(American Thoracic Society) -- Airway remodeling in asthma, which, over time, slowly becomes less reversible and manifests itself in impaired lung function, begins in childhood and continues into adult life, according to Canadian and New Zealand researchers.

For over a decade, the investigators studied a birth cohort of 1,037 New Zealand children born from 1972 to 1973. The youngsters received lung function tests at ages 9,11, 13, 15, 18, 21, and 26 years as part of an effort to determine the extent of airway remodeling. The researchers developed a lung function test ratio to serve as an airway caliber index. "Normal" study members with no history of asthma, no wheezing in the last year, and no smoking ever were used to determine sex- and age-specific base reference values for the remodeling ratio.

According to the authors, failure to achieve a ratio within the normal range despite the use of a bronchodilator suggested the presence of structural abnormalities in the airway wall, indicating a lack of full reversibility. Airway remodeling in this way occurred in 7.4 percent of the cohort at age 18 and 6.4 percent at age 26. This problem occurred in up to one-third of the patients with asthma. Remodeling was associated with male sex, low lung function values, asthma, and, in childhood, airway hyperresponsiveness.

The research appears in the first issue for June of the American Thoracic Society's peer- reviewed American Journal of Respiratory and Critical Care Medicine.