Role of comorbidities in a cohort of patients with COPD undergoing pulmonary rehabilitation

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is often associated with other chronic diseases. These patients are often admitted to hospital based rehabilitation programmes. OBJECTIVES: To determine the prevalence of chronic comorbidities in patients with COPD undergoing pulmonary rehabilitation and to assess their influence on outcome. DESIGN: Observational retrospective cohort study. SETTING: A single rehabilitation centre. PATIENTS: 2962 inpatients and outpatients with COPD (73\% male, aged 71 (SD 8) years, forced expiratory volume in 1 s (FEV(1)) 49.3 (SD 14.8)\% of predicted), graded 0, 1 or >/=2 according to the comorbidity categories and included in a pulmonary rehabilitation programme. Measurements: The authors analysed the number of self-reported comorbidities and recorded the Charlson Index. They then calculated the percentage of patients with a predefined positive response to pulmonary rehabilitation (minimum clinically important difference (MCID)), as measured by improvement in exercise tolerance (6 min walking distance test (6MWD)), dyspnoea (Medical Research Council scale) and/or health related quality of life (St George's Respiratory Questionnaire (SGRQ)). RESULTS: 51\% of the patients reported at least one chronic comorbidity added to COPD. Metabolic (systemic hypertension, diabetes and/or dyslipidaemia) and heart diseases (chronic heart failure and/or coronary heart disease) were the most frequently reported comorbid combinations (61\% and 24\%, respectively) among the overall diseases associated with COPD. The prevalence of patients with MCID was different across the comorbidity categories and outcomes. In a multiple categorical logistic regression model, the Charlson Index (OR 0.72 (96\% CI 0.54 to 0.98) and 0.51 (96\% CI 0.38 to 0.68) vs 6MWD and SGRQ, respectively), metabolic diseases (OR 0.57 (96\% CI 0.49 to 0.67) vs 6MWD) and heart diseases (OR 0.67 (96\% CI 0.55 to 0.83) vs SGRQ) reduced the probability to improve outcomes of rehabilitation. CONCLUSIONS: Most patients with COPD undergoing pulmonary rehabilitation have one or more comorbidities. Despite the fact that the presence of comorbidities does not preclude access to rehabilitation, the improvement in exercise tolerance and quality of life after rehabilitation may be reduced depending on the comorbidity.