Measurement of areal bone mineral density (BMDa, g/cm2) by dual-energy x-ray absorptiometry (DXA) is required by NASA for assessing skeletal integrity in astronauts. Advantages of DXA include the facts that BMDa is a widely-applied predictor of fractures in the aging population and that there are BMDa-based guidelines for identifying persons at high risk for osteoporotic fractures. In contrast to the 2-d imaging by DXA, quantitative computed tomography (QCT) is a 3D bone imaging technology that is used typically to scan the hip and spine. QCT is capable of measuring, volumetric BMD (BMD, mg/cm3) of separate cortical and trabecular sub-regions as well as of total (integral) bone. QCT is limited to research applications at this time because there is not enough medical evidence to determine how QCT data should be used in clinical practice. QCT however provides additional information on bone structure and increases the understanding of how bones respond to effectors of bone loss or gain. NASA recently convened a panel of clinical bone experts to review available medical and research information from astronauts who flew on long-duration space missions. As part of its charge, the panel identified a clinical trigger upon which the flight surgeon should have the astronaut evaluated further by a bone endocrinologist. Specifically, the Panel recommended that if restoration to preflight BMD is not observed for the hip trabecular compartment at two years after return to earth, then that astronaut should be evaluated for possible therapeutic intervention to prevent premature osteoporotic fractures.
This pilot study proposes to use preflight and postflight QCT scanning of the hips in International Space Station (ISS) astronauts to evaluate the ability of in-flight countermeasures to prevent the occurrence of this clinical trigger. This study further hypothesizes that QCT scanning can distinguish the effects of different categories of in-flight countermeasures/activities on distinct sub-regions of the hip bone. For example, this pilot study will demonstrate that biochemically-based countermeasures (e.g., dietary manipulation of acidic to basic amino acid intake or bisphosphonates medication) will have a detectable prevention of BMD loss in the hip trabecular compartment while biomechanically-based countermeasures (exercise regimens) will have detectable expansion of cortical bone apposition -- increasing both bone cross-sectional area and integral BMD as a consequence. These different effects on hip morphology will be subsequently translated to an effect on hip bone strength of the ISS astronaut. The combination of countermeasures that impact both compartments will more likely result in greater hip bone strength -- as estimated by analyzing QCT data by Finite Element Modeling (FEM) -- than of any singly applied countermeasure. This assertion will be approached in this pilot study by addressing the following objectives in each ISS astronaut:
1) Characterize the response of i) trabecular and cortical BMDs of the hip and ii) cross-sectional areas of cortical bone, trabecular bone and integral bone, to countermeasures that are either based upon biochemistry or mechanical-loading – with QCT measures.
2) Translate the QCT-measured changes in hip bone morphology to hip bone fracture loads (aka, “hip bone strength”) using FEM.
3) Characterize QCT-measured changes in hip bone morphology following a 12-month postflight period on earth and, in addition, translate these changes to the percentage recovery of preflight hip bone strength determined by FEM.
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QCT scanning of the hip will be performed at a local hospital (e.g., Christus St. John Hospital, GE VCT 64-slice scanner) on approximately L-45, R+5, R+360 and R+720. Cotton medical scrubs will be provided for the crewmember to wear during scans. The technician will position the crewmember in the CT scanner prior to scanning. The QCT scan should be performed at the scanning facility as close as possible to the final departure to Russia. QCT scanning of the hip shall be performed in the same hospital facility as the postflight scans to ensure that the same scanning QCT protocol is performed on the same CT machine. In addition, crewmembers will be asked to keep an exercise and medication log pre, in, and postflight.
This experiment is currently ongoing . Results will be available at a later date.
Areal bone mineral density BMDa
Bone mineral content BMC
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L1 Centr 3D bone mineral density BMD
L1 Intl 3D bone mineral density BMD
L1 trabecular 2D bone mineral density BMD
L1 trabecular 3D bone mineral density BMD
L2 Centr 3D bone mineral density BMD
L2 Intl 3D bone mineral density BMD
L2 trabecular 2D bone mineral density BMD
L2 trabecular 3D bone mineral density BMD
Crew health and performance is critical to successful human exploration beyond low Earth orbit.
The Human Research Program (HRP) investigates and mitigates the highest risks to human health
and performance, providing essential countermeasures and technologies for human space exploration.
Risks include physiological and performance effects from hazards such as radiation, altered gravity,
and hostile environments, as well as unique challenges in medical support, human factors,
and behavioral health support. The HRP utilizes an Integrated Research Plan (IRP) to identify
the approach and research activities planned to address these risks, which are assigned to specific
Elements within the program. The Human Research Roadmap is the web-based tool for communicating the IRP content.
The Human Research Roadmap is located at: https://humanresearchroadmap.nasa.gov/
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for information of how this experiment is contributing to the HRP's path for risk reduction.