Correlations between physical activity and prognostic markers in patients with idiopathic pulmonary fibrosis

Background: In this study, we investigated the associations between physical activity parameters and prognostic factors in patients with idiopathic pulmonary fibrosis (IPF). Methods: Physical activity was measured in IPF patients using a SenseWear armband. Demographic data, pulmonary function test results, the 6-minute walk distance (6MWD), the gender-age-physiology (GAP) index score, dyspnea severity (modified Medical Research Council, mMRC), and fatigue severity (Multidimensional Fatigue Inventory, MFI-20) were recorded. Results: Thirty-five IPF patients (29 males, aged 65.7 ± 8.0 years) were included in the study (forced vital capacity (FVC)=77±16.2%, diffusing capacity for carbon monoxide (DLCO)=55.7±16.4%, 6MWD=398.4±88 m, GAP index=3.4±1.1 (18 stage 1, 17 stage 2). Patients with GAP stage 2 had lower step counts than those with GAP stage 1 (3325.1±2253 steps vs. 7892±3132 steps, p<0.001). The time spent in moderate to vigorous physical activity (MVPA, defined as the time spent in activities ≥3.0 METs) was significantly shorter in GAP stage 2 patients than in GAP stage 1 patients (7 minutes [IQR: 1.5–18.5] vs 56 minutes [IQR: 30.5–139.5], p<0.001). The step count and GAP index score (Rs=-0.716, p<0.001), age (Rs=-0.381, p=0.024), FVC (Rs=0.443, p=0.008), DLCO (Rs=0.715, p<0.001), 6MWD (Rs=0.833, p<0.001), MFI-20 score (Rs=-0.783, p<0.001), and mMRC score (Rs=-0.833, p<0.001) were correlated. Multiple regression analysis revealed that the step count was independently associated with the 6MWD (p=0.005) and MFI-20 score (p=0.014). The MVPA time was correlated with the GAP index score (Rs=-0.810, p<0.001), age (Rs=-0.427, p=0.010), FVC (Rs=0.490 p=0.003), DLCO (Rs=0.736, p<0.001), 6MWD (Rs=0.809, p<0.001), MFI-20 score (Rs=-0.830, p<0.001) and mMRC score (Rs=-0.826, p<0.001). Multiple regression analysis revealed that the MVPA time was independently associated with the GAP index score (p=0.007). Conclusions: The physical activity parameters of IPF patients were associated with prognostic markers such as the GAP index score, pulmonary function parameters and the 6MWD.