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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Improved Hypoxia Modeling for Nutrient Control Decisions in the Gulf of Mexico

The Gulf of Mexico Modeling Framework is a suite of coupled models linking the deposition and transport of sediment and nutrients to subsequent bio-geo chemical processes and the resulting effect on concentrations of dissolved oxygen in the coastal waters of Louisiana and Texas. Here, we examine the potential benefits of using multiple NASA remote sensing data products within this Modeling Framework for increasing the accuracy of the models and their utility for nutrient control decisions in the Gulf of Mexico. Our approach is divided into three components: evaluation and improvement of (a) the precipitation input data (b) atmospheric constituent concentrations in EPA's air quality/deposition model and (c) the calculation of algal biomass, organic carbon and suspended solids within the water quality/eutrophication models of the framework.

Habib, Shahid↗
NASA NTRS2001

Transgene expression patterns indicate that spaceflight affects stress signal perception and transduction in arabidopsis

The use of plants as integral components of life support systems remains a cornerstone of strategies for long-term human habitation of space and extraterrestrial colonization. Spaceflight experiments over the past few decades have refined the hardware required to grow plants in low-earth orbit and have illuminated fundamental issues regarding spaceflight effects on plant growth and development. Potential incipient hypoxia, resulting from the lack of convection-driven gas movement, has emerged as a possible major impact of microgravity. We developed transgenic Arabidopsis containing the alcohol dehydrogenase (Adh) gene promoter linked to the beta-glucuronidase (GUS) reporter gene to address specifically the possibility that spaceflight induces the plant hypoxia response and to assess whether any spaceflight response was similar to control terrestrial hypoxia-induced gene expression patterns. The staining patterns resulting from a 5-d mission on the orbiter Columbia during mission STS-93 indicate that the Adh/GUS reporter gene was activated in roots during the flight. However, the patterns of expression were not identical to terrestrial control inductions. Moreover, although terrestrial hypoxia induces Adh/GUS expression in the shoot apex, no apex staining was observed in the spaceflight plants. This indicates that either the normal hypoxia response signaling is impaired in spaceflight or that spaceflight inappropriately induces Adh/GUS activity for reasons other than hypoxia.

manned↗
NASA NTRS2012

Alterations of Cellular Immune Reactions in Crew Members Overwintering in the Antarctic Research Station Concordia

Background: Concordia Station is located inside Antarctica about 1000km from the coast at an altitude of 3200m (Dome C). Hence, individuals living in this harsh environment are exposed to two major conditions: 1.) hypobaric hypoxia and 2.) confinement and extreme isolation. Both hypoxia and confinement can affect human immunity and health, and are likely to be present during exploration class space missions. This study focused on immune alterations measured by a new global immunity test assay, similar to the phased out delayed type hypersensitivity (DTH) skin test. Methods: After informed written consent 14 healthy male subjects were included to the CHOICE-study (Consequences-of-longterm-Confinement-and-Hypobaric-HypOxia-on-Immunity-in-the Antarctic-Concordia-Environment). Data collection occurred during two winter-over periods lasting each one year. During the first campaign 6 healthy male were enrolled followed by a second campaign with 8 healthy males. Blood was drawn monthly and incubated for 48h with various bacterial, viral and fungal antigens followed by an analysis of plasma cytokine levels (TNF-alpha, IL2, IFN-gamma, IL10). As a control, blood was incubated without stimulation ("resting condition"). Goals: The scope of this study was to assess the consequences of hypoxia and confinement on cellular immunity as assessed by a new in vitro DTH-like test. Results: Initial results indicate that under resting conditions the in vitro DTH-like test showed low cytokine levels which remained almost unchanged during the entire observation period. However, cytokine responses to viral, bacterial and fungal antigens were remarkably reduced at the first month after arrival at Concordia when compared to levels measured in Europe prior to departure for Antarctica. With incrementing months of confinement this depressed DTH-like response tended to reverse, and in fact to show an "overshooting" immune reaction after stimulation. Conclusion: The reduced in vitro DTH-like test response in the early phase of Antarctic wintering over con rms distinct immune suppressive effects seen after (sub-)acute hypobaric hypoxia. The reversal and overshooting reaction of cellular immune responses upon stimulation, but not the resting state, indicate either a) priming of immune answers and/or b) an uncoupled or disregulated control of cellular immune answers by auto-, para- and endocrine pathways. Further analyses and correlations are warranted. Acknowledgement: Supported by the European Space Agency (ESA), the French (IPEV) and Italian (PNRA) polar institutes, the German National Space Program (DLR, 50WB0719/WB0919), by BELSPO/PROEDEX/ESA (C90-380/-391), NASA and by the Concordia crews who have participated with great enthusiasm.

Crucian, Brian↗
NASA NTRS1993

Body fluid alterations during head-down bed rest in men at moderate altitude

To determine the effects of hypoxia on fluid balance responses to simulated zero-gravity, measurements were made in six subjects before and during -5 deg continuous head-down bed rest (HDBR) over 8 d at 10,678 ft. The same subjects were studied again at this altitude without HDBR as a control (CON) using a cross-over design. During this time, they maintained normal upright day-time activities, sleeping in the horizontal position at night. Fluid balance changes during HDBR in hypoxia were more pronounced than similar measurements previously reported from HDBR studies at sea level. Plasma volume loss was slightly greater and the diuresis and natriuresis were doubled in magnitude as compared to previous studies in normoxia and sustained for 4 d during hypoxia. These changes were associated with an immediate but transient rise in plasma atrial natriuretic peptide (ANP) to day 4 of 140 percent in HDBR and 41 percent in CON (p less than 0.005), followed by a decline towards baseline. Differences were less striking between HDBR and CON for plasma antidiuretic hormone and aldosterone, which were transiently reduced by HDBR. Plasma catecholamines showed a similar pattern to ANP in both HDBR and CON, suggesting that elevated ANP and catecholamines together accounted for the enhanced fluid shifts with HDBR during hypoxia.

Loeppky, J. A.↗
NASA NTRSDate not supplied

Oxygen Deficiency in Spaceflight & its Impact on Plants’ Adaptive Changes

The goal of this study was to investigate the effects of hypoxic conditions in spaceflight. The distribution of genes involved with hypoxia in Arabidopsis thaliana and Brassica rapa were analyzed with the results from past spaceflight experiments to evaluate genes for future studies. Transcriptomes data of two different spaceflight studies of Arabidopsis thaliana from the NASA GeneLab database, GLDS-7 and GLDS-17, were compared. DNA microarrays were utilized for transcription profiling to conduct these studies. For GLDS-7, the response in spaceflight was studied with approaches that collected gene expression data. Leaves, hypocotyls, and root tissues were compared to the whole plant. For GLDS-17, seedlings and undifferentiated cultured cells were placed in the Biological Research in Canisters (BRIC), specifically BRIC-16. The genes related to hypoxia in Arabidopsis thaliana from these two studies were compared to genes in Brassica rapa with the TOAST database to evaluate similarities. When transcriptomes were analyzed for GLDS-7 and 17, genes that were considered significant had p-values ≤ 0.05 and log fold change values ≤ -1 or ≥1. Sixteen genes fulfilled the criteria. The genes related to hypoxia were alcohol dehydrogenase, elongation factor, ethylene-responsive factor, GUS, heat-shock proteins, NAP, RAP2.12, and RD20. The genes most impacted by spaceflight were heat-shock proteins. These genes were compared with Brassica rapa through Arabidopsis Ensemble Orthology from the TOAST Database. Similarities were seen in alcohol dehydrogenase, elongation factor, ethylene-responsive factor, heat-shock proteins, NAP, and RAP2.12. Overall, transcription profiling indicates that plants’ survival in spaceflight is dependent on adaptive changes with gene expression. This study also indicates that there are similarities in gene expression between Arabidopsis thaliana and Brassica rapa with comparable gene expression. Future studies could include analyzing additional species to understand which genes could be modified to ensure better yield of space crops amid hypoxic conditions.

hypoxia↗
NASA NTRS1971

Erythropoietic radiosensitivity of the rat during altitude acclimatization.

The effect of a sublethal dose (300 R) of X-radiation upon the erythropoietic system of the rat, during 60-day acclimatization to moderate hypoxia (3,800 m altitude), was studied. Past work has shown that hypoxic animals are damaged less by radiation than animals irradiated in a normal environment; therefore, it was postulated that if, after acclimatization to hypoxia the bone marrow oxygen tension returns to sea-level values, these animals should suffer radiation damage equivalent to animals at sea level. The principal parameters followed were the rate of depletion of injected Fe-59 from the plasma of chronically catheterized rats, and its subsequent reappearance in the circulating erythrocytes. After 20 days of acclimatization, both parameters for altitude-irradiated animals returned to the values of animals irradiated at sea level, previously having reflected increased erythropoiesis. In altitude nonirradiated animals the parameters indicated erythropoietic stimulation persisting up to 45 days acclimatization. The protective effect of the hypoxia on the stem cells vanished during acclimatization, presumably as cellular oxygen tension rose.

Gaugl, J. F.↗
NASA NTRS1975

Mechanisms of radio-protection by catecholamines in the hamster /Mesocricetus auratus/

Experiments were conducted on normal and splenectomized male and female hamsters between 2 and 3 months old subjected to a whole-body exposure of 1000 or 2000 rads in a Co-60 source with a view toward evaluating their radio-protection by norepinephrine, isoproterenol, and phenylephrine. Vasoconstriction hypoxia mechanism of radio-protection is examined along with the hypothesis that isoproterenol protects by hypercalcemia-induced cell proliferation. Radiation experiment results are found to be consistent with the hypothesis that stimulation of alpha receptors results in radio-protection through a tissue hypoxia mechanism. Beta agonists seem to protect by a hypotensive-hypoxia mechanism. The catecholamines protect against the hematopoietic syndrome, but show no evidence of protection against the gastrointestinal syndrome.

Prewitt, R. L.↗
NASA NTRS1978

Use of a computer model in the understanding of erythropoietic control mechanisms

During an eight-week visit approximately 200 simulations using the computer model for the regulation of erythopoiesis were carries out in four general areas: with the human model simulating hypoxia and dehydration, evaluation of the simulation of dehydration using the mouse model. The experiments led to two considerations for the models. Firstly, a direct relationship between erythropoietin concentration and bone marrow sensitivity to the hormone and, secondly, a partial correction of tissue hypoxia prior to compensation by an increased hematocrit. This latter change in particular produced a better simuation of the effects of hypoxia on plasma erythropoietin concentrations.

Dunn, C. D. R.↗
NASA NTRS2007

Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles

To reduce denitrogenation time to prevent decompression sickness to support frequent extravehicular activities on the Moon, and to limit the risk of fire, a hypobaric (P(sub B) = 414 mmHg) and mildly hypoxic (ppO2 = 132 mmHg, 32% O2 - 68% N2) living environment is being considered during lunar missions for the Crew Exploration Vehicle (CEV) and Lunar Surface Access Module (LSAM). If the vehicular ppO2 is acutely changed from 145-178 mmHg at standard vehicular operating pressure to less than 125 mmHg at desired lunar surface outpost operating pressures, there is the possibility that some crewmembers may develop symptoms of Acute Mountain Sickness (AMS). The signs and symptoms of AMS (headache plus nausea, dizziness, fatigue, or sleeplessness), could impact crew health and performance on lunar surface missions. Methods: An exhaustive literature review on the topic of the physiological effects of reduced ppO2 and absolute pressure as may contribute to the development of hypoxia and altitude symptoms or AMS. The results of the nine most rigorous studies were collated, analyzed and contents on the physiological concerns associated with hypobaric operations, AMS and hypoxia symptoms summarized. Results: Although space vehicles have operated in hypobaric conditions previously, they have not operated in a mildly hypoxic ppO2. There is evidence for an absolute pressure effect per se on AMS, such that the higher the altitude for a given hypoxic alveolar O2 partial pressure (P(sub A)O2), the greater the likelihood of an AMS response. About 25% of adults are likely to experience mild AMS near 2,000 m (xxx mmHg) altitude following a rapid ascent from sea level while breathing air (6,500 feet, acute (P(sub A)O2) = 75 mmHg). The operational experience with the Shuttle staged denitrogenation protocol at 528 mmHg (3,048 m) while breathing 26.5% O2 (acute (P(sub A)O2) = 85 mmHg) in astronauts adapting to microgravity suggests a similar likely experience in the proposed CEV environment. Conclusions: We feel that the slightly elevated risk of AMS with the recommended exploration atmospheric parameters is offset by the DCS risk reduction and improved operational efficiency offered by the hypobaric lunar surface vehicular pressure. We believe the risk of mild AMS is greater given a (P(sub A)O2) of 77 mmHg at 4,876 m altitude while breathing 32% O2 than at 1,828 m altitude while breathing 21% O2. Only susceptible astronauts would develop mild and transient AMS with prolonged exposure to 414 mmHg (4,876 m) while breathing 32% O2 (acute (P(sub A)O2) = 77 mmHg). So the following may be employed for operational risk reduction: 1) develop procedures to increase P(sub B) as needed in the CEV, and use a gradual or staged reduction in cabin pressure during lunar outbound; 2) train crews for symptoms of hypoxia, to allow early recognition and consider pre-adaptation of crews to a hypoxic environment prior to launch, 3) consider prophylactic acetazolamide for acute pressure changes and be prepared to treat any AMS associated symptoms early with both carbonic anhydrase inhibitors and supplemental oxygen.

Scheuring, Richard A.↗
NASA NTRS2003

Oxygen-Partial-Pressure Sensor for Aircraft Oxygen Mask

A device that generates an alarm when the partial pressure of oxygen decreases to less than a preset level has been developed to help prevent hypoxia in a pilot or other crewmember of a military or other high-performance aircraft. Loss of oxygen partial pressure can be caused by poor fit of the mask or failure of a hose or other component of an oxygen distribution system. The deleterious physical and mental effects of hypoxia cause the loss of a military aircraft and crew every few years. The device is installed in the crewmember s oxygen mask and is powered via communication wiring already present in all such oxygen masks. The device (see figure) includes an electrochemical sensor, the output potential of which is proportional to the partial pressure of oxygen. The output of the sensor is amplified and fed to the input of a comparator circuit. A reference potential that corresponds to the amplified sensor output at the alarm oxygen-partial-pressure level is fed to the second input of the comparator. When the sensed partial pressure of oxygen falls below the minimum acceptable level, the output of the comparator goes from the low state (a few millivolts) to the high state (near the supply potential, which is typically 6.8 V for microphone power). The switching of the comparator output to the high state triggers a tactile alarm in the form of a vibration in the mask, generated by a small 1.3-Vdc pager motor spinning an eccentric mass at a rate between 8,000 and 10,000 rpm. The sensation of the mask vibrating against the crewmember s nose is very effective at alerting the crewmember, who may already be groggy from hypoxia and is immersed in an environment that is saturated with visual cues and sounds. Indeed, the sensation is one of rudeness, but such rudeness could be what is needed to stimulate the crewmember to take corrective action in a life-threatening situation.

Kelly, Mark↗
NASA NTRS2024

Evaluation of Sex Differences in Physiologic Responses to Submaximal Cycling Under Normoxic and Hypoxic Conditions

BACKGROUND: During Lunar missions, astronauts may live and operate in conditions where altered atmospheric pressure and oxygen concentrations may result in a mildly hypoxic environment. While the compensatory hemodynamic mechanisms ensuring adequate oxygen delivery to contracting muscles during exercise in hypoxic conditions are well-studied, less research has focused on potential sex differences in the responses to hypoxia exposure during exercise. As female astronauts make up half of the Artemis astronaut corps, understanding whether physiologic responses in a hypoxic environment differ between sexes may inform recommendations for exercising safely in exploration environments. METHODS: Fourteen subjects (7M/7F) from NASA’s Exploration Atmosphere Study performed two submaximal cycle exercise trials (10 min of exercise at 40% peak aerobic capacity [VO 2 pk]) ergometer under normobaric normoxic gas (21% O 2 ) and normobaric hypoxic (18% O 2 and balanced N 2 ) conditions in randomized order. Linear mixed models with Bonferroni post hoc corrections (fixed effects: condition, sex, VO 2 pk [covariate], body mass [BM, covariate]; random effects: subject, mission) were performed to evaluate the effect of condition and sex on physiologic responses to exercise (oxygen uptake [VO 2 ], carbon dioxide production [VCO 2 ], ventilation [VE], oxygen saturation [SpO 2 ], and heart rate [HR]). RESULTS: Males were comparable to females for age (36.6±4.7 vs 36.4±9.3 yrs; p>0.05) but had greater BM (87.3±10.9 vs 64.5±7.4 kg; p<0.001) and absolute VO2pk (3.5±0.6 vs 2.4±4.7 L/min; p<0.001). Additionally, males had higher VO2 (p=0.005), VCO2 (p=0.02), and VE (p=0.01) during exercise trials, independent of condition; however, when VO 2 pk was added as a covariate, the effect of sex was no longer significant. SpO 2 was reduced during hypoxic exercise compared to the normoxic condition (p<0.001), but neither sex nor environmental condition impacted HR. CONCLUSIONS: Though most physiologic responses to submaximal, short-duration exercise between normoxia and mild hypoxia were similar, females exhibited lower VO 2 , VCO 2 , and VE during both conditions, likely driven by lower aerobic capacity. Future research is needed to determine whether similar findings result from multiday hypobaric hypoxia experienced during missions.

N C Strock↗
NASA NTRS1972

Coronary flow and left ventricular function during environmental stress.

A canine model was used to study the effects of different environmental stresses on the heart and coronary circulation. The heart was surgically instrumented to measure coronary blood flow, left ventricular pressure, and other cardiovascular variables. Coronary flow was recorded by telemetry. Physiologic data were processed and analyzed by analog and digital computers. By these methods the physiologic response to altitude hypoxia, carbon monoxide, hypercapnia, acceleration, exercise, and the interaction of altitude hypoxia and carbon monoxide were described. The effects of some of these stresses on the heart and coronary circulation are discussed.

Erickson, H. H.↗
NASA NTRS1974

Correlation changes in EEG, conditioned and behavioral reactions with various degrees of oxygen insufficiency

The dynamics of change in bioelectric activity of the brain during acute hypoxia are studied for the time that working capacity and active consciousness are preserved, and to establish the correlation between EEG changes and behavioral reactions under oxygen starvation. Changes in body functions and behavioral disturbances are related to the degree of oxygen saturation in the blood, to bioelectric activity of the brain, and to an increase in conditioned reflexes. The capacity for adequate reaction to external signals and for coordinated psychomotor activity after loss of consciousness returns to man after 30 seconds. Repeated effects of hypoxia produce changes in the physiological reactions of the body directed toward better adaptation to changing gaseous environments.

Agadzhanyan, N. A.↗
NASA NTRS1998

Beta-Adrenergic Blockade Does not Prevent Polycythemia or Decrease in Plasma Volume in Men at 4300 m Altitude

When humans ascend to high altitude (ALT) their plasma volume (PV) and total blood volume (BV) decrease during the first few days. With continued residence over several weeks, the hypoxia-induced stimulation of erythropoietin increases red cell production which tends to restore BV. Because hypoxia also activates the beta-adrenergic system, which stimulates red blood cell production, we investigated the effect of adrenergic beta-receptor inhibition with propranolol on fluid volumes and the polycythemic response in 11 healthy unacclimatized men (21-33 years old exposed to an ALT of 4300 m (barometric pressure 460 Torr) for 3 weeks on Pikes Peak, Colorado. PV was determined by the Evans blue dye method (PV(sub EB)), BV by the carbon monoxide method (BV(sub CO)), red cell volume (RCV)was calculated from hematocrit (Hct) and BV(sub CO), and serum erythropoietin concentration ([EPO]) and reticulocyte count, were also determined. All determinations were made at sea level and after 9-11 (ALT-10) and 9-20 (ALT-20) days at ALT. At sea level and ALT, six men received propranolol (pro, 240 mg/day), and five received a placebo (pla). Effective beta-blockade did not modify the mean (SE) maximal values of [EPO] [pla: 24.9 (3.5) vs pro: 24.5 (1.5) mU/ml] or reticulocyte count [pla: 2.7 (0.7) vs pro: 2.2 (0.5)%]; nor changes in PV(sub EB)[pla: -15.8 (3.8) vs pro: -19.9 (2.8)%], RCV(sub CO) [pla: +7.0 (6.7) vs pro: +10.1 (6.1)%], or BV(sub CO) [pla: -7.3 (2.3) vs pro: -7.1 (3.9)%]. In the absence of weight loss, a redistribution of body water with no net loss is implied. Hence, activation of the beta-adrenergic system did not appear to affect the hypovolemic or polycythemic responses that occurred during 3 weeks at 4300 m ALT in these subjects.

Grover, R. F.↗
NASA NTRS1999

A Quantitative Study of Oxygen as a Metabolic Regulator

An acute reduction in oxygen (O2) delivery to a tissue is generally associated with a decrease in phosphocreatine, increases in ADP, NADH/NAD, and inorganic phosphate, increased rates of glycolysis and lactate production, and reduced rates of pyruvate and fatty acid oxidation. However, given the complexity of the human bioenergetic system and its components, it is difficult to determine quantitatively how cellular metabolic processes interact to maintain ATP homeostasis during stress (e.g., hypoxia, ischemia, and exercise). Of special interest is the determination of mechanisms relating tissue oxygenation to observed metabolic responses at the tissue, organ, and whole body levels and the quantification of how changes in tissue O2 availability affect the pathways of ATP synthesis and the metabolites that control these pathways. In this study, we extend a previously developed mathematical model of human bioenergetics to provide a physicochemical framework that permits quantitative understanding of O2 as a metabolic regulator. Specifically, the enhancement permits studying the effects of variations in tissue oxygenation and in parameters controlling the rate of cellular respiration on glycolysis, lactate production, and pyruvate oxidation. The whole body is described as a bioenergetic system consisting of metabolically distinct tissue/organ subsystems that exchange materials with the blood. In order to study the dynamic response of each subsystem to stimuli, we solve the ordinary differential equations describing the temporal evolution of metabolite levels, given the initial concentrations. The solver used in the present study is the packaged code LSODE, as implemented in the NASA Lewis kinetics and sensitivity analysis code, LSENS. A major advantage of LSENS is the efficient procedures supporting systematic sensitivity analysis, which provides the basic methods for studying parameter sensitivities (i.e., changes in model behavior due to parameter variation). Sensitivity analysis establishes relationships between model predictions and problem parameters (i.e., initial concentrations, rate coefficients, etc). It helps determine the effects of uncertainties or changes in these input parameters on the predictions, which ultimately are compared with experimental observations in order to validate the model. Sensitivity analysis can identify parameters that must be determined accurately because of their large effect on the model predictions and parameters that need not be known with great precision because they have little or no effect on the solution. This capability may prove to be important in optimizing the design of experiments, thereby reducing the use of animals. This approach can be applied to study the metabolic effects of reduced oxygen delivery to cardiac muscle due to local myocardial ischemia and the effects of acute hypoxia on brain metabolism. Other important applications of sensitivity analysis include identification of quantitatively relevant pathways and biochemical species within an overall mechanism, when examining the effects of a genetic anomaly or pathological state on energetic system components and whole system behavior.

Radhakrishnan, Krishnan↗