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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

human observational study inhalation not assessed

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
DOI
10.1007/978-1-4614-7411-1_42

Tags

Delivery:inhalation delivery (196) Mechanism:hydroxyl radical scavenging (352) oxidative stress (899) reactive oxygen species (774)

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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