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
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.
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.
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:
https://h2-papers.org/en/papers/23852510