Beth E. Lewandowski

Exercise Countermeasures and a New Ground-Based Partial-g Analog for Exploration

The enhanced Zero-gravity Locomotion Simulator (eZLS) at NASA Glenn Research Center is described and summary data from a pilot research study comparing comfort and pressure data from two different International Space Station crew exercise harness designs are presented. This new ground-based simulation capability was developed to help address the detrimental physiological effects of spaceflight on the musculoskeletal system through improved exercise countermeasures systems, and to evaluate exercise countermeasures devices and prescriptions for space exploration. Aside from space applications, experiments conducted using the eZLS may help medical researchers develop insights into the role of exercise in the prevention of osteoporosis in the terrestrial population since the mechanism of bone and muscle loss is very similar, though greatly accelerated during space travel. The eZLS will be used as a ground-based testbed to support future missions for Space Exploration, and will eventually be used to simulate planetary locomotion in partial gravity environments including the Moon and Mars.

Predicting head injury risk during International Space Station increments.

INTRODUCTION NASAs Human Research Program is using a probabilistic risk assessment approach to identify acute and chronic medical risks to manned spaceflight. The objective of this project was to estimate the likelihood of a neurological head injury to a crewmember severe enough to require medical assessment, treatment, or evacuation during a typical International Space Station (ISS) increment. METHODS A 2 degree-of-freedom analytical model of the human head was created to allow for analysis of the impact response. The output of the model is acceleration of the head, which was used to determine the probability that the simulated impact resulted in a head injury with an Abbreviated Injury Scale (AIS) score of 3 or greater. These data were then integrated into a probabilistic risk assessment, which outputs a likelihood of injury with a representative measure of the uncertainty. RESULTS A Monte Carlo simulation was performed to vary input parameters over their defined distributions. The mean probability of a moderate neurological injury (AIS 3 or greater) occurring due to a head impact by a crewmember translating through the ISS is 1.16 x 10(-4) per 6-mo mission increment (2.32 x 10(-4) per year). DISCUSSION Our head injury prediction model has shown that there is a low, yet not insignificant, probability of neurological head injury of AIS score 3 or greater. The results from this simulation will be input into the parent Integrated Medical Model, which incorporates the risks of over 80 different medical events in order to inform mission planning scenarios.

An extravehicular suit impact load attenuation study to improve astronaut bone fracture prediction.

INTRODUCTION Understanding the contributions to the risk of bone fracture during spaceflight is essential for mission success. METHODS A pressurized extravehicular activity (EVA) suit analogue test bed was developed, impact load attenuation data were obtained, and the load at the hip of an astronaut who falls to the side during an EVA was characterized. Offset (representing the gap between the EVA suit and the astronauts body), impact load magnitude, and EVA suit operating pressure were factors varied in the study. The attenuation data were incorporated into a probabilistic model of bone fracture risk during spaceflight, replacing the previous load attenuation value that was based on commercial hip protector data. RESULTS Load attenuation was more dependent on offset than on pressurization or load magnitude, especially at small offset values. Load attenuation factors for offsets between 0.1-1.5 cm were 0.69 +/- 0.15, 0.49 +/- 0.22, and 0.35 +/- 0.18 for mean impact forces of 4827, 6400, and 8467 N, respectively. Load attenuation factors for offsets of 2.8-5.3 cm were 0.93 +/- 0.2, 0.94 +/- 0.1, and 0.84 +/- 0.5 for the same mean impact forces. The mean and 95th percentile bone fracture risk index predictions were each reduced by 65-83%. The mean and 95th percentile bone fracture probability predictions were both reduced approximately 20-50%. DISCUSSION The reduction in uncertainty and improved confidence in bone fracture predictions increased the fidelity and credibility of the fracture risk model and its benefit to mission design and in-flight operational decisions.

Forecasting Postflight Hip Fracture Probability Using Probabilistic Modeling

A probabilistic model predicts hip fracture probability for post-flight male astronauts during lateral fall scenarios from various heights. A biomechanical representation of the hip provides impact load. Correlations relate spaceflight bone mineral density (BMD) loss and post-flight BMD recovery to bone strength. Translations convert fracture risk index, the ratio of applied load to bone strength, to fracture probability. Parameter distributions capture uncertainty and Monte Carlo simulations provide probability outcomes. The fracture probability for a 1 m fall 0 days post-flight is 15% greater than preflight and remains 6% greater than pre-flight at 365 days post-flight. Probability quantification provides insight into how spaceflight induced BMD loss affects fracture probability. A bone loss rate reflecting improved exercise countermeasures and dietary intake further reduces the post-flight fracture probability to 6% greater than preflight at 0 days post-flight and 2% greater at 365 days post-flight. Quantification informs assessments of countermeasure effectiveness. When preflight BMD is one standard deviation below mean astronaut preflight BMD, fracture probability at 0 days post-flight is 34% greater than the preflight fracture probability calculated with mean BMD and 28% greater at 365 days post-flight. Quantification aids review of astronaut BMD fitness for duty standards. Increases in post-flight fracture probability are associated with an estimated 18% reduction in post-flight bone strength. Therefore, a 0.82 deconditioning coefficient modifies force application limits for crew vehicles.