Variations in exhaled nitric oxide concentration after three types of dive.

Abstract

Introduction: An increase in exhaled nitric oxide concentration (FENO) occurs during an exacerbation of chronic obstructive lung disease or other inflammatory processes of the airway. Raised FENO levels are also observed during normobaric, mild hyperoxic exposures, whereas after hyperbaric hyperoxic exposure the FENO level is reduced. This study investigated the variations of FENO after three different types of dive. Methods: Military divers participated in either a closed circuit rebreather dive (CCR, n = 17, pO2 = 130 kPa), semi-closed circuit rebreather dive (S-CCR, n = 12, pO2 = 180 kPa) or a compressed air dive (scuba, n = 17, pO2 = 126 or attendant, n = 12, pO2 = 118 kPa). Before and after each dive, the FENO was measured using a hand-held electrochemical analyser (Niox Mino®). Results: All values for FENO fell within the normal range (5−25 ppb). A small decrease in FENO level was found after all dives. After CCR dives, FENO fell from 16.4 (± 8.0) pre-dive to 13.6 (± 7.5) ppb, after S-CCR from 16.2 (± 7.2) to 13.6 (± 6.3) ppb, scuba from 17.1 (± 5.6) to 16.1 (± 5.2) ppb and attendants from 17.7 (± 9.8) to 17.3 (± 9.1) ppb. Only after a CCR or S-CCR dive was this decrease statistically significant (P less than 0.05). Conclusion: In our divers, hyperbaric hyperoxia up to 180 kPa led to a small decrease in FENO in the conductive compartment of the lungs, the biological importance of which is unknown.