Introduction Relationships between improvements in lung function and other outcomes in COPD patients are not documented extensively. We examined the association between changes in FEV1 and patient-centred outcomes using pooled data from three indacaterol studies.
Methods We calculated correlations between changes in Transition Dyspnea Index (TDI) and St. George's Respiratory Questionnaire (SGRQ) scores (at 12, 26 and 52 weeks) and exacerbation frequency (rate/year) across five categories of ΔFEV1 with boundary points (in mls) between categories: –500 (lowest value), –50, +50, +150, +250, +500 (highest value), centred at –275, 0, 100, 200 and 375 ml. We also performed generalised linear modelling adjusting for covariates including baseline severity, treatment and ICS use.
Results 3313 patients with non-missing values of relevant variables were analysed, excluding extreme values of ΔFEV1 (outside ±500 ml). TDI and ΔSGRQ at 12 weeks improved and exacerbation rate declined with increasing positive ΔFEV1 (all p<0.001) (see Abstract P148 Table 1). Individual-level correlations were weak (0.06–0.18), reflecting the large variability in the outcomes, but cohort-level correlations were strong (0.76–0.93). Results for the proportion of patients demonstrating an improvement of at least the minimal clinically important difference (MCID) for TDI and SGRQ followed a similar pattern to the meaned data. In general, adjustments for baseline covariates, including level of airway obstruction, had little impact on the relationship between ΔFEV1 and outcomes.
Conclusions These results suggest that larger improvements in FEV1 with long-acting bronchodilator therapy are likely to be associated with larger patient-centred benefits across a range of outcomes.