Effect of Hydrogen Gas on Hyperbaric Oxygen Toxicity

Blekinge Institute of Technology

Status: Not yet enrolling

Conditions: Diving Medicine; Hyperbaric Oxygen; Hyperoxia; Oxidative Stress; Oxygen Toxicity; Hydrogen-oxygen Gas; Healthy Subjects (HS)

Treatments: Other: Inhaled Hydrogen-Enriched Oxygen Gas; Other: Inhaled Nitrogen-Enriched Oxygen Gas

Study type: Interventional

Funder types: Other

Identifiers

NCT07263399

BTH-6.1.1-0165-2025

5005113/22FMV2951 (Other Grant/Funding Number)

Details and patient eligibility

About

The goal of this trial is to investigate whether adding a small fraction of hydrogen gas to an oxygen-enriched breathing mixture can reduce pulmonary oxygen toxicity (POT) in healthy and active divers from the Swedish Armed Forces. The main questions it aims to answer are:

• Does hydrogen gas reduce oxidative stress and changes in pulmonary function associated with prolonged hyperbaric oxygen exposure?
• What are the underlying pathophysiological mechanisms of pulmonary oxygen toxicity?

Researchers will compare oxygen-enriched breathing gas with 1-2% hydrogen to oxygen-enriched gas with 1-2% nitrogen (control) to see if hydrogen provides protective effects against POT during hyperbaric exposure.

Participants will:

• Complete two hyperbaric exposure sessions (hydrogen vs. nitrogen), each lasting 240 minutes at 1.75 ATA
• Undergo pulmonary function tests and sampling of blod and urin before and after each session
• Serve as their own controls in a double-blind, randomized, crossover study design

Enrollment: 32 estimated patients

Sex: All

Ages: 20 to 64 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Military divers actively serving, aged 20-64 years
• Meeting the Swedish Armed Forces physical standards for diving

Exclusion criteria

• Ongoing infection or illness that may impact pulmonary function
• Use of alcohol or smoking cigarettes within 48 hours
• Diving with any breathing gas within 48 hours
• Diving with oxygen-enriched gas (100% O₂) within 2 weeks
• Use of medications that could affect oxidative stress, lung function, or neurological status
• Medical history of serious diving-related injuries or long-term complications

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Triple Blind

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32 participants in 2 patient groups

Hydrogen Gas Intervention

Experimental group

Description:

In this arm, participants will undergo a single hyperbaric exposure breathing a gas mixture composed of 98-99% oxygen and 1-2% hydrogen (H₂) at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate whether hydrogen gas has protective effects against pulmonary oxygen toxicity. Pulmonary function tests and blood and urin sampling for oxidative stress biomarkers will be performed both before and after the exposure session. The order of intervention and control exposures is randomized and the study is conducted in a double-blind fashion. A washout period of at least two weeks will follow before the control

Treatment:

Other: Inhaled Nitrogen-Enriched Oxygen Gas

Other: Inhaled Hydrogen-Enriched Oxygen Gas

Nitrogen Gas Control

Active Comparator group

Description:

In this arm, participants will undergo a single hyperbaric exposure breathing a gas mixture composed of 98-99% oxygen and 1-2% nitrogen (N₂) at a partial pressure of 1.75 ATA for 240 minutes. This exposure serves as the control condition and represents the standard oxygen-enriched breathing gas currently in use. Pulmonary function tests and blood and urin sampling for oxidative stress biomarkers will be performed both before and after the exposure session. Participants will be randomized to the order of exposures, and both participants and investigators will be blinded to the gas composition. A washout period of at least two weeks will follow before the intervention.

Treatment:

Other: Inhaled Nitrogen-Enriched Oxygen Gas

Other: Inhaled Hydrogen-Enriched Oxygen Gas