H₂ Papers

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Hydrogen inhalation is associated with a transient rightward shift in prefrontal oxyhemoglobin asymmetry and autonomic modulation.

水素吸入による前頭前野酸素化ヘモグロビン非対称性と自律神経調節の一過性変化

human observational study inhalation positive 99.9%

Abstract

This study examined acute cerebral and autonomic responses to a single 30-minute session of 99.9% hydrogen gas delivered via nasal cannula at 300 mL/min in healthy adults. Time-domain near-infrared spectroscopy (TD-NIRS) was used to quantify oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb) concentrations in the bilateral prefrontal cortex (PFC), along with interhemispheric asymmetry indices, measured before, immediately after, and at 30 and 90 minutes post-inhalation. Autonomic activity was evaluated via continuous ECG-derived heart rate variability metrics including LF, HF, and LF/HF ratio. During inhalation, a robust transient increase in right-PFC oxy-Hb asymmetry was observed alongside an elevated LF/HF ratio, indicating sympathetic activation. Following inhalation, heart rate declined, consistent with parasympathetic rebound. These concurrent cerebral and autonomic findings point to a coordinated neurovascular-autonomic coupling mechanism, suggesting that acute hydrogen inhalation transiently modulates PFC oxygenation lateralization and autonomic tone with potential implications for cognitive and cardiovascular regulation.

Mechanism

Hydrogen inhalation transiently elevated right-PFC oxy-Hb asymmetry concurrent with sympathetic activation (increased LF/HF ratio), followed by parasympathetic recovery post-inhalation, suggesting a coordinated neurovascular-autonomic coupling mechanism.

Bibliographic

Authors
Moriya M, Oyama K, Den Y, Yamada Y, Sakatani K
Journal
Sci Rep
Year
2026 (2026-01-25)
PMID
41582106
DOI
10.1038/s41598-026-36599-8
PMC
PMC12905198

Tags

Disease:cognitive decline (111) Delivery:inhalation delivery (196) Mechanism:endothelial function (35) anti-inflammatory (743) oxidative stress (899) reactive oxygen species (774)

Delivery context

In air, molecular hydrogen is reported to be combustible across approximately **4% (LFL, lower flammability limit) to 75% (UFL, upper flammability limit)**. Among high-concentration hydrogen inhalers, 66% output sits inside this range, and even pure-hydrogen (100%) output forms a 4–75% concentration-gradient layer at the device–air boundary (the UFL 75% paradox). Engineering principle would therefore call for operation below LFL (the classical 4%); that figure, however, was measured under closed, pre-mixed, static conditions. For the open, dynamic inhalation environment, the empirical value reported in the literature is **10%**, which is the figure referenced in practice as the operating ceiling. The 66% / 100% output devices are recorded in the Japanese Consumer Affairs Agency accident-information database, and from these considerations are not recommended.

→ Evidence by delivery route

Safety notes

In air, molecular hydrogen is reported to be combustible across approximately **4% (LFL, lower flammability limit) to 75% (UFL, upper flammability limit)**. Among high-concentration hydrogen inhalers, 66% output sits inside this range, and even pure-hydrogen (100%) output forms a 4–75% concentration-gradient layer at the device–air boundary (the UFL 75% paradox). Engineering principle would therefore call for operation below LFL (the classical 4%); that figure, however, was measured under closed, pre-mixed, static conditions. For the open, dynamic inhalation environment, the empirical value reported in the literature is **10%**, which is the figure referenced in practice as the operating ceiling. The 66% / 100% output devices are recorded in the Japanese Consumer Affairs Agency accident-information database, and from these considerations are not recommended.

See also:

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