Association of preserved ratio impaired spirometry with mortality and airflow obstruction in the silicotics: a longitudinal cohort study

Rationale Preserved ratio impaired spirometry (PRISm), defined as an impaired forced expiratory volume in one second (FEV1) with a preserved ratio of FEV1 to forced vital capacity (FVC), is associated with increased risk of airflow obstruction (AFO) and mortality in the general population. However, evidence is limited among the individuals with silicosis, an old occupational disease with an ongoing outbreak in some developed countries. Objectives To investigate the association of PRISm with the risk of mortality and incident AFO in a cohort of workers with silicosis. Methods A total of 4315 workers aged 18-80 years and diagnosed with silicosis at the Pneumoconiosis Clinic, Tuberculosis and Chest Service during 1981-2019 were enrolled in this study and followed up for a median of 12.3 years till 31 December 2019. Spirometry was included in the diagnostic examination of silicosis and follow-up reassessments. Lung function categories of participants were classified as normal spirometry (FEV1/FVC ≥ 0.7, FEV1 ≥ 80% predicted), PRISm (FEV1/FVC ≥ 0.7, FEV1 < 80% predicted), and AFO (FEV1/FVC < 0.7). The hazard ratio (HR) and 95% confidence intervals (95% CI) were estimated using Cox proportional hazards models adjusting for age, body mass index, tuberculosis history, smoking, and radiographic characteristics. Measurements and Main Results During the follow-up period, a total of 2399 (55.6%) subjects died, 1359 of whom died from respiratory-related diseases, and 780 subjects developed AFO. Subjects with PRISm had significantly increased multivariable-adjusted risk of all-cause death (adjusted HR=1.63, 95% CI 1.44-1.85) and respiratory-related mortality (adjusted HR=1.74, 95% CI 1.48-2.05) as compared with the those with normal spirometry. Besides, there was a higher risk of developing AFO in subjects with PRISm than in those with normal spirometry (adjusted HR=1.46, 95% CI 1.22-1.75). No significant interaction was observed between PRISm and smoking status in the risk of all-cause mortality and incident AFO. Conclusions PRISm is significantly associated with increased all-cause and respiratory-related mortality and a greater risk of progression to AFO among the individuals with silicosis.