Affiliations: [a] Neurotology Research, Legacy Holladay Park Medical Center, Clinical Research and Technology Center, Legacy Health System, Portland, OR, USA | [b] Life Sciences Research Laboratories, NASA Johnson Space Center, Houston, TX, USA | [c] Nihon University, Tokyo, Japan | [d] Naval Aerospace Medical Research Laboratory, Pensacola, FL, USA | [e] University of Michigan, Ann Arbor, MI, USA
Note: [*]
Grant support: National Aeronautics and Space Administration (NASA) First International Microgravity Laboratory (IML-1), Microgravity
Vestibular Investigations (MVI) and the NASA Extended Duration Orbiter Project (EDOMP) DSO 605. Supported in part
by research grants 2 RO1 DC 00205 from the National Institute on Deafness and Other Communication Disorders, National Institutes
of Health, NAGW-3799 from NASA and a grant from the Legacy Research Advisory Committee.
Note: [**] Correspondence: F.O. Black, P.O. Box 3950, Legacy Holladay Park Clinical Technology and Research Center, Portland OR 97208-3950, Tel.: +1 503 413 5353; Fax: +1 503 413 5348
Abstract: Postural instability (relative to pre-flight) has been observed in all shuttle astronauts studied upon return from orbital missions. Postural stability was more closely examined in four shuttle astronaut subjects before and after an 8 day orbital mission. Results of the pre- and post- flight postural stability studies were compared with a larger (n=34) study of astronauts returning from shuttle missions of similar duration. Results from both studies indicated that inadequate vestibular feedback was the most significant sensory deficit contributing to the postural instability observed post flight. For two of the four IML-1 astronauts, post-flight postural instability and rate of recovery toward their earth-normal performance matched the performance of the larger sample. However, post-flight postural control in one returning astronaut was substantially below mean performance. This individual, who was within normal limits with respect to postural control before the mission, indicated that recovery to pre-flight postural stability was also interrupted by a post-flight pitch plane rotation test. A similar, though less extreme departure from the mean recovery trajectory was present in another astronaut following the same post-flight rotation test. The pitch plane rotation stimuli included otolith stimuli in the form of both transient tangential and constant centripetal linear acceleration components. We inferred from these findings that adaptation on orbit and re-adaptation on earth involved a change in sensorimotor integration of vestibular signals most likely from the otolith organs.
Keywords: orbital space flight, postural instability, space adaptation syndrome, otolith control of posture, countermeasures
