Background: The 6-min walk test (6MWT) is commonly used to assess exercise capacity in patients with fibrotic idiopathic interstitial pneumonia (f-IIP). However, it is not known whether patients with f-IIP have reduced levels of physical activity in daily life (DLPA) or whether pulmonary function tests and the 6MWT correlate with their DLPA.
Methods: The aim of this study was to measure DLPA in patients with f-IIP and to determine the relationships between DLPA and the 6MWT, pulmonary functional parameters, and anxiety and depression scores. Fifty patients with f-IIP and 25 sex- and age-matched healthy control subjects were enrolled. Markers of DLPA were assessed with a physical activity monitor for 4 consecutive days. Hospital Anxiety and Depression Scale (HADS) scores were evaluated.
Results: DLPA parameters were significantly reduced in patients with f-IIP compared with control subjects (all P < .001). The mean number of steps per day correlated strongly with diffusing capacity of the lung for carbon monoxide (Dlco), FVC, the 6MWT distance, and the 6MWT lowest oxygen saturation as measured by pulse oximetry (Spo₂). DLPA was unrelated to HADS scores. Multivariate analysis showed that Dlco and 6MWT distance explained only 31% of the variance in the number of steps per day. Dlco, 6MWT distance, 6MWT lowest Spo₂, and DLPA were significant predictors of mortality, but only Dlco and 6MWT distance were independent predictors.
Conclusions: Quantitation of DLPA is a novel patient-centered approach to assess function in f-IIP and may be a useful tool for clinical care and assessing response to therapy.