Diseases of the Respiratory System - Allergic respiratory diseases
Hay fever ( allergic rhinitis ) and asthma are two very common allergic diseases of the respiratory tract. The two have much in common as to age at onset, seasonal manifestations, and causation. Hay fever involves the mucosa , or lining, of the upper respiratory tract only, whereas asthma is confined to the bronchial tubes of the lower respiratory tract. Physicians usually distinguish two main types of asthma, allergic and infectious. The infectious type of asthma resembles bronchitis, with cough and much wheezing as well. The discussion here will be confined to the allergic form of asthma.
In hay fever and asthma the allergenic substance causing the reaction is usually airborne, though it can be a food. In most cases the offender is pollen from a plant. The pollen is inhaled into the nostrils and alights upon the lining of the respiratory passages. In the allergic individual, antibodies react with the proteins in the pollen and cause various substances to be released from the tissue and blood cells in the immediate area. These substances, in turn, produce vessel enlargement in the area and an outpouring of mucus, plus certain irritating symptoms that result in a stuffy or runny nose and itchy eyes. The same reactions occur in the bronchial lining in asthma, but the substances released there also cause constriction of the bronchial muscle and consequent narrowing of the passages. This muscular effect and the narrowing caused by greatly increased amounts of mucus in the passages are both responsible for the wheezing in asthma.
Hay fever is never a threat to life, but in severe cases it can upset one's life patterns immensely. For unknown reasons it is more common in childhood, where it is often seen in conjunction with eczema or asthma. The tendency to develop hay fever, eczema, and asthma is hereditary. The transmission of the hereditary factors is complex, so that within a family group any number of individuals or none at all may exhibit the trait.
Most people with hay fever have their only or greatest difficulty in the summer months because of the airborne pollens from trees, grasses, flowers, and molds that are prevalent then. The most notorious of all pollens is the ragweed pollen. This weed pollinates around August 15 and continues to fill the air until late September. In many cities an official pollen count is issued every day, and those with severe difficulty can avoid some trouble by staying outside as little as possible on high-count days. Antihistamine drugs are used to counteract the nasal engorgement in hay fever. These drugs counteract the effect of histamine , which is one of the major substances released by the allergic reaction.
Allergic asthma is the result of the allergic reaction taking place in the bronchial mucosal lining rather than in the nasal lining. A person may suffer from both asthma and hay fever. The common inciting factors are pollens, hair from pets (especially cats), house dust, molds, and certain foods (especially shellfish). When foods are responsible, the reaction initially occurs within the bloodstream, but the major effect is felt within the lung, which is spoken of as the target organ.
Most allergic asthma is seen in children. Only the mildest cases of allergic asthma disappear at puberty. For those who continue to have difficulty after puberty, the role of infection as a cause for the asthma usually becomes more prominent. Allergic asthma attacks start abruptly and can usually be aborted rather easily with medication.
People with asthma are symptom-free much of the time. When exposed to high concentrations of pollen they begin wheezing and producing sputum. Wheezing refers to the high-pitched squeaking sound that is made by people exhaling through narrowed bronchi. Associated with the wheezing and sputum is a distinct sensation of shortness of breath that varies in severity according to the nature of the attack. Milder attacks of asthma often subside spontaneously, merely with relaxation. This is especially true when the wheezing is induced by nonspecific factors, such as a cloud of dust, cold air, or exercise. Asthmatic individuals have more sensitive air passages and they are more easily bothered by these nonspecific irritants.
For more severe attacks of asthma there are several types of treatment. There are oral medications that dilate the bronchi and offset the effects of the allergic reaction. (Antihistamines, however, exert no effect on asthma and may even worsen the condition.) Also available are injectable medications, such as adrenaline, and sprays that contain substances similar to adrenaline and that can be inhaled. Any or all of these methods may be employed by the physician. During times of high exposure it is often helpful to take one of the oral medications on a regular basis, thereby avoiding minor episodes of wheezing.
A recently discovered remedy for asthma is particularly useful to persons—primarily infants and small children, who cannot swallow tablets. The remedy comes in capsules containing tiny pellets of the drug theophylline. Once the capsule is twisted open, the pellets can be sprinkled on soft foods, including strained baby food, applesauce, pudding, or hot or cold cereal. The pellets give relief for about 12 hours, long enough to protect children during sleep.
The best therapy for asthma and hay fever is avoidance of the allergen responsible for attacks. Obviously, cats and certain foods can be avoided more readily than pollens and other airborne substances. The first requisite, however, is to identify the offender. The most important method of identification is the patient's medical history. Sometimes the problem is easy, as when the patient states that he only has trouble during the ragweed season. At other times a great amount of detective work may be required. Skin testing is used to complement the history. The skin test merely involves the introduction under the skin (usually within a tiny scratch) of various materials suspected of being allergens. If the individual has antibodies to these substances he will form a hive at the site of introduction. That he reacts does not necessarily mean that his asthma is due to that test substance, because many people have reactions but no hay fever or asthma. The skin test results need to be interpreted in the light of the history of exposure.
If the substance so identified cannot be avoided, then hyposensitization may prove useful. This form of treatment is based on the useful fact that the human body varies its ability to react depending upon the degree and the frequency of exposure. In a hyposensitizing program small amounts of pollen or other extract are injected frequently. Gradually the dose of extract is increased. By this technique many allergic individuals become able to tolerate moderate exposure to their offending material with few or no symptoms. Hyposensitization does not succeed in everyone, but it is usually worth attempting if other approaches are unsuccessful. For more information see Ch. 24, Allergies and Hypersensitivities .