# Molecular hydrogen inhalation attenuates postoperative cognitive impairment in rats.
> 水素ガス吸入による術後認知機能障害の軽減：ラットモデルを用いた検討


## Abstract

Using a rat tibial fracture surgery model under anesthesia, this study examined whether 2% H2 inhalation for 3 hours (starting 1 hour post-surgery) could mitigate postoperative cognitive dysfunction. Cognitive assessments via fear conditioning and Y-maze tests on days 1, 3, and 7 revealed significant impairment in surgery-only animals, which was substantially reversed by H2 inhalation. Biochemical analyses showed that H2 suppressed elevated levels of proinflammatory cytokines—TNF-α, IL-1β, IL-6, and HMGB1—in both serum and hippocampal tissue. Additionally, blood-brain barrier integrity was better preserved and hippocampal caspase-3 activity was reduced in H2-treated animals. The findings indicate that modulation of inflammatory signaling and apoptotic pathways underlies the neuroprotective effects of inhaled H2 in this surgical context.

### Mechanism

Inhaled H2 suppresses proinflammatory cytokines (TNF-α, IL-1β, IL-6, HMGB1) in serum and hippocampus, reduces caspase-3-mediated apoptosis, and preserves blood-brain barrier integrity, collectively attenuating surgery-induced cognitive decline.

## Bibliographic

- **Authors**: Xin Y, Liu H, Zhang P, Chang L, Xie K
- **Journal**: Neuroreport
- **Year**: 2017 (2017-08-02)
- **PMID**: [28614179](https://pubmed.ncbi.nlm.nih.gov/28614179/)
- **DOI**: [10.1097/WNR.0000000000000824](https://doi.org/10.1097/WNR.0000000000000824)
- **Study type**: animal study
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 2%

## 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 28614179. https://h2-papers.org/en/papers/28614179
> **Source**: PubMed PMID [28614179](https://pubmed.ncbi.nlm.nih.gov/28614179/)