Abstract Rationale Exertional desaturation during the six-minute walk test (6MWT) is a key prognostic indicator in fibrotic interstitial lung disease (ILD). However, the relative contribution of physiological parameters such as FVC, DLCO, and resting oxygenation remains unclear. Objectives To identify independent determinants of exertional desaturation and to visualize their combined effects using ordinal logistic regression and stratified probability modeling. Methods We conducted a single-center retrospective cohort study including patients with fibrotic ILD who underwent the 6MWT. Desaturation severity was categorized into three groups based on pre- and post-test SpO2: (1) no desaturation, SpO2 88% and ΔSpO2 4%; (2) occult desaturation, SpO2 88% and ΔSpO2 ≥ 4%; and (3) desaturation, SpO2 ≤ 88%. Ordinal logistic regression models were fitted using baseline FVC, DLCO, and pre-test SpO2 as explanatory variables. Bootstrap resampling (1000 iterations) was applied to estimate 95% confidence intervals for predicted probabilities. Stratified analyses and heatmaps were generated to visualize the joint effects of predictors. Measurements and Main Results A total of 1,273 patients were analyzed (no desaturation: 239; occult: 340; desaturation: 694). In univariable models, lower FVC (β = −0.0326, p 0.001), lower DLCO (β = −0.0554, p 0.001), and lower pre-test SpO2 (β = −0.3788, p 0.001) were each significantly associated with greater desaturation severity. In multivariable models, both FVC (β = −0.0131, OR = 0.987, 95% CI 0.981-0.993) and DLCO (β = −0.0504, OR = 0.951, 95% CI 0.945-0.957) remained independent predictors, as did pre-test SpO2 (β = −0.2463, OR = 0.782, 95% CI 0.726-0.842) in a separate model with DLCO. Stratified and heatmap analyses demonstrated a marked increase in desaturation probability with lower DLCO, further enhanced by reduced FVC or SpO2. Conclusions Reduced FVC, impaired DLCO, and lower resting oxygenation are independent and robust predictors of exertional desaturation in fibrotic ILD. Visualization using bootstrap-based stratified modeling intuitively illustrates these physiological interactions, underscoring DLCO as the most influential determinant. This abstract is funded by: None
Takei et al. (Fri,) studied this question.