Many divers have unusually large lungs and this trait may be a product of genes, rather than frequent underwater excursions, according to a new report.

In a study of 109 divers in the Israeli Navy, researchers found that younger, less experienced divers had similar lung volumes as their more seasoned comrades. This, according to the study authors, suggests that people with naturally larger lungs may be at home underwater - and that diving itself may not actually pump up lung volume.

“We suggest that large lungs represent part of the natural selection for diving, rather than a training effect,” the researchers, led by Dr. Yochai Adir of the Israel Naval Medical Institute in Haifa, report in the medical journal Chest.

Some studies have shown that divers frequently have large lungs, often along with lung function that suggests they could have airway obstruction. Specifically, divers may show a low FEV1 percentage, which means they are able to forcefully exhale relatively little air in relation to their total lung capacity. Ordinarily this would indicate potential airway obstruction, such as that seen in asthma.

But the new findings, according to Adir’s team, suggest that, in divers, a low FEV1 percentage does not necessarily arise from airway obstruction, but may instead simply be a reflection of their naturally larger lungs.

On the other hand, the researchers found, there was one difference between novice and experienced divers that suggests long-term diving can damage the airways. The oldest divers, who were between the ages of 36 and 44, showed poorer results on a test that reflects the functioning of the smaller branches of the airways.

This suggests that longtime divers may face the risk of small airways disease - inflammation in the narrower branches of the respiratory system, according to the authors.

Other researchers, they note, have reached a similar conclusion, with evidence suggesting that the high-pressure, oxygen-saturated air that divers breathe may eventually damage the lungs’ small airways.

SOURCE: Chest, July 2005.