Module 4: Chronic Obstructive Pulmonary Disease and Occupations - Global Burden of COPD.

GLOBAL BURDEN OF COPD:

Chronic Obstructive Pulmonary Disease, (COPD) is:

• The 6th most important cause of death globally in 1990.
• Expected to rise to 3rd most important cause by 2020.
• Lung cancer which shares many of the same risk factors is expected to rise from 10th to 5th.
• Most of this disease burden is attributed to tobacco smoking, mainly based on the epidemiological experience of the developed world. Although tobacco smoking is the major risk factor for obstructive lung diseases, other risk factors, both environmental and genetic are implicated.
• In developing countries, where there is much less information on the burden of COPD, additional factors have been implicated, in particular domestic exposures to smoke during cooking and infections, either in childhood or later in life.

DEFINITION OF COPD:

Chronic obstructive pulmonary disease (COPD) (Also know as COAD or simply OLD) includes the conditions known as chronic bronchitis and emphysema. It is a disease state resulting predominantly from smoking tobacco and is characterised by airflow obstruction which is generally progressive. It may be accompanied by hyper-reactive airways, and the airway obstruction may be partially reversible.

Description of COPD:

COPD can therefore be thought of as a combination of three conditions, which in any given case may be present in varying degrees of severity.

Chronic bronchitis:

Chronic bronchitis refers to the presence of a chronic productive cough for at least 3 months of the year in two or more successive years in the absence of other recognised causes of chronic cough.

The condition is caused by mucous hypersecretion consequent on mucous gland hyperplasia within chronically inflamed airways.

Emphysema:

Emphysema is a pathological diagnosis describing permanent abnormal enlargement of the airspaces distal to the terminal bronchioles, accompanied by destruction of alveolar walls.

The consequences of emphysema include a reduced surface area for gaseous exchange and loss of lung elasticity, resulting in dynamic collapse of conducting airways and hyperinflation of the lung.

Airflow obstruction:

• Airflow obstruction is a consequence of airways inflammation resulting in reduced diameter of the conducting airways, thereby increasing airflow resistance. Furthermore loss of lung elasticity results in the early closure of airways.
• Airflow obstruction in COPD is usually considered to be largely irreversible. There may be a reversible element as well, which is the component that is the objective of most therapies.
• In COPD the FEV1/FVC ratio is reduced, the FEV1 is reduced and the FVC may be normal or reduced.
• The flow/volume loop assumes a characteristic scooped appearance in airflow obstruction. At the end of expiration there is a prolonged period of low flow, reflecting the small airways disease that is very characteristic of COPD.

Since COPD is a somewhat complex combination of conditions it can be interpreted differently according to context. For example to the clinician COPD is a diagnostic rubric meant to include chronic bronchitis, emphysema and irreversible airflow limitation, or as a continuum where most theraputic modalities are directed at reversible airflow obstruction, or even as a hopeless and uninteresting self-inflicted disease.

To the public health specialist it is often seen simply as a condition suffered by smokers over the age of 40.

Spirometry in COPD:

Spirometry is essential for the detection, diagnosis, assessment and management of patients with COPD and should be performed by adequately trained persons using a spirometer that is of the approved standard, which is calibrated regularly.

Peak expiratory flow rate measurements while helpful in asthma are unsuitable for assessment of COPD.

Why perform spirometry?

1. Detection of airflow obstruction.
   • All patients with symptomatic COPD have airflow obstruction with a reduced FEV1.
   • To diagnose airflow obstruction.
   • To assess the severity of airflow obstruction.
   • Absence of airflow obstruction should alert to the possibility of an alternative diagnosis.
2. Assessment of degree of reversibility.
   • Spirometry should be performed before and twenty minutes after two puffs of a short-acting beta-2 agonist bronchodilator. An improvement in FEV1 ³ 12 % and > 200 ml signifies a significant reversible component and should alert to the possibility of asthma.
3. Monitoring of a trial of systemic corticosteroids.
   • For significant persistent breathlessness a trial of oral corticosteroids is given.
4. Monitoring disease progression.
   • COPD progresses slowly over years. More rapid deterioration indicates an alternative diagnosis e.g. asthma, cardiac failure, pneumothorax.

Staging severity of COPD:

In recent efforts international efforts have been made to increase the focus on COPD, support efforts for its prevention and achieve consensus on its management.

One such effort has been GOLD - the Global Initiative on Obstructive Lung Disease. This initiative has provided the staging of COPD severity shown in the next Table below. This staging is primarily based on FEV1 as % of predicted.