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
Military divers actively serving, aged 20-64 years
Meeting the Swedish Armed Forces physical standards for diving
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
Crossover
Inhaled Hydrogen-Enriched Oxygen Gas
Other interventionParticipants 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
Other interventionParticipants 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.
Change in Vital Capacity (ΔVC)
Absolute change in vital capacity (VC), calculated as the difference in liters (L) between pre-exposure and post-exposure spirometry values, measured after each hyperbaric oxygen exposure session.
Forced Expiratory Volume in One Second (FEV₁)
As part of the spirometric and plethysmographic measurements, Forced Expiratory Volume in 1 second (FEV₁) will be analyzed. This represents the change (ΔFEV₁) in liters (L) between pre- and post-exposure spirometry, indicating expiratory flow capacity. Measurements follow ATS/ERS 2019 standards.
Change in FEV₁/FVC ratio
As part of the spirometric and plethysmographic measurements, the ratio between Forced Expiratory Volume in 1 second and Forced Vital Capacity (FEV₁/FVC) will be calculated. The change (ΔFEV₁/FVC) is expressed as a percentage (%) to assess airflow limitation or restriction following hyperbaric oxygen exposure.
Change in Forced Expiratory Flow 25-75% (FEF25-75%)
As part of the spirometric and plethysmographic measurements, the mid-expiratory flow (FEF25-75%) will be assessed. This parameter reflects the mean expiratory flow between 25% and 75% of FVC and serves as an indicator of small airway function. Values are expressed in liters per second (L/s).
Change in Peak Expiratory Flow (PEF)
As part of the spirometric and plethysmographic measurements, Peak Expiratory Flow (PEF) will be analyzed. The change (ΔPEF) represents the maximum flow achieved during forced exhalation, measured in liters per second (L/s). This outcome evaluates large airway performance.
Anthropometric Measurements (Weight, Height, Sex, Age, BMI)
Anthropometric data will be recorded to assess body composition and physical characteristics of the study population and to enable adjustment for potential confounders in pulmonary function outcomes. This includes body weight (kg), height (cm), biological sex (M/F), age (years), and body mass index (BMI). These variables will not serve as primary endpoints but will describe baseline characteristics and support interpretation of within-subject changes in lung function.
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Blekinge Institute of Technology
Lead sponsor
Karolinska Institutet
Collaborator
Göteborg University
Collaborator
Lund University
Collaborator
Swedish Armed Forces Diving and Naval Medicine Centre
Collaborator
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