Prefrontal Oxygenation During Supine-to-Stand Transitions in Head-out Water Immersion as a Ground-based Microgravity Analog: An fNIRS Pilot Study
MICROGRAVITY SCIENCE AND TECHNOLOGY, cilt.38, sa.5, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 38 Sayı: 5
- Basım Tarihi: 2026
- Doi Numarası: 10.1007/s12217-026-10278-9
- Dergi Adı: MICROGRAVITY SCIENCE AND TECHNOLOGY
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Aerospace Database, BIOSIS, Compendex, INSPEC, Health Research Premium Collection (ProQuest), Technology Collection (ProQuest)
- Dokuz Eylül Üniversitesi Adresli: Evet
Özet
Background: Thermoneutral head-out water immersion is used as a ground-based microgravity analog, but prefrontal hemodynamic responses to postural transitions in water are poorly characterized. This pilot study tested whether immersion attenuates the post-standing oxygenated hemoglobin (O(2)Hb) reduction relative to land. Methods: Bilateral prefrontal O(2)Hb and deoxygenated hemoglobin (HHb) were recorded with functional near-infrared spectroscopy (fNIRS) in eight healthy adults (22.8 +/- 4.9 years; 4 males, 4 females) during counterbalanced, within-subject supine-to-stand transitions in water and on land. Responses were analysed in three 30-s epochs relative to condition-specific supine baselines. Conditions were compared using two-sided paired-samples t tests; exploratory one-sample t tests examined within-condition changes, with Cohen's dz as the effect size. Results: No between-condition comparison was statistically significant. The largest mean difference occurred for O(2)Hb at 60-90 s (land - water = - 1.87 & micro;mol/L, 95% CI [- 4.19, 0.45]; p = 0.098; d(z) = -0.68). Exploratory analyses showed O(2)Hb significantly below baseline on land at all three epochs (p <= 0.010), whereas the reduction in water was not statistically significant (p = 0.086-0.139). HHb did not differ from baseline or between conditions (p >= 0.324). Conclusions: The primary analysis did not support the hypothesis that immersion attenuates the post-standing O(2)Hb reduction. Although mean O(2)Hb reductions were numerically greater on land than in water, no between-condition comparison reached statistical significance, and this within-condition pattern does not establish a difference between environments. Given the small pilot sample, these null findings do not establish equivalence, and they do not support a microgravity analog effect.