Functional outcomes in patients with chronic obstructive pulmonary disease: a multivariate analysis

BACKGROUND: Multiple factors can influence the severity of chronic obstructive pulmonary disease (COPD) and the functioning of patients with COPD, such as personal characteristics and systemic manifestations. OBJECTIVE: To evaluate the different factors that can influence the activity and psychosocial impact domains of the Saint George's Respiratory Questionnaire (SGRQ) in COPD patients. METHOD: Participants, recruited in a university-based hospital, responded to the SGRQ, and in addition, personal, anthropometric, and clinical data were collected. The study was approved by the Institutional Ethics Committee. Data were analyzed using multiple linear regression models, with the SGRQ activity and psychosocial impact scores as outcome variables, and 10 explanatory variables (age, gender, forced expiratory volume in the first second - FEV(1), smoking load, body mass index, oxygen therapy, associated diseases, regular physical activity, participation in a formal rehabilitation program, and SGRQ symptoms score) were considered. RESULTS: The best regression model for predicting the SGRQ activity score (r(2)=0.477) included gender, FEV(1), and SGRQ symptoms. In contrast, the predictive model with the highest proportion of explained variance in psychosocial impact score (r(2)=0.426) included the variables gender, oxygen therapy, and SGRQ symptoms. CONCLUSIONS: The results indicate that the outcomes, while based on functioning parameters in COPD patients, could be partly explained by the personal and clinical factors analyzed, especially by the symptoms assessed by the SGRQ. Thus, it appears that the health conditions of these patients cannot be described by isolated variables, including pulmonary function parameters.