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NASA NTRS2009

NASA Exercise Physiology and Countermeasures Project Overview

Efficient exercise countermeasures are necessary to offset or minimize spaceflight-induced deconditioning and to maximize crew performance of mission tasks. These countermeasure protocols should use the fewest crew and vehicle resources. NASA s Exercise Physiology and Countermeasures (ExPC) Project works to identify, collect, interpret, and summarize evidence that results in effective exercise countermeasure protocols which protect crew health and performance during International Space Station (ISS) and future exploration-class missions. The ExPC and NASA s Human Research Program are sponsoring multiple studies to evaluate and improve the efficacy of spaceflight exercise countermeasures. First, the Project will measure maximal aerobic capacity (VO2max) during cycle ergometry before, during, and after ISS missions. Second, the Project is sponsoring an evaluation of a new prototype harness that offers improved comfort and increased loading during treadmill operations. Third, the Functional Tasks Test protocol will map performance of anticipated lunar mission tasks with physiologic systems before and after short and long-duration spaceflight, to target system contributions and the tailoring of exercise protocols to maximize performance. In addition to these studies that are actively enrolling crewmember participants, the ExPC is planning new studies that include an evaluation of a higher-intensity/lower-volume exercise countermeasure protocol aboard the ISS using the Advanced Resistive Exercise Device and second-generation treadmill, studies that evaluate bone loading during spaceflight exercise, and ground-based studies that focus on fitness for duty standards required to complete lunar mission tasks and for which exercise protocols need to protect. Summaries of these current and future studies and strategies will be provided to international colleagues for knowledge sharing and possible collaboration.

Loerch, Linda↗
NASA NTRS2010

Psychrophilic and Psychrotolerant Microbial Extremophiles in Polar Environments

The microbial extremophiles that inhabit the polar regions of our planet are of tremendous significance. The psychrophilic and psychrotolerant microorganisms, which inhabit all of the cold environments on Earth have important applications to Bioremediation, Medicine, Pharmaceuticals, and many other areas of Biotechnology. Until recently, most of the research on polar microorganisms was confined to studies of polar diatoms, yeast, fungi and cyanobacteria. However, within the past three decades, extensive studies have been conducted to understand the bacteria and archaea that inhabit the Arctic and Antarctic sea-ice, glaciers, ice sheets, permafrost and the cryptoendolithic, cryoconite and ice-bubble environments. These investigations have resulted in the discovery of many new genera and species of anaerobic and aerobic microbial extremophiles. Exotic enzymes, cold-shock proteins and pigments produced by some of the extremophiles from polar environments have the potential to be of great benefit to Mankind. Knowledge about microbial life in the polar regions is crucial to understanding the limitations and biodiversity of life on Earth and may provide valuable clues to the Origin of Life on Earth. The discovery of viable microorganisms in ancient ice from the Fox Tunnel, Alaska and the deep Vostok Ice has shown that microorganisms can remain alive while cryopreserved in ancient ice. The psychrophilic lithoautotrophic homoacetogen isolated from the deep anoxic trough of Lake Untersee is an ideal candidate for life that might inhabit comets or the polar caps of Mars. The spontaneous release of gas from within the Anuchin Glacier above Lake Untersee may provide clues to the ice geysers that erupt from the tiger stripe regions of Saturn s moon Enceladus. The methane productivity in the lower regimes of Lake Untersee may also provide insights into possible mechanisms for the recently discovered methane releases on Mars. Since most of the other water bearing bodies of our Solar system are frozen worlds, microbial extremophiles from the Polar Regions of Earth are of great importance to Astrobiology in understanding where and how to search for evidence of life elsewhere in the Cosmos.

Hoover, Richard B.↗
NASA NTRS2010

Maximum Oxygen Uptake During and After Long-Duration Space Flight

Decreased maximum oxygen consumption (VO2max) during and after space flight may impair a crewmember s ability to perform mission-critical work that is high intensity and/or long duration in nature (Human Research Program Integrated Research Plan Risk 2.1.2: Risk of Reduced Physical Performance Capabilities Due to Reduced Aerobic Capacity). When VO2max was measured in Space Shuttle experiments, investigators reported that it did not change during short-duration space flight but decreased immediately after flight. Similar conclusions, based on the heart rate (HR) response of Skylab crewmembers, were made previously concerning long-duration space flight. Specifically, no change in the in-flight exercise HR response in 8 of 9 Skylab crewmembers indicated that VO2max was maintained during flight, but the elevated exercise HR after flight indicated that VO2max was decreased after landing. More recently, a different pattern of in-flight exercise HR response, and assumed changes in VO2max, emerged from routine testing of International Space Station (ISS) crewmembers. Most ISS crewmembers experience an elevated in-flight exercise HR response early in their mission, with a gradual return toward preflight levels as the mission progresses. Similar to previous reports, exercise HR is elevated after ISS missions and returns to preflight levels by 30 days after landing. VO2max has not been measured either during or after long-duration space flight. The purposes of the ISS VO2max experiment are (1) to measure VO2max during and after long-duration spaceflight, and (2) to determine if submaximal exercise test results can be used to accurately estimate VO 2max.

Moore, Alan D., Jr.↗
NASA NTRS2006

Analysis of Membrane Lipids of Airborne Micro-Organisms

A method of characterization of airborne micro-organisms in a given location involves (1) large-volume filtration of air onto glass-fiber filters; (2) accelerated extraction of membrane lipids of the collected micro-organisms by use of pressurized hot liquid; and (3) identification and quantitation of the lipids by use of gas chromatography and mass spectrometry. This method is suitable for use in both outdoor and indoor environments; for example, it can be used to measure airborne microbial contamination in buildings ("sick-building syndrome"). The classical approach to analysis of airborne micro-organisms is based on the growth of cultureable micro-organisms and does not provide an account of viable but noncultureable micro-organisms, which typically amount to more than 90 percent of the micro-organisms present. In contrast, the present method provides an account of all micro-organisms, including cultureable, noncultureable, aerobic, and anaerobic ones. The analysis of lipids according to this method makes it possible to estimate the number of viable airborne micro-organisms present in the sampled air and to obtain a quantitative profile of the general types of micro-organisms present along with some information about their physiological statuses.

MacNaughton, Sarah↗
NASA NTRS2010

Treadmill Exercise Within LBNP as an Integrated Coutermeasure to Microgravity

An integrated exercise countermeasure for microgravity is needed to protect multiple physiologic systems and save crew time. Such a countermeasure should protect orthostatic tolerance, upright ambulatory capability (including sprinting), aerobic capacity, muscle strength/endurance, and other physiologic parameters relevant to human performance. We developed a novel physiologic countermeasure, treadmill exercise within LBNP, for preventing cardiovascular and musculoskeletal deconditioning associated with prolonged bed rest and spaceflight. We evaluated 40 min of daily LBNP treadmill exercise by a battery of physiologic parameters relevant to maintaining exercise performance and health of both women and men during bed-rest (simulated microgravity) studies lasting from 5 to 60 days. For 30 day studies, we employed identical twins with one twin as the control and the other twin as the exerciser to improve comparative power. During the WISE 60-day HDT study, the treadmill exercise within LBNP was performed 3-4 days each week and resistive exercise was performed 2-3 days each week. Our treadmill within LBNP protocol maintained plasma volume and sprint speed (30 day HDT bed-rest studies of identical twins), orthostatic tolerance to a degree, upright exercise capacity, muscle strength and endurance, and some bone parameters during 30 day (twin studies) and 60 day (WISE-2005) bed-rest simulations of microgravity. When combining treadmill exercise within LBNP and resistive exercise (WISE), cardiac mass increased significantly in the exercise (EX) group during bed rest relative to controls (CON). Upright peak VO2, and knee extensor strength and endurance decreased significantly in CON subjects; but these parameters were preserved in the EX group. In the 60 day WISE study, each LBNP exercise session was followed immediately by 10 minutes of static LBNP, and the last such session occurred three days before the end of bed rest. Still, orthostatic tolerance was better maintained in the EX group than in the CON group. Therefore, these collective peer-reviewed results document that our treadmill exercise within LBNP countermeasure safely and efficiently protects multiple physiologic systems in women and men during bed-rest studies of up to 60 days. Supported by NASA grants NNJ04HF71G and NAG 9-1425, NIH grant GCRC M01 RR00827 and by WISE support from ESA, NASA, CSA, and CNES.

Lee, Stuart↗
NASA NTRS2010

Statistical Challenges in Biomedical Research

Potentially debilitating effects of spaceflight environment include: a) Bone Demineralization - Osteoporosis. b)Impaired Fracture Healing - Non-Union. c) Renal Stone Formation & Soft Tissue Calcification. d) Orthostatic Intolerance (on return to gravity). e) Cardiac Arrhythmias. f) Dehydration (on return to gravity). g) Decreased Aerobic Capacity. h) Impaired Coordination. i) Muscle Atrophy (Loss of Strength). j) Radiation Sickness. k) Increased Cancer Risk. l) Impaired Immune Function. m) Behavioral Changes & Performance Decrements n) Altitude Decompression Sickness during EVA.

Feiveson, Alan H.↗
NASA NTRS2002

The Gravity of LBNP Exercise: Lessons Learned from Identical Twins in Bed for 30 Days

Microgravity leads to cardiovascular deconditioning in humans, which is manifested by post-flight reduction of orthostatic tolerance and upright exercise capacity. During upright posture on Earth, blood pressures are greater in the feet than at heart or head levels due to gravity's effects on columns of blood in the body. During exposure to Microgravity, all gravitational blood pressures disappear. Presently, there is no exercise hardware available for space flight to provide gravitational blood pressures to tissues of the lower body. We hypothesized that 40 minutes of supine treadmill running per day in a LBNP chamber at 1.0 to 1.2 body weight (approximately 50 - 60 mm Hg LBNP) with a 5 min resting, nonexercise LBNP exposure at 50 mm Hg after the exercise session will maintain aerobic fitness orthostatic tolerance, and selected parameters of musculoskeletal function during 30 days of bed rest (simulated microgravity). This paper is an interim report of some of our findings on 16 subjects.

Hargens, Alan R.↗
NASA NTRS2010

Managing the Risk for Early Onset Osteoporosis in Long-Duration Astronauts Due to Spaceflight

Early Onset Osteoporosis is probably the most recognized but poorly understood long-term health risk due to spaceflight. Osteoporosis management is primarily prophylactic and clinical interventions rely upon the ability to predict fractures which is currently determined by surrogate measures of bone strength. The RMAT for Early Onset Osteoporosis identified some open issues related to the fact that long-duration astronauts compose a unique group of subjects for which clinical approaches for osteoporosis management do not apply. Long-duration astronauts are healthy, young (25 to 55 years of age), predominantly male, and physical fit relative to the typical osteoporosis patient. Moreover, during prolonged space missions (typically 6-month missions) the skeleton not only adapts to weightlessness, but is influenced by numerous risk factors induced by operational constraints, e.g., inability to maintain preflight weight-bearing and aerobic activities, sub-optimal dietary intake (e.g., high sodium content for food stability, lack of fresh fruit and vegetables), suppression of vitamin D metabolism by uv shielding, and remote medicine care. Moreover, adaptation results in novel changes to astronauts bones that cannot be detected by current medically-useful measures. Consequently, a panel of clinicians (recognized leaders and policy-makers in osteoporosis) was convened to review the dataset of bone measures and bone loss risk factors in long-duration astronauts. Driven by the queries in the RMAT, the panel was charged to determine 1) if an intervention is required to prevent this risk, 2) what type and at what time would intervention be optimal, 3) what is the clinical trigger that would require a medical response from flight surgeons and 4) how should research data be used in the clinical care of astronauts. Hence, the RMAT determined that a bone health policy need to be formulated specific for this unique cohort subjected to a novel skeletal condition

Sibonga, Jean D.↗
NASA NTRS2010

NIRS-Derived Tissue Oxygen Saturation and Hydrogen Ion Concentration Following Bed Rest

Long-term bed rest (BR), a model of spaceflight, results in a decrease in aerobic capacity and altered submaximal exercise responses. The strongest BR-induced effects on exercise appear to be centrally-mediated, but longer BR durations may result in peripheral adaptations (e.g., decreased mitochondrial and capillary density) which are likely to influence exercise responses. PURPOSE: To measure tissue oxygen saturation (SO2) and hydrogen ion concentration ([H+]) in the vastus lateralis (VL) using near infrared spectroscopy (NIRS) during cycle ergometry before and after . 30 d of BR. METHODS: Eight subjects performed a graded exercise test on a cycle ergometer to volitional fatigue 7 d before (pre-BR) and at the end or 1 day after BR (post-BR). NIRS spectra were collected from a sensor adhered to the skin overlying the VL. Oxygen consumption (VO2) was measured by open circuit spirometry. Blood volume (BV) was measured before and after BR using the carbon monoxide rebreathing technique. Changes in pre- and post-BR SO2 and [H+] data were compared using mixed model analyses. BV and peak exercise data were compared using paired t-tests. RESULTS: BV (pre-BR: 4.3+/-0.3, post-BR: 3.7+/-0.2 L, mean+/-SE, p=.01) and peak VO2 (pre-BR: 1.98+/-0.24, post-BR: 1.48 +/-0.21 L/min, p<.01) were reduced after BR. As expected, SO2 decreased with exercise before and after BR. However, SO2 was lower post compared with pre-BR throughout exercise, including at peak exercise (pre-BR: 50+/-3, post-BR: 43+/-4%, p=.01). After BR, [H+] was higher at the start of exercise and did not increase at the same rate as pre-BR. Peak [H+] was not different from pre to post-BR (pre-BR: 36+/-2; post-BR: 38+/-2 nmol/L). CONCLUSIONS: Lower SO2 during exercise suggests that oxygen extraction in the VL is higher after BR, perhaps due to lower circulating blood volume. The higher [H+] after BR suggests a greater reliance upon glycolysis during submaximal exercise, although [H+] at peak exercise was unchanged. Taken together, these data suggest that longer duration BR induces a number of changes that result in peripheral adaptations which contribute to cardiovascular and muscular deconditioning as measured by NIRS-derived SO2 and [H+] in the VL and may contribute to lower post-BR exercise tolerance. Supported by the National Space Biomedical Research Institute through NASA NCC 9-58

Lee, S. M. C.↗
NASA NTRS2003

Rehabilitation After International Space Station Flights

Rehabilitating U.S. crew members to preflight status following flights on the Russian Mir Space Station required longer than six months for full functional recovery of some of the seven crew members. Additional exercise hardware has been added on the International Space Station as well as a rehabilitative emphasis on functional fitness/agility and proprioception. The authors will describe and present the results of the rehabilitation program for ISS and evaluate rehabilitative needs for longer missions. Pre- and in-flight programs emphasize strength and aerobic conditioning. One year before launch, crew members are assigned an Astronaut Strength and Conditioning specialist. Crew members are scheduled for 2 hours, 3 days a week, for pre-flight training and 2.5 hours, six days a week, for in-flight training. Crewmembers are tested on functional fitness, agility, isokinetic strength, and submaximal cycle ergometer evaluation before and after flight. The information from these tests is used for exercise prescriptions, comparison, and evaluation of the astronaut and training programs. The rehabilitation program lasts for 45 days and is scheduled for 2 hours during each crew workday. Phase 1 of the rehabilitation program starts on landing day and places emphasis on ambulation, flexibility, and muscle strengthening. Phase 2 adds proprioceptive exercise and cardiovascular conditioning. Phase 3 (the longest phase) focuses on functional development. All programs are tailored specifically for each individual according to their test results, preferred recreational activities, and mission roles and duties. Most crew members reached or exceeded their preflight test values 45 days after flight. Some crew members subjectively indicated the need for a longer rehabilitation period. The current rehabilitation program for returning ISS crew members seems adequate in content but may need to be extended for longer expeditions.

Chauvin, S. J.↗
NASA NTRS2011

Comparison of Ocular Outcomes in Two 14-Day Bed Rest Studies

Reports of astronauts visual changes raised concern about ocular health during long-duration spaceflight. Some of these findings included hyperopic shifts, choroidal folds, optic disc edema, retinal nerve fiber layer (RNFL) thickening, and cotton wool spots. While the etiology remains unknown, hypotheses speculate that hypertension in the brain caused by cephalad fluid shifts during spaceflight is a possible mechanism for these ocular changes. Head-down tilt (HDT) bed rest is a spaceflight analog that induces cephalad fluid shifts. In addition, previous studies of the HDT position demonstrated body fluid shifts associated with changes in intraocular pressure (IOP). For these reasons, vision monitoring of HDT bed rest subjects was implemented for NASA bed rest studies. Subjects selected for these studies were healthy adults (14 males and 5 females). Average age was 37.5 plus or minus 9.1 years, weight was 77.4 plus or minus 11.3 Kg, and height was 173.4 plus or minus 7.2 14 cm. Controlled conditions followed for all NASA bed rest studies were implemented. These conditions included factors such as eating a standardized diet, maintaining a strict sleep wake cycle, and remaining in bed for 24 hours each day. In one study, subjects maintained a horizontal (0 degree) position while in bed and were exercised six days per week with an integrated resistance and aerobic training (iRAT) program. In the other study, subjects were placed at 6 degrees HDT while in bed and did not engage in exercise. All subjects underwent pre- and post bed rest vision testing. While the battery of vision tests for each study was not identical, measures common to both studies will be presented. These measures included IOP and measures that provided an indication of optic disc swelling as derived from optical coherence tomography (OCT) testing: average retinal nerve fiber layer (RNFL) thickness (millimeters), disc area (square millimeters), rim area (square millimters), and average cup to disc (C/D) ratio. For all measures, there was no significant difference between subject groups for pre-bed rest testing. Post bed rest values also remained similar between groups. Comparison of pre- to post bed rest testing within each group did not demonstrate any statistical differences. These preliminary results from 14-day bed rest studies suggest that the combination of exercise and horizontal bed rest as compared to 6 degrees HDT bed rest did not produce differences in the ocular response with regard to IOP and optic disc parameters. The ocular measures reported here only included pre- and post bed rest time points. Further investigation is needed to examine both the acute response and long term adaptation of structural and functional ocular parameters in the bed rest platform and determine its usefulness for studying spaceflight phenomena. From a clinical perspective, the ability to study ocular responses in the controlled environment of the bed rest platform can provide valuable information for the care of patients restricted to bed rest.

Cromwell, R. L.↗
NASA NTRS2011

Ground and Airborne Methane Measurements Using Optical Parametric Amplifiers

We report on ground and airborne methane measurements with an active sensing instrument using widely tunable, seeded optical parametric generation (OPG). The technique has been used to measure methane, CO2, water vapor, and other trace gases in the near and mid-infrared spectral regions. Methane is a strong greenhouse gas on Earth and it is also a potential biogenic marker on Mars and other planetary bodies. Methane in the Earth's atmosphere survives for a shorter time than CO2 but its impact on climate change can be larger than CO2. Carbon and methane emissions from land are expected to increase as permafrost melts exposing millennial-age carbon stocks to respiration (aerobic-CO2 and anaerobic-CH4) and fires. Methane emissions from c1athrates in the Arctic Ocean and on land are also likely to respond to climate warming. However, there is considerable uncertainty in present Arctic flux levels, as well as how fluxes will change with the changing environment. For Mars, methane measurements are of great interest because of its potential as a strong biogenic marker. A remote sensing instrument that can measure day and night over all seasons and latitudes can localize sources of biogenic gas plumes produced by subsurface chemistry or biology, and aid in the search for extra-terrestrial life. In this paper we report on remote sensing measurements of methane using a high peak power, widely tunable optical parametric generator (OPG) operating at 3.3 micrometers and 1.65 micrometers. We have demonstrated detection of methane at 3.3 micrometers and 1650 nanometers in an open path and compared them to accepted standards. We also report on preliminary airborne demonstration of methane measurements at 1.65 micrometers.

Numata, Kenji↗
NASA NTRS2012

Analog Exercise Hardware to Implement a High Intensity Exercise Program During Bed Rest

Background: In order to evaluate novel countermeasure protocols in a space flight analog prior to validation on the International Space Station (ISS), NASA's Human Research Program (HRP) is sponsoring a multi-investigator bedrest campaign that utilizes a combination of commercial and custom-made exercise training hardware to conduct daily resistive and aerobic exercise protocols. This paper will describe these pieces of hardware and how they are used to support current bedrest studies at NASA's Flight Analog Research Unit in Galveston, TX. Discussion: To implement candidate exercise countermeasure studies during extended bed rest studies the following analog hardware are being utilized: Stand alone Zero-Gravity Locomotion Simulator (sZLS) -- a custom built device by NASA, the sZLS allows bedrest subjects to remain supine as they run on a vertically-oriented treadmill (0-15 miles/hour). The treadmill includes a pneumatic subject loading device to provide variable body loading (0-100%) and a harness to keep the subject in contact with the motorized treadmill to provide a ground reaction force at their feet that is quantified by a Kistler Force Plate. Supine Cycle Ergometer -- a commercially available supine cycle ergometer (Lode, Groningen, Netherlands) is used for all cycle ergometer sessions. The ergometer has adjustable shoulder supports and handgrips to help stabilize the subject during exercise. Horizontal Squat Device (HSD) -- a custom built device by Quantum Fitness Corp (Stafford, TX), the HSD allows for squat exercises to be performed while lying in a supine position. The HSD can provide 0 to 600 pounds of force in selectable 5 lb increments, and allows hip translation in both the vertical and horizontal planes. Prone Leg Curl -- a commercially available prone leg curl machine (Cybex International Inc., Medway, MA) is used to complete leg curl exercises. Horizontal Leg Press -- a commercially available horizontal leg press (Quantum Fitness Corporation) is used for leg press and heel raise exercises. Minor modifications were made to the device including adding 200 lbs to the weight stack, raising the frame by 12 inches, making the footplate adjustable, and providing removable handles. Conclusion: A combination of novel and commercial exercise hardware are used to mimic the exercise hardware capabilities aboard the ISS, allowing scientific investigation of new countermeasure protocols in a space flight analog prior to flight validation

Loerch, Linda↗
NASA NTRS2013

Use of the International Space Station as an Exercise Physiology Lab

The International Space Station (ISS) is now in its prime utilization phase with great opportunity to use the ISS as a lab. With respect to exercise physiology there is considerable research opportunity. Crew members exercise for up to 2 hours per day using a cycle ergometer, treadmill, and advanced resistive exercise device (ARED). There are several ongoing exercise research studies by NASA, ESA and CSA. These include studies related to evaluation of new exercise prescriptions (SPRINT), evaluation of aerobic capacity (VO2max), biomechanics (Treadmill Kinematics), energy expenditure during spaceflight (Energy), evaluation of cartilage (Cartilage), and evaluation of cardiovascular health (Vascular). Examples of how ISS is used for exercise physiology research will be presented.

Ploutz-Snyder, Lori↗
NASA NTRS2013

Countermeasures and Functional Testing in Head-Down Tilt Bed Rest (CFT 70)

This 70‐day bed rest campaign was comprised of 6 integrated studies and conducted at the NASA Flight Analogs Research Unit (FARU). The FARU is located at the University of Texas Medical Branch, Galveston, Texas and is a satellite unit of the Institute for Translational Sciences - Clinical Research Center. This presentation will describe the FARU, discuss the utility of the bed rest platform for use in these studies, and introduce the studies that participated in the CFT 70 bed rest campaign. Information in this presentation will serve as the background for subsequent talks from each individual study. Individual study presentations will discuss preliminary results from completed subjects. Studies included in CFT70 were:  Physiological Factors Contributing to Post Flight Changes in Functional Performance. J. Bloomberg, NASA  Integrated Resistance and Aerobic Training Study. L. Ploutz‐Snyder, USRA  Testosterone Supplementation as a Countermeasure Against Musculoskeletal losses during Space Exploration. R. Urban, University of Texas Medical Branch  Effects of Retronasal Smelling, Variety and Choice on Appetite & Satiety. J. Hunter, Cornell University  AD ASTRA: Automated Detection of Attitudes and States through Transaction Recordings Analysis. C. Miller, Smart Information Flow Technologies, LLC  Bed Rest as a Spaceflight Analog to Study Neuro‐cognitive Changes: Extent, Longevity, and Neural Bases. R. Seidler, University of Michigan

Cromwell, Ronita L.↗
NASA NTRS2014

Peak Oxygen Uptake during and after Long-duration Space Flight

Aerobic capacity (VO2peak) previously has not been measured during or after long-duration spaceflight. PURPOSE: To measure VO2peak and submaximal exercise responses during and after International Space Station (ISS) missions. METHODS: Astronauts (9 M, 5 F: 49 +/- 5 yr, 175 +/- 7 cm, 77.2 +/- 15.1 kg, 40.6 +/- 6.4 mL/kg/min [mean +/-SD]) performed graded peak cycle tests ~90 days before spaceflight, 15 d (FD15) after launch and every ~30 d thereafter during flight, and 1 (R+1), 10 (R+10), and 30 d (R+30) after landing. Oxygen consumption (VO2) and heart rate (HR) were measured from rest to peak exercise, while cardiac output (Q), stroke volume (SV), and arterial-venous oxygen difference (a-vO2diff) were measured only during rest and submaximal exercise. Data were analyzed using mixed-model linear regression. Body mass contributed significantly to statistical models, and thus results are reported as modeled estimates for an average subject. RESULTS: Early inflight (FD15) VO2peak was 17% lower (95% CI = - 22%, -13%) than preflight. VO2peak increased during spaceflight (0.001 L/min/d, P = 0.02) but did not return to preflight levels. On R+1 VO2peak was 15% (95% CI = -19%, -10%) lower than preflight but recovered to within 2% of preflight by R+30 (95% CI = -6%, +3%). Peak HR was not significantly different from preflight at any time. Inflight submaximal VO2 and a-vO2diff were generally lower than preflight, but the Q vs. VO2 slope was unchanged. In contrast, the SV vs. VO2 slope was lower (P < 0.001), primarily due to elevated SV at rest, and the HR vs. VO2 slope was greater (P < 0.001), largely due to elevated HR during more intense exercise. On R+1 although the relationships between VO2 and Q, SV, and HR were not statistically different than preflight, resting and submaximal exercise SV was lower (P < 0.001), resting and submaximal exercise HR was higher (P < 0.002), and a-vO2diff was unchanged. HR and SV returned to preflight levels by R+30. CONCLUSION: In the average astronaut VO2peak was reduced during spaceflight and immediately after landing but factors contributing to lower VO2peak may be different during spaceflight and recovery. Maintaining Q while VO2 is reduced inflight may be suggestive of an elevated blood flow to vascular beds other than exercising muscles, but decreased SV after flight likely reduces Q at peak exertion.

Moore, Alan D., Jr.↗
NASA NTRS2014

A Case for Hypogravity Studies Aboard ISS

Future human space exploration missions being contemplated by NASA and other spacefaring nations include some that would require long stays upon bodies having gravity levels much lower than that of Earth. While we have been able to quantify the physiological effects of sustained exposure to microgravity during various spaceflight programs over the past half-century, there has been no opportunity to study the physiological adaptations to gravity levels between zero-g and one-g. We know now that the microgravity environment of spaceflight drives adaptive responses of the bone, muscle, cardiovascular, and sensorimotor systems, causing bone demineralization, muscle atrophy, reduced aerobic capacity, motion sickness, and malcoordination. All of these outcomes can affect crew health and performance, particularly after return to a one-g environment. An important question for physicians, scientists, and mission designers planning human exploration missions to Mars (3/8 g), the Moon (1/6 g), or asteroids (likely negligible g) is: What protection can be expected from gravitational levels between zero-g and one-g? Will crewmembers deconditioned by six months of microgravity exposure on their way to Mars experience continued deconditioning on the Martian surface? Or, will the 3/8 g be sufficient to arrest or even reverse these adaptive changes? The implications for countermeasure deployment, habitat accommodations, and mission design warrant further investigation into the physiological responses to hypogravity. It is not possible to fully simulate hypogravity exposure on Earth for other than transient episodes (e.g., parabolic flight). However, it would be possible to do so in low Earth orbit (LEO) using the centrifugal forces produced in a live-aboard centrifuge. As we're not likely to launch a rotating human spacecraft into LEO anytime in the near future, we could take advantage of rodent subjects aboard the ISS if we had a centrifuge that could accommodate the rodent subjects for extended periods (weeks to months) at various hypogravity levels. Experiments aboard such a centrifuge could provide important insight into human exploration questions and simultaneously answer fundamental questions in gravitational physiology.

Paloski, William H.↗
NASA NTRS2014

VIIP Bedrest Analog Roadmap

The objective is to define successive bed rest campaigns leading to a potential VIIP (Vision Impairment and Intracranial Pressure) countermeasure. To determine if the analog is successful, changes need to occur in the following outcome measures (dependent variables): Intracranial pressure; Retinal nerve fiber layer; Choroidal engorgement; Globe flattening; Axial biometry; Optic nerve sheath diameter distention; Cycloplegic refraction; Visual acuity. Study parameters (independent variables) to include: CO2; Sodium; Exercise (resistive & aerobic); Strict tilt angle.

Villarreal, Jennifer D.↗