Background: Physical activity (PA) is associated with disease severity in idiopathic pulmonary fibrosis (IPF), but\nlongitudinal studies evaluating its prognostic value and changes over time are lacking.\nMethods: We measured PA (steps per day, SPD) in a cohort of 46 IPF-patients (mean age, 67 years; mean FVC, 76.\n1%pred.) by accelerometry at baseline, recorded survival status during 3 years follow-up and repeated measurements\nin survivors. We compared the prognostic value of PA to established mortality predictors including lung function\n(FVC, DLCO) and 6-min walking-distance (6MWD).\nResults: During follow-up (median 34 months) 20 patients (43%) died. SPD and FVC best identified non-survivors\n(AUROC-curve 0.79, p < 0.01). After adjustment for confounders (sex, age, therapy), a standardized increase (i.e. one SD)\nin SPD, FVC%pred. or DLCO%pred. was associated with a more than halved risk of death (HR < 0.50; p < 0.01).\nCompared to baseline, SPD, FVC, and 6MWD annually declined in survivors by 973 SPD, 130 ml and 9 m, resulting in\nrelative declines of 48.3% (p < 0.001), 13.3% (p < 0.001) and 7.8% (p = 0.055), respectively.\nConclusion: While PA predicts mortality of IPF patients similar to established functional measures, longitudinal decline\nof PA seems to be disproportionally large. Our data suggest that the clinical impact of disease progression could be\nunderestimated by established functional measures.
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