Comparison of Six-minute Walk Test Parameters by Severity of Idiopathic and Non-idiopathic Pulmonary Fibrosis

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Objectives: The 6-minute walk test (6MWT) is generally used to evaluate endurance in interstitial lung disease (ILD). In ILD, treatment efficacy differs between patients with idiopathic pulmonary fibrosis (IPF) and those with non-idiopathic pulmonary fibrosis (non-IPF), and the clinical profile varies according to disease severity. This study compared 6MWT parameters by severity of illness in patients with IPF and non-IPF. Methods: The participants were hospitalized patients with ILD and either IPF (n = 20) or non-IPF (n = 25). To compare IPF and non-IPF by severity, patients were classified using the gender–age–physiology (GAP) index as having GAP stage I (i.e., mild) or GAP stage II/III (i.e., moderate to severe). The evaluation parameters were the 6-minute walk distance (6MWD), minimum percutaneous oxygen saturation (SpO₂), heart rate recovery at 1 minute (HRR1) after the 6MWT, and modified Borg scale rating of perceived exertion. Results: The minimum SpO₂ value during exertion was significantly lower in the IPF group than in the non-IPF group (p < 0.05). Furthermore, when comparing by severity, patients with IPF and GAP stage I had a significantly lower 6MWD, HRR1, and SpO₂ value. In patients with GAP stage II/III, there were no significant differences in 6MWD, SpO₂ values, or dyspnea. Conclusions: Patients with mild IPF were more prone to hypoxemia, while in moderate-to-severe cases, we observed no significant hypoxemia- or endurance-related differences between IPF and non-IPF patients. This study highlights the importance of severity-based evaluation, particularly in guiding individualized rehabilitation and risk management for patients with IPF.