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NASA NTRSDate not supplied

Effects of Mild Hypobaric Hypoxia on Response From Mild Exercise in NASA Exploration Atmosphere Tests

INTRODUCTION: The NASA Exploration Atmosphere study aims to validate a new prebreathe protocol incorporating an alternate habitat atmosphere of 56.5 kPa (8.2psia), 34% O 2 , and 66% N 2 to control and mitigate decompression sickness risk associated with spaceflight extravehicular activities. This alternate atmosphere results in a mild hypoxic environment (PIO 2 of 128 mmHg) that may influence inhabitant physiological responses to exercise. Therefore, the responses to light exercise in relation to the mild hypobaric hypoxic environment were investigated. METHODS: Eight participants (4M/4F; age=38.3±9.0 yr; weight=76.0±13.1 kg; peak aerobic capacity [VO 2 pk]= 3.1±0.7 L/min) were exposed to a mild hypobaric hypoxic environment for 11 days in NASA’s 20-foot hypobaric chamber at Johnson Space Center. Participants alternated test days between a habitat atmosphere of 56.5 kPA/34% O 2 and simulated 6-hour EVA environment, 29.6 kPa/85% O 2 . Participants completed pre-mission graded VO 2 pk tests on a LODE cycle ergometer with ParvoMedics metabolic analyzer. Submaximal aerobic tests were performed pre and during the mission (10-minutes of exercise at a workload of 40% VO 2 pk).Pre-mission, performed submaximal exercise exposed to a breathing air mixture of, 18% O 2 and balance N 2 , to simulate the mildly hypoxic environment within the 20-foot chamber. Linear mixed models (fixed effect: test day; random effects: subject, age) were performed to determine whether physiological responses (oxygen uptake [VO 2 ], carbon dioxide production [VCO 2 ], ventilation [VE], oxygen saturation [SPO 2 ], heart rate [HR], respiratory exchange ratio [RER]) to submaximal exercise performed within the 20-foot hypobaric chamber every 2 days differed from the pre-mission (18% O 2 ) testing. Results are presented as estimated marginal means with lower and upper confidence limits, with significance set to 0.05. RESULTS AND DISCUSSION: Seven of eight participants completed the chamber study. Mixed models for VO 2 , VCO 2 , SpO 2 , HR, and RER indicated negligible impact of the mild hypoxic chamber environment compared to pre-mission testing (all p>0.05).Results for VE indicated a minor impact of chamber environment compared to pre-mission testing (37.0 L/min [30.8, 43.2]), with increased VE at test day 10 (40.4 L/min [34.2, 46.6]; p= 0.029).The aerobic performance data collected suggests limited physiologic responses to mild exercise when performed at normobaric hypoxia and hypobaric hypoxia.

B Siders↗
NASA NTRS1983

The diagnostic accuracy of exercise electrocardiography - A review

The cardiovascular 'stress test', and particularly the graded treadmill exercist test, has gained wide acceptance as a diagnostic aid in searching for ischemic heart disease and as a prognostic indicator for those with known coronary artery disease. Controversies still exist, however, in its use in mass screening and in interpreting equivocal tests. A review of the use and value of electrocardiographic exercise testing is presented. Topics such as its use in asymptomatic individuals, the adjuvant use of clinical examination, and the examination of ancillary treadmill parameters are presented. No attempt is made to detail the very significant contributions of radionuclide scanning. The positive exercise electrocardiogram in the asymptomatic subject is discussed and guidelines for clinical management are offered.

Johnson, R. L.↗
NASA NTRS2011

GeoLab's First Field Trials, 2010 Desert RATS: Evaluating Tools for Early Sample Characterization

As part of an accelerated prototyping project to support science operations tests for future exploration missions, we designed and built a geological laboratory, GeoLab, that was integrated into NASA's first generation Habitat Demonstration Unit-1/Pressurized Excursion Module (HDU1-PEM). GeoLab includes a pressurized glovebox for transferring and handling samples collected on geological traverses, and a suite of instruments for collecting preliminary data to help characterize those samples. The GeoLab and the HDU1-PEM were tested for the first time as part of the 2010 Desert Research and Technology Studies (DRATS), NASA's analog field exercise for testing mission technologies. The HDU1- PEM and GeoLab participated in two weeks of joint operations in northern Arizona with two crewed rovers and the DRATS science team.

Evans, Cindy A.↗
NASA NTRS2000

Effect of In-Flight Exercise and Extravehicular Activity on Postflight Stand Tests

The purpose of this study was to determine whether exercise performed by Space Shuttle crewmembers during short-duration spaceflights (9-16 days) affects the heart rate (HR) and blood pressure (BP) responses to standing within 2-4 hr of landing. Thirty crewmembers performed self-selected in-flight exercise and maintained exercise logs to monitor their exercise intensity and duration. A 10min stand test, preceded by at least 6 min of quiet supine rest, was completed 10- 15 d before launch (PRE) and within four hours of landing (POST). Based upon their in-flight exercise records, subjects were grouped as either high (HIex: = 3x/week, HR = 70% ,HRMax, = 20 min/session, n = 11), medium (MEDex: = 3x/week, HR = 70% HRmax, = 20 min/session, n = 10), or low (LOex: = 3x/week, HR and duration variable, n = 11) exercisers. HR and BP responses to standing were compared between groups (ANOVA, or analysis of variance, P < 0.05). There were no PRE differences between the groups in supine or standing HR and BP. Although POST supine HR was similar to PRE, all groups had an increased standing HR compared to PRE. The increase in HR upon standing was significantly greater after flight in the LOex group (36+/-5 bpm) compared to HIex or MEDex groups (25+/-1bpm; 22+/-2 bpm). Similarly, the decrease in pulse pressure (PP) from supine to standing was unchanged after spaceflight in the MEDex and HIex groups, but was significantly less in the LOex group (PRE: -9+/- 3, POST: -19+/- 4 mmHg). Thus, moderate to high levels of in-flight exercise attenuated HR and PP responses to standing after spaceflight compared.

Lee, Stuart M. C.↗
NASA NTRS1975

Physiological response to exercise after space flight - Apollo 14 through Apollo 17

Submaximal exercise stress tests were conducted preflight and postflight on the Apollo 14-17 crewmen. A bicycle ergometer was utilized to evoke target heart rates up to 160 beats/min while respiratory gas exchange, blood pressure, and cardiac output were measured. Three preflight tests were conducted during the month prior to flight to establish baseline values for postflight comparisons. Tachycardia was evidenced at rest and during exercise immediately postflight. This transitory tachycardia compensated for reduced stroke volume. Systolic blood pressure was reduced during exercise stress, but no consistent changes were observed in diastolic blood pressure. With the exception of the Apollo 15 crewmen, all crewmen had returned to preflight response levels by the day following recovery. No changes were observed in mechanical or respiratory efficiency immediately postflight.

Rummel, J. A.↗
NASA NTRS2012

Improving Flight Software Module Validation Efforts : a Modular, Extendable Testbed Software Framework

Ever since Explorer-1, the United States' first Earth satellite, was developed and launched in 1958, JPL has developed many more spacecraft, including landers and orbiters. While these spacecraft vary greatly in their missions, capabilities,and destination, they all have something in common. All of the components of these spacecraft had to be comprehensively tested. While thorough testing is important to mitigate risk, it is also a very expensive and time consuming process. Thankfully,since virtually all of the software testing procedures for SMAP are computer controlled, these procedures can be automated. Most people testing SMAP flight software (FSW) would only need to write tests that exercise specific requirements and then check the filtered results to verify everything occurred as planned. This gives developers the ability to automatically launch tests on the testbed, distill the resulting logs into only the important information, generate validation documentation, and then deliver the documentation to management. With many of the steps in FSW testing automated, developers can use their limited time more effectively and can validate SMAP FSW modules quicker and test them more rigorously. As a result of the various benefits of automating much of the testing process, management is considering this automated tools use in future FSW validation efforts.

flight software testing↗
NASA NTRS1998

T wave alternans as a predictor of recurrent ventricular tachyarrhythmias in ICD recipients: prospective comparison with conventional risk markers

INTRODUCTION: The current standard for arrhythmic risk stratification is electrophysiologic (EP) testing, which, due to its invasive nature, is limited to patients already known to be at high risk. A number of noninvasive tests, such as determination of left ventricular ejection fraction (LVEF) or heart rate variability, have been evaluated as additional risk stratifiers. Microvolt T wave alternans (TWA) is a promising new risk marker. Prospective evaluation of noninvasive risk markers in low- or moderate-risk populations requires studies involving very large numbers of patients, and in such studies, documentation of the occurrence of ventricular tachyarrhythmias is difficult. In the present study, we identified a high-risk population, recipients of an implantable cardioverter defibrillator (ICD), and prospectively compared microvolt TWA with invasive EP testing and other risk markers with respect to their ability to predict recurrence of ventricular tachyarrhythmias as documented by ICD electrograms. METHODS AND RESULTS: Ninety-five patients with a history of ventricular tachyarrhythmias undergoing implantation of an ICD underwent EP testing, assessment of TWA, as well as determination of LVEF, baroreflex sensitivity, signal-averaged ECG, analysis of 24-hour Holter monitoring, and QT dispersion from the 12-lead surface ECG. The endpoint of the study was first appropriate ICD therapy for electrogram-documented ventricular fibrillation or tachycardia during follow-up. Kaplan-Meier survival analysis revealed that TWA (P < 0.006) and LVEF (P < 0.04) were the only significant univariate risk stratifiers. EP testing was not statistically significant (P < 0.2). Multivariate Cox regression analysis revealed that TWA was the only statistically significant independent risk factor. CONCLUSIONS: Measurement of microvolt TWA compared favorably with both invasive EP testing and other currently used noninvasive risk assessment methods in predicting recurrence of ventricular tachyarrhythmias in ICD recipients. This study suggests that TWA might also be a powerful tool for risk stratification in low- or moderate-risk patients, and needs to be prospectively evaluated in such populations.

Non-NASA Center↗
NASA NTRS1990

Summary of results from the testing of three prototype thermal bus systems for Space Station Freedom

Three Space Station Freedom (SSF) prototype two-phase thermal bus systems, utilizing ammonia as the working fluid, underwent extensive evaluation during 1988 and 1989. All three test articles were exercised in a similar ambient test program to characterize performance under simulated SSF operating conditions. Additionally, thermal buses were integrated with heat pipe radiators and tested in a thermal vacuum (T/V) environment. Testing has shown that two-phase thermal bus performance can be generally bound in an ambient test program; however, integrated T/V testing with heat pipe radiators similar to those that will be used on SSF is required to fully characterize system performance.

Brady, T. K.↗
NASA NTRS2023

Airspace Automation Flight Tabletop Exercise

Interconnections of new systems are needed for airspace automation capabilities required in Urban Air Mobility (UAM). FAA Concept of Operations (CONOPS) V1.0 shows Provider of Services for UAM (PSU) at the center of the notional architecture; however, the functional role of the PSU in data exchange and the path to get there is unclear. In partnership with Wisk Aero, Avision, ANRA, Collins Aerospace, OneSky, SkyGrid, and AURA, the NASA National Campaign held discussions and tabletop exercises to test the functional allocations and work flows between an aircraft operator, airspace providers, Command and Control Communication Service Providers (C2CSP), and FAA air traffic in a real-world scenario. The exercise included preplanning and execution of a passenger mission with nominal, contingency, and conflict management scenarios for initial UAM operations. This working paper describes initial conditions for the flight tabletop exercise, exercise summaries, lessons learned, and recommendations for future work.

National Campaign↗
NASA NTRS1976

Exercise cardiac output following Skylab missions - The second manned Skylab mission

Cardiac output was measured during preflight and postflight exercise-stress tests on the Skylab astronauts. In the postflight tests immediately following the 28-, 59-, and 84-d earth orbital missions, the astronauts exhibited an approximate 30% decrease in cardiac output coupled with an approximate 50% decrease in cardiac stroke volume during exercise. These changes were accompanied by elevated heart rates and significant increases in total systemic peripheral vascular resistance. Mean arterial pressure was unchanged. All parameters returned to normal preflight values within 30 d of the end of the orbital period. Duration of the zero-G exposure did not appear to influence either the magnitude of the hemodynamic changes or the time-course of their return to normal. These results are discussed in relation to other cardiovascular findings and possible mechanisms responsible for the observations are outlined.

Buderer, M. C.↗
NASA NTRS1992

Exercise performance, core temperature, and metabolism after prolonged restricted activity and retraining in dogs

Physiological effects of restricted activity (RA) and subsequent retraining have been studied. Ten male mongrel dogs performed a submaximal exercise endurance test on a treadmill during kennel control, after 8 weeks of cage confinement and after eight weeks of retraining using the same treadmill protocol 1 h/d for 6 d/week. Data obtained show that RA reduces exercise endurance, the effectiveness of exercise thermoregulation, muscle glycogen stores, and the lipolytic response to exercise and to noradrenaline stimulation.

Nazar, K.↗
NASA NTRS2009

Using Maximal Isometric Force to Determine the Optimal Load for Measuring Dynamic Muscle Power

Maximal power output occurs when subjects perform ballistic exercises using loads of ~30-50% of one-repetition maximum (1-RM). However, performing 1-RM testing prior to power measurement requires considerable time, especially when testing involves multiple exercises. Maximal isometric force (MIF), which requires substantially less time to measure than 1-RM, might be an acceptable alternative for determining the optimal load for power testing. PURPOSE: To determine the optimal load based on MIF for maximizing dynamic power output during leg press and bench press exercises. METHODS: Twenty healthy volunteers (12 men and 8 women; mean +/- SD age: 31+/-6 y; body mass: 72 +/- 15 kg) performed isometric leg press and bench press movements, during which MIF was measured using force plates. Subsequently, subjects performed ballistic leg press and bench press exercises using loads corresponding to 20%, 30%, 40%, 50%, and 60% of MIF presented in randomized order. Maximal instantaneous power was calculated during the ballistic exercise tests using force plates and position transducers. Repeated-measures ANOVA and Fisher LSD post hoc tests were used to determine the load(s) that elicited maximal power output. RESULTS: For the leg press power test, six subjects were unable to be tested at 20% and 30% MIF because these loads were less than the lightest possible load (i.e., the weight of the unloaded leg press sled assembly [31.4 kg]). For the bench press power test, five subjects were unable to be tested at 20% MIF because these loads were less than the weight of the unloaded aluminum bar (i.e., 11.4 kg). Therefore, these loads were excluded from analysis. A trend (p = 0.07) for a main effect of load existed for the leg press exercise, indicating that the 40% MIF load tended to elicit greater power output than the 60% MIF load (effect size = 0.38). A significant (p . 0.05) main effect of load existed for the bench press exercise; post hoc analysis indicated that the effect of load on power output was: 30% > 40% > 50% = 60%. CONCLUSION: Loads of 40% and 30% of MIF elicit maximal power output during dynamic leg presses and bench presses, respectively. These findings are similar to those obtained when loading is based on 1-RM.

Spiering, Barry A.↗
NASA NTRS1985

Automatic Blood Pressure Measurements During Exercise

Microprocessor circuits and a computer algorithm for automatically measuring blood pressure during ambulatory monitoring and exercise stress testing have been under development at SRI International. A system that records ECG, Korotkov sound, and arm cuff pressure for off-line calculation of blood pressure has been delivered to NASA, and an LSLE physiological monitoring system that performs the algorithm calculations in real-time is being constructed. The algorithm measures the time between the R-wave peaks and the corresponding Korotkov sound on-set (RK-interval). Since the curve of RK-interval versus cuff pressure during deflation is predictable and slowly varying, windows can be set around the curve to eliminate false Korotkov sound detections that result from noise. The slope of this curve, which will generally decrease during exercise, is the inverse of the systolic slope of the brachial artery pulse. In measurements taken during treadmill stress testing, the changes in slopes of subjects with coronary artery disease were markedly different from the changes in slopes of healthy subjects. Measurements of slope and O2 consumption were also made before and after ten days of bed rest during NASA/Ames Research Center bed rest studies. Typically, the maximum rate of O2 consumption during the post-bed rest test is less than the maximum rate during the pre-bed rest test. The post-bed rest slope changes differ from the pre-bed rest slope changes, and the differences are highly correlated with the drop in the maximum rate of O2 consumption. We speculate that the differences between pre- and post-bed rest slopes are due to a drop in heart contractility.

Weaver, Charles S.↗
NASA NTRS2007

Artificial Gravity: Effects on Bone Turnover

The impact of microgravity on the human body is a significant concern for space travelers. Since mechanical loading is a main reason for bone loss, artificial gravity might be an effective countermeasure to the effects of microgravity. In a 21-day 6 head-down tilt bed rest (HDBR) pilot study carried out by NASA, USA, the utility of artificial gravity (AG) as a countermeasure to immobilization-induced bone loss was tested. Blood and urine were collected before, during, and after bed rest for bone marker determinations. Bone mineral density was determined by DXA and pQCT before and after bed rest. Urinary excretion of bone resorption markers (n-telopeptide and helical peptide) were increased from pre-bed rest, but there was no difference between the control and the AG group. The same was true for serum c-telopeptide measurements. Bone formation markers were affected by bed rest and artificial gravity. While bone-specific alkaline phosphatase tended to be lower in the AG group during bed rest (p = 0.08), PINP, another bone formation marker, was significantly lower in AG subjects than CN before and during bed rest. PINP was lower during bed rest in both groups. For comparison, artificial gravity combined with ergometric exercise was tested in a 14-day HDBR study carried out in Japan (Iwase et al. J Grav Physiol 2004). In that study, an exercise regime combined with AG was able to significantly mitigate the bed rest-induced increase in the bone resorption marker deoxypyridinoline. While further study is required to more clearly differentiate bone and muscle effects, these initial data demonstrate the potential effectiveness of short-radius, intermittent AG as a countermeasure to the bone deconditioning that occurs during bed rest and spaceflight. Future studies will need to optimize not only the AG prescription (intensity and duration), but will likely need to include the use of exercise or other combined treatments.

Heer, M.↗
NASA NTRS1992

Influences of chemical sympathectomy, demedullation, and hindlimb suspension on the VO2max of rats

Results from previous studies have shown that the reduction in maximal oxygen consumption (VO2max) with simulated microgravity is attenuated in chemically sympathectomized rats. To determine the contributions of the catecholamines from the adrenal medulla in this process, investigations were conducted with 65 saline injected (SAL) and chemically sympathectomized (SX) female rats that were either surgically demedullated (DM), or intact (IN). Microgravity conditions were simulated by head-down suspension (HDS) while controls were assigned to individual cages (CC). The experimental period was 14 d. The rats were tested for VO2max, treadmill run time (RT), and submaximal mechanical efficiency (ME) prior to suspension and on days 7 and 14. Saline injected rats that had intact adrenal medullas (SAL-IN) exhibited significantly reduced measures of VO2max after 7 and 14 d by 15% and 21%, respectively. No significant reduction in VO2max was observed with HDS in the SX-IN animals. Sympathectomized rats that were demedullated (SX-DM) also exhibited a significant reduction in VO2max (12%). In addition, HDS was associated with a marked and significant reduction in RT in all groups. ME for submaximal exercise was significantly reduced after HDS in SAL-IN rats but not in the SX-IN rats. SX-DM rats experienced significant reductions in ME similar in magnitude to the SAL-IN rats. These results confirm that chemical sympathectomy attenuates the expected decrease in VO2max with HDS and suggests that circulating epinephrine contributes to this response.

Non-NASA Center↗
NASA NTRS2001

Effects of 3-day bed rest on physiological responses to graded exercise in athletes and sedentary men

To test the hypotheses that short-term bed-rest (BR) deconditioning influences metabolic, cardiorespiratory, and neurohormonal responses to exercise and that these effects depend on the subjects' training status, 12 sedentary men and 10 endurance- and 10 strength-trained athletes were submitted to 3-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and heart rate (HR) were recorded continuously, and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate concentration ([LA]), epinephrine concentration ([Epi]), norepinephrine concentration ([NE]), plasma renin activity (PRA), human growth hormone concentration ([hGH]), testosterone, and cortisol determination. Reduction of peak oxygen uptake (VO(2 peak)) after BR was greater in the endurance athletes than in the remaining groups (17 vs. 10%). Decrements in VO(2 peak) correlated positively with the initial values (r = 0.73, P < 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased in the endurance athletes from 71 to 60% VO(2 peak) (P < 0.001); they also had an earlier increase in [NE], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion, reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.

NASA Center ARC↗
NASA NTRS2000

[Correction of autonomic reactions parameters in organism of cosmonaut with adaptive biocontrol method]

Presented are results of testing the method of adaptive biocontrol during preflight training of cosmonauts. Within the MIR-25 crew, a high level of controllability of the autonomous reactions was characteristic of Flight Commanders MIR-23 and MIR-25 and flight Engineer MIR-23, while Flight Engineer MIR-25 displayed a weak intricate dependence of these reactions on the depth of relaxation or strain.

Flight Experiment↗
DOE OSTI2025

Employing MACS/ViBRANT as a Surrogate MARVEL Reactor for Startup Reactivity Tuning and Supervisory Control Processes

Advanced nuclear reactors are a key part of the future of nuclear energy both in the United States and globally. They offer unique benefits for various energy-demanding applications, including use in remote locations, compact size, modular manufacturing, remote monitoring, low and/or variable power rating operation, and reliance on novel technologies to enhance operational safety. To achieve economic feasibility, advanced reactors must significantly reduce their workforces in comparison with the current fleet. Achieving this reduction will occur through reducing staff workloads using technology to achieve autonomous or semi-autonomous operations, demonstrated by comprehensive testing and validation activities. These operations will require both software and hardware platforms during the design and testing phases. While simulations are useful during the design phase, their performance can significantly deviate during actual deployment on hardware. This report presents the outcomes of a collaborative technical initiative between the U.S. Department of Energy (DOE) Microreactor Program (MRP) and Advanced Sensors and Instrumentation (ASI) Program. The collaboration utilized the Microreactor Automated Control System (MACS) hardware platform to bridge the gap between theoretical reactor design and actual startup and control operations. Two key use cases were investigated: facilitating the startup testing period and demonstrating supervisory control. The first use case details the key Microreactor Applications Research Validation and Evaluation (MARVEL) reactor startup physics testing activities conducted using the MACS platform. These activities included drum worth measurements, shutdown margin assessment, temperature feedback analysis, and scram time evaluation, as well as unique testing that would apply to the MARVEL reactor to demonstrate the testing methodologies in a low-risk environment. The MACS platform, serving as a surrogate representation of the MARVEL reactor, proved instrumental in performing these tests. The exercise revealed aspects that led to optimized processes, refined hardware design, and enhanced base software capabilities. By maturing methods and technologies in this manner, the initiative promises to reduce wasted time in the actual on-site reactor deployment effort, thereby saving significant time and resources. The second use case focuses on the development and implementation of supervisory control methods aimed at managing core tilt, which can result from asymmetrical operations or manufacturing imperfections in fuel rods or reactivity control devices. A key objective was to assess and compare the use of artificial intelligence (AI) for supervisory control. The effort aimed to define the role of supervisory control to enhance performance without risking control instability. This effort explored three distinct approaches: rules-based (RB) methods, optimization techniques, and reinforcement learning (RL) algorithms. Each approach was evaluated for its ease of implementation, its usability, and its effectiveness in responding to asymmetries in neutron flux. Comparative analysis of these approaches provided valuable insights into their applicability and effectiveness, offering a robust framework for advanced reactor operations. Together, these two use cases highlight the potential of hardware test beds to help streamline the design, operation, and control of advanced nuclear reactors. This collaborative effort underscores the importance of continued innovation and experimentation in achieving the next generation of safe, reliable, and economically viable nuclear energy solutions.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗