Chronic obstructive airways
disease} (COAD) is a term used to describe conditions in which there is chronic
limitation to air flow in the lungs.
Flow is reduced for one of two main reasons
: either because airways resistance is increased (normally by narrowing of
airways) or because the outflow pressure is reduced (elastic recoil of lungs is
The main diseases in this category are:
• chronic bronchitis
• asthma (narrowing of
• emphysema (loss of elastic
Heavy smokers who have
persistent cough with sputum, breathlessness on exertion, and airways
The main risk factors for
this type of disease are lifetime smoking exposure, and asthma in childhood.
Acute episodes of infection superimposed on COPD cause acute decline in lung
function and may precipitate acute deterioration of chronic cor pulmonale.
this reason, prophylaxis with pneumococcal and influenza vaccines is advisable
in this group of patients.
Although often suggested, there is no strong
epidemiological evidence that such repeated infection is related to the
long-term progression of airways obstruction seen in these cases.
Asthma is characterized by
reversible airways obstruction in small airways
Asthma is the most common
cause of recurrent breathlessness, cough and wheeze.
It is characterized by
obstruction of small airways by a combination of bronchospasm and mucus
plugging, which fluctuates with time and is frequently partially reversible with
It is a common disorder, affecting around 10% of children
and 5% of adults.
Asthma is due to a complex
chronic inflammatory response in bronchial mucosa
The pattern of responses is
seen in long-standing asthma, whatever the cause, and it has been difficult to
separate distinct mechanisms in asthma triggered by different causes. The
prevailing view is that asthma is a form of low-grade chronic inflammation of
the airways, with a variety of triggers causing acute exacerbations.
In severe disease (chronic
asthma), airway obstruction is persistent despite drug therapy; chronic alveolar
hypoventilation may cause pulmonary vasoconstriction and pulmonary hypertension.
Status asthmaticus refers to severe, acute disease that does not respond to drug
therapy and may cause death from acute respiratory insufficiency.
There have been recent
suggestions that the incidence of asthma is rising, with speculation that this
increase might relate to environmental atmospheric pollution.
Most people with asthma have
mild disease with acute episodes of bronchospasm that are triggered by
• Allergy, e.g. to house dust mites.
• Infection. Viral infection
triggers bronchoconstriction particularly in children.
• Occupational exposure.
Some agents act as allergens, others by direct irritation of airway.
• Drug-induced, e.g.
ß-antagonists and aspirin.
• Irritant gases, e.g.
sulphur dioxide, nitric oxide, ozone in smog.
• Psychological stress. •
Exertion. • Cold air.
The concept that there are
two types of asthma, extrinsic (due to allergy) and intrinsic (due to
constitutional factors), has not been borne out by research; there is much
overlap between asthma with different triggers.
Disease can be controlled by
drug therapy with ß2-adrenoceptor agonists and corticosteroids.
The main events that take
place in the airways in asthma are:
• Bronchoconstriction due to
increased responsiveness of bronchial smooth muscle.
• Hypersecretion of mucus
leading to plugging of airways.
• Mucosal oedema leading to
narrowing of airways.
• Extravasation of plasma in
sub-mucosal tissues due to leakage from vessels.
• Infiltration of bronchial
mucosa by eosinophils, mast cells, lymphoid cells and macrophages.
• Focal necrosis of airway
• Deposition of collagen
beneath bronchial epithelium in long-standing cases.
• Sputum contains
Charcot-Leyden crystals (derived from eosinophil granules) and Curschmann
spirals (composed of mucus plugs from small airways).