Can Nitrox Damage Blood Vessels?

Repeat scuba dives, particularly while breathing nitrox, appear to harm the endothelium, the inner lining of blood vessels. Emeline Van Craenenbroeck, M.D., of Antwerp University Hospital in Belgium led a small study of 10 divers that showed endothelial function, which regulates blood clotting and the forming of new blood vessels, dropped significantly after each Nitrox dive -- and didn't fully recover between dives. Endothelial repair mechanisms to fix problems appeared activated as well. Based on those results, Van Craenenbroeck said that, in her opinion, the use of regular compressed air was safer for blood vessels.

"We already knew diving was bad for the endothelium," Van Craenenbroeck told MedPage Today, noting that one prior study suggested endothelial function didn't return to baseline until more than six days after just a single dive. "Diving with nitrox generates less bubbles during decompression, but elicits more hyperoxia [excess oxygen]. We know that the hyperoxia during diving elicits oxidative stress and subsequent endothelial dysfunction."

What effect these repeated dings to blood vessels' function and repair mechanisms have on the cardiovascular outcomes for frequent divers isn't known, but Van Craenenbroeck said it might lead to more atherosclerosis and coronary artery disease. Still, she says, divers have a choice in the gas mix they use, and they could attempt to protect their vessels by, say, a pre-conditioning jog before going into the water, because this method boosts oxygenation in soccer players and stimulates endothelial progenitor cells in healthy individuals.

However, Petar DeNoble, senior research director of Divers Alert Network says the study sample of 10 divers is just too small to make results applicable to all divers. "I would like to see similar results reproduced in a larger sample before accepting the results as a fact.

He also has an issue with the researcher's explanation that nitrox elicits more vascular stress. "This assumes that nitrox induces more stress on [endothelial function] based on previous studies from the same institutions, but effects of nitrox on the endothelial dysfunction have not been shown consistent across the spectrum of available studies. The dynamic of changes in [new blood vessels] may be part of normal adaptive reactions and not a manifestation of disease or injury. Without specific knowledge about true meaning of these changes, in absence of any indicators of disease or injury, one should not consider them a valid indicator of beneficial or damaging effects of one breathing gas over another. . . No big conclusions should be based on this."