Reduced nitric oxide concentration in exhaled gas after exposure to hyperbaric hyperoxia

Area of Science:

• Pulmonary Medicine
• Biochemistry
• Hyperbaric Medicine

Background:

• Pulmonary oxygen toxicity is a concern during hyperbaric oxygen therapy (HBO2).
• Exhaled nitric oxide (FENO) and exhaled breath condensate (EBC) parameters (pH, H2O2) are potential biomarkers of lung inflammation and oxidative stress.

Purpose of the Study:

• To assess FENO, EBC pH, and H2O2 as markers of pulmonary oxygen toxicity during a 4-week HBO2 treatment course.
• To evaluate the acute and sustained effects of HBO2 exposure on these biochemical markers.

Main Methods:

• FENO, EBC pH, and H2O2 were measured in 8 patients undergoing HBO2 therapy and 8 controls.
• Measurements were taken during a 4-week treatment period, including assessments before and after single HBO2 exposures at the start and end of the study.
• HBO2 exposure protocol: 240 kPa for 90 minutes, 5 days/week for 4 weeks.

Main Results:

• A significant transient decrease in FENO was observed immediately after each HBO2 exposure (33.1% on Day 1, 40.7% on Day 25).
• EBC pH decreased only after the initial exposure.
• Baseline FENO, EBC pH, and H2O2 levels did not change significantly throughout the 4-week treatment period.

Conclusions:

• Single HBO2 exposures induce a temporary reduction in FENO.
• Repeated HBO2 exposures over 4 weeks do not appear to trigger lung inflammatory processes indicated by sustained increases in FENO.
• FENO and EBC parameters may not be reliable indicators of chronic lung inflammation due to prolonged HBO2 therapy.