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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

other inhalation not assessed

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
DOI
10.1186/s12931-026-03664-9

Tags

Delivery:inhalation delivery (196) Safety:high-concentration device (8) lower flammability limit (15) regulatory / guideline (7)

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.

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