急性脳虚血患者における水素ガス吸入の安全性確認：生理学的パラメータと血中水素濃度の測定に関する基礎的検討
This study examined the safety and pharmacokinetics of inhaled molecular hydrogen in patients with acute cerebral ischemia. Three patients inhaled 3–4% H2 gas for 30 minutes while arterial and venous blood hydrogen concentrations (HC) were measured by gas chromatography alongside continuous physiological monitoring. Blood HC reached a plateau approximately 20 minutes after inhalation onset, matching levels previously observed in animal studies. Following cessation of inhalation, HC declined to roughly 10% of plateau values within 6 minutes in arterial blood and 18 minutes in venous blood. No clinically meaningful changes in physiological parameters were detected across the three monitored patients. A consistency assessment in 10 patients revealed considerable variability in HC at the end of 30-minute sessions, though improved patient cooperation reduced this variability. The findings indicate that 3% H2 inhalation for 30 minutes achieves blood concentrations comparable to animal experimental levels without apparent safety concerns, while highlighting the need for more reliable delivery protocols.
Inhaled H2 diffuses into the bloodstream, reaching plateau concentrations within approximately 20 minutes; upon cessation, arterial blood HC drops to 10% of plateau within 6 minutes and venous blood within 18 minutes, reflecting rapid pulmonary clearance.
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/22916706