By Gene Emery

Boston - A controversial surgical treatment for emphysema may help some people with the disease breathe easier, but may do more harm than good for those with extensive lung damage, doctors reported on Tuesday.

The operation, known as lung volume reduction surgery, involves removing part of the lung in hopes of easing the breathing of people with emphysema, which affects two million American smokers and ex-smokers and is linked to the death of 100 000 people each year.

The new study, presented on Tuesday at a Seattle meeting of the American Thoracic Society, showed that when diseased tissue was in the upper lobes of the lungs and a patient had little ability to exercise, surgery produced a significant improvement and cut the risk of death nearly in half.

Yet among patients who could still exercise, even though the emphysema had spread throughout their lungs, surgery doubled the risk of death.

"The findings provide critical new information for weighing the benefits and risks of lung volume reduction surgery for the treatment of severe emphysema," said researcher Steven Piantadosi of Johns Hopkins.

Co-author Dr Robert Wise of Johns Hopkins said the findings can also determine which patients will respond well to surgery and which are at risk of complications.

Supporters of the operation said the new study validates their belief that it is an important treatment.

"The surgery improves patients' quality of life, which we believe is the most meaningful outcome for people with severe emphysema," said Joel Cooper of the Washington University School of Medicine in St Louis.

However, statistician James Ware sounded a note of caution in a commentary in the New England Journal of Medicine, where the study will be published on Thursday.

He said that among the 538 volunteers who underwent surgery, the benefits only lasted for two years and the overall death rate was not significantly lower than the 540 patients who did not.

The benefits for people with upper-lobe disease came to light only in an after-the-fact analysis of the data, which can be misleading, he said.

"The evidence does not meet the highest standard of proof," Ware said.

In an editorial in the journal, Jeffrey Drazen and Arnold Epstein said 30 percent of emphysema patients fall into a category where the risks of the surgery are clearly too high.

Among the other patients, they said, lung volume reduction surgery appears to have a benefit.