INTRODUCTION

Early detection of symptom progression is a top research priority to improve outcomes and quality of life in interstitial lung disease (ILD). Greater variability in home FVC may be associated with disease progression in fibrotic ILD (Veit et al. 2020).

OBJECTIVE

Assess whether trajectories of home spirometry variability were associated with dyspnoea.

METHODS

Clinical data at baseline and 3 months, paired with 105-day blinded home spirometry (1/day) via smartphone app, were obtained from a prospective observational study of fibrotic ILD (Khan et al. 2019). Quality assurance excluded a 15-day learning period, extreme outliers and low adherence (<20%). Standard deviation in weekly FVC, FEV1, PEF, and FEF25-75 were clustered into trajectories using latent class growth analysis. The primary endpoint was worse modified MRC dyspnoea score at 3-months compared to baseline. Logistic regression was adjusted for sex, age and baseline FVC.

RESULTS

A total of 101 individuals and 7,545 manoeuvres were included, median daily adherence 76.2%. Two clusters of trajectory were optimal in each spirometry measure, characterised by increasing and decreasing standard deviation. Worsening dyspnoea was not associated with variability in FVC or FEV1 over time. Decreasing variability in PEF and FEF25-75 was associated with greater risk of worse dyspnoea at 3 months, OR 4.05 (95%CI 1.05; 15.60) and OR 5.40 (95%CI 1.14; 25.61), respectively, compared to those with increasing variability over time.

CONCLUSION

Daily home spirometry distinguished trajectories of increasing or decreasing variability. Declining variability of peak expiratory and peripheral airway flow were associated with greater risk of worsening dyspnoea.