UPDATE 1-Device helps ease severe asthma-study

(Adds comments from CEO interview, paragraphs 6-9; 18-20)

* Device cut extreme asthma attacks, emergency room visits

* Treatment worked in 79 percent of patients

By Julie Steenhuysen

CHICAGO, May 18 (Reuters) - An experimental asthma treatment that uses heat to reduce airway constriction provided some relief from severe asthma that is poorly controlled with medications, U.S. researchers said on Monday.

They said the Alair device, made by privately held Asthmatx Inc of Sunnyvale, California, cut the rates of extreme asthma attacks by 32 percent and reduced trips to the emergency room by 84 percent in patients with severe asthma.

Patients missed fewer days of work or school because of asthma symptoms and had more symptom-free days compared with people who received a placebo, according to results of the late-stage clinical trial, which was presented at a meeting of the American Thoracic Society in San Diego.

The Alair device uses a thin tube to gently heat the walls of the lung's air passages, killing off some of the muscle tissue to reduce narrowing of the airways.

"In asthma, what happens is these patients develop enlarged smooth muscles surrounding their bronchial tubes. That contributes to asthma attacks. The idea is to decrease that," Dr. Mario Castro of Washington University in St. Louis, who led the study, said in a telephone interview.