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The study shows, In smokers with normal lung function, quantitative CT evidence of lung parenchymal overinflation independently predicts a rapid decline in lung function over the next 2 years.

"This study shows that imaging of the lung is a crucial component to understanding the development of the emphysema and its effect on lung health," Dr. Harvey O. Coxson from Vancouver General Hospital, Canada told Reuters Health by email.

Imaging studies have shown that subjects with normal lung function may have emphysematous destruction in their lungs, he and his colleagues point out in the November issue of the journal Thorax. This fueled their hypothesis that early emphysematous destruction might be associated with a subsequent rapid decline in FEV1 that leads to COPD.

To investigate, Dr. Coxson's team studied 38 current and 105 former heavy smokers who were participants in a lung cancer screening study. All had normal lung function at baseline, despite a smoking history of greater than 30 pack years. (Pack years are calculated by dividing the number of cigarettes smoked per day by 20 and multiplying this figure by the number of years the person has smoked.)

An inspiratory multislice CT scan was obtained for each subject at baseline. During the next 2.3 years, the subjects underwent lung function tests and repeat lung CT scans and the amount of emphysema was determined using custom software.

The mean annual change in FEV1 was -2.3% predicted, the investigators report. On multiple regression analysis, the annual change in FEV1% predicted was significantly associated with baseline percentage overinflated lung area measured on quantitative CT.

The group with greater percent overinflation at baseline showed a rate of decline in FEV1 beyond the normal values expected.

These observations, Dr. Coxson and colleagues conclude, "suggest that when the FEV1 is normal, a quantitative structural assessment by CT scan can distinguish the smokers who will develop COPD from those who will not."

Source: Reuters

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