Ross & Wilson Anatomy and Physiology in Health and Illness (119 page)

Bronchiectasis

This is permanent abnormal dilation of bronchi and bronchioles. It is associated with chronic bacterial infection, and sometimes with a history of childhood bronchiolitis and bronchopneumonia, cystic fibrosis, or bronchial tumour. The bronchi become obstructed by mucus, pus and inflammatory exudate and the alveoli distal to the blockage collapse as trapped air is absorbed. Interstitial elastic tissue degenerates and is replaced by fibrous adhesions that attach the bronchi to the parietal pleura. The pressure of inspired air in these damaged bronchi leads to dilation proximal to the blockage. The persistent severe coughing to remove copious purulent sputum causes intermittent increases in pressure in the blocked bronchi, leading to further dilation.

The lower lobe of the lung is usually affected. Suppuration is common. If a blood vessel is eroded, haemoptysis may occur, or pyaemia, leading to abscess formation elsewhere in the body, commonly the brain. Progressive fibrosis of the lung leads to hypoxia, pulmonary hypertension and right-sided heart failure.

Cystic fibrosis (mucoviscidosis)

This is one of the most common genetic diseases (
p. 435
), affecting 1 in 2500 babies. It is estimated that almost 5% of people carry the abnormal recessive gene which must be present in both parents to cause the disease.

The secretions of all exocrine glands have abnormally high viscosity, but the most severely affected are those of the lungs, pancreas, intestines, biliary tract, and the reproductive system in the male. Sweat glands secrete abnormally large amounts of salt during excessive sweating. In the pancreas, highly viscous mucus is secreted by the walls of the ducts and causes obstruction, parenchymal cell damage, the formation of cysts and defective enzyme secretion. In the newborn, intestinal obstruction may be caused by a plug of meconium and viscid mucus, leading to perforation and meconium peritonitis which is often fatal. In less acute cases there may be impairment of protein and fat digestion resulting in malabsorption, steatorrhoea and failure to thrive in infants. In older children:

•
digestion of food and absorption of nutrients is impaired

•
there may be obstruction of bile ducts in the liver, causing cirrhosis

•
bronchitis, bronchiectasis and pneumonia may develop.

The life span of affected individuals is around 40 years; the main treatments offered are aimed at controlling pulmonary infection. Chronic lung and heart disease are common complications.

Restrictive disorders

Learning outcomes

After studying this section, you should be able to:

describe the main pneumoconioses

outline the main causes and consequences of chemically induced lung disease.

Restrictive lung disorders are characterised by increasing stiffness (low compliance) of lung tissue, making it harder to inflate the lung and increasing the work of breathing. Chronic restrictive disease is often associated with progressive fibrosis caused by repeated inflammation of the lungs.

Pneumoconioses

This group of lung diseases is caused by inhaling dusts. Inhalation of work-related pollutants was a major cause of lung disease prior to the introduction of legislation that limits workers’ exposure to them. To cause disease, particles must be so small that they are carried in inspired air to the level of the respiratory bronchioles and alveoli, where they can only be cleared by phagocytosis. Larger particles are trapped by mucus higher up the respiratory tract and expelled by ciliary action and coughing. The risk increases with the duration and concentration of exposure, and in cigarette smokers.

Coal worker’s pneumoconiosis

Simple pneumoconiosis

Particles of coal dust lodge mainly in the upper two-thirds of the lungs, and are ingested by macrophages inside the alveoli. Some macrophages remain in the alveoli and others migrate into surrounding tissues and adhere to the outside of the alveolar walls, respiratory bronchioles, blood vessels and the visceral pleura. Macrophages are unable to digest inorganic particles, but their activation leads to an inflammatory response that can cause fibrosis in the lung tissue. Fibrosis is progressive during exposure to coal dust but tends to stop when exposure stops. Early in the disease there may be few clinical signs unless emphysema develops or there is concurrent chronic bronchitis.

Pneumoconiosis with progressive massive fibrosis

This develops in a small number of cases, sometimes even after the worker is no longer exposed to coal dust. Masses of fibrous tissue develop and progressively encroach on the blood vessels and bronchioles. Large parts of the lung are destroyed and emphysema is extensive, leading to pulmonary oedema, pulmonary hypertension and right-sided cardiac failure. The reasons for the severity of the disease are not clear. One factor may be hypersensitivity to antigens released by the large number of dead macrophages. About 40% of patients have tuberculosis.

Silicosis

This may be caused by long-term exposure to dust containing silicon compounds. High-risk industries are:

•
quarrying: granite, slate, sandstone

•
mining: hard coal, gold, tin, copper

•
stone masonry and sand blasting

•
glass and pottery work.

Inhaled silica particles accumulate in the alveoli. The particles are ingested by macrophages, and are actively toxic to these cells. The inflammatory reaction triggered when the macrophages die causes significant fibrosis.

Silicosis appears to predispose to the development of tuberculosis, which rapidly progresses to tubercular bronchopneumonia and possibly military TB. Gradual destruction of lung tissue leads to progressive reduction in pulmonary function, pulmonary hypertension and right-sided heart failure.

Asbestosis

Asbestosis, caused by inhaling asbestos fibres, usually develops after 10 to 20 years’ exposure, but sometimes after only 2 years. Asbestos miners and workers involved in making and using some products containing asbestos are at risk. There are different types of asbestos, but blue asbestos is associated with the most serious disease.

In spite of their large size, asbestos particles penetrate to the level of respiratory bronchioles and alveoli. Macrophages accumulate in the alveoli and ingest shorter fibres. The larger fibres form
asbestos bodies
, consisting of fibres surrounded by macrophages, protein material and iron deposits. Their presence in sputum indicates exposure to asbestos but not necessarily asbestosis. The macrophages that have engulfed fibres migrate out of the alveoli and accumulate around respiratory bronchioles and blood vessels, stimulating the formation of fibrous tissue. Lung tissue is progressively destroyed, with the development of dyspnoea, chronic hypoxia, pulmonary hypertension and right-sided cardiac failure. The link between inhaled asbestos and fibrosis is not clear. It may be that asbestos stimulates the macrophages to secrete enzymes that promote fibrosis or that it stimulates an immune reaction causing fibrosis. Asbestos is linked to the development of mesothelioma (
p. 262
).

Byssinosis

This is caused by the inhalation of fibres of cotton, flax and hemp over several years. The fibres cause bronchial irritation and possibly the release of histamine-like substances. At first, breathless attacks similar to asthma occur only when the individual is at work. Later, they become more persistent and chronic bronchitis and emphysema may develop, leading to chronic hypoxia, pulmonary hypertension and right-sided heart failure.

Extrinsic allergic alveolitis

This group of conditions is caused by inhaling materials contaminated by moulds and fungi, e.g. those in
Table 10.3
. The contaminants act as antigens causing antigen/antibody reactions in the walls of the alveoli. There is excess fluid exudate and the accumulation of platelets, lymphocytes and plasma cells. The alveolar walls become thick and there is progressive fibrosis, leading to pulmonary hypertension and right-sided heart failure.

Table 10.3 
Conditions caused by inhaled contaminants

Chemically induced lung diseases

Paraquat

Within hours of ingestion of this weedkiller, it is blood-borne to the lungs and begins to cause irreversible damage. The alveolar membrane becomes swollen, pulmonary oedema develops and alveolar epithelium is destroyed. The kidneys are also damaged and death may be due to combined respiratory and renal failure or cardiac failure.

Cytotoxic drugs

Busulfan, bleomycin, methotrexate and other drugs used in cancer treatment may cause inflammation that heals by fibrosis of interstitial tissue in the lungs and is followed by alveolar fibrosis.

Oxygen toxicity

The lungs may be damaged by a high concentration of oxygen administered for several days, e.g. in intensive care units, to premature babies in incubators. The mechanisms involved are unknown but effects include:

•
progressive decrease in lung compliance

•
pulmonary oedema

•
fibrosis of lung tissue