Introduction Idiopathic pulmonary fibrosis (IPF) is an incurable chronic progressive lung disease with a poor prognosis. Decline in forced vital capacity (FVC) is the primary outcome measure in most clinical trials. However, slowing lung function decline does not translate into patients feeling better. We investigated the acceptability of activity monitoring as a patient centred outcome measure in IPF and correlated results with lung function and quality of life (QoL) measures.

Methods IPF Subjects underwent activity monitoring 23 h a day for a minimum of 8 days using the SenseWear armband (Bodymedia, Philadelphia). Monitoring data from the first and last monitored days were discarded to prevent clinic visits impacting the results. Participants completed the St George’s Respiratory Questionnaire (SGRQ) as a QoL measure. Lung function measurements performed within 3 months were collected and correlations assessed using Pearsons correlation coefficient. Data are presented as mean±SD.

Results 17 IPF subjects (Age 76 ± 6.3, 82% males, FVC%predicted 82.3 ± 16.1%, TLCO% predicted 48.3 ± 13.3%) were monitored. There was excellent compliance – armbands were worn for an average of 23 h and 9 min per day (range: 22 h and 10 min to 24 h) for 6.2 ± 0.6 complete days. Activity levels measured in METs were 1.25 ± 0.2 with a daily step count of 3364 ± 2504. IPF subjects were physically active (METs >3) for 83.8 ± 57.4 min per day. Mean daily METs inversely correlated with SGRQ score (r=-0.64, p = <0.01). Mean daily METs correlated with FVC (% predicted) (r = 0.50, p = 0.04) but there was no correlation with TLCO (% predicted) (r = 0.39, p = 0.13). Conversely TLCO inversely correlated with SGRQ score (r=-0.55, p = 0.03) but FVC did not (r=-0.29, p = 0.26).

Conclusion Activity monitoring is an acceptable, well tolerated means of measuring functional status in IPF patients. Mean daily activity level correlates well with QoL measures and FVC. Neither individual lung function measurement performed as well in terms of correlation with QoL and activity level. A larger longitudinal study is required to further evaluate the role of activity monitoring in IPF and identify its utility in prognostication.