{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:25:42Z","timestamp":1787027142614,"version":"build-2736575974"},"reference-count":22,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,2,24]],"date-time":"2025-02-24T00:00:00Z","timestamp":1740355200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Physiol."],"abstract":"<jats:p>After longer duration space missions, some astronauts experience structural and functional changes in the eye and structural changes in the brain, termed Spaceflight-Associated Neuro-Ocular Syndrome (SANS). Countermeasures against SANS are required to minimize potential operation impacts and negative long-term health consequences. Headward fluid shifts, which appear to promote SANS, provide a target for countermeasures. The SANS countermeasures study, a 30 days strict head down tilt bed rest (HDTBR) study, tested two mechanical countermeasures aimed at reversing cephalad fluid overload. This work presents design and methodology of the study with a focus on countermeasure implementation and tolerability. Following baseline evaluations, participants were randomized to four groups and HDTBR commenced: Daily application of 25\u00a0mmHg lower body negative pressure for 6\u00a0h, six-hour bilateral venous constrictive thigh cuffs following moderate cycling exercise on 6 days per week, a negative control group without countermeasures, and a positive control group with HDTBR interruption for 6\u00a0h per day by sitting upright. The potential of these countermeasures for future space applications was examined in 86 different experiments, which will be reported elsewhere. Comfort ratings ranging from 1 (very uncomfortable) to 5 (very comfortable) were used to asses tolerability. Overall, 47 participants (20 women) completed the study. Out of 4,032\u00a0h scheduled for both countermeasures, 10.5\u00a0h were not performed due to medical issues unrelated to the countermeasures. Mean comfort ratings were 3.9 in men and 4.4 in women in the lower body negative pressure group (p = 0.1356) and 4.2 in men and 3.9 in women in the thigh cuff group (p = 0.1604). We conclude that both countermeasures were well tolerated and applied under well controlled conditions, thus, allowing for meaningful analyses of efficacy in attenuating HDTBR effects.<\/jats:p>","DOI":"10.3389\/fphys.2025.1530783","type":"journal-article","created":{"date-parts":[[2025,2,24]],"date-time":"2025-02-24T01:46:16Z","timestamp":1740361576000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":7,"title":["Mechanical countermeasures for spaceflight-associated neuro-ocular syndrome during 30-days of head down tilt bed rest: design, implementation, and tolerability"],"prefix":"10.3389","volume":"16","author":[{"given":"Stefan","family":"Moestl","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laura","family":"De 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