Abstract
The transition dyspnea index (TDI) is widely used to measure changes in subjectively perceived dyspnea over time in COPD patients. The original interview version assesses the impact of daily activities on dyspnea in the subdomains of functional impairment, magnitude of task, and magnitude of effort, which are further condensed into a summary score. However, the TDI is often used as a self-administered paper-and-pencil questionnaire. The validity of this questionnaire format has not been tested, which was the aim of the present study. We tested 190 patients with COPD at start and end of a 3-week inpatient pulmonary rehabilitation program (PR). Dyspnea was assessed with the modified Medical Research Council Scale (mMRC), a questionnaire version of the TDI (TDI-quest), and an interview version of the TDI (TDI-int). Group means for the TDI questionnaire and interview version were widely comparable for the TDI summary score (4.3 vs. 4.5) and for the subdomains functional impairment (1.2 vs. 1.4), magnitude of task (1.8 vs. 1.8), and magnitude of effort (1.3 vs. 1.3). The scores of both TDI versions were strongly correlated and showed comparable, but only modest, correlations with changes during PR in FEV1, FVC, and mMRC. Improvement in dyspnea after PR was observed in 89% of patients when using the summary score of TDI-quest, but only in 34% of patients when using the mMRC. The findings suggest that a self-administered questionnaire version of the TDI provides widely comparable results as those obtained by interviewers. Furthermore, the responsiveness of this instrument to changes in dyspnea during PR appears greater than the responsiveness of the mMRC.