Diseases of the respiratory system
Pneumoconiosis The term pneumoconiosis means 'dust in the lung', but medically refers to the reaction of the lung to the presence of dust.
Body defence to inhalation of dust During inspiration particles of dust in the air larger than 10mm in diameter are filtered off by the nasal hairs. Others, which enter through the mouth, are deposited in the upper respiratory tract. Particles between 5 mm and 10 mm tend to settle in the mucus covering the bronchi and bronchioles and are then wafted upward by tiny hairs (ciliary escalator) towards the throat. They are then coughed or spat out, though some may be swallowed. Particles less than 5mm in diameter are more likely to reach the lung tissue. However, fibres (e.g. asbestos) which predispose to disease have a length to diameter ratio of at least 3:1 with a diameter of 3 mm or less; the stronger the fibre the more damaging it may be.
Respirable dust Respirable dust is that dust in the air which on inhalation may be retained by the lungs. The amount of dust deposited depends on the duration of exposure, the concentration of dust in the respired air, the volume of air inhaled per minute and the nature of the breathing. Slow, deep, respirations are likely to deposit more dust than rapid, shallow breathing. Dust in the lung causes a tissue reaction, which varies in nature and site according to the type of dust.
Causes of pneumoconiosis
(a) Benign: The inhalation of some metal dusts, such as iron, tin and barium, results in very little structural change in the lungs and, therefore, few symptoms. The tissue reaction, nevertheless, is detectable on X-ray as a profusion of tiny opacities.
(b) Symptomatic: The most important causes include coal dust, silica and asbestos. Symptoms of a cough an breathlessness develop usually after many years of exposure, but only in the later stages of disease
Beryllium dust causes acute and chronic symptoms. Early features are breathlessness, cough with bloody sputum and chest pain. Recovery follows removal from exposure, but a chronic state can develop insidiously with cough, breathlessness and loss of weight.
Organic dusts, such a mouldy hay, when inhaled cause a disease known as extrinsic allergic alveolitis with 'flu like symptoms; cough, difficulty in breathing occurs within a few hours of exposure. Repeated exposure leads to further lung damage and chronic breathlessness.
Talc is a white powder consisting of hydrous magnesium silicate. Although some talc presents little risk to health, commercial grades a may contain asbestos and quartz and provoke pneumoconiosis and lung cancer.
Cobalt combined with tungsten carbide forms a hard metal used for the cutting tips of machine tools and drills. Inhalation of the dust may give rise to fibrosis of the lungs causing cough, wheezing and shortness of breath.
Man-made mineral fibres irritate the skin, eyes and upper respiratory tract. A maximum exposure limit has been set based on the risk of lung cancer because a 'no-adverse-effect' level cannot be established with reasonable certainty.
Diagnosis of pneumoconiosis
This depends on:
- A complete occupational history of all jobs.
- A characteristic appearance on the chest X-ray. There is an international grading system used to assess radiologically the extent of the disease.
- A clinical examination.
- Lung function tests.
- In some cases involving organic dust, specific blood tests.
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