Rapid Improvement in Lung Function After Asthmatics Quit Smoking

GLASGOW, Scotland, July 19 -- Within six weeks of their last cigarette, patients with asthma showed a "clinically significant" 15.2% improvement in lung function, found researchers here.

"This demonstrates that there is a reversible component to the harmful effects of smoking on the airways in asthma," according to Neil Thomson, M.D., of the University of Glasgow.

In fact, even after a week off cigarettes, there was a noticeable improvement in lung function, Dr. Thomson and colleagues reported in the second July issue of the American Journal of Respiratory and Critical Care Medicine.

The researchers recruited 32 smokers with asthma from the ages of 18 and 60. Their baseline forced expiratory volume in one second (FEV₁) was less than 85% of predicted and had a 15% or greater reversibility of FEV₁ after nebulized albuterol. They had a smoking history of at least 10 pack-years and smoked at least 10 cigarettes a day.

Of the 32 patients, 11 opted not to stop smoking, and served as a control group, while the remainder attempted to quit, the researchers reported. Ten were able to quit for the full six weeks of the study.

All the participants underwent spirometry and induced sputum at baseline and at one, three, and six weeks. The cutaneous vasoconstrictor response to topical beclometasone, airway response to oral prednisolone, and the sensitivity of peripheral blood lymphocytes to corticosteroids were all measured before smoking cessation and at six weeks.

Even a week after they stopped smoking, the quitters showed a "considerable degree" of improvement in lung function, Dr. Thomson and colleagues found: The mean change in FEV₁ was 356 mL, while there was no change in the smokers. The difference was statistically significant at P=0.015.

At six weeks, they found:

• The mean improvement in FEV₁ was 407 mL for the quitters (ranging from 21 to 793), which was significantly different from the smokers at P=0.04.
• The proportion of neutrophils in sputum was reduced by 29 (ranging from 51 to eight) for the quitters compared to the smokers. Again the difference was significant, at P=0.039.
• The total cutaneous vasoconstrictor response score to topical beclometasone improved after smoking cessation with a mean difference of 3.56 (ranging from 0.84 to 6.28), between quitters and smokers; the difference was significant, at P=0.042.
• Airway corticosteroid responses did not change after smoking cessation.

The researchers noted that members of the quit group remained in the study unless they admitted to re-starting smoking; this method is likely to overstate the number who manage to stay off cigarettes for the full six weeks of the study. However, if some of the quit group were actually smoking, that would tend to cause an underestimate of the effects of quitting, they added.