The Integrated Medical Model (IMM) is a decision-analysis tool using the principles of probabilistic risk assessment to help optimize astronaut health and mission integrity during space missions by predicting the risk of medical hazards, including cardiac arrest, radiation exposure, kidney stones, and bone fracture. The observation that astronauts in space lose bone mass more quickly than their counterparts on Earth leads to the concern that the crew members are vulnerable to bone fracture, particularly during long-duration space flight. Since treatment facilities are scarce and crew and mission consequences are severe, the reliable prediction of bone fracture is crucial. In support of multi-NASA-center IMM development, a team from the NASA Glenn Research Center and the Cleveland Clinic developed the Bone Fracture Risk Module (BFRM) to analyze fracture risk in any specified mission scenario.
Description of the BFRM. BMD, bone mineral density.
Long description of figure.
Using the latest biomechanical and clinical research, the BFRM evaluates the risk of bone fracture in the hip and spine. Crew- and mission-specific data are input, as shown in the figure, to define relevant mission scenarios and crew capabilities. The forces generated by hazards, such as falling from a ladder or lifting heavy objects, are input to biomechanical models that quantify applied skeletal load. The bone quality is then assessed to determine the maximum load that can be tolerated by the bone; that is, the ultimate load, which varies with time in space as a result of bone loss, aging, bone structural changes, and skeletal location. These measures are used to estimate the likelihood of fracture under such conditions. Outcomes from the evaluation of treatment options are coupled with the fracture risk prediction to generate a sensitivity analysis. This analysis identifies the parameters that can most affect the likelihood and successful treatment of fracture, such as spacesuit padding or medical training and supplies. On the basis of these results, the BFRM generates an assessment of crew impairment and mission impact.
Mission planning can be iterated to avoid hazardous activities during a mission as preventive treatment. Secondary treatment includes countermeasures such as exercise, medication, and dietary supplements. If a fracture does occur, tertiary treatment is recommended by evaluating outcomes from available treatment protocols. Optimization simulations can be performed to determine the most likely combination of countermeasures, medical equipment, supplies, and training to reduce mission impact due to fracture.
Although preliminary results indicate that the risk of bone fracture during a Mars mission is small, it does not appear to be negligible. In the event of fracture, the impact of astronaut impairment in an environment with limited treatment options is large. Consequently, future work aims at increasing the scope of the biomechanical models to improve precision in fracture prediction. One key area is the evaluation of repetitive or repeated loading on bone quality, which can result in fracture at substantially reduced loading levels (stress fracture progression). In summary, the BFRM can be used as an aid in planning missions before launch, in determining countermeasures during missions, and in prescribing treatment in the event of a fracture.
Glenn contact: Dr. Jerry G. Myers, 216-433-2864, Jerry.G.Myers@nasa.govLast updated: August 30, 2007
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