Clinical characteristics and functional parameters in significant smokers with preserved FEV1/FVC ratio: correlation with quality of life and exercise capacity

<bold>Background:</bold> Spirometry typically defines COPD through airflow obstruction (FEV1/FVC < 0.7), but many significant smokers maintain a preserved FEV1/FVC ratio. <bold>Objective:</bold> Our study aimed to investigate significant smokers with normal spirometry. The goal was to detect smoking-induced airway obstruction before conventional obstruction criteria are met. We explored secondary spirometric parameters and correlated them with symptom severity using various questionnaires. <bold>Methods:</bold> We conducted a study involving 60 participants divided into symptomatic (CAT score ≥ 10) and asymptomatic (CAT score < 10) groups. We assessed associations between quality of life (QOL), exercise capacity, and functional parameters. Questionnaires used included the CAT, SGRQ, and mMRCds. <bold>Results:</bold> Symptomatic smokers, despite preserved FEV1/FVC ratios, exhibited reduced forced expiratory flow (FEF25: 76.8 vs. 86.7, FEF50: 71.4 vs. 88.4, FEF75: 75.1 vs. 90.7 as a percentage of predicted values) and peak expiratory flow (PEF: 84.2% vs. 93.7% of predicted value) compared to asymptomatic counterparts. QOL indicators (SGRQ-Activity Score: 49.4 vs. 23.3, SGRQ-Impact Score: 29.5 vs. 7.8) significantly differed between groups. Strong negative correlations were found between the 6-minute walk test and CAT score in symptomatic group (−0.69), indicating reduced exercise capacity and poorer QOL. <bold>Conclusion:</bold> Our findings emphasize the importance of exploring novel parameters beyond traditional spirometry to identify early manifestations of smoking-induced airway obstruction. Integrating QOL assessments and exercise capacity indicators enhances its understanding.