Rescue workers who responded to the World Trade Center attacks on September 11, 2001 continued to have diminished lung capacity seven years after the attack, researchers reported on Wednesday. Breathing problems among New York Fire Department employees, caused by dust, smoke, and other toxic chemicals, became apparent one year after the twin towers collapsed. Their lung capacity typically diminished as if they had aged 12 years. Doctors had hoped their lungs would gradually rebound, as they often do from routine smoke exposure. But over the next six years, their lungs continued to worsen, said a doctor of the Albert Einstein College of Medicine in New York, who led the study. Firefighters who had never smoked tobacco lost about 25 milliliters of lung volume annually. Emergency medical services personnel lost about 40 milliliters, the researchers reported in the New England Journal of Medicine. The city has been conducting lung capacity tests on its rescue personnel since 1997. Before September 11, very few firefighters scored below normal for their age on the test. Years later, 13 percent did. Among emergency medical services workers, 11 percent had below-normal results before the collapse of the twin towers; seven years later, 23 percent scored low. The study also compared rescue workers who were at the scene initially and those who showed up a day or more later, and found that the early responders suffered the most.