Supplementary Material for: The association between preserved-ratio impaired spirometry and depression: results from a prospective population-based study

Introduction: The relationship between preserved-ratio impaired spirometry (PRISm) and depression remains unclear. This study aimed to assess the bidirectional relationship between PRISm and depression using data from a national cohort.
Methods: Data from Wave 2 (2004–2005) to Wave 4 (2008–2009) of the English Longitudinal Study of Ageing (ELSA) were analyzed. Lung function and depressive symptoms were measured at baseline and follow-up. Cox proportional hazard models were used to calculate the hazard ratio (HR) of PRISm with depression (Study 1) and depression with PRISm (Study 2).
Results: Studies 1 and 2 included 2,934 and 2,277 participants, respectively. The follow-up period extended from Wave 2 to Wave 4. In univariate analyses, a bidirectional association between PRISm and depression was observed, with unadjusted HRs of 1.49 (95% confidence interval [CI], 1.12-1.99; P=0.007) in Study 1 and 1.69 (95% CI, 1.13-2.52; P=0.010) in Study 2. However, in multivariable Cox models, baseline PRISm was not associated with subsequent depression development (adjusted HR 1.26; 95% CI, 0.94-1.69; P=0.128). Conversely, participants with depression had a significantly higher risk of developing PRISm compared to those without depression (adjusted HR 1.54; 95% CI, 1.03-2.32; P=0.038). These findings were consistent with z-score-based interpretive strategies, with an adjusted HR of 1.30 (95% CI, 0.95-1.77; P=0.105) in Study 1 and 1.59 (95% CI, 1.03-2.47; P=0.038) in Study 2.
Conclusions: Depression was associated with an increased risk of developing PRISm, whereas PRISm did not increase the risk of developing depression. Physicians should be vigilant for potential PRISm development in patients with depression.