Time course of the reduction in nitric oxide concentration in exhaled gas after exposure to hyperbaric hyperoxia.

Exposure to hyperoxia is associated with oxidative stress and is known to cause inflammation in the lung and the airways. Exhaled nitric oxide concentration (FENO) is a marker of some inflammatory processes in the lung and airways, and is reduced immediately after a single session of hyperbaric oxygen (HBO) exposure. The purpose of this study was to characterize the time course of this decrease in FENO. Ten patients who had HBO treatment were included. The daily HBO exposures were at a pressure of 240 kPa for 90 min. FENO was measured before a single HBO treatment session and immediately after and 30, 60, 120, and 240 minutes after. Thirteen healthy controls had FENO measured at the same time intervals as the patients without hyperoxic or hyperbaric exposure. FENO was significantly reduced by 30.0 (SD 22.3) % (P = 0.009) immediately after HBO treatment. It remained reduced by 27.3 (SD 19.6) % (P = 0.013) at 120 min, and had not recovered completely by 240 min. There were no changes in FENO in the control group. The results confirm the finding of a decrease in FENO immediately after exposure to hyperbaric hyperoxia. The reduction in FENO persists for up to 240 min.