Evaluation of the short-form 36-item questionnaire to measure health-related quality of life in patients with COPD

STUDY OBJECTIVE: To evaluate the short-form 36-item questionnaire (SF-36) as an instrument for measuring health-related quality of life (HRQL) in patients with symptomatic COPD. DESIGN: Observational data at a single point in time. SETTING: Outpatient pulmonary clinic. PATIENTS: Fifty male patients with COPD and no significant comorbidity. MEASUREMENTS AND RESULTS: HRQL was assessed with the SF-36, which consists of 36 questions that cover nine health domains. Clinical ratings of dyspnea were measured by the multidimensional baseline dyspnea index (BDI). Pulmonary function tests included forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and maximal inspiratory mouth pressure (PImax). The mean (+/- SD) age of the patients was 72 +/- 8 years. The BDI focal score was 5.6 +/- 2.3, FEV1 was 1.32 +/- 0.60 L (48 +/- 22% pred), and PImax was 62 +/- 23 cm H2O. The BDI focal score was significantly correlated with seven of nine components of the SF-36 (range of r, 0.42 to 0.91; p < 0.05). The FEV1 percent of predicted and PImax were significantly correlated with five of nine health components (range of r, 0.30 to 0.65 and 0.31 to 0.61, respectively). Using linear regression model analysis with the different SF-36 components as the dependent variable and BDI, FVC, FEV1, and PImax as independent variables, the BDI score was the only significant predictor of social and physical functioning, role-physical, vitality, pain, health perceptions, and health transition (p < 0.05). CONCLUSIONS: The SF-36 is a valid instrument to measure HRQL in patients with COPD. The severity of dyspnea but not respiratory function was a significant predictor of various components of HRQL.