# Respiratory-physiology modeling of therapeutic hydrogen inhalation: defining the fraction of inspired hydrogen (FiH) and flow-rate requirements.
> 水素吸入における呼吸生理学的モデリング：吸入水素分率（FiH）と流量要件の定義


## Abstract

This study applied respiratory physiology modeling to characterize the fraction of inspired hydrogen (FiH) and the flow-rate requirements associated with hydrogen inhalation. By establishing quantitative definitions for these parameters, the work aims to provide a foundational framework for designing safe and effective hydrogen inhalation protocols. The modeling approach addresses key variables governing hydrogen delivery to the respiratory system, offering guidance for standardizing inhalation conditions in research and clinical settings.

### Mechanism

Respiratory physiology modeling was used to quantitatively define the relationship between the fraction of inspired hydrogen (FiH) and flow-rate parameters, establishing conditions necessary for adequate hydrogen delivery to the respiratory tract.

## Bibliographic

- **Authors**: LeBaron TW, Ohno K, Salomez-Ihl C, Cinquin P, Boucher F, Sano M, et al.
- **Journal**: Respir Res
- **Year**: 2026 (2026-04-28)
- **PMID**: [42050516](https://pubmed.ncbi.nlm.nih.gov/42050516/)
- **DOI**: [10.1186/s12931-026-03664-9](https://doi.org/10.1186/s12931-026-03664-9)
- **Study type**: other
- **Delivery route**: inhalation
- **Effect reported**: not assessed

## 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 42050516. https://h2-papers.org/en/papers/42050516
> **Source**: PubMed PMID [42050516](https://pubmed.ncbi.nlm.nih.gov/42050516/)