The UCSD shortness of breath questionnaire has longitudinal construct validity in idiopathic pulmonary fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease that often causes disabling dyspnea. In IPF and other lung diseases, patient-reported outcomes (PROs)-questionnaires designed to gather information from the patient's perspective-can determine whether therapies affect dyspnea or other outcomes meaningful to patients. Before a PRO can be used confidently as an outcome measure in a longitudinal trial, studies must demonstrate the PRO's ability to capture change over time in the target population. Our goal in this study was to examine whether the UCSD Shortness of Breath Questionnaire does so in patients with IPF.

Methods: We used data from the Sildenafil Trial of Exercise Performance in Idiopathic Pulmonary Fibrosis (STEP-IPF) to perform analyses that examined associations between UCSD scores and five external measures (anchors) at baseline and over time. Anchors included the Activity domain from St. George's Respiratory Questionnaire (SGRQ-A), the Physical Functioning domain from the SF-36 (SF36-PF), forced vital capacity (FVC), diffusing capacity of the lung for carbon monoxide (DLCO), and distance walked during a timed walk test (6MWD). Linear regression models were used to examine relationships between UCSD scores and anchors over time.

Results: At baseline, UCSD scores were weakly correlated with percent predicted FVC (-0.21, p = 0.005) and percent predicted DLCO (-0.20, p = 0.008), moderately correlated with 6MWD (-0.39, p < 0.0001) and strongly correlated with SGRQ-A (0.79, p < 0.0001) and SF36-PF (-0.72, p < 0.0001). Change over time in UCSD scores was associated with change in FVC (estimate = 2.54, standard error [SE] = 1.23, p = 0.04), SGRQ-A (estimate = 7.94, SE = 1.11, p < 0.0001), SF36-PF (estimate = 6.00, SE = 1.13, p < 0.0001), and 6MWD (estimate = 4.23, SE = 1.18, p = 0.0004) but not DLCO (estimate = 0.33, SE = 1.33, p = 0.80).

Conclusions: These results support the validity of the UCSD to assess change in dyspnea over time in patients with IPF.