Abstract Rationale: COPD is typically characterized by persistent airflow limitation, associated with small airway disease and emphysematous changes, while PRISM often presents with impaired lung function without meeting the full diagnostic criteria for COPD. This distinction is particularly relevant in identifying early markers of airway dysfunction that may guide intervention strategies for those at risk of progression from PRISM to COPD. By analyzing structural and functional lung parameters, we aim to clarify the physiological and structural differences between COPD, PRISM, and ever-smokers with normal lung function, enhancing diagnostic and predictive insights for these patient populations. Methods: Using the retrospective chart review, 36 patients were analyzed. These patients were checked for age, sex, smoking status, conventional spirometry, impulse oscillometry, and inspiratory-expiratory chest CT. In addition, we performed the structural analysis based on CT images and checked the airway wall thickness (WT), Luminal diameter (Dh), Anisotropic deformation index (ADI) and Jacobian. Results: Of 36 patients, patients with COPD were 21, PRISM (preserved ratio of impaired spirometry) patients were 6, and ever-smoker with normal lung function were 9. COPD patients were oldest (COPD, 68.24±9.27; PRISM 59.67±12.74; Smoker with normal lung function 54.22±6.59). Compared to ever-smokers with normal lung function, COPD and PRISM groups showed significant differences in impulse oscillometry variables, parametric response mapping (PRM), ADI, and Jacobian values. Notably, PRISM, often considered a pre-COPD state, demonstrated marked differences in small airway dysfunction (measured as R5-R20 difference and AX) and in PRM analysis, highlighting early indicators of airway abnormalities. Conclusion: The findings suggest a continuum of airway and structural lung changes across the groups, with certain variables serving as key markers to differentiate early or mild airway dysfunction. These insights reinforce the value of monitoring structural and functional markers in PRISM patients to identify potential progression toward COPD and offer potential pathways for targeted early intervention.