OBJECTIVES:
Astronauts experience alterations in multiple physiological systems due to exposure to the microgravity conditions of space flight. These physiological changes include, among others, sensorimotor disturbances, cardiovascular deconditioning, and loss of muscle mass and strength. Changes in these systems clearly lead to disruption in the ability to ambulate and perform functional tasks during the initial reintroduction to a gravitational environment following a prolonged weightless transit and may cause significant impairments in performance of operational tasks immediately following landing on a planetary surface. Severe impairments may lead to loss of mission. To date changes in functional performance have been systematically studied for short-duration space flights and has recently begun on the long duration International Space Station (ISS) space flights. As important as these observed postflight functional changes have been, responses within hours following landing and a recovery time constant beginning as near to the time of landing as possible through full functional recovery has never been investigated or established for long-duration flights. The objective of this study is to address this gap in knowledge, allowing investigators to understand the impact on functional performance on tasks that are representative of critical mission requirements that the crews of exploratory missions will be expected to perform after an unassisted landing following flights from 6 to 12 months in duration. Findings from this investigation will provide the information needed for planning future Mars, or other deep space missions, with unassisted landings, including water landings.
The primary goal of this study is to determine functional performance in long duration space flight crews beginning as soon after landing as possible with one to three immediate follow-up measurements on the day of landing. This goal has both sensorimotor and cardiovascular elements including an evaluation of NASA’s new Gradient Compression Garment (GCG) and the Russian traditional Kentavr garment.
Specific Aims:
- Quantify functional performance from measurements on long duration crewmembers taken as close in time to landing as possible.
- Develop a recovery timeline of functional performance on long-duration crewmembers.
- Determine the efficacy of U.S. and Russian compression garments as countermeasures for alleviating orthostatic intolerance.
APPROACH:
Preflight and postflight subjects completed familiarization sessions, with the data collection team giving a thorough explanation of each test as the subject completed it. Subjects began each test session with Computerized Dynamic Posture. For this test, the subject was instructed to maintain stable upright posture for 20 seconds with feet positioned shoulder width apart, eyes closed, and arms folded across the chest while positioned on a sway-referenced support surface intended to disrupt somatosensory feedback. Three trials were performed with the head upright and then with the head moving. Inertial sensors placed on the head, torso and lower leg captured body kinematics. Subjects were then transported to different rooms to complete Postural Muscle Tone/Compliance. The subject was instructed to lie in a relaxed, prone position with the myotonometer applied to the skin overlying the muscle to be measured. Vibration was applied to the muscle and the muscle vibration response was measured. Next the subject was instrumented with the remaining hardware (motions sensors, heart rate monitor, Portapres, pressure sensors, electrodes) for the following tests:
1. Hand/Eye Coordination - rapid and accurate target acquisition with the finger, or stylus, on a computer touch screen
2. Sit-to-Stand - transition from an upright seated position to a standing position and remain stationary for approximately 10 seconds.
3. Recovery from Fall - lying face down on a mat for two minutes, then standing up again as quickly as possible when a command to stand is issued, followed by quietly on a stable surface for three minutes.
4. Cerebellar Function Tests were also conducted. The first required the subject to touch their finger to the operator’s finger, then to touch their own nose, repeating this several times with one hand, then with the other hand. The second test required the subject to follow the operator’s finger with their eyes only, keeping their head still. The third test required the subject to hold one arm out to the side, shoulder height, and to resist when operator pushes their arm down, repeating it with the other arm.
5.Seat Egress and Walk Test - beginning in an upright seated position, subject assumes a vertical stance and remain stationary for approximately 5 to 10 seconds, walk approximately 10 steps, turn, and then walk back to the chair. On the traverse back to the chair, the subject was required to step over a barrier that increases in height with each subsequent trial.
6.Tandem Heel-to-Toe Walk, - subjects attempted to walk 10 steps on the floor with their eyes closed, arms and hands folded across the chest, while placing their feet in the traditional tandem heel-to-toe position. Trails were first conducted with subjects' eyes closed for three trials and then with eyes open for one trial.
7. Push Test - while standing upright with arms crossed in front of the chest and eyes closed, a random force was applied approximately every 10 seconds to a plastic plate fixed at the center of the chest while the subject attempted to maintain balance.
8. Dynamic Visual Acuity - subjects used a hand-held joystick to indicate the perceived orientation of the gap in a series of letter Cs presented on a computer screen using both “accurate and quick” guidelines. Subjects were seated in a spring-suspended portable seat and performed the task first without moving, then again with the chair oscillating vertically at 2 Hz, ±2 cm.
9. Force Discrimination (Foot and Hand) - measured the ability of the subject to differentiate between forces that are self-generated. The subjects attempted to increase force from one cycle to the next.
10. Jump Down Test - subjects used a two-footed hop to jump from a height of 30 cm and land on a force plate to measure the peak vertical impact force on landing.
11. Simulated Rock or Payload Translation - subjects selected one of three weights (2.7, 4.5, 9 kg) to carry at their side for a distance of 2.5 m, then placed it in a receptacle positioned at 51 cm above the floor. This procedure was repeated until all three weights were individually transferred to the receptacle.
Finally, the subject was de-instrumented to complete the baseline data collection (BDC) session.
For Aim 3, on landing day after removal of the Sokol suit, subjects designated to wear the GCG removed the Kentavr and donned the GCG prior to testing. While changing clothes, Postural Muscle Tone/Compliance was collected on the calf muscle (before the GCG is donned) and on the lower back. For the subjects that did not wear the GCG, Postural Muscle Tone/Compliance was only collected on the lower back. Subjects were encouraged to wear the GCG during the return to the US or Star City. At the completion of each task, subjects were asked to rate their level of motion sickness.
RESULTS:
The Field Test has resulted in several key deliverables contributing to gap closures and stimulating further study.
First, Aims 1 and 2 provided evidence for characterization of the Risk of Altered Sensorimotor/Vestibular Function Impacting Critical Mission Tasks. Two primary goals of this research were to determine functional abilities beginning as soon after landing as possible (Aim 1) and to develop a recovery timeline of functional performance on long duration crewmembers (Aim 2). Measures such as sit-to-stand, recovery-from-fall, obstacle walk and tandem walking helped better characterize the effects of long-duration spaceflight on postural control and locomotion. Measures of dysmetria and eye-hand coordination characterized the effects of long-duration spaceflight on fine motor control, as well as incidence of re-entry motion sickness. While there was considerable variability in the postflight outcome measures across crewmembers, the level of vestibular/cerebellar and sensorimotor impairment was greater than previously observed during shorter spaceflight missions. Most striking was the higher incidence of motion sickness even without constraining the standard medical interventions. Motion sensitivity prevented some crewmembers from attempting and/or completing the early testing. Aim 3 provided early postflight cardiovascular measures during the stand test that further characterized the effects of long-duration spaceflight related to the Risk of Cardiovascular Adaptations Contributing to Adverse Mission Performance and Health Outcomes.
Second, the results of the Field Test were instrumental in developing sensorimotor guidelines for exploration design reference missions. The recovery timeline varied with task complexity, generally taking longer when either the basis of support was limited (e.g., tandem walk) or visual cues were deprived (eyes closed). Based on this evidence, mission planners need to expect a range of responses across individuals and tasks following G-transitions. The data from Field Test now serves as reference for developing new sensorimotor exploration assessments of crew readiness. These individual health assessments are recommended along with development of pre-worked, prioritized content and timelines, with the ability to change roles depending on crew readiness. Handholds and balance aids are recommended to help stabilize the crewmembers to perform specific tasks (e.g., touch screen selection) or to allow the crewmember the ability to rest with onset of symptoms. Based on anecdotal reports and performance on computerized dynamic posturography, multiple testing on landing day appeared to be beneficial for some participants, while others may have pushed beyond their motion tolerance limit in an effort to complete more objectives. Instead of delaying planetary surface operations to allow for recovery, these results suggest that early mobility may be important. Early active self-administered retraining, individualized based on the level of initial impairment and motion sensitivity, will enable a more efficient motor learning and enhance crew performance.
Finally, Aim 3 provided final verification of the customized gradient compression garment (GCG) following ISS missions as an effective countermeasure in preventing orthostatic intolerance after long-duration spaceflight. Wearing the GCG after spaceflight prevented the tachycardia that normally occurs while standing after spaceflight without compression garments and protected against a decrease in blood pressure during a short stand test. Further, it appears that the GCG may provide greater reliability in mitigating orthostatic intolerance relative to the Kentavr. These findings are important for future autonomous landings to help preserve crewmember capabilities in the minutes and hours after landing.
