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POSTURAL STABILITY OF COSMONAUTS AFTER LONG SPACE FLIGHTS

Nikita V. Shishkin1*, Vladimir V. Kitov1*, Tatiana A. Shigueva1, Elena S. Tomilovskaya1* and Inessa B. Kozlovskaya1
  • 1 Institute of Biomedical Problems (RAS), Russia

The studies of the characteristics of postural stability has revealed deep disorders of equilibrium function after space flight of different duration (Kozlovskaya et al., 1981-1990; Paloski et al., 1992; Wood, 2012-2015). The resuls of the works of American researchers, who were using the method of computer dynamic stabilometry, have shown that the restoration of the vertical balance function after short 4-10-day space missions occued in the first hours after landing, covering up to 50% of the post-flight decrease in the comprehensive assessment of EquiScore equilibrium during the first 3 hours (Black, Paloski, 1998). The method of computer dynamic stabilometry included 6 Sensory Organization Tests (SOT), namely – the posture with eyes open or closed in stable or moving visual environment or support surface, during which the motion of the center of pressure of the subject is recorded. Later modified SOT2 tests (posture with eyes closed on a fixed surface) and SOT5 tests (eyes closed, movable support surface) were added to the series of tests. Modification consisted in addition to the tasks the dynamic head movements in the sagittal plane with a frequency of 0.33 Hz and an amplitude of 40o (Jain et al., 2010). More recent studies of the postural stability after long-term space flights (Wood et al. 2012, 2015) showed that the basic recovery of EqScore rate in the original SOT2 and SOT5 tests can be clearly detected within the first 3 days after the flight, decelerating over the next 7 days, while the restoration of stability in the modified tests is ongoing throughout the ten-day study period with reduce of this improving’s dynamic. The authors assumed that the greater complexity of the tests, including dynamic head movements, is associated with the readaptation of the vestibular system, expressed in the reassessment of otolith signals and complete blocking of slow otolith signals. Postural stability studies, included in the Russian scientific-reseach program of post-flight studies, do not capture the early recovery period after the flight, focusing on the features of restoration of posture regulation system in the period from 3 to 10 days after the SF. 26 Russian cosmonauts - members of ISS crews took part in the research. The flight duration ranged from 115 to 199 days. All participants signed an informed consent to participate in the experiment. The examination was performed using the method of computerized dynamic posturography developed by L. Nashner in the 1970s with modifications introduced by NASA researchers (Black, Paloski, 1982-1993). During the examination, the cosmonaut was in a vertical position on the tensometric platform of the NeuroCom «SMART EquiTest» installation equipped with a controlled screen closing the field of vision of the subject from three sides – from the front, right and left. The support surface and visual environment rotates in direct proportion to anterior-posterior (AP) body sway (sway referencing). By disrupting somatosensory feedback and removing vision, this condition is sensitive to adaptive changes in how vestibular feedback is used for postural control The study was carried out twice before flight and on the 3rd, 7th (8) and 10th (11) days after landing. The 1-way ANOVA with Bonferroni’s multiple comparisons test has been used for statistical analysis of the results. The analyzed parameter of the tests is the value of Equilibrium Score calculated by the formula EqScore = [1-(P-Psway)/12,5˚]*100, where (P-Psway) – the angle between the maximum deviations of the center of gravity in the sagittal plane during the test; 12.5˚ - maximum (P-Psway), observed in the normal population. Before flight, this parameter ranged from 91 to 93 during vertical stance with eyes open, naturally decreasing along the growing complexity of the task: for example, in the SOT2 test (eyes closed) it varied in a range from 88 to 90 points, in the SOT5 test (eyes closed, the movable surface) – from 55 to 63 points. The lowest values of the indicator were recorded in the SOT5 test with dynamic head movements - from 28 to 41 points. The analysis of the obtained data showed that the gradual decrease in the rate of recovery of the EqScore index after 3 days after landing is observed only in standard tests, while in the tests with head movements this did not happen. Thus, at a vertical posture on a fixed surface with eyes closed (SOT2), the values of the studied indicator on the 3rd, 7th and 10th days did not differ significantly, averaging 87.14+0.86 points, and when performing a similar test with head movements (SOT2m) the difference between the preflight data (82+2.03) and 10th day (78.21+2.48) becomes insignificant. 3rd and 7th days data (74.56+2.44 and 74.73+2.69) have the significant difference with the preflight. In the test of vertical stance with closed eyes on the movable support (SOT5), EqScore values increased significantly from 3 to 10 days after the SF completion (52.75+2.85 and 61.25+2.58. When performing the complicated test with dynamic head movements (SOT5m), the values of the studied indicator were 20.19+4.54 on the 3rd day after the SF, progressively increasing in the course of further studies-up to 26.96+3.58 on the 7th day and up to 35.78 + 3.24 on the 10th day after the flight in opposition to reduce of improving’s dynamic in similar American study (Wood, 2015). Our study has shown that recovery of EqScore to the initial level in standard tests SOT1-5 was observed during on the 7th day after landing. In tests with addition of dynamic head tilts(SOT2m and SOT5m) progressive recovery of the studied index continued up to day 10 after landing. Unlike in american studies (Wood et al., 2015), there was no decrease in the dynamics of SOT2m(Fig. 1) and SOT5m(Fig. 2) EqScores. The period from 7 to 10 days after landing coincides with the period of recovery of the otolith function (Kornilova et al. 2012), which suggests that the restoration of the stability index in the SOT2m test on the 10th day could be associated with the restoration of the ability of the Central nervous system to quickly track the orientation of the head in space, associated with the function of the otolith apparatus. Funding The study is supported by Russian Academy of Sciences 63.1.

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References

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Keywords: Human postural stability, Computerized dynamic posturography (CDP), Cosmonaut, Vestibular postural reactions, Space physiology

Conference: 39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018.

Presentation Type: Extended abstract

Topic: Neurosciences and psychology

Citation: Shishkin NV, Kitov VV, Shigueva TA, Tomilovskaya ES and Kozlovskaya IB (2019). POSTURAL STABILITY OF COSMONAUTS AFTER LONG SPACE FLIGHTS. Front. Physiol. Conference Abstract: 39th ISGP Meeting & ESA Life Sciences Meeting. doi: 10.3389/conf.fphys.2018.26.00043

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Received: 02 Dec 2018; Published Online: 16 Jan 2019.

* Correspondence:
Mr. Nikita V Shishkin, Institute of Biomedical Problems (RAS), Moscow, Russia, chachaturan@yandex.ru
Mr. Vladimir V Kitov, Institute of Biomedical Problems (RAS), Moscow, Russia, arctg@yandex.ru
PhD. Elena S Tomilovskaya, Institute of Biomedical Problems (RAS), Moscow, Russia, finegold@yandex.ru