A total of 15 of 30 long duration astronauts have participated in this study to date. Testing has been on hold for most of this past year due to COVID travel restrictions. During this timeframe, we have focused our efforts in three main areas.
(1) To supplement our quantitative post-flight outcome measures, a new survey was added to capture participant’s subjective self-rating of how severely their adaptation impacted their ability to perform functional tasks and how long it took to adapt (recover) so that they were no longer restricting movement (both early inflight and postflight). This survey will be completed retrospectively for previous participants using a Qualtrics link and will be obtained prospectively for future participants.
(2) Dr. Koppelmans (University of Utah) has performed additional neuro-imaging processing using a new myelin mapping pipeline to augment the prior Diffusion Tensor Imaging analyses. It was determined that a software upgrade at the Victory Lakes imaging facility during the middle of the testing timeframe required a correction step that may limit the utility of this pipeline.
(3) The six degree-of-freedom platform that is used for some of the sensory dependency and adaptability tests has been upgraded (MOOG model 130 to model 170). This changeout allowed upgrades to the software (unsupported DOS to Windows based), increased payload rating, and improved the emergency stop functionality. The LabView code for stimulus control and data acquisition was also upgraded. Participant recruitment was recently resumed for the study and Qualtrics survey data collection on the existing 15 participants is ongoing.
Preliminary results (presented at the February Investigator Workshop-IWS): The 15 participants to date include 13M/2F and 9 veterans/6 first time flyers. The behavioral and genetic measures have been obtained an average of 3.4 years following the last mission (range 0.5 – 14.1 yr).
Post-flight Outcome Measures: Posturography data is available for all 15 participants. Field testing (recovery from fall and tandem walk) are available for 14 of 15 subjects. Of the two posture conditions (Sensory Organization Test (SOT) 5 and 5M)), trials requiring head movements with eyes closed on a sway-referenced (unstable) surface resulted in more variable responses. A ratio score (post-flight performance / pre-flight performance) was calculated, with a ratio of 1.0 being representing recovery to preflight baseline levels. The range of SOT-5 (head erect) ratios was 0.57-1.09 while the range of SOT-5M (head moving) was 0.08-1.07. Thus, the SOT-5M ratio scores are preferred to understand the variability in performance given the timeframe of these measures (>R+24hrs). Ratios for both recovery from fall and tandem walk were highly correlated across the three landing day test sessions (R0a medical tent/airport, R0b refueling stop, R0c JSC-Johnson Space Center). Since there were additional missing data from the R+0a and R0b sessions, the R0c session data was used for this preliminary analysis. The range of ratios for the recovery from fall was 0.32-1.24 and for tandem walk was 0.00-0.61. Given the differences in recovery time constants, and differences in what sensorimotor functions they are designed to reflect (e.g., eyes open versus eyes closed), it is not surprising that the ratio scores for this limited sample set were not correlated.
Sensory Dependency Measures: Sensitivity to visual motion was measured during treadmill walking while viewing a moving (virtual hallway) visual scene. The dependent variable was lateral torso translation during scene oscillation (amplitude at 0.3 Hz scene motion). Higher visual dependency appears related with lower recovery on tandem walk eyes closed (rho = -0.47). Vestibular sensitivity involves a perceptual direction-recognition task while seated with eyes closed during lateral translations. The dependent variables (threshold and bias) were derived from psychometric curve fit. Although data was only available for 9 subjects for this task, preliminary analysis suggests higher vestibular sensitivity was correlated with higher recovery on SOT-5M (rho = -0.71, p=0.03). The ability to balance using proprioception is assessed by monitoring medial-lateral center of pressure (COP) during one-legged stance on a horizontal air-bearing surface (eyes open & eyes closed). Measures include both range and root mean square (RMS) center of pressure (COP) although medial-lateral and anterior-posterior directions from the force plate. The resultant COP Range varied between 20 – 150 mm with eyes closed.
Sensory Adaptability Measures: The Adaptive Functional Mobility Test (AFMT) measured the time to complete navigating an obstacle course while wearing up/down reversing prisms (10 trials). While the performance continued to improve on average throughout the 10 trials, the variability in performance was greatest during the first trial (range 65 – 422 sec to complete the course). Slower AFMT times were significantly correlated with lower recovery on tandem walk eyes closed (n=14, rho = -0.62, p=0.02). Adaptability is also being assessed with the Treadmill Sensory Discordance Test. Changes in both stride frequency and reaction time to an auditory cue while walking with a virtual linear hallway on an oscillating treadmill are recorded after 1 and 4 min of walking on the oscillating treadmill.
Neuroimaging measures: Individual differences in regional brain volumes (using Structural MRI) and white matter microstructure (using Diffusion Tensor Imaging) are analyzed as potential predictors of adaptive capacity. Based on our preliminary analysis, differences in cerebellar volume Lobule VI (involved in sensorimotor adaptation) appears positively correlated with higher post-flight scores on SOT-5M (p=.044, eta2=.35) and higher recovery ratios on RFF prone-to-stand test (left: p=<.001, eta2=.75).
Genetic measures: Variations in four genes have been analyzed from saliva samples, including Catechol-O-methyltransferase (COMT), Dopamine Receptor D2 (DRD2), Brain-derived neurotrophic factor (BDNF), and the a2-adrenergic receptor. The distribution of the different alleles were within expected range. There does not appear to a clear pattern of alleles in any of the four genes that predict post-flight performance.
Summary of Preliminary Findings: There is considerable variability among the post-flight performance outcomes for the 15 participants to date. While there is a strong association within tests obtained at different R+0 timepoints, by R+24 hr performance on one post-flight test does not necessarily correlate with performance on other post-flight tests. There are apparent relationships between individual measures and specific post-flight outcome measures; however, additional data is needed to draw conclusions. Preliminary statistical analysis indicates combining biomarkers will increase predictive power and this will be explored with future analyses.