The University of Texas Health Science Center at San Antonio is recruiting hundreds of current and former smokers because doctors are trying to find out if certain genes make people more prone to developing chronic obstructive pulmonary disease.

COPD, also known as emphysema, causes tiny air sacs in the lungs to become hyper-inflated, making it hard to breathe.

The volunteers will have their breathing evaluated, then will donate blood so that the National Institutes of Health can see if there is a genetic component to the disease.

"We're really trying to figure out why some people who smoke have a lot of copd, really bad lungs, and other people don't have much disease at all," said Sandra Adams, M.D., pulmonologist.

The UT Health Science Center needs 1,000 current or former smokers over the age of 45 to volunteer for the study.