# A basic study on molecular hydrogen (H2) inhalation in acute cerebral ischemia patients for safety check with physiological parameters and measurement of blood H2 level.
> 急性脳虚血患者における水素ガス吸入の安全性確認：生理学的パラメータと血中水素濃度の測定に関する基礎的検討


## Abstract

This study examined the safety and pharmacokinetics of inhaled molecular hydrogen in patients with acute cerebral ischemia. Three patients inhaled 3–4% H2 gas for 30 minutes while arterial and venous blood hydrogen concentrations (HC) were measured by gas chromatography alongside continuous physiological monitoring. Blood HC reached a plateau approximately 20 minutes after inhalation onset, matching levels previously observed in animal studies. Following cessation of inhalation, HC declined to roughly 10% of plateau values within 6 minutes in arterial blood and 18 minutes in venous blood. No clinically meaningful changes in physiological parameters were detected across the three monitored patients. A consistency assessment in 10 patients revealed considerable variability in HC at the end of 30-minute sessions, though improved patient cooperation reduced this variability. The findings indicate that 3% H2 inhalation for 30 minutes achieves blood concentrations comparable to animal experimental levels without apparent safety concerns, while highlighting the need for more reliable delivery protocols.

### Mechanism

Inhaled H2 diffuses into the bloodstream, reaching plateau concentrations within approximately 20 minutes; upon cessation, arterial blood HC drops to 10% of plateau within 6 minutes and venous blood within 18 minutes, reflecting rapid pulmonary clearance.

## Bibliographic

- **Authors**: Ono H, Nishijima Y, Adachi N, Sakamoto M, Kudo Y, Kaneko K, et al.
- **Journal**: Med Gas Res
- **Year**: 2012 (2012-08-23)
- **PMID**: [22916706](https://pubmed.ncbi.nlm.nih.gov/22916706/)
- **DOI**: [10.1186/2045-9912-2-21](https://doi.org/10.1186/2045-9912-2-21)
- **PMC**: [PMC3457852](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3457852/)
- **Study type**: human case report
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 3–4%

## 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 22916706. https://h2-papers.org/en/papers/22916706
> **Source**: PubMed PMID [22916706](https://pubmed.ncbi.nlm.nih.gov/22916706/)