Asthma pressure may shrink airways.

The chest tightness that an asthma patient experiences may be in part the cause of the disease as well as a symptom.

Most physicians and scientists have believed that inflammation alone causes air passages to gradually narrow in asthmatics. However, researchers at the Massachusetts Institute of Technology have discovered that the tightening of chest muscles during an asthma attack can trigger long-term changes in airways that constrict the passages.

"Inflammation doesn't explain the whole story," says Barbara Ressler, who is now at Genzyme Corp. in Framingham, Mass. Ressler and her colleagues at MIT and Brigham and Women's Hospital in Boston realized that cells lining asthma-tightened airways are under lots of mechanical stress.

The researchers examined how that stress might affect the cells in asthmatics. To simulate an asthma attack, Ressler grew airway cells from rats in a culture dish and then applied air pressure to mimic muscle tightening.

Cells under pressure activated the genes for at least three proteins that promote cell growth, the researchers found. These growth factors could cause airway-lining cells to reproduce, eventually thickening the lining and narrowing the air passage, says Ressler.

The growth factors could continue thickening the airway lining long after the muscles relax, Ressler says. Although the thickening could occur even when there's no inflammation, swelling from inflammation would exacerbate the problem, she says.

These results probably won't lead to dramatic new treatments for asthma, Ressler says. Bronchial dilators currently used by many asthmatics do a good job of keeping the air passages open and may reduce the mechanical stress on airway cells, she says.