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Mediators of Inflammation
Volume 2006 (2006), Article ID 72620, 6 pages
Research Communication

Exhaled Nitric Oxide is Decreased by Exposure to the Hyperbaric Oxygen Therapy Environment

1UNSW and Department of Respiratory Medicine, Faculty of Medicine, Prince of Wales Hospital, Randwick 2031, NSW, Australia
2Hyperbaric Unit, Prince of Wales Hospital, Randwick 2031, NSW, Australia

Received 30 May 2006; Revised 24 August 2006; Accepted 25 August 2006

Copyright © 2006 Zudin A. Puthucheary et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Exhaled nitric oxide (eNO) detects airway inflammation. Hyperbaric oxygen therapy (HBOT) is used for tissue hypoxia, but can cause lung damage. We measured eNO following inhalation of oxygen at different tensions and pressures. Methods. Part 1, eNO was measured before and after HBOT. Part 2, normal subjects breathed 40% oxygen. Results. Baseline eNO levels in patients prior to HBOT exposure were significantly higher than in normal subjects (P < .05). After HBOT, eNO significantly decreased in patients (15.4 ± 2.0 versus 4.4 ± 0.5 ppb, P < .001), but not in normal subjects, after either 100% O2 at increased pressure or 40% oxygen, 1 ATA. In an in vitro study, nitrate/nitrite release decreased after 90 minutes HBOT in airway epithelial (A549) cells. Conclusion. HBO exposure causes a fall in eNO. Inducible nitric oxide synthase (iNOS) may cause elevated eNO in patients secondary to inflammation, and inhibition of iNOS may be the mechanism of the reduction of eNO seen with HBOT.