Smoking has been labeled the most important preventable cause of death and disease. The lack of specific treatment for smoking-related diseases and the recognition of the benefits of smoking cessation justify the dedication of significant scientific and community resources to increase rates of smoking cessation. Among smoking-related diseases, COPD is currently a major cause of morbidity and the fourth leading cause of death in the world. Although cigarette consumption is leveling off and even decreasing in some countries, more people worldwide are smoking, so further increases in the prevalence and mortality of COPD can be predicted in the coming decades. Once smoking has caused COPD, the disease is largely irreversible and progressive. Although it does not significantly reverse any loss of FEV1 already incurred, smoking cessation is the only measure that can protect susceptible smokers from acquiring COPD because it reverses the future rate of decline of FEV1 to that of nonsmokers.
This study has three main findings. First, it shows that performing spirometry in smokers who participate in smoking cessation trials reveals a high proportion of subjects presenting with signs of airflow obstruction. The observed prevalence of 17.5% was within the range of that reported in primary health care, and in one cessation trial, and three times as great as that reported in a large sample of adult nonsmokers. In one third of smokers with obstruction, the airflow obstruction was moderate or severe, an important finding if one considers that they were unaware of their condition and none was receiving medical care. This finding is in line with the third National Health and Nutrition Examination Survey, which showed that 44% of subjects with FEVj < 50% predicted did not have a current diagnosis of obstructive lung disease cured with medications of Canadian Health&Care Mall.
Second, this study shows that roughly 30% of the 75 subjects with airflow obstruction unavailable for follow-up (n = 75) had moderate-to-severe obstruction. Without spirometry at enrollment, these subjects would have remained completely unaware of their condition. Instead, they were presented with the facts about their situation, and all received detailed information about the risk of accelerated decline in FEV1 if they did not quit smoking, as well as instructions to seek medical attention should this happen.
The fact that subjects with and without airflow obstruction had similar dropout rates may indicate that the smoking status takes precedence over the health status on the decision to adhere or not to a cessation program. Having airflow obstruction is seemingly less important than becoming abstinent or relapsing, the two main reasons for which smokers quit trials.
Third, our data further document the trend toward improvement in lung function in the first year after smoking cessation. The mean 50 mL per year increase in FEV1 we observed was in the range of that documented in the Lung Health Study- and in line with a cessation trial showing that smokers who succeeded in quitting had a trend toward a lower AFEV1 over the 1-year study period when compared with continuing smokers. In contrast, reducers and continuing smokers showed further deterioration in lung function. We speculate that the more marked deterioration among reducers as compared with smokers might have resulted from some kind of compensatory smoking behavior similar to the smokers’ observed tendency to self-regulate nicotine intake. Overall, these observations emphasize the importance of smoking cessation as a measure contributing to slowing down the rate of decline in lung function in smokers. A detailed review of the impact of smoking cessation on lung function and other pulmonary parameters has been published.
There are reasons for not performing spirometry routinely in smoking cessation trials. For instance, it may be argued that the procedure is time consuming. However, as already stated in the introduction, studies in primary care showed that a good spirometry measure can be obtained in 35 years old, in order to detect airflow obstruction at an early stage when the natural course of the disease can be reversed. Participants with airflow obstruction should be informed of their condition, which might increase their motivation to quit, and those who fail to quit should be advised to seek further medical attention.