What Causes Bronchitis?

Bronchitis is an inflammation of the bronchi or air passages of the lung. To understand this disease and related respiratory problems, it helps to understand the functions of our breathing organs. We breathe to exchange gases – to take in oxygen and to expel carbon dioxide. This exchange takes place in the lungs.

When we take a breath, air enters the mouth or the nose – the nasal route is better because hairs in the nose filter out some of the larger dust particles, and the air is warmed as it passes through. This air then enters the trachea, a large tube that passes down the throat into the chest, where it divides in two and becomes the right and left bronchus leading to the right and left lung.

Inside the lungs, these bronchial tubes then divide into smaller branches (called bronchioles), just like the branches of a tree. At the end of each of the smallest bronchioles is the alveolus, a thin air sac surrounded by small, thin blood vessels called capillaries. The exchange of gases occurs across the walls of the alveoli and the capillaries – the sacs are small and clustered together like grapes to give the maximum surface area.

Acute bronchitis occurs when there are infection and inflammation in the walls of the bronchial tubes. The infection can cause a cough, fever, the production of sputum or phlegm, and sometimes shortness of breath. This is a short-lived condition that clears quickly with treatment or of its own accord.

Chronic bronchitis appears to be a different illness, with different causes. In chronic bronchitis mucous glands in the wall of the bronchus enlarge. These overactive glands produce an excess of mucus and this is coughed up by the sufferer.

So, cough and mucus are the signs of this disorder. There may be repeated acute infections as well, an obstruction may develop slowly in the bronchial tubes, and the distal air sacs, the alveoli, may enlarge later on. When they do, their number is reduced, the total surface area is smaller and thus there is less effective lung tissue. This is known as emphysema.

There are some well-recognized factors that cause chronic bronchitis but also some that are as yet uncertain. Smoking and air pollution are the main causes. Air pollution depends on the amount of smoke and sulfur dioxide present in the air. But it is little use forcing the industry to stop polluting the atmosphere while people provide their own pollution by smoking. Some children who smoke have been shown to have developed bronchitis while still in their early teens.

Social class, exposure to cold, and the dusts of the industry may also be involved. It is thought that the chronic or recurrent respiratory infections of childhood, instead of clearing during adolescence, may only lie dormant and then recur in the adult and develop into chronic bronchitis.

Obstruction may develop in the bronchial tubes owing to retained mucus or to scarring from damage to the lining of the walls. This combination of chronic bronchitis, obstructed bronchioles, and emphysema is now known as “chronic obstructive airways disease“, often abbreviated to COAD.

Untreated, this condition usually worsens over many years. At the beginning there is just the cough and sputum; later on, shortness of breath becomes marked during exertion, then may be present even at rest.

The person’s red blood cells may increase in number in an effort to transport more oxygen to the tissues. This is called polycythemia and leads to a dark pinkish-blue complexion. Cyanosis or the blue discoloration of the skin due to too much carbon dioxide in the tissues also becomes apparent. This is the stage of respiratory failure which may then lead to heart failure as well.

The chest X-ray may appear normal until the last stages of this disorder – it is of most use in detecting changes due to dust or in acute infection. The tests for lung function, which involve breathing into a tube and having a record made on a graph, are accurate and also show changes at an early stage. They are most useful in monitoring progress and in checking the response to treatment. Prevention is, of course, far better than attempts at cure.

The most useful preventative measure is to stop smoking. For those who become aware that they may be developing chronic bronchitis, then stopping smoking may prevent the disease from getting worse and may lead to a reversal of the symptoms. Antibiotics are used in treating attacks of acute infection. They are also of use in preventing infection and for this reason, are used in small doses over many months.

If the sputum gets thick and sticky it may be difficult to clear. Steam works well in loosening it; iodides and other drugs may also help. The antihistamine drugs tend to make this worse. Narrowing of the bronchial tubes due to spasm of the muscle in the wall produces obstruction as in asthma and this can respond to the bronchodilating drugs that are used for asthmatic conditions.

Cortisone, by mouth or injection, may have a dramatic effect in improving the symptoms, especially where an obstruction is marked, but it affects the whole body. A newer derivative of cortisone, beclomethasone, can be taken into the lung by means of an aerosol spray. This works directly on the bronchial tubes and the lungs, but little is absorbed into the general circulation of the body.

Where there is marked respiratory distress it may be necessary to use oxygen, but it can be dangerous and may worsen the condition, so it should be used only under proper supervision.

Chronic bronchitis, emphysema, and COAD may occur separately or in combination; they may have different or the same causes. But whatever the causes, continued smoking does not help.

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