Prevalence and risk factors for COPD in subjects with preserved ratio impaired spirometry

BACKGROUND: Chronic obstructive pulmonary disease (COPD) has been found to be caused by impairment of lung development. Preserved ratio impaired spirometry (PRISm) is thought to be a subtype of lung growth impairment and is associated with COPD. PRISm is heterogeneous and the prevalence and progression to COPD are not yet clear. To prove this, we examined the association by using the medical check-up data. METHODS: This retrospective study included medical check-up subjects who visited the Kochi Medical Check-up Clinic at least twice for both period 1 (P1) (2014–2016) for the first visit and period 2 (P2) (2017–2019) for the final visit. The mean duration between visits was 1042±323 days. COPD was defined as a forced expiratory volume in 1 s (FEV(1)):forced vital capacity (FVC) ratio <lower limit of normal (LLN), and PRISm was defined as an FEV(1):FVC ratio >LLN and per cent forced expiratory volume in 1 s (%FEV(1)) (FEV(1)/predicted FEV(1)) of <80% without bronchodilators in this study. RESULTS: Of 1672 subjects (mean age±SD 56.5±9.5), 976 (58.4%) were male. The prevalence of PRISm was 10.5% in P1 and 8.9% in P2. The percentage of subjects who progressed to COPD was higher in PRISm than in the normal lung function group (OR 2.62, p=0.014). In logistic regression analysis, PRISm was an independent risk factor for developing COPD (OR 3.75, p<0.001). The best cut-off value of %FEV(1) for prediction of progression to COPD was 86%. The proportion of the PRISm group increased (23.6%) in this cut-off. CONCLUSION: The prevalence of PRISm was around 10% but increased up to 23.6% at the best cut-off for progression to COPD, and careful follow-up is necessary in these groups even if FEV(1)/FVC is normal.