# 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


## 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](https://pubmed.ncbi.nlm.nih.gov/41582106/)
- **DOI**: [10.1038/s41598-026-36599-8](https://doi.org/10.1038/s41598-026-36599-8)
- **PMC**: [PMC12905198](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12905198/)
- **Study type**: human observational study
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 99.9%

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 41582106. https://h2-papers.org/en/papers/41582106
> **Source**: PubMed PMID [41582106](https://pubmed.ncbi.nlm.nih.gov/41582106/)