Distribution and determinants of Preserved Ratio Impaired Spirometry( PRISm) in smokers attending a tertiary care centre in South India
Background Preserved Ratio Impaired Spirometry (PRISm) is an increasingly recognized spirometric phenotype characterized by reduced forced expiratory volume in one second (FEV₁) despite a preserved FEV₁/forced vital capacity (FVC) ratio. It has been associated with obesity, smoking, metabolic disorders, and increased risk of progression to chronic obstructive pulmonary disease (COPD). However, data regarding PRISm among Indian smokers remain limited. Methods A hospital-based analytical cross-sectional study was conducted among 72 adult smokers attending the Department of Respiratory Medicine of a tertiary care teaching hospital. Eligible participants underwent clinical evaluation, chest radiography, and standardized spirometry according to ATS/ERS recommendations. Demographic characteristics, smoking index, body mass index (BMI), comorbidities, chest radiographic findings, and spirometric parameters were recorded. PRISm was defined as FEV₁ <80% predicted with FEV₁/FVC ≥0.70. Statistical analysis was performed using SPSS version 26.0. Continuous variables were expressed as mean ± standard deviation, while categorical variables were presented as frequency and percentage. Associations were analysed using the independent t-test, Chi-square test, or Fisher's exact test, with a p value <0.05 considered statistically significant. Results The mean age of participants was 54.71 ± 9.60 years, and all were males. PRISm was identified in 37 (51.4%) participants. Obesity demonstrated a significant association with PRISm (p=0.033), with all obese participants exhibiting preserved ratio impaired spirometry. Diabetes mellitus (68.4% vs. 31.6%; p=0.049) and dyslipidaemia (69.2% vs. 30.8%; p=0.015) were significantly more frequent among PRISm patients. The mean smoking index was higher in participants with PRISm (357.51 ± 136.01) than in those without PRISm (309.94 ± 100.32), although the difference was not statistically significant (p=0.097). Most participants with PRISm (91.9%) demonstrated the restrictive phenotype. A significant proportion of PRISm patients had normal chest radiographs despite impaired pulmonary function. Conclusion PRISm is highly prevalent among adult smokers attending a tertiary care centre and is strongly associated with obesity, diabetes mellitus, dyslipidaemia, and restrictive ventilatory impairment. Routine spirometric screening combined with cardiometabolic risk assessment may facilitate early identification of high-risk individuals, enabling timely preventive interventions to reduce future respiratory and cardiovascular complications.