Dose-dependent reduction of optic nerve sheath diameter during graded lower body negative pressure in healthy adults of both sexesBergauer, Andrej (Avtor) Urevc, Janez (Avtor) Steuber, Bianca (Avtor) Schimd-Zalaudek, Karin (Avtor) Pivec, Vid (Avtor) Goswami, Nandu (Avtor) cardiovascular physiologycentral hypovolemiaintracranial pressurelower body negative pressurenetwork physiologyoptic nerve sheath diametersex differencesultrasoundmicrogravityBackground: 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.20262026-08-07 15:05:09Članek v reviji185534sl