Abstract
Artificial gravity through short-arm centrifugation has potential as a multi-system countermeasure for deconditioning and cranial fluid shifts that may underlie ocular issues in microgravity. However, the optimal short-arm centrifugation protocol that is effective whilst remaining tolerable has yet to be determined. Given that exposure to centrifugation is associated with presyncope and syncope and in addition motion sickness an intermittent protocol has been suggested to be more tolerable. Therefore, we assessed cardiovascular loading and subjective tolerability of daily short arm centrifugation with either an intermittent or a continuous protocol during long-term head-down bed rest as model for microgravity exposure in a mixed sex cohort. During the Artificial Gravity Bed Rest with European Space Agency (AGBRESA) 60 day 6° head down tilt bed rest study we compared the tolerability of daily +1 Gz exposure at the center of mass centrifugation, either performed continuously for 30 minutes, or intermittedly (6 x 5 minutes). Heart rate and blood pressure were assessed daily during centrifugation along with post motion sickness scoring and rate of perceived exertion. During bed rest, 16 subjects (6 women, 10 men), underwent 960 centrifuge runs in total. Ten centrifuge runs had to be terminated prematurely, 8 continuous runs and 2 intermittent runs, mostly due to pre-syncopal symptoms and not motion sickness. All subjects were, however, able to resume centrifuge training on subsequent days. We conclude that both continuous and intermittent short-arm centrifugation protocols providing artificial gravity equivalent to +1 Gz at the center of mass is tolerable in terms of cardiovascular loading and motion sickness during long-term head down tilt bed rest. However, intermittent centrifugation appears marginally better tolerated, albeit differences appear minor.
Highlights
Long term space missions elicit multi-system deconditioning including reduced skeletal muscle strength [1], bone mineral density [2], and central blood volume [3,4,5]
Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; we enable the publication of all of the content of peer review and author responses alongside final, published articles
The 16 participants allocated to the two centrifuge groups comprised 10 men and 6 women (71.6 ± 7.4 kg, 33 ± 9.9 yrs, 173 ± 8.8 cm) who experienced 960 centrifuge runs in total
Summary
Long term space missions elicit multi-system deconditioning including reduced skeletal muscle strength [1], bone mineral density [2], and central blood volume [3,4,5]. In an attempt to counter deconditioning on the International Space Station, integrated resistance and aerobic training is prescribed using a number of dedicated devices [10]. Despite the substantial investment of time, resource and effort this approach is not entirely effective in mitigating musculoskeletal [13], nor aerobic [5, 14] deconditioning, physical rehabilitation is required following return to Earth. No effective countermeasures against space associated neuro-ocular syndrome currently exist. More effective and ideally more efficient countermeasures are required for future missions to the Moon, and beyond [15]
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