Spirometry and Dyspnea in Patients With COPD*: When Small Differences Mean Little.
Redelmeier, Donald A. MD MSc; Goldstein, Roger S. MD FCCP; Min, Simon T. MD; Hyland, Robert H. MD FCCP
[Article] Chest. 109(5):1163-1168, May 1996.

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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 FEV sub 1 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.

(CHEST 1996; 109:1163-68)

Copyright (C) 1996 by the American College of Chest Physicians