Engineering topics

Fisher, E. A.

Publications and source records attributed to Fisher, E. A..

23 records · Page 2

NASA NTRS2010

Stretch Reflex as a Simple Measure to Evaluate the Efficacy of Potential Flight Countermeasures Using the Bed Rest Environment

INTRODUCTION: Spaceflight is acknowledged to have significant effects on the major postural muscles. However, it has been difficult to separate the effects of ascending somatosensory changes caused by the unloading of these muscles during flight from changes in sensorimotor function caused by a descending vestibulo-cerebellar response to microgravity. It is hypothesized that bed rest is an adequate model to investigate postural muscle unloading given that spaceflight and bed rest may produce similar results in both nerve axon and muscle tissue. METHODS: To investigate this hypothesis, stretch reflexes were measured on 18 subjects who spent 60 to 90 days in continuous 6 head-down bed rest. Using a motorized system capable of rotating the foot around the ankle joint (dorsiflexion) through an angle of 10 deg at a peak velocity of approximately 250 deg/sec, a stretch reflex was recorded from the subject's left triceps surae muscle group. Using surface electromyography, about 300 reflex responses were obtained and ensemble-averaged on 3 separate days before bed rest, 3 to 4 times in bed, and 3 times after bed rest. The averaged responses for each test day were examined for reflex latency and conduction velocity (CV) across gender and compared with spaceflight data. RESULTS: Although no gender differences were found, bed rest induced changes in reflex latency and CV similar to the ones observed during spaceflight. Also, a relationship between CV and loss of muscle strength in the lower leg was observed for most bed rest subjects. CONCLUSION: Even though bed rest (limb unloading) alone may not mimic all of the synaptic and muscle tissue loss that is observed as a result of spaceflight, it can serve as a working analog of flight for the evaluation of potential countermeasures that may be beneficial in mitigating unwanted changes in the major postural muscles that are observed post flight.

Cerisano, J. M.↗

NASA NTRS2010

The Walk on Floor Eyes Closed Tandem Step Test as a Quantitative Measure of Ataxia After Space Flight

INTRODUCTION Posture and locomotion are among the functions most affected by space flight. Postflight ataxia can be quantified easily by using the walk on the floor line test with the eyes closed (WOFEC). Data from a modified WOFEC were obtained as part of an ongoing interdisciplinary pre- and postflight study (Functional Task Test, FTT) designed to evaluate both postflight functional performance of astronauts and related physiological changes. METHODS Five astronauts with flight durations of 12 to 16 days participated in this study. Performance measurements were obtained in 2 preflight sessions, on landing day, and 1, 6, and 30 days after landing. The WOFEC test consisted of walking with the feet placed heel to toe in tandem, arms folded across the chest and eyes closed, for 10 steps. A trial was initiated after the eyes were closed and the front foot was aligned with the rear foot. The performance metric was the average percentage of correct steps completed over 3 trials. A step was not counted as correct if the crewmember sidestepped, opened eyes, or paused for more than 3 seconds between steps. Step accuracy was scored independently by 3 examiners. RESULTS Immediately after landing subjects seemed to be unaware of their foot position relative to their body or the floor. The percentage of correct steps was significantly decreased on landing day. Partial recovery was observed the next day, and full recovery to baseline on the sixth day post landing. CONCLUSION These data clearly demonstrate the sensorimotor challenges facing crewmembers after they return from space flight. Although this simple test is intended to complement the FTT battery of tests, it has some stand-alone value as it provides investigators with a means to quantify vestibular ataxia as well as provide instant feedback on postural stability without the use of complex test equipment.

Fisher, E. A.↗

NASA NTRS2010

Postflight Quiet Stance Stability of Astronauts Following Recovery From a Simulated Fall

INTRODUCTION: Astronauts returning from space flight universally present with postural ataxia. Throughout the Space Shuttle Program, measurement of ataxia has concentrated on sway in the anterior-posterior plane. Implementation of an interdisciplinary pre- and postflight study (Functional Task Test, FTT) designed to evaluate both astronaut postflight functional performance and related physiological changes has allowed the investigation of postural instability by characterizing dynamic stabilographic sway patterns. METHODS: Six astronauts from short-duration (Shuttle) and three from long-duration (ISS) flights were required to recover from a simulated fall. Subjects with eyes open, wearing running shoes lay prone on the floor for 2 minutes and then quickly stood up, maintained a quiet stance for 3 minutes, arms relaxed along the side of the body, and feet comfortably placed on the force plate. Crewmembers were tested twice before flight, on landing day (Shuttle only), and 1, 6, and 30 days after flight. Anterior-posterior (AP) and medial-lateral (ML) center-of-pressure (COP) coordinates were calculated from the ground reaction forces collected at 500 Hz. The 3-minute quiet stance trial was broken into three 1-minute segments for stabilogram diffusion analysis. A mean sway speed (rate of change of COP displacement) was also calculated as an additional postural stability parameter. RESULTS/CONCLUSION: While there was considerable variation, most of crewmembers tested exhibited increased stochastic activity evidenced by larger short-term COP diffusion coefficients postflight in both the AP and ML planes, suggesting significant changes in postural control mechanisms, particularly control of lower limb muscle function. As expected, postural instability of ISS astronauts on the first day postflight was similar to that of Shuttle crewmembers on landing day. Recoveries of stochastic activity and mean sway speed to baseline levels were typically observed by the 30th day postflight for both long-duration and short-duration crewmembers. Dynamic postural stability characteristics obtained in this low-impact study complement the data measured with computerized dynamic posturography.

Reschke, M. F.↗

NASA NTRS2010

Walk on Floor Eyes Closed Test as a Measure of Postflight Ataxia

INTRODUCTION: Astronauts returning from space flight universally exhibit impaired posture and locomotion. Measurement of this impairment is an evolving process. The walk on the floor line test with the eyes closed (WOFEC) provides a unique procedure for quantifying postflight ataxia. Data from a modified WOFEC were obtained as part of an ongoing NASA interdisciplinary pre- and postflight study (Functional Task Test, FTT) designed to evaluate astronaut postflight functional performance. METHODS: Seven astronauts (5 short duration with flights of 12-16 days; 2 long duration crewmembers with flights of 6 months) were tested twice before flight, on landing day (short duration only), and 1, 6, and 30 days after flight. The WOFEC consisted of walking for 10 steps (repeated twice) with the feet heel to toe in tandem, arms folded across the chest and the eyes closed. The performance metric (scored by three examiners from video) was the percentage of correct steps completed over the three trials. A step was not counted as correct if the crewmember sidestepped, opened their eyes, or paused for more than three seconds between steps. RESULTS/ CONCLUSIONS: There was a significant decrease in percentage of correct steps on landing day (short duration crew) and on first day following landing (long duration) with partial recovery the following day, and full recovery beginning on day sixth after flight. Both short and long duration fliers appeared to be unaware of foot position relative to their bodies or the floor. Postflight, deviation from a straight path was common, and the test for two crewmembers elicited motion sickness symptoms. These data clearly demonstrate the sensorimotor challenges facing crewmembers after returning from spaceflight. The WOFEC test has value providing the investigator or crew surgeon with a simple method to quantify vestibular ataxia, as well as providing instant feedback of postural ataxia without the use of complex test equipment.

Reschke, M. F.↗

NASA NTRS1979

The evaluation of ceramic turbine stators

A ceramic turbine stator evaluation program administered by the NASA Lewis Research Center and supported by the Department of Energy is outlined. The objectives of the program are to evaluate the durability of ceramic stators over a highly dynamic automotive gas turbine duty cycle and to assess the capability of current ceramic design methodology to predict the durability of the stators over the selected duty cycle for times in excess of 200 hours. The program also provides an assessment of the ability of the ceramic industry to fabricate complex geometry monolithic stators by near-net-shape forming processes. A summary of results obtained to date is presented and future plans are discussed.

Fisher, E. A.↗