Study objective: To determine the physiologic factors that influence the health-related quality of life (HRQL) in patients with stable COPD and to identify the factors that most influence HRQL.
Methods: The Nottingham Health Profile (NHP) was used as a general HRQL measure and the Chronic Respiratory Disease Questionnaire (CRQ) was used as a disease-specific HRQL measure to investigate 132 patients with stable COPD, and measurements of HRQL were compared with physiologic measures.
Results: Vital capacity, FEV1, the ratio of the FEV1 to the FVC, diffusion capacity for carbon monoxide, diffusion capacity corrected for alveolar volume, lifetime cigarette consumption expressed as pack-years, and age were weakly correlated with several dimensions of both the NHP and the CRQ. Factor analysis reduced these variables to three factors. Two factors mainly referring to airflow limitation and diffusing capacity were weakly correlated with several dimensions of both the NHP and the CRQ. Logistic regression analysis identified 4 independent predictors of HRQL: airflow limitation (odds ratio [OR] = 0.59 to 0.69), diffusing capacity (OR = 0.75 to 0.82), pack-years (OR = 1.20 to 1.23), and age (OR = 2.13). The CRQ was more sensitive to impairment of HRQL than the NHP.
Conclusions: The HRQL of patients with stable COPD is partly determined by airflow limitation, diffusing capacity, pack-years, and age. However, these factors could not predict the whole spectrum of HRQL, and the contribution of these factors to HRQL was limited. Therefore, HRQL should be measured directly in addition to physiologic measures.