SPIROMETRY AND DYSPNEA IN PATIENTS WITH COPD - WHEN SMALL DIFFERENCESMEAN LITTLE

Objective: To determine when a difference in FEV(1) is sufficiently la rge to be associated with a noticeable difference in dyspnea symptoms for patients with chronic lung disease. Design: Cross-sectional analys is of 15 groups (n=112 patients, 832 contrasts).Setting: Respiratory r ehabilitation program. Patients: Patients with COPD (mean FEV(1)=35% p redicted). Measures: Patients' perspectives assessed through subjectiv e comparison ratings of dyspnea and of overall health. Relation betwee n the FEV(1) and patients' perspectives determined the smallest differ ence in spirometry that was associated with a noticeable difference in patients' symptoms. Results: The FEV(1) was moderately correlated wit h patients' ratings of dyspnea (r=0.29; 95% confidence interval (CI), 0.22 to 0.35). In contrast, the FEV(1) was minimally con,elated with p atients' ratings of overall health (r=0.10; 95% CI, 0.03 to 0.17). The FEV(1) needed to differ by 4% predicted for the average patient to st op rating his or her dyspnea as ''about the same'' and start rating hi s or her dyspnea as either ''a little bit better'' or ''a little bit w orse'' relative to other patients (95% CI, 1.5 to 6.5), This was equiv alent to the average patient's FEV(1) increasing by 112 mL (starting f rom 975 mL and ending at 1,087 mL). Conclusions: Some statistically si gnificant differences in the FEV(1) are so small that they may not rep resent important differences in symptoms for the average patient with severe COPD; an awareness of the smallest difference in FEV(1) that is noticeable to patients can help clinicians interpret the effectivenes s of symptomatic treatments.