Dose-dependent reduction of optic nerve sheath diameter during graded lower body negative pressure in healthy adults of both sexes

Bergauer, Andrej (author), Urevc, Janez (author), Steuber, Bianca (author), Schimd-Zalaudek, Karin (author), Pivec, Vid (author), Goswami, Nandu (author)

Background: Optic nerve sheath diameter (ONSD) measured by ultrasound provides a non-invasive surrogate of intracranial pressure. Although lower body negative pressure (LBNP) is widely used to simulate central hypovolemia, the dose-response relationship between graded LBNP and ONSD, and possible sex differences therein, are incompletely characterized.Methods: Forty-four healthy young adults (22 female, 22 male) underwent graded LBNP (−10 to −40 mmHg) in the supine position; valid ONSD data were available in 37 participants (18 female, 19 male) who constituted the analytical sample. ONSD was measured from transbulbar B-mode ultrasound images 3 mm posterior to the globe, with three representative frames averaged per condition. Relative changes from individual supine baseline were analyzed using a linear mixed-effects model with state, sex, and their interaction as fixed effects.Results: A progressive and statistically significant reduction in ONSD was observed at every LBNP level in both sexes. Female participants showed reductions of approximately −4.4 % (LBNP10, p = 0.001), −9.1 % (LBNP20, p < 0.001), −13.2 % (LBNP30, p < 0.001) and −15.9 % (LBNP40, p < 0.001) relative to supine baseline. Male-specific contrasts showed comparable reductions (LBNP10: −3.0 %, p = 0.022; LBNP20: −7.9 %, p < 0.001; LBNP30: −10.1 %, p < 0.001; LBNP40: −13.4 %, p < 0.001). The main effect of sex was not significant (p = 1.00), and no state × sex interaction reached significance (all p > 0.1). ONSD returned to baseline during recovery (female: p = 0.173; male: p = 0.059).Conclusion: Graded LBNP induces a progressive, dose-dependent reduction in ONSD that is detectable already at mild LBNP (−10 mmHg) and reaches approximately −15 % at −40 mmHg. No statistically significant sex-related differences in the ONSD response to graded LBNP were detected in the present study. These findings support the use of transbulbar ONSD ultrasound as a sensitive non-invasive marker consistent with intracranial-pressure reductions during simulated central hypovolemia. By linking a systemic cardiovascular perturbation to a cerebro-ocular pressure readout, the study offers a network-physiology view of central-hypovolemia responses relevant to spaceflight and orthostatic-stress research.

• Language: English
• Keywords: cardiovascular physiology, central hypovolemia, intracranial pressure, lower body negative pressure, network physiology, optic nerve sheath diameter, sex differences, ultrasound, microgravity
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 11 str.
• Numbering: Vol. 6, art. 1908460
• PID: 20.500.12556/RUL-185534
• UDC: 531.5:612.819
• ISSN on article: 2674-0109
• DOI: 10.3389/fnetp.2026.1908460
• COBISS.SI-ID: 287272195
• Publication date in RUL: 07.08.2026

Record is a part of a journal

• Title: Frontiers in network physiology
• Shortened title: Front. netw. physiol.
• Publisher: Frontiers Media SA
• ISSN: 2674-0109
• COBISS.SI-ID: 75774211

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: kardiovaskularna fiziologija, centralna hipovolemija, intrakranialni tlak, negativni tlak spodnjega dela telesa, premer ovojnice vidnega živca, spolne razlike, transorbitalna ultrasonografija, mikrogravitacija

Projects

• Funder: Other - Other funder or multiple funders
• Funding programme: European Space Agency
• Project number: 4000137614/22/NL/SC
• Name: Prediction model of countermeasures efficiency on cardiovascular system and fluid shifting in simulated microgravity conditions

• Funder: Other - Other funder or multiple funders
• Project number: MBRU-CM-RG2021-06