Effect of Hydrogen Gas on Hyperbaric Oxygen Toxicity

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

NOT_YET_RECRUITING

Clinical Phase

NA

Total Enrollment

32 participants

Study Classification

INTERVENTIONAL

Study Start Date

2026-01-31

Study Completion Date

2030-12-31

Brief Summary

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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

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Detailed Description

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Conditions

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

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

This is a human randomized, double-blind, crossover trial in which each participant undergoes two separate hyperbaric oxygen exposures: one with hydrogen-enriched breathing gas (1-2% H₂) and one with nitrogen-enriched breathing gas (1-2% N₂) as control. Before and after each exposure session, participants complete standardized pulmonary function tests and provide blood and urin samples for analysis of oxidative stress biomarkers. A washout period of at least two weeks is maintained between sessions to minimize carryover effects.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

TRIPLE

Participants Investigators Outcome Assessors

Study Groups

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Hydrogen Gas Intervention

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

Group Type EXPERIMENTAL

Inhaled Hydrogen-Enriched Oxygen Gas

Intervention Type OTHER

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% hydrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Inhaled Nitrogen-Enriched Oxygen Gas

Intervention Type OTHER

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% nitrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Nitrogen Gas Control

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.

Group Type ACTIVE_COMPARATOR

Inhaled Hydrogen-Enriched Oxygen Gas

Intervention Type OTHER

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% hydrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Inhaled Nitrogen-Enriched Oxygen Gas

Intervention Type OTHER

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% nitrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Interventions

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Inhaled Hydrogen-Enriched Oxygen Gas

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% hydrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Intervention Type OTHER

Inhaled Nitrogen-Enriched Oxygen Gas

Participants will inhale a gas mixture consisting of 98-99% oxygen and 1-2% nitrogen via a breathing circuit during a single hyperbaric exposure. The exposure will be conducted at a partial pressure of 1.75 ATA for 240 minutes. The intervention aims to evaluate the protective effect of hydrogen gas against pulmonary oxygen toxicity.

Intervention Type OTHER

Eligibility Criteria

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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

Minimum Eligible Age

20 Years

Maximum Eligible Age

64 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

Yes