# Molecular hydrogen consumption in the human body during the inhalation of hydrogen gas.
> 水素ガス吸入時における人体内での分子水素消費量の定量的評価


## Abstract

This study quantified the rate of molecular hydrogen consumption in the human body during inhalation of low-concentration H2 gas (160 ppm mixed with purified artificial air). Inspired and expired H2 levels were measured by gas chromatography with a semiconductor sensor, and a ventilation equation incorporating O2, CO2, and H2 concentrations along with expired minute ventilation volume was applied to calculate the consumption rate. The resulting value was approximately 0.7 μmol/min/m² body surface area, consistent with previously reported data obtained using hydrogen-rich water ingestion. When subjects did not undergo pre-measurement fasting to suppress colonic fermentation, baseline exhaled H2 exceeded 10 ppm and the consumption rate showed marked variability. The authors propose that this inhalation-based measurement approach may serve as a noninvasive method for monitoring hydroxyl radical production in vivo.

### Mechanism

Inhaled H2 is consumed throughout the body at approximately 0.7 μmol/min/m² body surface area, likely reflecting scavenging of reactive oxygen species including hydroxyl radicals. Endogenous H2 from colonic fermentation competes with inhaled H2, necessitating fasting pretreatment for accurate measurement.

## Bibliographic

- **Authors**: Shimouchi A, Nose K, Mizukami T, Che DC, Shirai M
- **Journal**: Adv Exp Med Biol
- **Year**: 2013
- **PMID**: [23852510](https://pubmed.ncbi.nlm.nih.gov/23852510/)
- **DOI**: [10.1007/978-1-4614-7411-1_42](https://doi.org/10.1007/978-1-4614-7411-1_42)
- **Study type**: human observational study
- **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 23852510. https://h2-papers.org/en/papers/23852510
> **Source**: PubMed PMID [23852510](https://pubmed.ncbi.nlm.nih.gov/23852510/)