1.2.1 What is COPD?
COPD is a chronic inflammation of the airways leading to fixed airflow obstruction and restricted gas exchange. The term COPD includes two basic respiratory pathologies: chronic bronchitis and emphysema (GOLD, 2006) that are described below. The condition is not reversible and may progressively worsen with time (NICE, 2010).
Chronic bronchitis: is the narrowing of the bronchi and bronchioles due to thickening of the airway walls and enlargement of mucus glands from chronic inflammation (Hogg, 2008). COPD caused by chronic bronchitis is characterized by excessive mucus production and expectoration, with mucus plugging contributing to obstruction of the bronchial tree, leading to symptoms of wheeze and shortness of breath.
Emphysema: is characterized by destruction of the lung parenchyma and alveolar enlargement leading to loss of alveolar attachments, loss of functional gas exchange surface and loss of elastic tissue recoil (CosioPiqueras and Cosio, 2001). Together these changes lead to airflow obstruction and breathlessness.
1.2.2 COPD definition and stages
Clinically, COPD and its severity are defined by the presence and magnitude of airflow obstruction. This is assessed with spirometry. Airflow obstruction is measured, post-bronchodilator, as the ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC), with a value of < 0.7 indicating presence of airflow flow obstruction and therefore COPD (GOLD, 2006). The severity of COPD is clinically categorised into four stages by the Global initiative for Obstructive Lung Disease (GOLD), based on the predicted percentage (%) of normal FEV1, in subjects presenting with < 0.7 FEV1/FVC post-bronchodilator ratio (GOLD,2006) (Table 1.1).
Table 1.1: GOLD stages of COPD severity GOLD 2016
All the stages had FEV1/FVC ratio <0.7, post-bronchodilator
Although a useful guide, severity assessment based on FEV1 alone is considered a weak marker for predicting morbidity and mortality as there is a poor association between extent of airflow obstruction and common COPD symptoms like breathlessness, exercise capacity and health status, (Celli et al., 2004). Several other measures such as the BODE (body mass index (B), airflow obstruction (O), dyspnoea (D), exercise capacity (E)) and ADO (age (A), dyspnoea (D) and airflow obstruction (O) indices have been developed and are superior for accurately defining disease severity (Puhan et al., 2009).
1.2.3 COPD symptoms
COPD patients experience shortness of breath and suffer from tightness in their chest, which leads to wheezing and laboured breathing. Damage to the lung parenchyma and recoiling mechanisms causes poor oxygenation of blood and accumulation of carbon dioxide (GOLD, 2006). COPD is characterized by persistent cough, sputum production due to excess mucus secretion by damaged airways and impaired ciliary mucus clearance. Expectoration of green or yellow coloured purulent sputum is also observed in some cases and has been associated with bacterial infective COPD (Miravitlles et al., 2010). All these symptoms lead to COPD patients having an impaired quality of life, weight loss, anxiety, depression and fatigue.
1.2.4 COPD burden
COPD is a major cause of morbidity and mortality both in well- and poorly- resourced countries. COPD is one of the leading causes of death contributing 5.8% of all deaths and, globally, ranks fourth (WHO, 2008). In the UK it ranks third among respiratory diseases and is the fifth most frequent cause of death (National Clinical Guideline Centre, 2010). The World Health Organization (WHO) predicts that COPD will be the third biggest killer globally by 2030.
The economic burden of healthcare for COPD is substantial. In England, COPD is one of the most costly inpatient conditions treated and is the 2nd commonest cause of emergency admission to hospital (National Clinical Guideline Centre, 2010). The economic impact includes both healthcare costs and costs associated with loss of earnings and productivity due to morbidity and premature mortality in patients of working age (National Clinical Guideline Centre, 2010).
The prevalence of COPD is grossly underestimated due to sufferers being unaware, stigma associated with smoking related diseases and misdiagnosis of the condition when healthcare advice is sought. It is estimated that in the UK about two thirds of COPD cases are undiagnosed (British Lung Foundation, 2007), representing a reservoir of disease with implications for future healthcare. Many patients will eventually present at a late stage of disease and require hospital admission. COPD is also associated with several comorbidities including cardiovascular disease, cancer and mental health problems (Decramer and Janssens, 2013). The cost and complexity of care escalates with the number of these co-morbid conditions.
1.2.5 COPD cause and risk factors
Several environmental and genetic factors play a key role in development of COPD. Topmost among these are smoking and working in a polluting environment.
Tobacco smoking and inhalation: Approximately 85% of COPD cases are attributed to smoking making it the leading risk factor for COPD (Department of Health, 2012). Tar and harmful chemicals released from cigarettes and tobacco smoke causes damage to all parts of respiratory system from the major to smaller peripheral airways and gas exchange areas. Damage can be caused by both active and passive smoking. Smokers compared to non-smokers show significant shortening and reduced beating of their airway cilia, leading to impairment of mucocilliary defence and increased risk of infection (Leopold et al., 2009). Long term smoking causes hyper-mucus secretion, infiltration of inflammatory cells and many of the structural changes described for COPD. Smoking is a global problem and mortality from COPD is projected to increase by more than 30% in the next decade without interventions to reduce the number of smokers (WHO, 2012).
Coal, Air pollutants and other harmful toxic fumes: COPD is also commonly seen in coal miners due to long term exposure to coal. Long term and persistent exposure to indoor pollutants such as biomass fuel used for cooking and heating is a significant risk factor in developing countries. Outdoor pollutants like toxic chemical fumes and fumes associated with vehicular pollution are also potential risk factors for COPD (WHO, 2012).