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

Authors

Andrej Bergauer, Janez Urevc, Bianca Steuber, Karin Schmid-Zalaudek, Vid Pivec, Nandu Goswami

Published in

Frontiers in network physiology. Volume 6. Pages 1908460. Epub Aug 07, 2026.

Abstract

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.
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.
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 $\times$ sex interaction reached significance (all p $>$ 0.1). ONSD returned to baseline during recovery (female: p = 0.173; male: p = 0.059).
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.

PMID:
42630170
Bibliographic data and abstract were imported from PubMed on 22 Aug 2026.

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