Spirometry and Dyspnea in Patients With COPD: When Small Differences Mean Little

doi:10.1378/chest.109.5.1163

Chest

Volume 109, Issue 5, May 1996, Pages 1163-1168

https://doi.org/10.1378/chest.109.5.1163 Get rights and content

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.

Section snippets

Setting

We recruited individuals with severe COPD who were participating in a supervised respiratory rehabilitation program. Participants admitted to the rehabilitation program came from the community, were receiving maximal medical therapy, and had no other active medical conditions (including congestive heart failure, significant anemia, or substantial obesity).⁵ Most individuals in the rehabihtation program had been referred because of reduced exercise tolerance, inability to perform activities of

RESULTS

We recruited 112 patients in groups of between 5 and 13 individuals (15 groups). The typical participant was 67 years old with symptomatic COPD for 10 years. Half were men and half were women. The distributions of age, gender, and spirometry were similar to the general characteristics of patients enrolled in the respiratory rehabilitation program.⁷ Patients varied in their severity of disease, with FEV₁ values ranging from 12% predicted to 86% predicted. The mean FEV₁ was 35% predicted (SD=16),

DISCUSSION

Dyspnea in patients with chronic lung disease is a complex subjective phenomenon accompanied by complex neurophysiology.⁸ In this study, we estimated the threshold at which a difference in FEV₁ tended to be associated with a small but noticeable difference in breathing for the average patient with severe COPD. By comparing objective differences in FEV₁ to subjective comparison ratings of breathing ability, we found that the threshold for the FEV₁ was about 112 mL for patients who had an average

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: This project was funded through an Ontario Career Scientist award (Dr. Redelmeier), an Ontario Ministry of Health Research Personnel Development Fellowship award (Dr. Min), and grants from the Ontario Thoracic Society, the National Cancer Institute of Canada, and the West Park Hospital Foundation (Dr. Redelmeier).

View full text

Chest

Spirometry and Dyspnea in Patients With COPD: When Small Differences Mean Little

Objective

Design

Setting

Patients

Measures

Results

Conclusions

Section snippets

Setting

RESULTS

DISCUSSION

J Clin Epidemiol

Lancet

Chest

Pulmonary-function testing

N Engl J Med

Evaluation of clinical methods for rating dyspnea

Chest

The natural history of chronic airflow obstruction

BMJ

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Can Med Assoc J

Standardization of spirometry, 1994 update

Am J Respir Crit Care Med

Exertional breathlessness in patients with chronic airflow limitation: the role of lung hyperinflation

Am Rev Respir Dis

Lung function testing: selection of reference values and interpretative strategies

Am Rev Respir Dis

Assessing the clinical importance of symptomatic improvements: an illustration in rheumatology

Arch Intern Med

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J Rheumatol