Susceptibility to rhinovirus infection in chronic bronchitis

Mechanisms and impact of the frequent exacerbator phenotype in chronic obstructive pulmonary disease

Exacerbations of chronic obstructive pulmonary disease (COPD) are important events that carry significant consequences for patients. Some patients experience frequent exacerbations, and are now recognized as a distinct clinical subgroup, the 'frequent exacerbator' phenotype. This is relatively stable over time, occurs across disease severity, and is associated with poorer health outcomes. These patients are therefore a priority for research and treatment. The pathophysiology underlying the frequent exacerbator phenotype is complex, with increased airway and systemic inflammation, dynamic lung hyperinflation, changes in lower airway bacterial colonization and a possible increased susceptibility to viral infection. Frequent exacerbators are also at increased risk from comorbid extrapulmonary diseases including cardiovascular disease, gastroesophageal reflux, depression, osteoporosis and cognitive impairment. Overall these patients have poorer health status, accelerated forced expiratory volume over 1 s (FEV1) decline, worsened quality of life, and increased hospital admissions and mortality, contributing to increased exacerbation susceptibility and perpetuation of the frequent exacerbator phenotype. This review article sets out the definition and importance of the frequent exacerbator phenotype, with a detailed examination of its pathophysiology, impact and interaction with other comorbidities.

COPD exacerbations . 2: aetiology

Exacerbations of COPD are thought to be caused by complex interactions between the host, bacteria, viruses, and environmental pollution. These factors increase the inflammatory burden in the lower airways, overwhelming the protective anti-inflammatory defences leading to tissue damage. Frequent exacerbations are associated with increased morbidity and mortality, a faster decline in lung function, and poorer health status, so prevention or optimal treatment of exacerbations is a global priority. In order to evolve new treatment strategies there has been great interest in the aetiology and pathophysiology of exacerbations, but progress has been hindered by the heterogeneous nature of these episodes, vague definitions of an exacerbation, and poor stratification of known confounding factors when interpreting results. We review how an exacerbation should be defined, its inflammatory basis, and the importance of exacerbations on disease progression. Important aetiologies, with their potential underlying mechanisms, are discussed and the significance of each aetiology is considered.

Chronic obstructive pulmonary disease . 6: The aetiology of exacerbations of chronic obstructive pulmonary disease

Exacerbations of COPD are thought to be caused by interactions between host factors, bacteria, viruses, and changes in air quality to produce increased inflammation in the lower airway. The evidence for this and the potential mechanisms by which they result in the characteristic symptoms of exacerbations is reviewed. A better understanding of the causes and processes is needed for the appropriate use of existing treatments and the development of new ones. Future studies need to define populations clearly, stratify for known confounding factors, and should aim to identify clinical correlates so that clinical practice can be modified appropriately.