The findings appear in the second issue for July 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
Neil C. Thomson, M.D., of the Departments of Respiratory Medicine and Immunology at the University of Glasgow, and seven associates studied 11 asthmatics who continued to smoke and 10 who quit for six weeks. After only one week of no cigarettes, the researchers said that the lung function test results of the non-smoking patients had improved to a "considerable degree."
"The improvement in lung function seen after smoking cessation was clinically significant," said Dr. Thomson. "It demonstrates that there is a reversible component to the harmful effects of smoking on the airways in asthma."
"The degree of improvement noted for smoking cessation far exceeds that of high-dose anti-inflammatory treatment, such as oral prednisolone, 40 mg daily for 2 weeks, which had no effect on lung function in smokers in our current study and in our previous work," he continued. "The improvement could be due to the removal of the acute bronchoconstrictor effects of cigarette smoke or a reduction in the proinflammatory effects of cigarette smoke on the airways."
In addition to the improved lung function test scores, the "quit" group also showed a reduction in sputum neutrophil counts when compared to those of smokers. Neutrophils are white blood cells (phagocytes) that engulf bacterial and fungal infections, along with ingesting foreign debris.
"Sputum neutrophil counts are reported to be increased in heavy smokers with asthma compared with nonsmokers with asthma," said Dr. Thomson.
The authors noted that in many developed countries, more than 20 percent of adults with asthma are active smokers, with particularly high rates of acute a sthmatics visiting hospital emergency rooms.
The smokers with asthma recruited for this study were aged 18 to 60 and had lung function score results of less than 85 percent of their predicted level. They all had a cigarette history of over 10-pack-years and smoked more than 10 cigarettes a day. The investigators saw no differences in the baseline physiological characteristics between the smoking group and those who quit.
Of the 10 subjects who successfully stopped smoking and completed the six-week study, five used nicotine patches, one employed acupuncture and four quit without any aid. The researchers believe that their findings highlight the importance of smoking cessation for adults with asthma.