Effects of Long-duration Microgravity and Gravitational Transitions on Fine Motor Skills.

OBJECTIVE: Assess the effects of long-duration microgravity and gravitational transitions on fine motor skills using a tablet-based test battery of four fine motor tasks: Pointing, Dragging, Shape Tracing, and Pinch-Rotate. BACKGROUND: While there have been some studies on fine motor skills in microgravity, few have measured the fine motor skills that are core components of interaction with computer-based devices, and none have measured performance systematically, to include preflight, inflight, and postflight space mission time periods. METHODS: Seven astronauts completed the Fine Motor Skills test battery 30-40 times before, during, and up to 30 days after standard duration International Space Station missions, while a matching set of seven ground-based control participants also completed the battery over a comparable period of time. Response time and accuracy were the primary outcome measures. RESULTS: Relative to controls, astronauts experienced fine motor skill decrements at gravitational transitions (first week on orbit, and first month post landing). No decrements were found inflight after the first week of adaptation. CONCLUSION: Gravitational transitions appear to negatively impact fine motor skills needed to operate small controls with accuracy, such as those on touchscreen interfaces. This raises concerns for future long-duration crewmembers who will land on a planetary surface and need to perform critical tasks accurately, such as configuring spacesuits, powering up a habitat, or teleoperating rovers. APPLICATION: Results from this study highlight the need for confirmatory research, and the possible need for countermeasure development. The Fine Motor Skills test battery may have application outside of NASA as a fine motor skills diagnostic screening, rehabilitation, or readiness-to-perform tool.

DNA Damage and Radiosensitivity in Blood Cells from Subjects Undergoing 45 Days of Isolation and Confinement: An Explorative Study.

The effect of confined and isolated experience on astronauts' health is an important factor to consider for future space exploration missions. The more confined and isolated humans are, the more likely they are to develop negative behavioral or cognitive conditions such as a mood decline, sleep disorder, depression, fatigue and/or physiological problems associated with chronic stress. Molecular mediators of chronic stress, such as cytokines, stress hormones or reactive oxygen species (ROS) are known to induce cellular damage including damage to the DNA. In view of the growing evidence of chronic stress-induced DNA damage, we conducted an explorative study and measured DNA strand breaks in 20 healthy adults. The participants were grouped into five teams (missions). Each team was composed of four participants, who spent 45 days in isolation and confinement in NASA's Human Exploration Research Analog (HERA). Endogenous DNA integrity, ex-vivo radiation-induced DNA damage and the rates of DNA repair were assessed every week. Our results show a high inter-individual variability as well as differences between the missions, which cannot be explained by inter-individual variability alone. The ages and sex of the participants did not appear to influence the results.

A novel approach for establishing fitness standards for occupational task performance.

PURPOSE: To identify strength and performance thresholds below which task performance is impaired. METHODS: A new weighted suit system was used to manipulate strength-to-body-weight ratio during the performance of simulated space explorations tasks. Statistical models were used to evaluate various measures of muscle strength and performance on their ability to predict the probability that subjects could complete the tasks in an acceptable amount of time. Thresholds were defined as the point of greatest change in probability per change in the predictor variable. For each task, median time was used to define the boundary between "acceptable" and "unacceptable" completion times. RESULTS: Fitness thresholds for four space explorations tasks were identified using 23 physiological input variables. Area under receiver operator characteristic curves varied from a low of 0.68 to a high of 0.92. CONCLUSION: An experimental analog for altering strength-to-body weight combined with a probability-based statistical model for success was suitable for identifying thresholds for task performance below which tasks could either not be completed or time to completion was unacceptably high. These results provide data for strength recommendations for exploration mission ambulatory task performance. Furthermore, the approach can be used to identify thresholds for other areas where occupationally relevant tasks vary considerably.

Single-Cell RNA-Sequencing Identifies Activation of TP53 and STAT1 Pathways in Human T Lymphocyte Subpopulations in Response to Ex Vivo Radiation Exposure.

Detrimental health consequences from exposure to space radiation are a major concern for long-duration human exploration missions to the Moon or Mars. Cellular responses to radiation are expected to be heterogeneous for space radiation exposure, where only high-energy protons and other particles traverse a fraction of the cells. Therefore, assessing DNA damage and DNA damage response in individual cells is crucial in understanding the mechanisms by which cells respond to different particle types and energies in space. In this project, we identified a cell-specific signature for radiation response by using single-cell transcriptomics of human lymphocyte subpopulations. We investigated gene expression in individual human T lymphocytes 3 h after ex vivo exposure to 2-Gy gamma rays while using the single-cell sequencing technique (10X Genomics). In the process, RNA was isolated from ~700 irradiated and ~700 non-irradiated control cells, and then sequenced with ~50 k reads/cell. RNA in each of the cells was distinctively barcoded prior to extraction to allow for quantification for individual cells. Principal component and clustering analysis of the unique molecular identifier (UMI) counts classified the cells into three groups or sub-types, which correspond to CD4+, naïve, and CD8+/NK cells. Gene expression changes after radiation exposure were evaluated using negative binomial regression. On average, BBC3, PCNA, and other TP53 related genes that are known to respond to radiation in human T cells showed increased activation. While most of the TP53 responsive genes were upregulated in all groups of cells, the expressions of IRF1, STAT1, and BATF were only upregulated in the CD4+ and naïve groups, but were unchanged in the CD8+/NK group, which suggests that the interferon-gamma pathway does not respond to radiation in CD8+/NK cells. Thus, single-cell RNA sequencing technique was useful for simultaneously identifying the expression of a set of genes in individual cells and T lymphocyte subpopulation after gamma radiation exposure. The degree of dependence of UMI counts between pairs of upregulated genes was also evaluated to construct a similarity matrix for cluster analysis. The cluster analysis identified a group of TP53-responsive genes and a group of genes that are involved in the interferon gamma pathway, which demonstrate the potential of this method for identifying previously unknown groups of genes with similar expression patterns.

Synergistic Effects of Weightlessness, Isoproterenol, and Radiation on DNA Damage Response and Cytokine Production in Immune Cells.

The implementation of rotating-wall vessels (RWVs) for studying the effect of lack of gravity has attracted attention, especially in the fields of stem cells, tissue regeneration, and cancer research. Immune cells incubated in RWVs exhibit several features of immunosuppression including impaired leukocyte proliferation, cytokine responses, and antibody production. Interestingly, stress hormones influence cellular immune pathways affected by microgravity, such as cell proliferation, apoptosis, DNA repair, and T cell activation. These pathways are crucial defense mechanisms that protect the cell from toxins, pathogens, and radiation. Despite the importance of the adrenergic receptor in regulating the immune system, the effect of microgravity on the adrenergic system has been poorly studied. Thus, we elected to investigate the synergistic effects of isoproterenol (a sympathomimetic drug), radiation, and microgravity in nonstimulated immune cells. Peripheral blood mononuclear cells were treated with the sympathomimetic drug isoproterenol, exposed to 0.8 or 2 Gy γ-radiation, and incubated in RWVs. Mixed model regression analyses showed significant synergistic effects on the expression of the ß2-adrenergic receptor gene (ADRB2). Radiation alone increased ADRB2 expression, and cells incubated in microgravity had more DNA strand breaks than cells incubated in normal gravity. We observed radiation-induced cytokine production only in microgravity. Prior treatment with isoproterenol clearly prevents most of the microgravity-mediated effects. RWVs may be a useful tool to provide insight into novel regulatory pathways, providing benefit not only to astronauts but also to patients suffering from immune disorders or undergoing radiotherapy.

Reactivation of Latent Epstein-Barr Virus: A Comparison after Exposure to Gamma, Proton, Carbon, and Iron Radiation.

Among the many stressors astronauts are exposed to during spaceflight, cosmic radiation may lead to various serious health effects. Specifically, space radiation may contribute to decreased immunity, which has been documented in astronauts during short- and long-duration missions, as evidenced by several changes in cellular immunity and plasma cytokine levels. Reactivation of latent herpes viruses, either directly from radiation of latently infected cells and/or from perturbation of the immune system, may result in disease in astronauts. Epstein‒Barr virus (EBV) is one of the eight human herpes viruses known to infect more than 90% of human adults and persists for the life of the host without normally causing adverse effects. Reactivation of several latent viruses in astronauts is well documented, although the mechanism of reactivation is not well understood. We studied the effect of four different types of radiation, (1) 137Cs gamma rays, (2) 150-MeV protons, (3) 600 MeV/n carbon ions, and (4) 600 MeV/n iron ions on the activation of lytic gene transcription and of reactivation of EBV in a latently infected cell line (Akata) at doses of 0.1, 0.5, 1.0, and 2.0 Gy. The data showed that for all doses used in this study, lytic gene transcription was induced and median viral loads were significantly higher for all types of radiation than in corresponding control samples, with the increases detected as early as four days post-exposure and generally tapering off at later time points. The viability and size of EBV-infected Akata cells were highly variable and exhibited approximately the same trend in time for all radiation types at 0.1, 0.5, 1.0, and 2.0 Gy. This work shows that reactivation of viruses can occur due to the effect of different types of radiation on latently infected cells in the absence of changes or cytokines produced in the immune system. In general, gamma rays are more effective than protons, carbon ions, and iron ions in inducing latent virus reactivation, though these high-energy particles did induce more sustained and later reactivation of EBV lytic gene transcription. These findings also challenge the common relative biological effectiveness concept that is often used in radiobiology for other end points.

Probability of hypobaric decompression sickness including extreme exposures.

INTRODUCTION: The fitting of probabilistic decompression sickness (DCS) models is more effective when data encompass a wide range of DCS incidence. We obtained such data from the Air Force Research Laboratory Altitude Decompression Sickness Research Database. The data are results from 29 tests comprising 708 human altitude chamber exposures (536 men and 172 women). There were 340 DCS outcomes with per-test DCS incidence ranging from 0 to 88%. The tests were characterized by direct ascent at a rate of 5000 ft x min(-1) (1524 m x min(-1)) to a range of altitudes (226 to 378 mmHg) for 4 h after prebreathe times of varying length and with varying degrees of physical activity while at altitude. METHODS: Logistic regression was used to develop an expression for the probability of DCS [P(DCS)] using the Hill equation with decompression dose as the main predictor. Here, decompression dose is defined in terms of either the tissue ratio (TR) or a bubble growth index (BGI). Other predictors in the model were gender and peak exercise intensity at altitude. RESULTS: All three predictors (decompression dose, gender, and exercise intensity) were important contributions to the model for P(DCS). DISCUSSION: Higher TR or BGI, male gender, and higher exercise intensity at altitude all increased the modeled decompression dose. Using either TR or BGI to define decompression dose provided comparable results, suggesting that a simple TR is adequate for simple altitude exposures as an abstraction of the true decompression dose. The model is primarily heuristic and limits estimates of P(DCS) to only a 4-h exposure.

Effects of exercise countermeasures on multisystem function in long duration spaceflight astronauts.

Exercise training is a key countermeasure used to offset spaceflight-induced multisystem deconditioning. Here, we evaluated the effects of exercise countermeasures on multisystem function in a large cohort (N = 46) of astronauts on long-duration spaceflight missions. We found that during 178 ± 48 d of spaceflight, ~600 min/wk of aerobic and resistance exercise did not fully protect against multisystem deconditioning. However, substantial inter-individual heterogeneity in multisystem response was apparent with changes from pre to postflight ranging from -30% to +5%. We estimated that up to 17% of astronauts would experience performance-limiting deconditioning if current exercise countermeasures were used on future spaceflight missions. These findings support the need for refinement of current countermeasures, adjunct interventions, or enhanced requirements for preflight physiologic and functional capacity for the protection of astronaut health and performance during exploration missions to the moon and beyond.

Response of Arabidopsis thaliana and Mizuna Mustard Seeds to Simulated Space Radiation Exposures.

One of the major concerns for long-term exploration missions beyond the Earth's magnetosphere is consequences from exposures to solar particle event (SPE) protons and galactic cosmic rays (GCR). For long-term crewed Lunar and Mars explorations, the production of fresh food in space will provide both nutritional supplements and psychological benefits to the astronauts. However, the effects of space radiation on plants and plant propagules have not been sufficiently investigated and characterized. In this study, we evaluated the effect of two different compositions of charged particles-simulated GCR, and simulated SPE protons on dry and hydrated seeds of the model plant Arabidopsis thaliana and the crop plant Mizuna mustard [Brassica rapa var. japonica]. Exposures to charged particles, simulated GCRs (up to 80 cGy) or SPEs (up to 200 cGy), were performed either acutely or at a low dose rate using the NASA Space Radiation Laboratory (NSRL) facility at Brookhaven National Lab (BNL). Control and irradiated seeds were planted in a solid phytogel and grown in a controlled environment. Five to seven days after planting, morphological parameters were measured to evaluate radiation-induced damage in the seedlings. After exposure to single types of charged particles, as well as to simulated GCR, the hydrated Arabidopsis seeds showed dose- and quality-dependent responses, with heavier ions causing more severe defects. Seeds exposed to simulated GCR (dry seeds) and SPE (hydrated seeds) had significant, although much less damage than seeds exposed to heavier and higher linear energy transfer (LET) particles. In general, the extent of damage depends on the seed type.

On-orbit prospective echocardiography on International Space Station crew.

OBJECTIVES: A prospective trial of echocardiography was conducted on six crew members onboard the International Space Station. The main objective was to determine the efficacy of remotely guided tele-echocardiography, including just-in-time e-training methods and determine what is "space normal" echocardiographic data. METHODS: Each crew member operator (n = 6) had 2-hour preflight training. Baseline echocardiographic data were collected 55-167 days preflight. Similar equipment was used in each 60-minute in-flight session (mean microgravity exposure--114 days [34--190]). On-orbit ultrasound (US) operators used an e-learning system within 24 hours of these sessions. Expert assistance was provided using US video downlink and two-way voice. Testing was repeated 5-16 days after landing. Separate ANOVA was used on each echocardiographic variable (n = 33). Within each ANOVA, three tests were made: (a) effect of mission phase (preflight, in-flight, postflight); (b) effect of echo technician (two technicians independently analyzed the data); (c) interaction between mission phase and technician. RESULTS: Eleven rejections of the null hypothesis (mission phase or technician or both had no effect) were found that could be considered for possible follow up. Of these, eight rejections were for significant technician effects, not space flight. Three rejections of the null hypothesis (aortic valve time velocity integral, mitral E-wave velocity, and heart rate) were attributable to space flight but determine to not be clinically significant. No rejections were due to the interaction between technician and space flight. CONCLUSION: Thus, we found no consistent clinically significant effects of long-duration space flight on echocardiographic variables of the given group of subjects.

Sonography for determining the optic nerve sheath diameter with increasing intracranial pressure in a porcine model.

OBJECTIVES: This study investigated whether it is feasible to use sonography to monitor changes in the optic nerve sheath diameter in a porcine model. METHODS: A fiber-optic intracranial pressure transducer was surgically placed through the frontal sinus directly into the brain parenchyma of adult Yorkshire pigs (n = 5). A second bolt was placed on the contralateral side for intraparenchymal fluid infusion. Optic nerve sheath diameter measurements were acquired by each of 2 ultrasound operators around the leading edge of the nerve, 3 to 5 mm distal from the origin of the optic nerve. To induce a change in diameter, intracranial pressure was manipulated by injecting normal saline into the intraparenchymal infusion catheter located in the symmetric contralateral position as the pressure-monitoring probe. RESULTS: Data from 1 pig were unusable because of a cerebrospinal fluid leak into the sinus and orbital fissure. Saline aliquots of 1 to 10 mL were able to generate intracranial pressures typically starting from 10 to 15 mm Hg and increasing to 75 to 90 mm Hg, which eventually evoked a Cushing response. Fluid injection was controlled to increase pressures by 60 mm Hg over a 15- to 20-minute period. Regression analysis of all animals showed that the optic nerve sheath diameter increased by 0.0034 mm/mm Hg of intracranial pressure; however, this slope ranged from 0.0025 to 0.0046, depending on the animal measured. There was no discernible effect of the ultrasound operator on the slope; however, measurements made by 1 operator were consistently higher than the others by about 8% of the overall diameter range. CONCLUSIONS: These results suggest that the use of the optic nerve sheath diameter to noninvasively confirm acute changes in intracranial pressure over 1 hour is feasible in a porcine model. We recommend that this method be validated in humans using direct intracranial pressure measurement where possible to confirm it as a screening tool for acute and chronically increased diameters secondary to elevated pressure in clinical settings.

Predicting chromosome damage in astronauts participating in international space station missions.

Space radiation consists of energetic protons and other heavier ions. During the International Space Station program, chromosome aberrations in lymphocytes of astronauts have been analyzed to estimate received biological doses of space radiation. More specifically, pre-flight blood samples were exposed ex vivo to varying doses of gamma rays, while post-flight blood samples were collected shortly and several months after landing. Here, in a study of 43 crew-missions, we investigated whether individual radiosensitivity, as determined by the ex vivo dose-response of the pre-flight chromosome aberration rate (CAR), contributes to the prediction of the post-flight CAR incurred from the radiation exposure during missions. Random-effects Poisson regression was used to estimate subject-specific radiosensitivities from the preflight dose-response data, which were in turn used to predict post-flight CAR and subject-specific relative biological effectiveness (RBEs) between space radiation and gamma radiation. Covariates age, gender were also considered. Results indicate that there is predictive value in background CAR as well as radiosensitivity determined preflight for explaining individual differences in post-flight CAR over and above that which could be explained by BFO dose alone. The in vivo RBE for space radiation was estimated to be approximately 3 relative to the ex vivo dose response to gamma irradiation. In addition, pre-flight radiosensitivity tended to be higher for individuals having a higher background CAR, suggesting that individuals with greater radiosensitivity can be more sensitive to other environmental stressors encountered in daily life. We also noted that both background CAR and radiosensitivity tend to increase with age, although both are highly variable. Finally, we observed no significant difference between the observed CAR shortly after mission and at > 6 months post-mission.

Joint modeling of performance and subjective reporting to assess sensitivity to drug-induced sleepiness.

In an NASA ground study, two forms of cognitive tests were evaluated in terms of their sensitivity to sleepiness induced by the drug promethazine (PMZ). Performance for the two test modes (Y(1) and Y(2)), PMZ concentration, and a self-reported sleepiness using the Karolinska Sleepiness Scale (KSS) were monitored for 12 h post dose. A problem arises when using KSS to establish an association between true sleepiness and performance because KSS scores are discrete and also because they tend to concentrate on certain values. Therefore, we define a latent sleepiness measure X as an unobserved continuous random variable describing a subject's actual state of sleepiness. Under the assumption that drug concentration affects X, which then affects Y(1), Y(2), and KSS, we use Bayesian methods to estimate joint equations that permit unbiased comparison of the performance measures' sensitivity to X. The equations incorporate subject random effects and include a negativity constraint on subject-specific slopes of performance with respect to sleepiness.

Locomotor function after long-duration space flight: effects and motor learning during recovery.

Astronauts returning from space flight and performing Earth-bound activities must rapidly transition from the microgravity-adapted sensorimotor state to that of Earth's gravity. The goal of the current study was to assess locomotor dysfunction and recovery of function after long-duration space flight using a test of functional mobility. Eighteen International Space Station crewmembers experiencing an average flight duration of 185 days performed the functional mobility test (FMT) pre-flight and post-flight. To perform the FMT, subjects walked at a self selected pace through an obstacle course consisting of several pylons and obstacles set up on a base of 10-cm-thick, medium-density foam for a total of six trials per test session. The primary outcome measure was the time to complete the course (TCC, in seconds). To assess the long-term recovery trend of locomotor function after return from space flight, a multilevel exponential recovery model was fitted to the log-transformed TCC data. All crewmembers exhibited altered locomotor function after space flight, with a median 48% increase in the TCC. From the fitted model we calculated that a typical subject would recover to 95% of his/her pre-flight level at approximately 15 days post-flight. In addition, to assess the early motor learning responses after returning from space flight, we modeled performance over the six trials during the first post-flight session by a similar multilevel exponential relation. We found a significant positive correlation between measures of long-term recovery and early motor learning (P < 0.001) obtained from the respective models. We concluded that two types of recovery processes influence an astronaut's ability to re-adapt to Earth's gravity environment. Early motor learning helps astronauts make rapid modifications in their motor control strategies during the first hours after landing. Further, this early motor learning appears to reinforce the adaptive realignment, facilitating re-adaptation to Earth's 1-g environment on return from space flight.

Accuracy of advanced versus strictly conventional 12-lead ECG for detection and screening of coronary artery disease, left ventricular hypertrophy and left ventricular systolic dysfunction.

BACKGROUND: Resting conventional 12-lead ECG has low sensitivity for detection of coronary artery disease (CAD) and left ventricular hypertrophy (LVH) and low positive predictive value (PPV) for prediction of left ventricular systolic dysfunction (LVSD). We hypothesized that a approximately 5-min resting 12-lead advanced ECG test ("A-ECG") that combined results from both the advanced and conventional ECG could more accurately screen for these conditions than strictly conventional ECG. METHODS: Results from nearly every conventional and advanced resting ECG parameter known from the literature to have diagnostic or predictive value were first retrospectively evaluated in 418 healthy controls and 290 patients with imaging-proven CAD, LVH and/or LVSD. Each ECG parameter was examined for potential inclusion within multi-parameter A-ECG scores derived from multivariate regression models that were designed to optimally screen for disease in general or LVSD in particular. The performance of the best retrospectively-validated A-ECG scores was then compared against that of optimized pooled criteria from the strictly conventional ECG in a test set of 315 additional individuals. RESULTS: Compared to optimized pooled criteria from the strictly conventional ECG, a 7-parameter A-ECG score validated in the training set increased the sensitivity of resting ECG for identifying disease in the test set from 78% (72-84%) to 92% (88-96%) (P < 0.0001) while also increasing specificity from 85% (77-91%) to 94% (88-98%) (P < 0.05). In diseased patients, another 5-parameter A-ECG score increased the PPV of ECG for LVSD from 53% (41-65%) to 92% (78-98%) (P < 0.0001) without compromising related negative predictive value. CONCLUSION: Resting 12-lead A-ECG scoring is more accurate than strictly conventional ECG in screening for CAD, LVH and LVSD.

Risk of herniated nucleus pulposus among U.S. astronauts.

INTRODUCTION: Astronauts have complained of back pain occurring during spaceflight, presumably due to the elongation of the spine from the lack of gravity. Herniated nucleus pulposus (HNP) is known to occur in aviators exposed to high Gz and has been diagnosed in several astronauts in the immediate post-spaceflight period. It is unknown whether astronauts exposed to microgravity are at added risk for developing HNP in the post-spaceflight period due to possible in-flight intervertebral disc changes. METHODS: For a preset study period, incidence rates of HNP were compared between the U.S. astronaut population and a matched control population not involved in spaceflight using the Longitudinal Study of Astronaut Health database. Using a Weibull survival model, time trends of the risk of HNP prior to and after spaceflight were compared within the astronaut group. HNP incidences in other populations that have previously been reported in the literature were also compared with results in this study. RESULTS: The incidence of HNP was 4.3 times higher in the U.S. astronaut population (N=321) compared to matched controls (N=983) not involved in spaceflight. For astronauts, there was relatively more HNP in the cervical region of the spine (18 of 44) than for controls (3 of 35); however, there was no clear increase of HNP incidence in those astronauts who were high performance jet aircraft pilots. There was evidence suggesting that the risk is increased immediately after spaceflight. CONCLUSIONS: Astronauts are at higher risk of incurring HNP, especially immediately following spaceflight.

Diagnostic accuracy of dynamic posturography testing after short-duration spaceflight.

INTRODUCTION: Astronauts face transient disruptions of sensorimotor functions after spaceflight. Computerized dynamic posturography (CDP) testing has been used to document functional recovery; however, its objective value in return-to-duty decision-making has not been established. Therefore, we studied the diagnostic accuracy of CDP to determine the most effective test components for probing post-spaceflight sensorimotor deficits. METHODS: There were 11 first-time astronauts and 11 matched controls who were evaluated by CDP before and after spaceflight (controls did not fly). All CDP testing was conducted with eyes closed while standing on a computer-controlled force plate. Somatosensory influences were either unperturbed (stationary force plate) or altered (unstable force plate), and vestibular influences were either unperturbed (head erect) or altered by static (head pitched forward or back by 200) or dynamic (head pitched voluntarily in cadence with an auditory signal: +/- 20 degrees at 0.33 Hz) challenges. Using equilibrium (EQ) scores derived from peak A-P sway as the dependent measure, we determined the sensitivity and specificity of each test condition and then constructed receiver operator characteristic (ROC) curves to determine their diagnostic accuracies. RESULTS: The greatest diagnostic accuracy was obtained from the test requiring the subject to make dynamic head movements while standing on an unstable force plate (94.9% sensitivity 96.6% specificity, area under ROC curve = 0.991). By contrast, the estimated ROC area for the standard clinical Romberg test (fixed support, head erect), which is often used to make postflight return-to-duty decisions, was 0.718. CONCLUSION: We recommend that results from this test paradigm be considered during postflight return-to-duty decision-making.

Efficacy of Gradient Compression Garments in the Hours After Long-Duration Spaceflight.

The incidence of presyncopal events is high soon after a long-duration spaceflight;>60% of returning astronauts could not complete a 10-min 80° head-up tilt test on landing day (R+0) after ~6 months of spaceflight. The objective of this study was to demonstrate the ability of a lower body gradient compression garment (GCG) to protect against an excessive increase in heart rate and a decrease in blood pressure during standing after long-duration spaceflight. Methods: Eleven astronauts (9 M, 2 F) volunteered to participate. The stand test protocol consisted of 2 min of prone rest followed by 3.5 min of standing. Subjects completed one familiarization session, two preflight data collection sessions in standard clothing, and three tests on landing day while wearing GCG. Postflight tests were conducted 1-4 h (R+0A), ~12 h (R+0B), and ~28 h after landing (R+0C). Results: All astronauts completed the stand test preflight. Three astronauts were unable to attempt the stand test at R+0A, and one of these was unable to start the test at R+0B. One astronaut was unable to complete 3.5 min of standing at R+0B (test ended at 3.3 min). Review of the individual's blood pressure data revealed no hypotension but the astronaut reported significant motion sickness. Of the astronauts who participated in testing on landing day, the heart rate and mean arterial pressure responses to standing (stand-prone) were not different than preflight at any of the postflight sessions. Conclusion: Wearing the GCG after spaceflight prevented the tachycardia that normally occurs while standing after spaceflight without compression garments and protected against a decrease in blood pressure during a short stand test.

Arterial structure and function during and after long-duration spaceflight.

Spaceflight missions expose astronauts to increased risk of oxidative stress and inflammatory damage that might accelerate the development of asymptomatic cardiovascular disease. The purpose of this investigation was to determine whether long-duration spaceflight (>4 mo) results in structural and functional changes in the carotid and brachial arteries. Common carotid artery (CCA) intima-media thickness (cIMT), CCA distensibility and stiffness, and brachial artery endothelium-dependent and -independent vasodilation were measured in 13 astronauts (10 men, 3 women) ~180 and 60 days before launch, during the mission on ~15, 60, and 160 days of spaceflight, and within 1 wk after landing. Biomarkers of oxidative stress and inflammation were measured at corresponding times in fasting blood samples and urine samples from 24- or 48-h pools. Biomarkers of oxidative stress and inflammation increased during spaceflight, but most returned to preflight levels within 1 wk of landing. Mean cIMT, CCA stiffness, and distensibility were not significantly different from preflight at any time. As a group, neither mean endothelium-dependent nor -independent vasodilation changed from preflight to postflight, but changes within individuals in endothelial function related to some biomarkers of oxidative stress. Whereas biomarkers of oxidative stress and inflammation are elevated during spaceflight, CCA and brachial artery structure and function were not changed by spaceflight. It is unclear whether future exploration missions, with an extended duration in altered gravity fields and higher radiation exposure, may be problematic.NEW & NOTEWORTHY Carotid artery structure and stiffness did not change on average in astronauts during long-duration spaceflight (<12 mo), despite increased oxidative stress and inflammation. Most oxidative stress and inflammation biomarkers returned to preflight levels soon after landing. Brachial artery structure and function also were unchanged by spaceflight. In this group of healthy middle-aged male and female astronauts, spaceflight in low Earth orbit does not appear to increase long-term cardiovascular health risk.