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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Fitness, autonomic regulation and orthostatic tolerance

Work on this grant has consisted of two major studies of cardiovascular regulation in athletes along with several smaller supporting studies. This summary will give a brief overview of two major studies, and then conclude with an analysis of what the findings from these studies mean practically, and how they can be applied to current problems with post-flight orthostatic intolerance. The first study addresses a cross-sectional analysis of orthostatic intolerance in highly aerobically trained individuals; the second addresses ventricular pressure/volume relationships in athletes.

Buckey, Jay C.↗
NASA NTRS1993

Cellular track model for study of heavy ion beams

Track theory is combined with a realistic model of a heavy ion beam to study the effects of nuclear fragmentation on cell survival and biological effectiveness. The effects of secondary reaction products are studied as a function of depth in a water column. Good agreement is found with experimental results for the survival of human T-l cells exposed to monoenergetic carbon, neon, and argon beams under aerobic and hypoxia conditions. The present calculation, which includes the effect of target fragmentation, is a significant improvement over an earlier calculation because of the use of a vastly improved beam model with no change in the track theory or cellular response parameters.

Shinn, Judy L.↗
NASA NTRS1993

Design and testing of a unique randomized gravity, continuous flow bioreactor

A rotating, null gravity simulator, or Couette bioreactor was successfully used for the culture of mammalian cells in a simulated microgravity environment. Two limited studies using Lipomyces starkeyi and Streptomyces clavuligerus were also conducted under conditions of simulated weightlessness. Although these studies with microorganisms showed promising preliminary results, oxygen limitations presented significant limitations in studying the biochemical and cultural characteristics of these cell types. Microbial cell systems such as bacteria and yeast promise significant potential as investigative models to study the effects of microgravity on membrane transport, as well as substrate induction of inactive enzyme systems. Additionally, the smaller size of the microorganisms should further reduce the gravity induced oscillatory particle motion and thereby improve the microgravity simulation on earth. Focus is on the unique conceptual design, and subsequent development of a rotating bioreactor that is compatible with the culture and investigation of microgravity effects on microbial systems. The new reactor design will allow testing of highly aerobic cell types under simulated microgravity conditions. The described reactor affords a mechanism for investigating the long term effects of reduced gravity on cellular respiration, membrane transfer, ion exchange, and substrate conversions. It offers the capability of dynamically altering nutrients, oxygenation, pH, carbon dioxide, and substrate concentration without disturbing the microgravity simulation, or Couette flow, of the reactor. All progeny of the original cell inoculum may be acclimated to the simulated microgravity in the absence of a substrate or nutrient. The reactor has the promise of allowing scientists to probe the long term effects of weightlessness on cell interactions in plants, bacteria, yeast, and fungi. The reactor is designed to have a flow field growth chamber with uniform shear stress, yet transfer high concentrations of oxygen into the culture medium. The system described allows for continuous, on line sampling for production of product without disturbing fluid and particle dynamics in the reaction chamber. It provides for the introduction of substrate, or control substances after cell adaptation to simulated microgravity has been accomplished. The reactor system provides for the nondisruptive, continuous flow replacement of nutrient and removal of product. On line monitoring and control of growth conditions such as pH and nutrient status are provided. A rotating distribution valve allows cessation of growth chamber rotation, thereby preserving the simulated microgravity conditions over longer periods of time.

Lassiter, Carroll B.↗
NASA NTRS1994

Thermoregulatory effects of caffeine ingestion during rest and exercise in men

Body temperatures and thermoregulatory responses were measured at rest and during submaximal exercise under normal ambient conditions in 11 aerobically-conditioned men (age = 29.2 +/- 6.2 yr, VO2(max) = 3.73 +/- 0.46 min(sup -1), relative body fat = 12.3 +/- 3.7 percent, mean +/- SD) with (CT) and without (NCT) the ingestion of 10 mg of caffeine per kg of body weight. Oxygen uptake (VO2), heart rate (HR), and rectal (T(sub re)) and mean skin (T-bar(sub sk)) temperatures were recorded for 100 minutes starting one minute after ingestion of caffeine or a placebo. Data were collected throughout 30 minutes of rest (sitting) and the following 70 minutes of sitting leg ergometer exercise using the same constant load (1,088 +/- 153 kgm/min) in both NCT and CT. The load resulted in a mean relative exercise intensity equal to approximately 68 percent of VO2(sub max). Skin heat conductance (H(sub sk)) and sweat rate were calculated. Two-way analysis of covariance revealed no significant (P greater than 0.05) differences between NCT and CT in VO2, HR, T(sub re), T-bar(sub sk), or H(sub sk). A dependent t-test indicated no significant difference between NCT and CT in sweat rate. Thus, a high level of caffeine ingestion has no detrimental effects on body temperatures and thermoregulatory responses during moderately heavy exercise in normal ambient conditions.

Dunagan, Nancy↗
NASA NTRS1994

Aortic baroreflex control of heart rate after 15 days of simulated microgravity exposure

To determine the effects of simulated microgravity on aortic baroreflex control of heart rate, we exposed seven male subjects to 15 days of bed rest in the 6 deg head-down position. The sensitivity of the aortic-cardiac baroreflex was determined during a steady-state phenylephrine-induced increase in mean arterial pressure combined with lower body negative pressure to counteract central venous pressure increases and neck pressure to offset the increased carotid sinus transmural pressure. The aortic-cardiac baroreflex gain was assessed by determining the ratio of the change in heart rate to the change in mean arterial pressure between baseline conditions and aortic baroreceptor-isolated conditions (i.e., phenylephrine + lower body negative pressure + neck pressure stage). Fifteen days of head-down tilt increased the gain of the aortic-cardiac baroreflex. Reductions in blood volume and/or maximal aerobic capacity may represent the underlying mechanism(s) responsible for increased aortic baroreflex responsiveness after exposure to a ground-based analogue of microgravity.

Crandall, Craig G.↗
NASA NTRS1995

On-line removal of volatile fatty acids from CELSS anaerobic bioreactor via nanofiltration

The CELSS (controlled ecological life support system) resource recovery system, which is a waste processing system, uses aerobic and anaerobic bioreactors to recover plants nutrients and secondary foods from the inedible biomass. The anaerobic degradation of the inedible biomass by means of culture of rumen bacteria,generates organic compounds such as volatile fatty acids (acetic, propionic, butyric, VFA) and ammonia. The presence of VFA in the bioreactor medium at fairly low concentrations decreases the microbial population's metabolic reactions due to end-product inhibition. Technologies to remove VFA continuously from the bioreactor are of high interest. Several candidate technologies were analyzed, such as organic solvent liquid-liquid extraction, adsorption and/or ion exchange, dialysis, electrodialysis, and pressure driven membrane separation processes. The proposed technique for the on-line removal of VFA from the anaerobic bioreactor was a nanofiltration membrane recycle bioreactor. In order to establish the nanofiltration process performance variables before coupling it to the bioreactor, a series of experiments were carried out using a 10,000 MWCO tubular ceramic membrane module. The variables studied were the bioreactor slurry permeation characteristics, such as, the permeate flux, VFA and the nutrient removal rates as a function of applied transmembrane pressure, fluid recirculation velocity, suspended matter concentration, and process operating time. Results indicate that the permeate flux, VFA and nutrients removal rates are directly proportional to the fluid recirculation velocity in the range between 0.6 to 1.0 m/s, applied pressure when these are low than 1.5 bar, and inversely proportional to the total suspended solids concentration in the range between 23,466 to 34,880. At applied pressure higher than 1.5 bar the flux is not more linearly dependent due to concentration polarization and fouling effects over the membrange surface. It was also found that the permeate flux declines rapidly during the first 5 to 8 hours, and then levels off with a diminishing rate of flux decay.

Colon, Guillermo↗
NASA NTRS1995

An analysis of alternative technologies for the removal of ethylene from the CELSS biomass production chamber

A variety of technologies were analyzed for their potential to remove ethylene from the CELSS Biomass Production Chamber (BPC). During crop production (e.g., lettuce, wheat, soybean, potato) in the BPC ethylene can accumulate in the airspace and subsequently affect plant viability. The chief source of ethylene is the plants themselves which reside in plastic trays containing nutrient solution. The main sink for ethylene is chamber leakage. The removal technology can be employed when deleterious levels (e.g., 50 ppb for potato) of ethylene are exceeded in the BPC and perhaps to optimize the plant growth process once a better understanding is developed of the relationship between exogenous ethylene concentration and plant growth. The technologies examined were catalytic oxidation, molecular sieve, cryotrapping, permanganate absorption, and UV degradation. Upon analysis, permanganate was chosen as the most suitable method. Experimental data for ethylene removal by permanganate during potato production was analyzed in order to design a system for installation in the BPC air duct. In addition, an analysis of the impact on ethylene concentration in the BPC of integrating the Breadboard Scale Aerobic Bioreactor (BSAB) with the BPC was performed. The result indicates that this unit has no significant effect on the ethylene material balance as a source or sink.

Rakow, Allen L.↗
NASA NTRS1996

Modeling Advance Life Support Systems

Activities this summer consisted of two projects that involved computer simulation of bioregenerative life support systems for space habitats. Students in the Space Life Science Training Program (SLSTP) used the simulation, space station, to learn about relationships between humans, fish, plants, and microorganisms in a closed environment. One student complete a six week project to modify the simulation by converting the microbes from anaerobic to aerobic, and then balancing the simulation's life support system. A detailed computer simulation of a closed lunar station using bioregenerative life support was attempted, but there was not enough known about system restraints and constants in plant growth, bioreactor design for space habitats and food preparation to develop an integrated model with any confidence. Instead of a completed detailed model with broad assumptions concerning the unknown system parameters, a framework for an integrated model was outlined and work begun on plant and bioreactor simulations. The NASA sponsors and the summer Fell were satisfied with the progress made during the 10 weeks, and we have planned future cooperative work.

Pitts, Marvin↗
NASA NTRS1996

A Comparison of the Physiology and Mechanics of Exercise in LBNP and Upright Gait

Bone, muscular strength, aerobic capacity, and normal fluid pressure gradients within the body are lost during bed rest and spaceflight. Lower Body Negative Pressure (LBNP) exercise may create musculoskeletal and cardiovascular strains equal to a greater than those experienced on Earth and elucidate some of the mechanisms for maintaining bone integrity. LBNP exercise simulates gravity during supine posture by using negative pressure to pull subjects inward against a treadmill generating footward forces and increasing transmural pressures. Footward forces are generated which equal the product of the pressure differential and the cross-sectional area of the LBNP waist seal. Subjects lie supine within the chamber with their legs suspended from one another via cuffs, bungee cords, and pulleys, such that each leg acts as a counterweight to the other leg during the gait cycle. The subjects then walk or run on a treadmill which is positioned vertically within the chamber. Supine orientation allows only footward force production due to the negative pressure within the chamber. The purpose of this study was to determine if the kinematics, kinetics, and metabolic rate during supine walking and slow running on a vertical treadmill within LBNP are similar to those on a treadmill in 1-g environment in an upright posture.

Boda, W. L.↗
NASA NTRS1995

Effects of Space Missions on the Human Immune System: A Meta-Analysis

Future spaceflight will require travelers to spend ever-increasing periods of time in microgravity. Optimal functioning of the immune system is of paramount importance for the health and performance of these travelers. A meta-analysis statistical procedure was used to analyze immune system data from crew members in United States and Soviet space missions from 8.5 to 140 days duration between 1968 and 1985. Ten immunological parameters (immunoglobulins A, G, M, D, white blood cell (WBC) count, number of lymphocytes, percent total lymphocytes, percent B lymphocytes, percent T lymphocytes, and lymphocyte reactivity to mitogen) were investigated using multifactorial, repeated measure analysis of variance. With the preflight level set at 100, WBC count increased to 154 +/- 14% (mean +/- SE; p less than or equal to 0.05) immediately after flight; there was a decrease in lymphocyte count (83 +/- 4%; p less than or equal to 0.05) and percent of total lymphocytes (69 +/- 1%; p less than or equal to 0.05) immediately after flight, with reduction in RNA synthesis to phytohemagglutinin (PHA) to 51 +/- 21% (p less than or equal to 0.05) and DNA synthesis to PHA to 61 +/- 8% (p less than or equal to 0.05) at the first postflight measurement. Thus, some cellular immunological functions are decreased significantly following spaceflight. More data are needed on astronauts' age, aerobic power output, and parameters of their exercise training program to determine if these immune system responses are due solely to microgravity exposure or perhaps to some other aspect of spaceflight.

Greenleaf, J. E.↗
NASA NTRS1989

Characteristics and Preliminary Observations of the Influence of Electromyostimulation on the Size and Function of Human Skeletal Muscle During 30 Days of Simulated Microgravity

During 30 days (d) of bedrest, the practicality of using Elec- troMyoStimulation (EMS) as a deterrent to atrophy and strength loss of lower limb musculature was examined. An EMS system was developed that provided variable but quantifiable levels of EMS, and measured torque. The dominant log of three male subjects was stimulated twice daily in a 3-d on/1-d off cycle during bedrest. The non-dominant leg of each subject acted as a control. A stimulator, using a 0.3 ms monophasic 60 Hz pulse waveform, activated muscle tissue for 4 s. The output waveform from the stimulator was sequenced to the Knee Extensors (KE), Knee Flex- ors (KF), Ankle Extensors (AE), and Ankle Flexors (AF), and caused three isometric contractions of each muscle group per minute. Subject tolerance determined EMS Intensity. Each muscle group received four 5-min bouts of EMS each session with a 10 -min rest between bouts. EMS and torque levels for each muscle action were recorded directly an a computer. Overall average EMS Intensity was 197, 197, 195, and 188 mA for the KE, KF, AF, and AE, respectively. Overall average torque development for these muscle groups was 70, 16, 12, and 27 Nm, respectively. EMS intensity doubled during the study, and average torque increased 2.5 times. Average maximum torque throughout a session reached 54% of maximal voluntary for the KE and 29% for the KF. Reductions in leg volume, muscle compartment size, cross-sectional area of slow and fast-twitch fibers, strength, and aerobic enzyme activities, and increased log compliance were attenuated in the legs which received EMS during bedrest. These results indicate that similar EMS levels induce different torques among different muscle groups and that repeated exposure to EMS increases tolerance and torque development. Longer orien- tation periods, therefore, may enhance its effectiveness. Our preliminary data suggest that the efficacy of EMS as an effective countermeasure for muscle atrophy and strength loss during long duration space travel warrants further investigation.

Duvoisin, Marc R.↗
NASA NTRS1994

Associations of Methanotrophs With the Roots and Rhizomes of Aquatic Vegetation

Results of an in vitro assay revealed that root-associated methane consumption was a common attribute or diverse emergent wetland macrophytes from a variety of habitats. Maximum potential uptake rates (V(sub maxp)) varied between about 1 and 10 micro mol g/ (dry weight) h, with no obvious correlation between rate and gross morphological characteristics of the plants. The V(sub maxp) corresponded to about 2 x 10(exp 18) to 2 x 10(exp 9) methanotrophs g/ (dry weight), assuming that root-associated methanotrophs have cell-specific activities comparable to those of known isolates. V(sub maxp) varied seasonally for an aquatic grass, Calamogrostis canadensis, and for the cattail, Typha latifolia, with highest rates in late summer. V(sub maxp) was well correlated with ambient temperature for C. canadensis but weakly correlated for T. Wifolia. The seasonal changes in V(sub maxp), as well as inferences from apparent half-saturation constants for methane uptake (K(sub app); generally 3 to 6 micro M), indicated that oxygen availability might be more important than methane as a rate determinant. In addition, roots incubated under anoxic conditions showed little or no postanoxia aerobic methane consumption, indicating that root-associated metbanotrophic populations might not tolerate variable oxygen availability. Hybridization of oligodeoxynucleotide probes specific for group 1 or group 2 methylotrophs also varied seasonally. The group 2-specific probe consistently hybridized to a greater extent than the group 1 probe, and the relative amount of group 2 probe hybridization to C. canadensis root extracts was positively correlated with V(sub maxp).

King, Gary M.↗
NASA NTRS1994

Survival and Recovery of Methanotrophic Bacteria Starved Under Oxic and Anoxic Conditions

The effects of carbon deprivation on survival of methanotrophic bacteria were compared in cultures incubated in the presence and absence of oxygen in the starvation medium. Survival and recovery of the examined methanotrophs were generally highest for cultures starved under anoxic conditions as indicated by poststarvation measurements of methane oxidation, tetrazolium salt reduction, plate counts, and protein synthesis. Methylosinus trichosporium OB3b survived up to 6 weeks of carbon deprivation under anoxic conditions while maintaining a physiological state that allowed relatively rapid (hours) methane oxidation after substrate addition. A small fraction of cells starved under oxic and anoxic conditions (4 and 10%, respectively) survived more than 10 weeks but required several days for recovery on plates and in liquid medium. A non-spore-forming methanotroph, strain WP 12, displayed 36 to 118% of its initial methane oxidation capacity after 5 days of carbon deprivation. Oxidation rates varied with growth history prior to the experiments as well as with starvation conditions. Strain WP 12 starved under anoxic conditions showed up to 90% higher methane oxidation activity and 46% higher protein production after starvation than did cultures starved under oxic conditions. Only minor changes in biomass and niorpholow were seen for methanotrophic bacteria starved tinder anoxic conditions. In contrast, starvation under oxic conditions resulted in morphology changes and an initial 28 to 35% loss of cell protein. These data suggest that methanotrophic bacteria can survin,e carbon deprivation under anoxic conditions by using maintenance energy derived Solelyr from an anaerobic endogenous metabolism. This capability could partly explain a significant potential for methane oxidation in environments not continuously, supporting aerobic methanotrophic growth.

Roslev, Peter↗
NASA NTRS1997

Evaluation of an Anaerobic Digestion System for Processing CELSS Crop Residues for Resource Recovery

Three bioreactors, connected in series, were used to process CELSS potato residues for recovery of resources. The first stage was an anaerobic digestor (8 L working volume; cow rumen contents inoculum; fed-batch; 8 day retention time; feed rate 25 gdw/day) that converted 33% of feed (dry weight loss) to CO2 and "volatile fatty acids" (vfa, 83:8:8 mmolar ratio acetic:propionic:butyric). High nitrate-N in the potato residue feed was absent in the anaerobic effluent, with a high portion converted to NH4(+)-N and the remainder unaccounted and probably lost to denitrification and NH4(+) volatilization. Liquid anaerobic effluent was fed to an aerobic, yeast biomass production vessel (2 L volume; Candida ingens inoculum; batch [pellicle] growth; 2 day retention time) where the VFAs and some NH4(+)-N were converted into yeast biomass. Yeast yields accounted for up to 8% of potato residue fed into the anaerobic bioreactor. The third bioreactor (0.5 L liquid working volume; commercial nitrifier inoculum; packed-bed biofilm; continuous yeast effluent feed; recirculating; constant volume; 2 day hydraulic retention time) was used to convert successfully the remaining NH4(+)-N into nitrate-N (preferred form of N for CELSS crop production) and to remove the remaining degradable soluble organic carbon. Effluents from the last two stages were used for partial replenishment of minerals for hydroponic potato production.

Strayer, R. F.↗
NASA NTRS1998

Develop Recovery Systems for Separations of Salts from Process Streams for use in Advanced Life Support System

The main objectives of this project were the development of a four-compartment electrolytic cell using high selective membranes to remove nitrate from crop residue leachate and convert it to nitric acid, and the development of an six compartment electrodialysis cell to remove selectively sodium from urine wastes. The recovery of both plant inedible biomass and human wastes nutrients to sustain a biomass production system are important aspects in the development of a controlled ecological life support system (CELSS) to provide the basic human needs required for life support during long term space missions. A four-compartment electrolytic cell has been proposed to remove selectively nitrate from crop residue and to convert it to nitric acid, which is actually used in the NASA-KSC Controlled Ecological Life Support System to control the pH of the aerobic bioreactors and biomass production chamber. Human activities in a closed system require large amount of air, water and minerals to sustain life and also generate wastes. Before using human wastes as nutrients, these must be treated to reduce organic content and to remove some minerals which have adverse effects on plant growth. Of all the minerals present in human urine, sodium chloride (NACl) is the only one that can not be used as nutrient for most plants. Human activities also requires sodium chloride as part of the diet. Therefore, technology to remove and recover sodium chloride from wastes is highly desirable. A six-compartment electrodialysis cell using high selective membranes has been proposed to remove and recover NaCl from human urine.

Colon, Guillermo↗
NASA NTRS1999

Space Physiology Studies

Calculations suggest that exercise in space to date has lacked sufficient loads to maintain musculoskeletal mass. Lower body negative pressure (LBNP) produces a force at the feet equal to the product of the LBNP and body cross-sectional area at the waist. Supine exercise within 50-60 mm Hg LBNP improves tolerance to LBNP and produces forces similar to those occurring during upright posture on Earth. Thus, exercise within LBNP may help prevent deconditioning of astronauts by stressing tissues of the lower body in a manner similar to gravity and also, may provide a safe and effective alternative to centrifugation in terms of cost, mass, volume, and power usage. We hypothesize that supine treadmill exercise during LBNP at one body weight (50-60 mm Hg LBNP) will provide cardiovascular and musculoskeletal loads similar to those experienced while upright in lg. Also, daily supine treadmill running in a LBNP chamber will maintain aerobic fitness, orthostatic tolerance, and musculoskeletal structure and function during bed rest (simulated microgravity).

Hargens, A. R.↗
NASA NTRS2000

Inflight Exercise Regimen for the 2-Hour Prebreathe Protocol

A 10 min aerobic prebreathe exercise up to 75% V-O2(sub max) on a dual-cycle ergometer, included in the 2-hour prebreathe protocol, has been shown to dramatically reduce the incidence of decompression sickness (DCS) at altitude. In-flight only leg ergometry will be available. A balanced exercise was developed using surgical tubing with the ergometer on-orbit. We hypothesize that a 75% V02max workload, individually prescribed, would be achieved using a target heart rate to regulate the intensity of the arm exercise. VO2, heart rate (HR) / ECG, V-CO2 /V-O2, V(sub E), and V(sub T), and rate of perceived exertion (Borg scale) were measured in eleven healthy subjects who passed a US Air Force Class III Physical examination. A V-O2 peak test was performed to assess the sub-maximal exercise prescription. Two series of sub-maximal tests were performed: (1) leg ergometer/hand ergometer and (2) leg ergometer/surgical tubes. We found no significant differences (P > 0.05) in comparing the means for V-O2 and HR between the predicted and measured values during the final 4 minute-stage at "75% V-O2 workload" or between the two types of sub-maximal tests. The prescribed prebreathe sub-maximal exercise performed with flight certified surgical tubes was achieved using the target HR.

Foster, Philip P.↗
NASA NTRS2000

NASA Countermeasures Evaluation and Validation Project

To support its ISS and exploration class mission objectives, NASA has developed a Countermeasure Evaluation and Validation Project (CEVP). The goal of this project is to evaluate and validate the optimal complement of countermeasures required to maintain astronaut health, safety, and functional ability during and after short- and long-duration space flight missions. The CEVP is the final element of the process in which ideas and concepts emerging from basic research evolve into operational countermeasures. The CEVP is accomplishing these objectives by conducting operational/clinical research to evaluate and validate countermeasures to mitigate these maladaptive responses. Evaluation is accomplished by testing in space flight analog facilities, and validation is accomplished by space flight testing. Both will utilize a standardized complement of integrated physiological and psychological tests, termed the Integrated Testing Regimen (ITR) to examine candidate countermeasure efficacy and intersystem effects. The CEVP emphasis is currently placed on validating the initial complement of ISS countermeasures targeting bone, muscle, and aerobic fitness; followed by countermeasures for neurological, psychological, immunological, nutrition and metabolism, and radiation risks associated with space flight. This presentation will review the processes, plans, and procedures that will enable CEVP to play a vital role in transitioning promising research results into operational countermeasures necessary to maintain crew health and performance during long duration space flight.

Lundquist, Charlie M.↗