STEM TODAY July 2017, No.22
STEM TODAY July 2017 , No.22
CONTENTS OPÂ04: We do not know the extent to which spaceflight deconditioning decreases injury tolerance for dynamic loads
Editorial Editor: Mr. Abhishek Kumar Sinha Editor / Technical Advisor: Mr. Martin Cabaniss
STEM Today, July 2017, No.22
Disclaimer ( Non-Commercial Publications ) STEM Today is dedicated for STEM Education and Human Spaceflight. This newsletter is designed for Teachers and Students with interests in Human Spaceflight and learning about NASA’s Human Research Roadmap. The opinion expressed in this newsletter is the opinion based on fact or knowledge gathered from various research articles. Appropriate credit is given to its original authors. The results or information included in this newsletter are from various research articles and appropriate credits are added. The citation of articles are included in Reference Section. The newsletter is not sold for a profit or included in another media or publication that is sold for a profit. Cover Page Starry Night and Aurora Expedition 52 Flight Engineer Jack Fischer of NASA photographed the glowing nighttime lights of an aurora from his vantage point in the International Space Station’s cupola module on June 19, 2017. Part of the station’s solar array is also visible. Image Credit: NASA
Back Cover Deployment of the Space Station’s Roll Out Solar Array Experiment Over the weekend of June 17-18, 2017, engineers on the ground remotely operated the International Space Station’s robotic Canadarm2 to extract the Roll Out Solar Array (ROSA) experiment from the SpaceX Dragon resupply ship. The experiment will remain attached to the Canadarm2 over seven days to test the effectiveness of ROSA, an advanced, flexible solar array that rolls out like a tape measure. Traditional solar panels used to power satellites can be bulky with heavy panels folded together using mechanical hinges. This new solar array’s design rolls up to form a compact cylinder for launch with significantly less mass and volume, potentially offering substantial cost savings as well as an increase in power for satellites. ROSA was developed as part of the Solar Electric Propulsion project sponsored by NASA’s Space Technology Mission Directorate. NASA tested the ROSA technology in vacuum chambers on Earth several years ago, and this is its first test in space. This solar array technology was developed to power large spacecraft using highlyefficient electric propulsion on missions to deep space including Mars and the moon. Image Credit: NASA
STEM Today , July 2017
Editorial Dear Reader
STEM Today, July 2017, No.22
All young people should be prepared to think deeply and to think well so that they have the chance to become the innovators, educators, researchers, and leaders who can solve the most pressing challenges facing our world, both today and tomorrow. But, right now, not enough of our youth have access to quality STEM learning opportunities and too few students see these disciplines as springboards for their careers. According to Marillyn Hewson, "Our children - the elementary, middle and high school students of today - make up a generation that will change our universe forever. This is the generation that will walk on Mars, explore deep space and unlock mysteries that we can’t yet imagine". "They won’t get there alone. It is our job to prepare, inspire and equip them to build the future - and that’s exactly what Generation Beyond is designed to do." STEM Today will inspire and educate people about Spaceflight and effects of Spaceflight on Astronauts. Editor Mr. Abhishek Kumar Sinha
Editorial Dear Reader The Science, Technology, Engineering and Math (STEM) program is designed to inspire the next generation of innovators, explorers, inventors and pioneers to pursue STEM careers. According to former President Barack Obama, " Science is more than a school subject, or the periodic table, or the properties of waves. It is an approach to the world, a critical way to understand and explore and engage with the world, and then have the capacity to change that world..." STEM Today addresses the inadequate number of teachers skilled to educate in Human Spaceflight. It will prepare , inspire and educate teachers about Spaceflight. STEM Today will focus on NASA’S Human Research Roadmap. It will research on long duration spaceflight and put together latest research in Human Spaceflight in its monthly newsletter. Editor / Technical Advisor Mr. Martin Cabaniss
STEM Today, July 2017, No.22
Human Factors and Behavioral Performance (HFBP) OP-04: We do not know the extent to which space ight deconditioning decreases injury tolerance for dynamic loads Space ight deconditioning has been shown to cause decrements in bone and muscle. How these decrements translate to injury risk due to dynamic loads is unknown. Currently deconditioning factors are used, but there is insu cient data available to assess the e cacy of these factors.
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Lumbar Spine PSM and IVD Height Changes in Astronauts
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The lumbar paraspinal muscles (PSM) provide postural stability, enabling gait and supporting upper extremity movements. They are critical to function in a gravitational environment. In particular, these muscles facilitate vertebral motion, and protect articular structures, discs, and ligaments from excessive strain and injury. Atrophy of these muscles is evidenced by altered fat content, cross-sectional area (CSA), and higher proportions of type II fast-twitch fibers, and is strongly associated with low back pain on Earth. How these muscles function and respond during space flight is, however, not well described.
With microgravity exposure in space, several spine related issues are observed among crewmembers. The torso lengthens 4 to 6 cm, approximately 2 to 3 times the normal diurnal increase (1-2 cm) on Earth. This reportedly occurs because of spinal unloading, flattening of spinal curvature, loss of paravertebral muscle tone, and vertebral disc degeneration. Flight medical data indicate that more than half of the US astronauts report spine pain during their mission. While in space, astronauts report that a lumbar flexed, "fetal tuck" position to stretch is the most effective way of alleviating back pain. The back pain is described with a moderate to severe level of intensity for 14% to 28% percent of the US astronauts. Shuttle crewmembers described pain lasting for 15% to 100% of their mission. The location of pain is reported most frequently in the following anatomic regions: 50% low back, 11% midback, 11% neck, and 1% chest. Even after their return to Earth, approximately 40% of crewmembers report spine pain. Another indication of lumbar pain is vertebral hypomobility from guarding, and preliminary data indicate such spinal stiffness is seen with prolonged space flight.
The purpose of this research [Chang et al. 2016] is to evaluate lumbar PSM CSA and IVD heights following a 6- month International Space Station (ISS) mission and a 33 to 67 day postflight recovery period. Six ISS crewmembers volunteered for the study, 1 woman and 5 men. The range of crewmember ages spanned 46 to 55 years, height 168 to 183 cm, and body mass 60 to 93 kg. The mission duration on the ISS ranged from 117 to 213 days. This project represents 4 years of active data collection, through 2016. Supine lumbar spine magnetic resonance imaging (MRI) scans were conducted preflight, immediate postflight, and at least 30 days postflight recovery after an ISS mission (Figure 1 A, B). Preflight imaging was performed on average 214 days before launch. While on the ISS, the astronauts engaged in 2 to 3 hours of daily exercise with a treadmill, stationary cycle, and resistive strength training of the large muscle groups. After landing in Kazakhstan, the "immediate" postflight imaging was performed within 1 to 2 days, in Houston. The astronauts completed typical post-flight astronaut strength, conditioning, and rehabilitation exercise and activities, including a brief trip back to Russia, and return to Houston, TX where they were imaged again. These "Recovery" period images were performed an average of 46 days (range 33-67 days) after landing. The imaging time points are summarized in Table 1.
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Results
Lumbar paraspinal FCSA decreased by 19% on average from a preflight value of 8737 ± 1758 mm2 (avg ± standard deviation) down to a postflight value of 7049 ± 1822 mm2 . Later, there was a change in FCSA up to a recovery value of 8195 ± 1900 mm2 . ANOVA testing indicates a significant difference in FCSA measured at the three time points, with F ratio 23.39, R2 0.82, and P=0.0002. Post-hoc testing indicates the FCSA changed significantly from pre to postflight, and from postflight to postflight recovery. The FCSA data at the recovery time point were less than the preflight values, representing a 68% recovery of the postflight loss, a difference not significantly different as determined by posthoc testing. In comparison, the total lumbar paraspinal CSA (that encompass the unthresholded manual outlines, and therefore includes both lean muscle and nonlean muscle components) followed a similar trend at the three time points, but with non significant changes (F ratio 1.44, R2 0.22, P=0.2832, Table 2).
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Expressed as a percentage of the total lumbar CSA, the relative proportion of lumbar lean muscle FCSA decreased from preflight to postflight by 14 percentage points from 86% ± 5% down to 72% ± 7%.
The fraction of lumbar muscle FCSA recovered nine percentage points during the next 6 weeks to an average of 81% ± 4%.
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ANOVA testing indicates a significant difference in percentage FCSA measured at the three time points, with F ratio 22.25, R2 0.82, and P=0.0002. Post-hoc testing indicates the FCSA changed significantly from pre to postflight, and from postflight to postflight recovery. This resulted in a significantly lower lean muscle fractional content at recovery compared with the preflight values (Figure 3).
Among the six crewmembers studied, average disc height did not change in the lumbar spine. There was no consistent pattern before and after the mission (Table 3). There was considerable disc height variability from
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crewmember to crewmember, over various lumbar spine levels, and along anterior-middle-posterior locations of the disc. The present study showed reductions in total CSA with longduration space flight, but even more dramatic reductions in functional CSA, a proxy for lean muscle mass. At 6 weeks postmission, the FCSA and CSA trended toward preflight levels. After the mission, the lumbar paraspinal extensors recovered 68% of the loss after approximately 46 days back on Earth. These ISS data are comparable to previous long duration Mir data obtained approximately 20 years ago, where intrinsic back muscle total CSA decreased to 84% of preflight values, and psoas CSA decreased to 96%.
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Authors[Chang et al. 2016] focused on the L3/4 lumbar level. They elected not to measure the lower lumbar levels due to the greater difficulty in identifying clear muscle boundaries in a region that typically has a greater degree of fatty atrophy/intermuscular fascial connections (e.g., lumbar intermuscular aponeurosis, lumbosacral ligaments) in the multifidi/erector spinae muscles, and a fanning/thinning of the psoas and erector spinae muscles as they traverse normally away from the lumbar spine.
They evaluated both total and functional CSA measurements. This provides insight into lean-muscle mass changes separated from the effects of water retention or fatty replacement. In contrast to PSM data, individual disc height changes in the lumbar spine were small and demonstrated no consistent changes across time points. Specifically, disc height increases were not seen in a significant or consistent fashion postflight. So far, the data are compatible to previous lumbar disc height and lumbar length measurements after shortduration space flight, and preliminary data from in-flight ultrasound studies of cervical and lumbar disc heights, which also do not indicate significant disc height increases or swelling. These measurements run counter to previous hypotheses about the effects of microgravity on disc swelling, and suggest that the torso lengthening observed in crewmembers may be due to factors other than swelling of the IVDs. Specifically, postural straightening (i.e., a flattening of spinal lumbar lordosis and thoracic kyphosis into a "neutral body posture" in microgravity) is an important factor. The sample size of this experiment is, however, presently small for the study of IVD heights, and we have no in-flight images. Further spine analysis with additional crewmembers and in-flight ultrasound imaging will be forthcoming.
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Microgravity-Induced Back Pain and Intervertebral Disc Herniation
The preliminary results presented by authors [Sayson et. al.] here are derived from the complete set of pre and post-flight data from 5 crewmembers after 180 day missions on board the International Space Station (ISS).
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These data are inclusive of the on-going ISS flight study, "Risk of Intervertebral Disc Damage after Prolonged Space Flight" approved for 12 astronauts under NASA grants NNX10AM18G and NNX13AM89G.
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Preliminary Results
From the analysis of data collection derived from the initial 5 crewmembers tested pre- and postflight, the major results to date are: • Water content changes in the IVD are variable between crewmembers. There were noted IVD changes that were variable between crewmembers and between spinal levels. • No significant changes in disc height or lumbar length.
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• One episode of HNP 30 days post-flight (Figure 7).
• Decreased functional extensor time (Biering-Sørensen test). • Decreased functional cross-sectional area of lumbar and cervical muscles (Figure 8). On an average, 4/5 crewmembers lost 14% CSA of the lumbar paraspinal muscle and cervical functional CSA reduced 17%. • Partial recovery from paraspinal atrophy by R+45 (only 21% recovery in cervical spine compared to 67% recovery in lumbar spine). • Increased spine stiffness in flexion (Figure 9). • Increased spine straightening due to reduction of lumbar lordosis. All 5 crewmembers have an average 11% reduction of lumbar lordosis. • Decreased quality of vertebral bodies. • Anterior wedging of the lumbar vertebral bodies (Figure 10). • Endplate irregularities were observed (Figure 11).
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The preliminary results do confirm measurable changes in the spines of crewmembers pre- and post-flight after 180 day missions on board the International Space Station. Authors [Sayson et. al.] initially anticipated that microgravity exposure will induce a supraphysiologic swelling of the IVD, decreases in lumbar lordosis and decreases in spinal muscle CSA. The current findings do not show IVD swelling from five ISS crew members tested to date. However, due to the small sample size, no significant changes in disc height and lumbar length can be currently reported. In one crewmember post-flight Modic changes (vertebral bone inflammation) have been observed indicating vertebral bone inflammation which may present as another possible pain generator. Reduced bone mass during exposure to microgravity coupled with relatively high compression to the vertebrae may contribute to bone inflammation in the absence of infection. In a state of weakened trabeculae of the vertebra, endplate protrusions into adjacent vertebral bodies may be caused by high compressive loading using the Advanced Resistive Exercise Device or upon the impact of the Soyuz capsule landing when returning to Earth. Decreased quality of vertebral bodies was observed in this initial set of data with anterior wedging of the lumbar vertebral bodies of the crewmembers. In the case of ISS crewmembers, wedging of lumbar vertebrae may indicate the same pathomechanism as above where greater magnitude of anterior compression meets weakened vertebral trabeculae. Decreased functional extensor time (Biering-Sørensen test) is consistent with weakness of the supportive spinal muscles as a maladaptation to microgravity in the absence of the usual gravitational stress challenges for upright postures. Weakness parallels the observed decreased functional cross-sectional area of lumbar and cervical muscles. On an average, 4/5 crewmembers lost 14% CSA of the lumbar paraspinal muscle and cervical functional CSA reduced 17% despite the re-acclimation protocols and rehabilitation exercises. These results further necessitate the development of more precise exercise protocols designed for specific muscles of the spine in conjunction with an artificially induced gravitational field or spine loading by development of novel compression harnesses, new exercise equipment, or a combination of both. Increased spine stiffness in flexion was noted with dynamic fluoroscopy. The stiffness was measurable in each intervertebral segment and consistent with the initial hypothesis that authors anticipated that microgravity induced IVD swelling which may cause tensioning of the annulus and paraspinal ligamentous tissues, leading to
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decreased passive ROM at each lumbar level. During re-adaptation to gravity, there may be a relatively-slow equilibration of nucleus water content, volume, and disc height to pre-flight values. Increased spine straightening due to reduction of lumbar lordosis was observed among the 5 crewmembers with an average 11% reduction of lumbar lordosis. This phenomenon appears consistent with effects of IVD swelling whereas when the anterior heights of the IVD occurs in the absence of a compressive load to the lumbar spines, the bowstring effect described as lordosis is also reduced. Vertebral endplate irregularities were observed. Endplates serve as a loadbearing interface between the vertebral body and IVD with a balanced amount of porosity to facilitate cyclical influx and efflux of fluids and nutrition. The irregularities postflight may be consistent with degenerative changes where applied loading between the intervertebral segments whether in-flight or post-flight may be relatively become excessive when cartilage properties become less resilient perhaps through structural weakening from biomechanical and chemical factors as a result of altered homeostasis with reduced cyclical loading in space. Post-flight low back pain may arise from mechanical stimulation of chemically sensitized endplate nociceptors.
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Combined Effects of Spaceflight and Age in Astronauts
The possibility for premature fragility fractures in astronauts with prolonged exposure to space (>100 days) during their career - is a concern for the Bone Discipline at NASA Johnson Space Center.To address this risk, the laboratory personnel of the Johnson Space Center’s Bone & Mineral Laboratory monitors changes in skeletal health in astronauts with triennial measurements of areal bone mineral density by DXA. This surveillance is performed during an astronaut’s active years on spaceflight missions and during retirement years, or when the astronaut is no longer flying in space. In addition, pre and postflight DXA scans are performed for typical 6-month missions on the International Space Station. In this report, authors evaluated trends in the areal bone mineral density and in trabecular bone score to evaluate the combined effects of spaceflight and aging in retired astronauts.Trends were evaluated in serial DXA scans of the lumbar spine (L1-4) obtained from a total of 311 individual astronauts (covered age range, 41 to 80 years; 302 males; 3 females). Astronauts were categorized by the following spaceflight exposures: • Short-duration missions (<30 days) • Long-duration mission (>100 days) • Combined short- and long-duration missions
Nonlinear models were applied to describe trends in observations (bone mineral density or trabecular bone score, not astronauts) plotted as a function of astronaut age. Authors fitted 1175 observations of 311 astronauts, obtained from both pre- and postflight scans; observations denoted as "postflight" were from selected DXA scans obtained 3 years after landing or after astronaut’s bone mineral density was restored to within 2% of preflight, that is, a "recovered" state. Data trends for males and females were are reported separately. Observations were then grouped and defined as follows: • Long duration: after exposure to at least 1 long duration spaceflight >100
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• Short duration: before long duration and after exposure to at least 1 short duration spaceflight <30 days
Results
Short-duration observations revealed that trabecular bone score and bone mineral density had similar curvilinear declines with age for both male and female astronauts. Long-duration observations showed trabecular bone score declining with age while bone mineral density appeared stable or trending upward. Female (n=8) long-duration observations were too few to discern a trend.
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Trabeculae cannot be replaced or reconnected if lost or completely separated ; disconnected trabeculae is an underlying cause of vertebral compression fractures and of reduced vertebral bone strength. Hence, a capability to monitor changes in trabecular bone microarchitecture of the spine is required for possible intervention, that is, before irreversible changes have occurred.
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Trabecular bone score enables an analysis of active astronauts with minimal impact on launch schedules and facilitates a retrospective analysis of archived DXA scans. Multiple studies validating the clinical utility of trabecular bone score are emerging in terrestrial clinical research to inform the trabecular bone score interpretation. This study suggests that trabecular bone score captures the combined effects of age and of spaceflight on bone microarchitecture independent from changes in areal bone mineral density.
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Limitations: • Evaluated trends in data observations and not in individual astronauts • Astronauts population and fracture incidence are low and not likely to reach the required level of evidence to identify an intervention threshold. • Baseline bone mineral density of trabecular compartment of the lumbar spine of astronauts may be too high to detect micro-architectural degradation.
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• The data from females were too scarce (<10) to discern the combined effect of menopause and spaceflight
Skeletal Health in Long-Duration Astronauts
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Concern about the risk of bone loss in astronauts as a result of prolonged exposure to microgravity prompted the NASA to convene a Bone Summit with a panel of experts at the Johnson Space Center to review the medical data and research evidence from astronauts who have had prolonged exposure to spaceflight. The panel was asked to review data relevant to mineral metabolism and to bone structure, density, turnover, and strength that were collected from long-duration astronauts from 1994 to 2010. Over this period, data were acquired from 35 long-duration astronauts. All measures conducted immediately postflight were within 1 month of landing. These data included (1) the effects of resistive exercise during flight on aBMD (g/cm2 ) as measured immediately postflight by DXA, (2) levels of endocrine regulators and biochemical markers of bone. This section summarizes the data presented and the panelâ&#x20AC;&#x2122;s conclusions and recommendations.
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Results
DXA Figure 1 displays astronaut medical data that were available at the time of the Bone Summit, which includes the first 23 ISS expeditions. Changes in aBMD due to spaceflight have been quantified by serial DXA whole-body measures or regional scanning of the hip total hip, femoral neck, and trochanter) lumbarspine, and forearm (Fig. 2). Notably, after spaceflight all long-duration astronauts showed a loss in aBMD exceeding the least significant change (LSC) in at least one of these skeletal regions, and some astronauts had a >10% aBMD loss at both the hip and lumbar spine. (Note: Hologic QDR 4500 and QDR 2000 were used for measurement of astronaut BMD. For QDR 4500, LSC is 0.019 [trochanter], 0.035 [femoral neck], and 0.025 g/cm2 [lumbar spine], and the LSC for the Hologic QDR 2000 was 0.024 [trochanter], 0.050 [femoral neck], and 0.035 [lumbar spine]. All values g/cm2 .) However, no long-duration astronaut returned from spaceflight with a hip or lumbar spine T-score less than or equal to -2.5. The panel was asked how NASA should interpret and utilize these data to assess fracture risk in astronauts.
According to NASA medical health standards, the preflight aBMD requirement for flight certification is based on an estimated total spaceflight related decline in aBMD originally reported in 18 cosmonauts. An average monthly rate of aBMD loss was calculated from data from Mir missions (conducted from 1995 to 1998) ranging in duration from 4 to 14 months and was used to predict likely aBMD loss for other mission designs.
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Although there were insufficient measurements to assess whether the loss during flight was linear, there was an overall average 1.0% to 1.5% aBMD decline per month for hip and lumbar spine. This finding highlighted the accelerated rate of aBMD loss at weight-bearing skeletal sites during spaceflight contrasting starkly with the typical age-related rate of bone loss of 0.5% to 1.0% per year for comparable sites in older individuals on Earth. A similar rate of flight-related bone loss was found in U.S. crewmembers on ISS expeditions flown from 2000 to 2009. Since 2009, the availability of the ARED on the ISS (Fig. 3A) may have attenuated the aBMD decline in the astronauts by providing load-bearing exercise up to 600 pound force (lbf). This exercise capability contrasts with that of the previously used interim resistive exercise device (iRED) (Fig. 3B), which provided only onehalf of the resistance loading of the ARED. Coincident with the change from using iRED to ARED, the average monthly loss in aBMD decreased from roughly 1.0% (n=24 iRED users) to 0.3% to 0.5% per month (n=11 ARED users to-date, unpublished NASA data). Likewise, there is a consistent trend, observed in data from 45 different long-duration crewmember for aBMD to increase in the postflight period (Fig. 4). However, there is considerable heterogeneity in the extent to which aBMD is regained after flight with some astronauts appearing to have a persistent deficit. Notably, DXA measurement of aBMD is often the only index considered when evaluating the efficacy of inflight bone loss countermeasures and the return of bone health following flight. Overall, there is concern that DXA may underestimate skeletal risks due to spaceflight and reambulation on Earth, highlighting the potential utility of expanding measurements of bone beyond DXA aBMD to obtain enhanced estimations of bone strength and fracture risk. Quantitative computed tomography In 1998, a flight experiment was conducted to evaluate the effects of spaceflight on QCT parameters at the hip and lumbar spine in ISS astronauts. Whole-bone geometry and vBMD of cortical, trabecular, and integral bone (cortical+trabecular) were measured 30 to 60 days before spaceflight, 7 to 10 days after landing, and 1 year after landing. In ISS astronauts (n=16), vBMD declined at variable rates (Table 2A) at lumbar spine and hip trabecular and integral bone measurement sites. Spaceflight resulted in a reduction in total hip bone mineral content. As reported, the reduced volume of cortical tissue (cm3 ), in combination with a stable total
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tissue volume (cm3 ) suggested that cortical thickness was reduced because of endocortical resorption. In the spine, accelerated vBMD losses that occurred in integral bone were comparable to losses in trabecular bone. QCT measures of the lumbar spine did not provide additional information about spaceflight-induced changes above and beyond DXA aBMD. In contrast, as further described in Table 2B, QCT can provide additional information at the hip regarding spaceflight-induced changes, and recovery after return. QCT revealed that after 12 months of reambulation on Earth, total hip bone volume increased at both the proximal femur (total hip) and femoral neck whereas the vBMD was still decreased (ratio postflight vBMD/preflight vBMD <1; Table 2B). This readaptation to Earthâ&#x20AC;&#x2122;s 1g field in middleaged astronauts is reminiscent of the expansion of boneâ&#x20AC;&#x2122;s crosssectional area observed with
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aging in terrestrial populations and with weight loss. Therefore, as part of a study extension, a fourth QCT hip scan was obtained 2 to 4 years after flight in 8 of the original 16 ISS crewmembers. Figure 5 displays different patterns of recovery in the hip and spine as assessed by DXA and QCT scans. In Fig. 5A, there is a tendency for aBMD to recover in the lumbar spine (L1 -L4 ) after return, whereas trabecular vBMD, in QCT scans of L1 and L2 (Fig. 5B), declines after the first year in all but 1 astronaut. A similar discordant pattern is noted in Fig. 5C, D, where femoral neck aBMD in most individuals increased over the first year after return to Earth; however, 1 astronaut whose femoral neck aBMD exceeded preflight measurements 4 years after return, showed a reduction in trabecular vBMD over the same period.
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FEM To translate bone density data to an estimation of bone strength, FE models were developed from hip QCT scans of 11 ISS astronauts. FEM is a computational tool that estimates hip strength (in Newtons, N, of force) for specific loading orientations (Table 3). FEM detected a significant decline in hip strength after spaceflight (group means Âą SD) for two modeled orientations of loading (axial loading in one-legged stance and posterolateral loading that assumes falling backward to the side). When declines in hip strength were divided by total months in space, as similarly reported for loss of DXA aBMD, the monthly decrease in FEM estimates of hip strength are approximately double the monthly rate of decrease in aBMD (Table 3). Figure 6 shows the correlation between the spaceflight-related (preflight to postflight) changes in FEM strength and aBMD. There was little correlation between DXA and either of the two loading models (R2 =0.23 for one-legged stance and R2 =0.05 for posterolateral fall). These data do not indicate whether DXA or FEM is superior in predicting bone health but do suggest that FEM may capture changes in bone that DXA does not. Bone turnover markers Figure 7 displays the group trends in biochemical markers of bone turnover from U.S. crewmembers aboard both the ISS and Russian Mir spacecraft. The data for N-telopeptide (NTX) measures from 24-hour non-fasted urine specimens suggest that bone resorption increased early during long-duration missions and remained elevated throughout the period of weightlessness but was restored to baseline status upon return to Earth. In contrast, the concentration of bone-specific alkaline phosphatase (BAP), a marker of bone formation (Fig. 7), was reduced or unchanged during spaceflight, suggesting that an uncoupling of bone resorption and formation occurs. The increase in bone resorption, without an increase in bone formation, could be expected to yield net loss of bone mass.
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In-flight countermeasure evaluations Resistive exercise is the only countermeasure routinely used to mitigate bone loss in all long-duration astronauts. The ARED (Fig. 3A) was flown to the ISS in December 2008 to supplement the iRED (Fig. 3B), along with the cycle ergometer and treadmill exercise hardware that have also been used in flight since 2000.
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In the few ARED users in which data have been obtained (Fig. 2), the average monthly loss in aBMD (n=8) was reduced to 0.47% ± 0.53% (group mean± SD) at the total hip with an average monthly gain of 0.30% ± 0.94% at the lumbar spine- compared with monthly losses of 1.1% ± 0.45% (total hip) and 0.71% ± 0.51% (lumbar spine) in aBMD with use of the iRED (n=24).
Pharmacologic measures are also being considered to counter flight-related bone loss. Bisphosphonate therapy during spaceflight is being studied in a joint experiment by NASA and the Japan Aerospace Exploration Agency (JAXA). The study is testing bisphosphonates (alendronate or zoledronic acid) to prevent loss of bone mass, structure, and strength at the hip, quantified by DXA, QCT, and FEM, in long-duration astronauts.
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References Chang DG, Healey RM, Snyder AJ, Sayson JV, Macias BR, Coughlin DG, Bailey JF, Parazynski SE, Lotz JC, Hargens AR. Lumbar Spine Paraspinal Muscle and Intervertebral Disc Height Changes in Astronauts After LongDuration Spaceflight on the International Space Station. Spine (Phila Pa 1976). 2016 Dec 15;41(24):19171924. PubMed PMID: 27779600.
Sayson JV, Lotz JC, Parazynski SE, Chang DG, Healey RM, Hargens AR. Microgravity-induced back pain and intervertebral disc herniation: International Space Station results. 66th International Astronautical Congress, Jerusalem, Israel; 2015 October 19 pp.
JD Sibonga, ER Spector, R Ploutz-Snyder, HJ Evans, L King, NB Watts, D Hans, SA Smith , Combined Effects of Spaceflight and Age in Astronauts as Assessed by Areal Bone Mineral Density and Trabecular Bone Score , NTRS , NASA.
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Orwoll ES, Adler RA, Amin S, Binkley N, Lewiecki EM, Petak SM, Shapses SA, Sinaki M, Watts NB, Sibonga JD. Skeletal health in long-duration astronauts: nature, assessment, and management recommendations from the NASA Bone Summit. J Bone Miner Res. 2013 Jun;28(6):1243-55. doi: 10.1002/jbmr.1948. Review. PubMed PMID: 23553962.
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Pool-Goudzwaard AL, Belavâ&#x20AC;&#x2122;y DL, Hides JA, Richardson CA, Snijders CJ. Low Back Pain in Microgravity and Bed Rest Studies. Aerospace Medicine and Human Performance. 2015 June; 86(6): 541-547. DOI: 10.3357/AMHP.4169.2015.
Hides JA, Lambrecht G, Stanton WR, Damann . Changes in multifidus and abdominal muscle size in response to microgravity: possible implications for low back pain research. European Spine Journal. 2015 November 18; epub: 8 pp. DOI: 10.1007/s00586-015-4311-5. PMID: 26582165.
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Alex Snyder, Brandon Macias, Rob Healey, Jacquelyn Holt, Douglas Chang, Jeffrey Lotz, and Alan Hargens, Lumbar Paraspinal Muscle Atrophy during Long Duration Spaceflight , Physiology - Reduced Gravity and Hyperbaric Environments , FASEB J April 2015 29:990.4.