Comparison of clinical features between non-smokers with COPD and smokers with COPD: a retrospective observational study

Background: Smoking is a major risk factor for chronic obstructive pulmonary disease (COPD); however, the similarities and differences in clinical presentation between smokers and nonsmokers are not fully described in patients with COPD. This study was designed to address this issue in a general teaching hospital in the People's Republic of China. Methods: The medical records of patients hospitalized with a lung mass for further evaluation at Zhongshan Hospital, Fudan University, from January 2006 to December 2010 were reviewed and the data of interest were collected. The definition of COPD was according to Global-Initiative for Chronic Obstructive Lung Disease (GOLD) spirometric criteria. Participants who had a previous exacerbation within 4 weeks of admission, airflow limitation due to abnormalities in the large airways, or with other pulmonary diseases were excluded. Included subjects were divided into nonsmokers with COPD and smokers with COPD by a cutoff of a 5 pack-year smoking history. Results: A total of 605 subjects were included in the final analysis. The average age was 64.8 +/- 8.5 years and 62.0% (375/605) were smokers. Eighty percent of the patients had mild to moderate disease (GOLD grade 1-2). Age and years with COPD were comparable between the two groups. Compared with smokers with COPD, nonsmokers with COPD were more likely to be female, reported less chronic cough and sputum, have less emphysema on radiologic examination, and higher measures of forced expiratory volume in the first second percent predicted (FEV1), forced expiratory volume in one second/forced vital capacity (FEV1/FVC%) percent predicted, maximal voluntary ventilation percent predicted, diffusing capacity of lung (DLCO) percent predicted, and DLCO/alveolar volume percent predicted, with lower levels of residual volume percent predicted and residual volume/total lung capacity percent predicted. There were no significant differences between the two groups with regard to distribution of disease severity, vital capacity percent predicted, total lung capacity percent predicted, PaO2, PaCO2, modified Medical Research Council dyspnea score, wheezing, airway reversibility, and comorbidities. Smoking amount (pack-years) was correlated negatively with FEV1 percent predicted, FEV1/FVC% percent predicted, inspiratory capacity percent predicted, inspiratory capacity/total lung capacity percent predicted, and DLCO percent predicted, and correlated positively with GOLD grade and symptoms. Conclusion: Non-smokers with COPD had less impairment in airflow limitation and gas exchange, and a lower prevalence of emphysema, chronic cough, and sputum compared with their smoking counterparts. Tobacco cessation is warranted in smokers with COPD.