Nitric oxide and carbon monoxide diffusing capacity after a 1-h oxygen dive to 9 m of sea water

To prevent extensive pulmonary lesions in submerged oxygen divers lung function like the forced vital capacity (FVC) or the diffusing capacity for carbon monoxide (DL,co) are used to monitor pulmonary oxygen toxicity (POT). As the diffusing capacity for nitric oxide (DL,no) measures more accurately the membrane diffusing capacity compared to DL,co we hypothesized that DL,no is superior in monitoring the onset of physiological changes indicative of POT as compared to DL,co or FVC.

26 healthy divers (mean age 30.7 ± 6.2 years) made two submerged dives to 190 kPa for 1 h on two randomized separate days, whilst breathing 100% oxygen or compressed air. FVC, DL,no, DL,co and alveolar volume (VA ) were measured 6 times during a 26-h period.

Up to 8 h no significant differences in outcomes were found between the oxygen and air dives. However, at 8 h after the oxygen dives there was a significant reduction in DL,no, DL,co and VA as compared with air dives. In contrast, the reduction in FVC was significantly greater after the air dive. At 22 h there were no longer differences in outcomes between the dives.

These data show that DL,no and DL,co are significantly reduced 8 h after submerged oxygen dives as compared to similar air dives. Together with the reduction in VA this may be indicative of interstitial edema as an early sign of POT. Our data warrant validation of the superiority of DL,no and DL,co over FVC in the practical monitoring of divers.