A basic study on molecular hydrogen (H2) inhalation in acute cerebral ischemia patients for safety check with physiological parameters and measurement of blood H2 level.
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
Abstract
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.
Mechanism
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.
Bibliographic
- Authors
- Ono H, Nishijima Y, Adachi N, Sakamoto M, Kudo Y, Kaneko K, et al.
- Journal
- Med Gas Res
- Year
- 2012 (2012-08-23)
- PMID
- 22916706
- DOI
- 10.1186/2045-9912-2-21
- PMC
- PMC3457852
Tags
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.
Safety notes
See also: