A new study published in the New England Journal of Medicine on 11th May, 2016, has shown that current or former smokers who do not fall into the category of chronic obstructive pulmonary disease (COPD) can still suffer from respiratory exacerbations, limitation of activity and wall thickening of their lungs.
COPD is an umbrella term used to describe a group of diseases characterised by increasing difficulty in breathing, cough, sputum production and wheezing. It is a progressive disease, meaning it worsens over time.
Cigarette smoking is the leading cause of COPD. Most people who have COPD smoke or used to smoke. Long-term exposure to other lung irritants, such as air pollution, chemical fumes or dust may also contribute to COPD.
COPD is diagnosed by measuring the deficits in the rate at which one can forcefully exhale. The ratio (called FEV/FEV1 ratio) must be less than 0.7 for the patient to be diagnosed with COPD. However, many current and former smokers who do not fall into the category of COPD (but have preserved pulmonThere Is No Such Thing As A “Healthy Smoker”ary function) still suffer from symptoms such as cough, sputum production and breathlessness.
This newly published research has attempted to study this intermediary class of patients, who suffer from symptoms of respiratory dysfunction, but are not yet serious enough to be classified as suffering from COPD.
The study was carried out by physicians and researchers from nine different medical centres and universities (eight of them in the US and one in the UK). It lasted over five years and was a multi-centre observational study funded by the National Heart, Lung, and Blood Institute (NHLBI) and by the Foundation for the National Institutes of Health (FNIH).
The study collected data on 2,736 patients from during the period of 2010-2015. They were either healthy patients who had never smoked or current/former smokers with a history of more than 20 years of smoking.
Patients were studied during a stable phase of their disease and exacerbation history was obtained every three months using a structured questionnaire. All participants underwent multiple tests which included a lung function test called spirometry and determining the distance they walked in six minutes. The participants also had high-resolution computed tomography, done to study airway wall thickness.
Results showed that 50% of all current or former smokers with preserved pulmonary function had respiratory symptoms. The rate of exacerbations was higher among current or former smokers, being particularly high among symptomatic smokers as compared to asymptomatic smokers. The mean distance travelled in six minutes was also shorter in symptomatic smokers than in asymptomatic smokers or healthy individuals. Symptomatic smokers did not have a higher percentage of lung volume with emphysematous changes as compared to asymptomatic smokers or healthy individuals. However symptomatic smokers did have greater airway wall thickening and slightly lower lung function.
Since the patients in the study had significant differences in age, ethnicity, body mass index and current smoking status, multiple statistical methods were used to take into account these confounding factors. However, even after adjusting for all these factors, the findings persisted.
The study challenges the term “healthy smoker” by showing presence of respiratory symptoms, activity limitations and abnormalities in the lung in smokers who are not yet ill enough to be considered diseased according to the current definitions of COPD.
The study also raises the question of whether the clinical definition of COPD needs to be modified, or a new entity needs to be created to cater to this intermediary group of patients who are suffering from respiratory symptoms and limitation of activity, but are not being classified under any category/disease.
The danger of not classifying these patients lies in the fact that unless they are treated for their symptoms, smoking will only make their condition worse until it becomes so severe that they fall into the COPD category.
An important limitation of this study lies in the method of patient recruitment. Patients were not randomly selected from the population but were referred from physicians or volunteered themselves. It is possible that patients who were experiencing symptoms were more likely to volunteer. Thus these findings cannot be used to estimate the population prevalence of symptoms in smokers with preserved lung function. However, neither point invalidates the central conclusion reached by the study.
In summary, smokers suffer from respiratory symptoms and exacerbations even if they have normal lung function according to the current standards of diagnosis. Many of these patients are taking medication for their symptoms, yet there is no evidence from clinical trials to support the use of such medication. Clinical trials are needed to determine whether maintenance therapy with bronchodilators or inhaled glucocorticoids will alleviate symptoms and reduce the rate of respiratory exacerbations in this group.
The current cut-off limits for diagnosis of respiratory dysfunction should be modified to adequately cover the wide range of symptoms experienced by patients. Furthermore, there is a need for further clinical trials in these large and under-studied groups of population. This will enable authorities to develop the best treatment protocols, so that patient symptoms can be controlled before they progress to the stage of COPD.