Introduction Klaus F. Rabe*,#, Jadwiga A. Wedzicha" and Emiel F.M. Wouters+ *Dept of Internal Medicine, Christian Albrechts University Kiel, Kiel. # Lung Clinic Grosshansdorf, Grosshansdorf, Germany. " Centre for Respiratory Medicine, University College London, London, UK. + Maastricht University Medical Center, Maastricht University, Maastricht, the Netherlands. Correspondence: J.A. Wedzicha, Centre for Respiratory Medicine, University College London, Rowland Hill Street, London, NW3 2PF, UK. Email: COPD is a common and progressive chronic inflammatory condition that is responsible for a large amount of morbidity and mortality globally, and affects millions of people worldwide. It is now recognised that COPD is a heterogeneous disease and that the severity of the airflow obstruction, as determined by the forced expiratory volume in 1 second (FEV1), is not the best determinant of the severity of COPD and its impacts. Thus, severity of this disease is now determined by the combination of symptoms, future risk that is mainly related to exacerbation frequency, and FEV1 stage. COPD is not only associated with airway inflammation but also with considerable systemic inflammation, though the precise relationship between the airway and systemic inflammatory processes in COPD remains to be elucidated. It has been proposed that this systemic inflammation is responsible for the considerable comorbidity that is seen in COPD. Thus, COPD is a disease that reaches far outside the lung, and comorbidity is found in all stages of COPD even in patients with mild and moderate COPD by FEV1 stage. Cigarette smoking is the main risk factor for COPD and it is also a risk factor for other major diseases, such as cancer and cardiovascular disease, which are also more common with increasing age. These comorbidities will have an influence on the severity of COPD, and need to be addressed in severity and impact scores for COPD. Management of comorbidities will also have an effect on outcome in COPD there is, for example, emerging data that COPD patients with cardiovascular risk who are treated with beta blockers have a better outcome, particularly when admitted to hospital with COPD exacerbations. Similarly, bronchodilator and anti-inflammatory therapy in COPD may impact on the degree of comorbidity, although historically, COPD patients with comorbidities have been excluded from clinical trials. This issue of European Respiratory Monograph (ERM) aims to address the inter-relationships of COPD and comorbidity, a very wide and diverse topic, as can be seen from the contents list. There has been considerable recent emphasis on the study of comorbidity in COPD and a number of new studies have been published. Thus, the chapters are up to date, well referenced and written by a team of international experts with a clinical focus. The ERM starts with a description of the epidemiology of comorbidity as applied to COPD, and this is followed by a description of inflammatory mechanisms of COPD and how these relate to comorbidity. The chapters that follow discuss cardiovascular disease in COPD there has been much interest in cardiovascular comorbidity as it accounts for a considerable amount of mortality in COPD. However, cardiovascular disease is often unrecognised in COPD and it is important to understand its impact both during exacerbations and when patients are stable. Heart failure is common in an ageing population and thus frequently coexists in COPD with overlap of symptoms. Pulmonary hypertension affects the prognosis of COPD but may often be undetected. Airway infection contributes to the mechanisms of both stable COPD and exacerbations, and it is known that airway infection may be associated with increased cardiovascular events and haematological abnormalities. Pneumonia is an important comorbidity in COPD, with recent data Eur Respir Monogr 2013 59: ix–x. Printed in UK all rights reserved, Copyright ERS 2013. European Respiratory Monograph DOI: 10.1183/1025448x.10001213. Print ISBN: 978-1-84984-032-3. Online ISBN: 978-1-84984-033-0. Print ISSN: 1025-448x. Online ISSN: 2075-6674. ix
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