The respiratory system represents a compromise. On one hand, it must provide a large and effective area for exchanging oxygen with the environment; on the other, it must prevent harmful environmental agents from reaching deep into the body. Disorders of the system are generally characterized by ineffective gas exchange or failure of defenses. The whole system from the nose to the bronchioles (with an extension to the middle ear) is lined by specialized mucosa, and these structures are therefore considered together.
Infections that spread from the nose or pharynx usually affect the middle ear. The Eustachian tube can be blocked by inflammation of nasal tissues, and this can cause acute ear infection (otitis media), or serous otitis, caused by accumulation of fluid in the middle ear. The latter is usually treated with antihistamines, to reduce the inflammation and allow the fluid to drain, though surgery may be required to equalize pressure in the ear by inserting a small tube (grommet) in the eardrum. In some cases, the adenoids (lymphatic tissue at the back of the nose) need to be removed to cure persistent inflammation and blockage.
Untreated middle ear infections can spread to the mastoid bone behind the ear. The honeycomb structure of this bone allows infection to develop to such an extent that antibiotics may be ineffective, and if so, only surgery can eradicate the disease. Untreated mastoiditis can spread farther to destroy the inner ear, or to cause meningitis or an abscess in the brain.
Deafness can result from a scarred or ruptured eardrum whether from infection or from an accident but is more commonly caused by degeneration (ostosclerosis) of the small bones of the middle ear, which transmit sound. Persistent exposure to loud noise can also damage the ear and cause progressive hearing loss. Formerly unbeatable, such damage can now be repaired by microsurgical techniques: a new eardrum can be fashioned from the lining of the ear canal and damaged bones can be removed or replaced by plastic components. Deafness can also be caused by obstructions of the ear canal (external auditory meatus), with wax, inflammatory tissue, or fibrosis after infection, or even a foreign body.
Sounds similar to those of bells, rushing water, rustling leaves, or even aircraft taking off, may all be generated within the ear, and afflict those who suffer from tinnitus. These symptoms may be due to aging or degeneration of the cochlea, but this is not known for certain. Until recently there was no treatment, but now many patients benefit from “masking therapy” which, paradoxically, produces actual noise in a device worn like a hearing aid.
Most disorders affecting the nose are caused by pathogens primarily viruses or allergens, such as dust mites or pollen grains.
The common cold is caused by viruses. Treatment concentrates on relieving the symptoms; there is still no specific cure. A new drug, interferon, may help to prevent colds, but it is still undergoing clinical trials.
Cigarette smoke and atmospheric pollution are among the commonest and are certainly the most preventable causes of lung disease. Disorders due to smoking range from minor ones, such as laryngitis, to serious, usually fatal, conditions, such as chronic bronchitis and lung cancer.
Chronic bronchitis a persistent cough producing sputum increases susceptibility to other chest infections. It may also lead to emphysema, in which lung tissue loses its normal elasticity and oxygen-uptake is reduced, causing breathlessness. Complications of chronic bronchitis can lead easily to respiratoryfailure. Treatment is with antibiotics and possibly oxygen therapy until the infection is controlled.
The most common infections of the lungs are lobar pneumonia, usually caused by pneumococci, and bronchial pneumonia. If an infection reaches the lining of the lung (pleura), pleurisy can result. The chief symptom is painful breathing, which is also a symptom of viral pneumonia. The bacteria causing a similar infection, Legionnaire’s disease, has been identified recently as Legionella pneumophila.
The occurrence of lung cancer is almost entirely a result of smoking and is closely linked to total numbers of cigarettes smoked and their tar content. Although this is the commonest type of cancer in Western countries, the incidence has begun to approach a leveling-off as the public becomes more conscious of the dangers of smoking. Lower tar content and filtered cigarettes may also be beneficial. There are three main methods of treatment—surgery, radiation therapy, and cytotoxic chemotherapy, used alone or in combination. Surgery is most useful if the disease has notspread outside the lung, and may be curative. Radiation therapy is valuable in controlling more advanced disease, especially secondary deposits in the bones or brain, but it rarely provides a cure. Chemotherapy shows great promise, especially when combined with radiation therapy, in controlling and possibly even curing one particular kind of lung cancer, called oat cell carcinoma.
The symptoms of asthma are a combination of wheezing and a sensation of shortness of breath, caused by constrictions of the bronchial tubes and thickening of their walls by fluid. It is a common disease, affecting approximately 3.8 per cent of the total population and is thought to be an allergic reaction to inhaled dust particles.
In most cases, the allergen is unknown and treatment is directed toward relieving the airway constriction. Depending on the severity and frequency of the attacks, this may mean taking bronchodilators by an inhaler or may require powerful steroids and, occasionally, hospitalization. Recently developed drugs that patients inhale show great promise in preventing asthmatic attacks, especially in children. Treatment by desensitization injections and by special exercise programs have not been shown to alter the frequency or severity of attacks.