Lung function differences between subjects with tobacco smoke-induced COPD (TS-COPD) and biomass smoke-induced COPD (BS-COPD) in an Indian population

Exposure to biomass fuel smoke is as an important risk factor for COPD (BS-COPD), but it is not known whether this phenotype is different from tobacco-smoke induced COPD (TS-COPD) with reference to lung physiological changes. Aim: To compare lung function profiles between subjects with BS-COPD and TS-COPD. Methods: 17 BS-COPD (mean 43 yrs exposure) and 35 TS-COPD (mean 43 smoking pack yrs) subjects underwent pre and post bronchodilator spirometry to measure FEV1, FVC and FEF25-75%, bodyplethysmography to measure residual volume (RV) and total lung capacity (TLC), impulse oscillometry (IOS) to measure R5Hz and R20Hz and single-breath DLCO to measure lung diffusion. Two sample “t” test was used to compare mean (±SD) lung function parameters between the two groups. Results: There were no significant differences in% predicted values for FEV1, FVC, R20Hz, RV and TLC between TS-COPD and BS-COPD (all p values >0.05). However, BS-COPD showed a trend towards greater small airway obstruction indicated by lower FEF25-75% predicted values [BS: 9% (±3%) vs TS: 12% (±5%), p= 0.02], higher R5Hz% predicted values [BS: 272% (±65%) vs TS: 222% (±94%), p= 0.05] and higher R5-20Hz values normalised to total airway resistance [BS: 0.53 (±0.07) vs TS: 0.46 (±0.13) p=0.05], while TS-COPD showed lower% predicted values for DLCO [TS: 53% (±24%) vs BS: 71% (±33%); p=0.03]. Conclusion: BS-COPD shows similar decrements in Spirometric, IOS and body plethysmographic parameters as TS-COPD. However, BS-COPD was associated with greater small airways obstruction, while TS-COPD was associated with lower DLCO values.