More recent evidence supports the clustering of certain comorbidities with COPD [68], thereby suggesting potential common pathobiological pathways for these diseases. There is also increasing evidence that acute exacerbations of respiratory symptoms in patients with COPD may be caused by extrapulmonary mechanisms and exacerbations of concomitant chronic diseases, such as systemic arterial hypertension, acute heart decompensation, atrial fibrillation and pulmonary embolism [69]. Conversely, COPD exacerbations appear to impact the risk of cardiovascular events [70]. Although acute exacerbations of respiratory symptoms occur more frequently in patients with COPD, they also occur with significant frequency in smokers without COPD, suggesting that they are not specific for COPD [71, 72]. Patients with COPD have a similar prevalence of sleep apnoea as the general population. When this overlap syndrome exists, patients are treated with continuous positive airway pressure, because this has been
shown to decrease mortality [73].