{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,28]],"date-time":"2026-07-28T05:00:02Z","timestamp":1785214802815,"version":"3.55.0"},"reference-count":24,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,7,28]],"date-time":"2026-07-28T00:00:00Z","timestamp":1785196800000},"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:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>\n                      Spaceflight-associated neuro-ocular syndrome (SANS) is hypothesized to arise from a headward fluid shift that elevates intracranial pressure and distends the optic nerve sheath. Head-down tilt (HDT) is the ground-based analog of microgravity, and optic nerve sheath diameter (ONSD) measured by transorbital B-mode ultrasound is a candidate non-invasive marker of intracranial pressure. Before a definitive trial in which lower body negative pressure (LBNP) is added to 12\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT as a putative countermeasure, we conducted a pilot study to (i) confirm that 12\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT detectably elevates ONSD with a high-frequency linear probe, (ii) identify the time of peak response, (iii) optimize the measurement schedule, and (iv) provide effect-size estimates for powering.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      Eight healthy young participants (4 women, 4 men; mean age 30.9 years) underwent two conditions in a randomized, balanced two-period crossover with a 14-day washout: supine (0\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT) and 12\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT. Bilateral transorbital B-mode ultrasound was recorded with a 17-MHz linear probe (Philips iU22) at 0, 30, 60, 90, 120, 150, 180, 210 and 240\u00a0min. Five frames per clip were measured offline and averaged across both eyes. The primary analysis was a 2-way repeated-measures ANOVA (Condition \u00d7 Time) with Greenhouse\u2013Geisser correction. Posthoc paired comparisons at each time point used Bonferroni adjustment. Gender was examined in a secondary mixed model.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      The Condition \u00d7 Time interaction was highly significant (\n                      <jats:italic>p<\/jats:italic>\n                      <jats:sub>GG<\/jats:sub>\n                      <jats:italic>&amp;lt;<\/jats:italic>\n                      0.001). ONSD did not differ between conditions up to 60\u00a0min but was larger under 12\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT from 90\u00a0min onward, peaking at 150\u00a0min with a mean increment of 0.79\u00a0mm (95% CI 0.62\u20130.97), then partially regressing. No gender effect was detected, and baseline ONSD did not differ between visits, consistent with adequate washout.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>\n                      A 12\n                      <jats:sup>\u25e6<\/jats:sup>\n                      HDT exposure of \u2265 90\u00a0min produces a reproducible, large-magnitude ONSD increase peaking at 150\u00a0min in healthy adults; a 0\u2013180 min measurement window is sufficient. These data support a full three-arm crossover trial of LBNP as a candidate countermeasure, with graduated lower-limb compression included as a mechanistic positive control to verify that headward fluid redistribution is the aggravating factor.\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fphys.2026.1890637","type":"journal-article","created":{"date-parts":[[2026,7,28]],"date-time":"2026-07-28T04:26:13Z","timestamp":1785212773000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Optic nerve sheath diameter increases during 12\u25e6 head-down tilt in healthy volunteers: a crossover pilot study informing the design of a spaceflight countermeasure trial"],"prefix":"10.3389","volume":"17","author":[{"given":"Andrej","family":"Bergauer","sequence":"first","affiliation":[{"name":"Division of Physiology, Otto Loewi Research Center of Vascular Biology, Immunity and Inflammation, Medical University of Graz","place":["Graz, Austria"]},{"name":"Department of Surgery, General Hospital (LKH S\u00fcdweststeiermark)","place":["Wagna, Austria"]},{"name":"University of Ljubljana, Faculty of Mechanical Engineering","place":["Ljubljana, Slovenia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Janez","family":"Urevc","sequence":"additional","affiliation":[{"name":"University of Ljubljana, Faculty of Mechanical Engineering","place":["Ljubljana, Slovenia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bianca","family":"Steuber","sequence":"additional","affiliation":[{"name":"Division of Physiology, Otto Loewi Research Center of Vascular Biology, Immunity and Inflammation, Medical University of Graz","place":["Graz, Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karin","family":"Schmid\u2013Zalaudek","sequence":"additional","affiliation":[{"name":"Division of Physiology, Otto Loewi Research Center of Vascular Biology, Immunity and Inflammation, Medical University of Graz","place":["Graz, Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vid","family":"Pivec","sequence":"additional","affiliation":[{"name":"Division of Physiology, Otto Loewi Research Center of Vascular Biology, Immunity and Inflammation, Medical University of Graz","place":["Graz, Austria"]},{"name":"Department of Surgery, General Hospital (LKH S\u00fcdweststeiermark)","place":["Wagna, Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nandu","family":"Goswami","sequence":"additional","affiliation":[{"name":"Division of Physiology, Otto Loewi Research Center of Vascular Biology, Immunity and Inflammation, Medical University of Graz","place":["Graz, Austria"]},{"name":"Center for Space and Aviation Health, Mohammed Bin Rashid University of Medicine and Health Sciences","place":["Dubai, United Arab Emirates"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,7,28]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.3389\/fphys.2017.00547","article-title":"Human pathophysiological adaptations to the space environment","volume":"8","author":"Demontis","year":"2017","journal-title":"Front. 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