabolic rate of oxygen. Mean transit time has a greater contribution than the heterogeneity for oxygen extraction fraction. This is found to be opposite for metabolic rate of oxygen. These results provide information on the role of the cerebral microvasculature and its effects on flow and metabolism. They thus open up the possibility of obtaining additional valuable clinical information for diagnosing and treating cerebrovascular diseases.

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Search relative literature according to key words,focus parameters of oxygen metabolism in the diag-nosis and treatment of shock on progress. The importance of hemodynamic monitoring is reflected in the correct interpre-tation of the monitoring results and takes simultaneously the appropriate treatment strategy according to the correct inter-pretation of the results. The essence of the shock is body tissue hypoperfusion,which result in tissue hypoxia and organ dysfunction,the essence of the hemodynamic imbalance is the imbalance of oxygen supply and oxygen consumption. The end point of the fluid resuscitation for shock is now increasing emphasis on monitoring mixed / central venous oxygen saturation and the concentration of blood lactate,the rate of lactate clearance.

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BACKGROUND AND AIMS: Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh. METHODS: Responses to complete submergence in terms of stem internal O2 dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O2 levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured. KEY RESULTS: Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O2 profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O2 concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O2 in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa. CONCLUSIONS: The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged.

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