Objective: To determine when a difference in FEV1 is sufficiently large to be associated with a noticeable difference in dyspnea symptoms for patients with chronic lung disease.
Design: Cross-sectional analysis of 15 groups (n = 112 patients, 832 contrasts).
Setting: Respiratory rehabilitation program.
Patients: Patients with COPD (mean FEV1 = 35% predicted).
Measures: Patients' perspectives assessed through subjective comparison ratings of dyspnea and of overall health. Relation between the FEV1 and patients' perspectives determined the smallest difference in spirometry that was associated with a noticeable difference in patients' symptoms.
Results: The FEV1 was moderately correlated with patients' ratings of dyspnea (r = 0.29; 95% confidence interval (CI), 0.22 to 0.35). In contrast, the FEV1 was minimally correlated with patients' ratings of overall health (r = 0.10; 95% CI, 0.03 to 0.17). The FEV1 needed to differ by 4% predicted for the average patient to stop rating his or her dyspnea as "about the same" and start rating his or her dyspnea as either "a little bit better" or "a little bit worse" relative to other patients (95% CI, 1.5 to 6.5). This was equivalent to the average patient's FEV1 increasing by 112 mL (starting from 975 mL and ending at 1,087 mL).
Conclusions: Some statistically significant differences in the FEV1 are so small that they may not represent important differences in symptoms for the average patient with severe COPD; an awareness of the smallest difference in FEV1 that is noticeable to patients can help clinicians interpret the effectiveness of symptomatic treatments.