Suzanne McLaughlin, age 16, of Scottsdale, Ariz., for her question:

WHAT CAUSES EMPHYSEMA?

Emphysema is a lung disease in which the victim has difficulty exhaling. The disease destroys the small air sacs in the lungs through which oxygen enters the blood and carbon dioxide leaves it. The cause of emphysema is unknown, but many doctors say that air pollution and cigarette smoking should take much of the blame.

About 13 times as many smokers as nonsmokers get emphysema. More than a million people in the United Staes and Canada have emphysema. In 1970 the disease killed more than 30,000 people while it killed fewer than 1,500 in 1950.

Although emphysema cannot be cured, victims may have long and reasonably active lives with early treatment.