Oxygen Depletion Rates Research Articles

A novel, dynamic, in vivo, non-contact method of measuring oxygen depletion rate of the anterior eye

Despite the importance of oxygen measurements, techniques have been limited by their invasive nature and small corneal area of assessment. The aim of this study was to assess a non-contact way of measuring oxygen uptake of the whole anterior eye. The device consisted of a goggle with an oxygen sensitive material on the inner surface. As the output is affected by temperature, a second probe was inserted into the goggle to compensate. The goggle was positioned over the eye on 10 subjects (mean age 30.5±5.0 years, 3:2 male:female) to assess the oxygen depletion of the unrestricted, blinking eye. Measurements were taken over a 3 min period. The volume contained within the goggle and bone structure of individual eyes was measured by water volume displacement and the output corrected to O(2)% reduction/cm(3) over a 30s period. To check the discriminatory ability of the device, measurements were taken in open-eye and closed-eye conditions, along with on the subjects' skin (cheek) for comparisons. The oxygen depletion measure over 30s was on average 3.10±1.51 O(2)%cm(3) during open eye condition, significantly more than during closed eye conditions (1.26±1.52 O(2)%cm(3)). The skin (control) showed a negligible oxygen uptake (0.19±0.33 O(2)%cm(3)). The results demonstrated good repeatability with a mean standard deviation of around 0.4 O(2)%cm(3) (equating to 11%). The technique demonstrated a non-invasive, non-contact method of measuring consumption of oxygen within the goggle (oxygen depletion rate) and showed good within-visit repeatability.

Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern Poland

Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern PolandThe oxygen content in a lake is a fundamental factor in lake ecology. In stratified lakes, deep waters are isolated from the atmosphere for several months during the summer; therefore, oxygen (substantially consumed by biological and chemical processes at this time) cannot be replaced before the autumnal mixing period. Hypolimnetic oxygen depletion has been considered an indicator of lake productivity since the early twentieth century. Many recent studies have been in opposition to this view by showing that the areal hypolimnetic oxygen depletion rate (AHOD) is poorly correlated with seston biomass and/or phosphorus concentration. The objective of this study is to show relationships between the mean values of total phosphorus (TP), total nitrogen (TN), chlorophyll a, and water transparency (Secchi disk depth, SDD) during the thermal stratification formation period and the AHOD rate. Hypolimnetic oxygen conditions in five dimictic lakes in northern Poland were examined in 2009 and 2010. Two of them were studied in the previous year. Monthly oxygen profiles taken from April to August, midsummer temperature profiles, and morphological data of the lakes were used to determine the AHOD rate. Standard water quality parameters such as concentrations of chlorophyll a, TP, and TN, as well as water transparency measured at the same time were used to calculate the trophic state indices (TSI) according to the Carlson-type formulas. On the basis of the collected data it is shown that AHOD is highly correlated with the TSI value for chlorophyll a, and poorly correlated with the TSI values for water transparency and phosphorus content. The best correlation between AHOD and TSI has been found for chlorophyll a (r2=0.702; p<0.001), as well as for overall TSI, determined by averaging separate component indices (r2=0.826; p<0.000). No correlation was found between AHOD and total nitrogen concentration. The research also confirmed previous observations, which pointed to a significant role of the hypolimnion depth in increasing oxygen deficits.

A re-evaluation of the empirical relationships connecting dissolved oxygen and phosphorus loading after dreissenid mussel invasion in Lake Simcoe

Lake Simcoe has had many stressors in the past decades. High total phosphorus (TP) loads into the lake led to end-of-summer volume-weighted hypolimnetic dissolved oxygen (MVWHDO) levels that were lethal to coldwater fish species. Additionally, dreissenid mussels became established in the lake around 1996, and may have affected nutrient cycling and phytoplankton abundance. Using data averaged over two time periods following dreissenid mussel establishment, we re-evaluated empirical relationships connecting TP loading rate and MVWHDO concentration that were developed with pre-dreissenid data. Oxygen depletion rate predicted chlorophyll (Chla) well within the range of other Ontario lakes. Measured Chla corresponded well with Chla predicted from lake TP concentration except at the shallowest station, indicating that the lake may becoming more spatially heterogeneous. Interestingly though, the Chla:TP temporal trend increased post-dreissenids when it is often observed to decrease (e.g., Great Lakes). Measured lake TP concentration was better predicted by TP loads when averaged over the ice-free season compared with the spring. The final model predicted MVWHDO directly from TP load very closely except for the 2002–2006 time period when the end-of-summer date was September 15 rather than September 30, suggesting that the date when MVWHDO is determined should be continuously re-evaluated. Additionally, trend analyses on each variable from 1980 to 2008 did not identify any changes that coincided with dreissenid establishment. Given that this model appears to be sound for the post-dreissenid period, an estimated TP load of 44 tonnes/yr was predicted that would yield the current MVWHDO target level of 7 mg/L.

“Dead Zone” dynamics in Lake Erie: the importance of weather and sampling intensity for calculated hypolimnetic oxygen depletion rates

Calculated hypolimnetic oxygen depletion (HOD) rates depend not only on environmental factors but also logistical ones. In particular, lack of understanding of the effects of weather in addition to how sampling effort determines calculated HOD rates complicates ecological understanding and environmental management of lake ecosystems. To better determine the roles of weather and sampling effort, we combined (1) weekly measurements of temperature and dissolved oxygen (DO) concentrations from seven stations in the Sandusky subbasin of Lake Erie’s central basin during 2005, (2) contemporaneous measures of storm activity and tributary discharge, and (3) a two-dimensional coupled hydrodynamic, chemical, and biological model of Lake Erie to investigate (1) how increased storm activity and tributary discharge affected short- (daily) and long-term (seasonal) dynamics of hypolimnetic hypoxia, and (2) how spatial (number of sites sampled) and temporal (sampling frequency) sampling effort affected calculated HOD rates. Our model closely replicated field-observed DO dynamics. When comparing baseline modeled dynamics to those in a second simulation with twice the number of days with high winds, however, we found that with more storm activity (1) periods of entrainment became more frequent, (2) the hypolimnion was warmer, (3) thermal stratification occurred 1 month later, whereas autumnal turnover occurred at least 1 week earlier shortening the duration of stratification by 1–2 months, and (4) HOD rates increased 12%. Further, spatial and temporal sampling intensity also affected calculated HOD rates. Consequently, adequately quantifying actual HOD rates requires sufficient sampling effort and the particular role of weather should be assessed with rigorous field and simulation studies, especially if HOD rates are used to indicate management success.

Hypoxia. 2. Hypoxia regulates cellular metabolism

Adaptation to lowering oxygen levels (hypoxia) requires coordinated downregulation of metabolic demand and supply to prevent a mismatch in ATP utilization and production that might culminate in a bioenergetic collapse. Hypoxia diminishes ATP utilization by downregulating protein translation and the activity of the Na-K-ATPase. Hypoxia diminishes ATP production in part by lowering the activity of the electron transport chain through activation of the transcription factor hypoxia-inducible factor-1. The decrease in electron transport limits the overproduction of reactove oxygen species during hypoxia and slows the rate of oxygen depletion to prevent anoxia. In this review, we discuss these mechanisms that diminish metabolic supply and demand for adaptation to hypoxia.

Oxygen depletion properties of glucose-grafted polyethylene resins filled with sodium ascorbate/modified iron compounds

Oxygen scavenging plastic can react with oxygen that was trapped in the packaging materials or permeated into the packages, and then, extend the shelf life of food contained in packages. Sodium ascorbate (SA) and modified iron (MFe) compounds were chosen as the main components of oxygen scavengers to prepare the oxygen scavenging LDPE plastics. However, the widely used hydrophobic LDPE packaging material will slow down the oxygen depletion rate of these oxygen scavenger compounds. So glucose was used to modify the hydrophobic property of LDPE to improve the oxygen depletion properties of LDPE oxygen scavenging plastic. The oxygen depletion efficiency of L95[SAx(MFe)y]5 series samples improved initially as the weight ratios of SA/MFe increase, and reached the best as the weight ratios of SA/MFe approach 7/3. After modifying LDPE with glucoses, the oxygen depletion efficiency of each ML95[SAx(MFe)y]5 specimen improved even better than that of the corresponding L95[SAx(MFe)y]5 specimen with the same loading of oxygen scavenger compound, wherein the oxygen depletion efficiency of ML95[SAx(MFe)y]5 series specimens reached the best as the weight ratios of SA/MFe approach 1/9. In consistent with the oxygen depletion properties found in the previous section, the peroxide values of modeled food samples tested in the airtight flask with L95[SAx(MFe)y]5 and ML95[SAx(MFe)y]5 series samples reduce consistently as their oxygen depletion properties improve. In order to understand the interesting oxygen depletion properties of L95[SAx(MFe)y]5 and ML95[SAx(MFe)y]5 series samples, Fourier transform infrared spectroscopy, scanning electron microscope and energy dispersive X-rays analysis of these samples were performed.

The effect of mayfly ( Hexagenia spp.) burrowing activity on sediment oxygen demand in western Lake Erie

Previous studies support the hypothesis that large numbers of infaunal burrow-irrigating organisms in the western basin of Lake Erie may increase significantly the sediment oxygen demand, thus enhancing the rate of hypolimnetic oxygen depletion. We conducted laboratory experiments to quantify burrow oxygen dynamics and increased oxygen demand resulting from burrow irrigation using two different year classes of Hexagenia spp. nymphs from western Lake Erie during summer, 2006. Using oxygen microelectrodes and hot film anemometry, we simultaneously determined oxygen concentrations and burrow water flow velocities. Burrow oxygen depletion rates ranged from 21.7 mg/nymph/mo for 15 mm nymphs at 23 °C to 240.7 mg/nymph/mo for 23 mm nymphs at 13 °C. Sealed microcosm experiments demonstrated that mayflies increase the rate of oxygen depletion by 2–5 times that of controls, depending on size of nymph and water temperature, with colder waters having greater impact. At natural population densities, nymph pumping activity increased total sediment oxygen demand 0.3–2.5 times compared to sediments with no mayflies and accounted for 22–71% of the total sediment oxygen demand. Extrapolating laboratory results to the natural system suggest that Hexagenia spp. populations may exert a significant control on oxygen depletion during intermittent stratification. This finding may help explain some of the fluctuations in Hexagenia spp. population densities in western Lake Erie and suggests that mayflies, by causing their own population collapse irrespective of other environmental conditions, may need longer term averages when used as a bio-indicator of the success of pollution-abatement programs in western Lake Erie and possibly throughout the Great Lakes.

An Idealized Model and Systematic Process Study of Oxygen Depletion in Highly Turbid Estuaries

The sensitivity of oxygen depletion in turbid estuaries to parameters like freshwater discharge, depth, and sediment availability is investigated using an idealized model. The model describes tidally averaged circulation and suspended sediment concentration (SSC), which are input into an advection–diffusion sink module of dissolved oxygen (DO). Based on the analysis of field data collected in the Ems estuary, the modeled oxygen depletion rates are proportional to SSC. The model is calibrated to the observed variation of DO with SSC and temperature. Modeled DO closely tracks changes to the estuarine turbidity zone (ETZ): increased channel depth, decreased freshwater discharge, and decreased mixing move the ETZ upstream, amplify SSCs, and decrease DO. Summertime temperatures produce lower DO than cooler periods. Model results are consistent with historical measurements in the Ems, which indicate that hypoxic events (DO concentrations < 2 mg l−1) have occurred more frequently after deepening from 5 to 7 m.

Oxygen depletion in lake hypolimnia

The Livingstone and Imboden (1996) model for the oxygen depletion rate in lake hypolimnia was evaluated with field results in 32 lakes. The volumetric oxygen consumption rate (JV) was strongly related to lake trophic state, as represented by the growing season mean chlorophyll a (Chl a) and annual mean total phosphorus concentration, and might reach a maximum of 0.23‐0.24 g O2 m−3 d−1 in eutrophic lakes. The areal oxygen consumption rate (JA) was not related to trophic state and was lower than the value estimated by the sediment core method, particularly in eutrophic lakes; the mean was 0.0816 6 0.0150 g O2 m−2 whole sediment d−1. We modified the model and it was used to confirm that the field JA, the average for the hypolimnion for the deoxygenation period, is influenced by JV and the range of sediment area to water volume ratio, α(Z) (Z is water depth), in the hypolimnion, as well as the oxygen consumption rate in whole sediment (R). It was suggested that this is the reason for the difference between field and sediment core JA values. The R in 10 lakes varied from 7 to 460 g O2 m−3 whole sediment d−1. Overall, the Livingstone and Imboden model with constant JA and with a JV value derived from an empirical relationship with either measure of trophic state was considered to be a suitable condensed model for oxygen depletion in lake hypolimnia.

Simultaneous measurement of pulmonary partial pressure of oxygen and apparent diffusion coefficient by hyperpolarized3He MRI

Hyperpolarized (3)He (HP (3)He) MRI shows promise to assess structural and functional pulmonary parameters in a sensitive, regional, and noninvasive way. Structural HP (3)He MRI has applied the apparent diffusion coefficient (ADC) for the detection of disease-induced lung microstructure changes at the alveolar level, and HP (3)He pulmonary partial pressure of oxygen (pO(2)) imaging measures the oxygen transfer efficiency between the lung and blood stream. Although both parameters are affected in chronic obstructive pulmonary disease (COPD), a quantitative assessment of the regional correlation of the two parameters has not been reported in the literature. In this work, a single acquisition technique for the simultaneous measurement of ADC and pO(2) is presented. This technique is based on the multiple regression method, in which a general linear estimator is used to retrieve the values of ADC and pO(2) from a series of measurements. The measurement uncertainties are also analytically derived and used to find an optimal measurement scheme. The technique was first tested on a phantom model, and then on an in vivo normal pig experiment. A case study was performed on a COPD patient, which showed that in a region of interest ADC was 29% higher while oxygen depletion rate was 61% lower than the corresponding global average values.

Effect of hypolimnetic oxygenation on oxygen depletion rates in two water-supply reservoirs

Oxygenation systems, such as bubble-plume diffusers, are used to improve water quality by replenishing dissolved oxygen (DO) in the hypolimnia of water-supply reservoirs. The diffusers induce circulation and mixing, which helps distribute DO throughout the hypolimnion. Mixing, however, has also been observed to increase hypolimnetic oxygen demand (HOD) during system operation, thus accelerating oxygen depletion. Two water-supply reservoirs (Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR)) that employ linear bubble-plume diffusers were studied to quantify diffuser effects on HOD. A recently validated plume model was used to predict oxygen addition rates. The results were used together with observed oxygen accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Plume-induced mixing correlated well with applied gas flow rate and was observed to increase HOD. Linear relationships between applied gas flow rate and HOD were found for both SHR and CCR. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that HOD is controlled by induced mixing. Despite transient increases in HOD, oxygenation caused an overall decrease in background HOD, as well as a decrease in induced HOD during diffuser operation, over several years. This suggests that the residual or background oxygen demand decreases from one year to the next. Despite diffuser-induced increases in HOD, hypolimnetic oxygenation remains a viable method for replenishing DO in thermally-stratified water-supply reservoirs such as SHR and CCR.

Comprehensive watershed planning in New York State: The Conesus Lake example

Conesus Lake and its agricultural watershed exemplify many of the challenges of effectively managing land and water resources for multiple uses. One of the smaller of New York's Finger Lakes, Conesus Lake is eutrophic with abundant growth of rooted aquatic plants and algae. The trophic condition of the lake has been relatively stable for decades as measured by phosphorus concentrations and hypolimnetic dissolved oxygen depletion rates. However, recent changes to the lake ecosystem have led to diminished water clarity, higher density of macrophytes in shallower water, and the proliferation of nearshore macroalgae. These water quality changes caused serious concern regarding the ultimate causes of the degradation; community conflict was evident between the upland agricultural producers and shoreline residents. With funding from the New York State Department of State, Livingston County Planning Department led a successful effort to engage the community in a science-based assessment of the interrelationship of land use and lake water quality. The planning process was designed to develop consensus that the lake is a shared resource and that effective solutions require changes by many stakeholders. The outcome of this effort was the Conesus Lake Watershed Management Plan. An intermunicipal Conesus Lake Watershed Council was formed to implement the plan's recommendations. The Council has been active for 5 years and has weathered two local elections with full community support. Although many factors contribute to the success of this watershed planning initiative, the importance of a science-based foundation and ongoing efforts to build political consensus cannot be overstated.

PENGUINS SHUNT BLOOD TO STOCK UP ON O2

Any air-breathing animal that dives must manage its oxygen stores with care. How emperor penguins manage their limited oxygen supply intrigues Paul Ponganis and his colleagues from the Scripps Institution of Oceanography. Travelling to Antarctica, Ponganis and his team fitted minute electrodes in either the aorta or vena cava of penguins, as well as ingeniously collecting blood samples from the birds while they were diving, to find out how they manage their oxygen stores while submerged(p. 217).Analysing the diving birds' blood oxygen levels, the team realised that the birds shunt oxygenated blood from the arteries to the venous system (which usually carries deoxygenated blood), probably via the wings for oxygen storage prior to the dive. During the dive the birds absorb oxygen from the lungs, continue shunting oxygenated blood into the venous system to increase oxygen storage, and also appear to isolate muscle from the rest of their circulatory system. Using these strategies, the birds are able to maximise use of oxygen stored in the lungs, reduce their blood oxygen depletion rate by isolating muscle from the circulation and maximise pre-dive blood oxygen storage by shunting oxygenated arterial blood through the wings into the venous system.Given that the diving penguins' muscle tissue is isolated from the animals'circulation, Ponganis suspects that the increase in lactate found in penguins at the surface after a dive that has exceeded their aerobic dive limit is caused by the release of lactate from the muscle where it accumulated during the dive.

Physical processes and hypoxia in the central basin of Lake Erie

The circulation and exchange processes during summer stratification were examined using time‐series data of horizontal velocity, temperature, and dissolved oxygen profiles during 2004 and 2005 in the mid‐central basin of Lake Erie. The current and temperature spectra showed a prominent peak at around 18 h, indicating the presence of clockwise rotating inertial waves. The mean bottom currents were strong (&gt;0.1 m s‐1) and flowed in opposite direction to winds because of the surface pressure gradient due to wind set‐up. The general range of horizontal exchange coefficients in the central basin is 0.2‐1.2 m2 s‐1. Vertical exchange coefficients varied from 1 × 10‐5 to 1 × 10‐4 m2 s‐1. The high values usually occurred in the surface layer because of surface winds. The source of turbulent energy is current shear due to near‐inertial oscillations in and above the thermocline and shearing stress due to the effect of mean currents and wave‐induced motions during energetic wind events at the lake bottom. During strong wind episodes significant wave‐induced currents were observed close to the bottom. The short‐term oxygen depletion rates varied considerably between +0.87 mg L‐1 d‐1 and ‐1.16 mg L‐1 d‐1 in 2004 mainly because of physical processes in the central basin. When the hypolimnion depth is sufficiently thick (4 m), shortterm changes in dissolved oxygen concentrations were partly due to vertical mixing and partly due to horizontal transport and mixing.

Investigation of the oxygen depletion properties of novel oxygen‐scavenging plastics

AbstractThe oxygen depletion and tensile properties of EVA resins blended with varying compositions and sizes of iron (Fe), modified iron (MFe) and ascorbic acid (Vc) oxygen scavengers were systematically investigated. After blending Vc together with varying sizes of MFe in EVA resins, “synergistic” oxygen depletion properties were found in each EVcMFe‐30, EVcMFe‐5, and EVcMFe‐1 series samples, as their weight ratios of Vc to MFe are between 3/7 to 5/5, 3/7 to 7/3 and 1/9 to 9/1, respectively. The oxygen depletion rates of EVcMFe series samples increase significantly as the particle sizes of MFe powders reduce. In fact, the oxygen‐scavenging resins with better oxygen depletion properties always result in lower peroxide values for modeled food samples stored in the airtight flasks of EVcMFe series samples. Further tensile experiments show that the tensile properties of the EVcMFe series samples increase significantly as their Vc loadings or the sizes of the MFe powders reduce. To understand these interesting oxygen depletion, lipid oxidation, and tensile properties of EVcMFe series samples, SEM and EDX analysis of the compositions on the surfaces of EVcMFe series samples were performed. Possible mechanisms accounting for these interesting properties of EVc, EFe, EMFe, and EVcMFe series samples are proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Measurement of Pulmonary Partial Pressure of Oxygen and Oxygen Depletion Rate with Hyperpolarized Helium-3 MRI: A Preliminary Reproducibility Study on Pig Model

Pulmonary partial pressure of oxygen (pO(2)) and oxygen depletion rate (R) are two important parameters of lung function. The dependence of hyperpolarized (3)He (HP (3)He) T(1) on local oxygen concentration provides the basis for high-resolution mapping of the regional distributions of pO(2) and R in the lung. Although the oxygen-sensitive HP (3)He magnetic resonance imaging technique has been applied in human subjects and several animal species, reproducibility studies are rarely reported in the literature. This work presents a preliminary reproducibility study on a pig model. In this study, important scan parameters, such as measurement timing and flip angle, are optimized to minimize the noise-induced measurement uncertainty. In the in vivo study, five normal pigs and one diseased pig with simulated pulmonary emboli were scanned with a small flip angle gradient echo sequence. The pulmonary oxygen measurement was repeated two to four times in each pig. In each measurement, a series of six images were acquired with optimal timing and flip angle. The parametric maps were generated using a bin-based data processing procedure that applied the multiple regression fitting method to extract the pO(2) and R. Variations of global mean, percentiles, and regions of interest were calculated from the maps to analyze reproducibility. The global statistical analyses show that average variation of global mean is 10.7% for pO(2) and 23.8% for R, and that the average variation of percentiles (10th, 25th, 50th, 75th, and 90th) and interquartile range is 14.8% for pO(2) and 30.4% for R. The region-of-interest analysis on the manually selected regions shows that the average variation of mean is 12.6% for pO(2) and 21.9% for R. In this work, a preliminary study on the reproducibility of measuring pO(2) and R with HP (3)He magnetic resonance imaging on a pig model is presented.

Introduction to Water Use From Arctic Lakes: Identification, Impacts, and Decision Support1

Introduction to Water Use From Arctic Lakes: Identification, Impacts, and Decision Support¹

A Tool for Modeling the Winter Oxygen Depletion Rate in Arctic Lakes1

Abstract: Many arctic lakes freeze completely in winter. The few that retain unfrozen water for the entire winter period serve as overwintering fish habitat. In addition to serving as fish habitat, water in arctic lakes is needed for industrial and domestic use. Permits for water extraction seek to maximize water use without impacting dissolved oxygen (DO) levels and endangering fish habitat. The relationship between lake volume, winter DO budget, and extraction of water through pumping has historically not been well understood. A management model that could estimate end‐of‐winter DO would improve our understanding of the potential impacts of different management strategies. Using under‐ice DO measurements (November to April) taken from two natural lakes and one flooded gravel mine on the North Slope of Alaska, a physically based model was developed to predict end‐of‐winter DO concentration, water‐column DO profiles, and winter oxygen depletion rate in arctic lakes during periods of ice cover. Comparisons between the measured and model‐predicted oxygen profiles in the three study lakes suggest that the depth‐based DO modeling tool presented herein can be used to adequately predict the amount of DO available in arctic lakes throughout winter.

Sugarcane spirit extracts of oak and Brazilian woods: antioxidant capacity and activity

Sugarcane spirit extracts of six different Brazilian woods for potential use in manufacturing aging casks were compared with similar extracts of five oak samples from different geographic origin and heat treatment regarding: (1) content of phenolics and copper; (2) radical reducing capacity and reactivity toward 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·); and (3) effect on the rate of oxygen depletion rate in a peroxidating lipid model system. Total phenolic contents of the Brazilian wood extracts ranged from 0.65 (canela-sassafras) to 6.4 (jatoba) mmolGAE L−1 and from 1.39 to 2.87 mmolGAE L−1 for oak extracts. Flavonoids ranged from 1.54 × 10−4 (ipe) to 6.5 × 10−2 (oak) mmolrutin L−1, and tannins from below the detection limit to 0.22 (jatoba) mmoltannic acid L−1. Correlation was observed for the antioxidant capacity versus phenolics/flavonoids/tannins content, where oak extracts exhibit the highest radical scavenging capacity compared to Brazilian woods. Rate constant for radical scavenging by the extracts ranged from 4.9 × 103 M−1 s−1 (canela-sassafras) to 9.7 × 104 M−1 s−1 (oak). The oxygen consumption index showed the Brazilian woods amendoim and jatoba to be more efficient inhibitors than the oak extracts for lipid autoxidation initiated by metmyoglobin, despite that the oak extracts seem to be more efficient to scavenge DPPH·. No simple correlation with phenolics or copper content could be established, and a prooxidative tendency was observed for the extracts of canela-sassafras, castanheira, and louro-canela.

Optimization of scan parameters in pulmonary partial pressure oxygen measurement by hyperpolarized 3He MRI

The dependence of hyperpolarized (HP) (3)He T(1) on local oxygen concentration provides the basis for measuring the partial pressure of oxygen (pO(2)) and oxygen depletion rate (R) in the lungs. Precise measurements of this type are difficult because the oxygen effect manifests itself through a decay of signal, leading to noisy images at the end of the series. The depolarization caused by RF excitation pulses further complicates the problem. It is therefore important to optimize scan parameters, such as measurement timing and flip angle, to obtain accurate and reproducible measurements. This work presents a new single-acquisition technique in conjunction with the multiple regression fitting method for data evaluation. Analytical expressions for the measurement uncertainties are derived. A total of four types of single-acquisition timing schemes are investigated; simulation shows a large uncertainty variation between these schemes (pO(2): 7.5-30.2%; R: 47.4-173.7%). A basic procedure for optimizing scan parameters is then described. A phantom experiment was conducted to verify the simulation results. Repeated in vivo measurements with the optimal scheme in a rabbit experiment showed that average variation of global mean is 6.2% for pO(2) and 12.0% for R, and that the average variation of percentiles (10th, 25th, 50th, 75th, and 90th) is 8.7% for pO(2) and 19.0% for R.