In contrast to previous studies, postflight measures of both otolith-ocular function and orthostatic tolerance were unimpaired in four payload crewmembers exposed to artificial gravity generated by inflight centrifugation during the Neurolab (STS-90) mission. The aim of the SPIN study is to obtain control measures of otolith and orthostatic function following long-duration missions, utilizing the centrifugation and autonomic testing techniques developed for the Neurolab mission, from crewmembers who have not been exposed to in-flight centrifugation. This will enable a direct comparison with data obtained from the Neurolab crew.
When otolith-ocular deficits are observed in the crewmembers that are not exposed to intermittent artificial gravity in flight, this would support the hypothesis that in-flight centripetal acceleration is a countermeasure for otolith deconditioning. Furthermore, a correlation between postflight otolith deconditioning and orthostatic intolerance would establish an otolithic basis for deficits in sympathetic outflow related to orthostatic stress.
These would be highly significant findings for future long-duration space missions, where providing an artificial gravity countermeasure for otolith and orthostatic deconditioning may prove critical to the well being of the crew, particularly during emergency egress.
These findings are also relevant to studies of imbalance and orthostatic intolerance on Earth. Many of the postural and locomotor deficits observed in astronauts postflight are similar to those seen in patients with vestibular disease, and findings from this study may shed light on the otolithic basis for these conditions.