Asthma tends to run in families, and the fact that many asthmatics have relatives with the problem lends strong weight to the notion of an inherited (or genetic) basis for the disorder. If one parent has it, there is a 25 percent chance that his or her offspring will also have it. When both parents do, the chance of the child having it climbs to 50 percent.
Asthma may make its first appearance at any age. While it frequently begins during infancy, it has also been known to strike without prior warning around the time of menopause. In childhood, the majority of sufferers experience their first symptoms sometime before the first grade. In general, for any age range in the United States, more males are affected than females.
What Causes It
Not all cases of asthma are triggered by allergies. When it is, the condition is described as extrinsic asthma, or asthma arising from an outside cause. When allergies do not appear to play a role, the condition is known as intrinsic asthma, meaning that it stems from factors within the individual. Most cases of asthma are not so clear-cut, however; they may result from a combination of both allergic and nonallelic factors. Nevertheless, one thing that asthma is not is contagious. In other words, you cannot give your asthma to your friends or contract it from anyone else.
Allergic (Extrinsic) Asthma
Allergic asthma tends to be triggered by the same kinds of allergens as those known to provoke seasonal and perennial allergic rhinitis, namely dust, dander, molds, and pollens. Certain food additives (such as metabisulfites and monosodium glutamate [MSG]), industrial and occupational chemicals, and a number of medications (aspirin, for example) have also been linked to asthma in some cases. Regardless of the allergen, the allergic events that lead to asthma, after exposure to a particular allergen, share much in common with what occurs in, say, pollen allergies. One major distinction, however, is that asthma affects the lower breathing tubes and the lungs, while seasonal and perennial allergies primarily involve the nasal passages and sinuses.
Nonallergic (Intrinsic) Asthma
Although our concern is with allergic conditions, no discussion of asthma would be complete without describing the various nonallergic triggers of the disorder. These include stress, exercise, sex, upper gastrointestinal problems, upper respiratory virus infections, and pollutants.
Years ago many people contended that asthma was a psychosomatic disorder, the product of "nerves." Today we know that it is not a condition that is "just in the head." At the same time, stress does play a role. Many asthmatics steadfastly maintain that their symptoms are triggered or aggravated by episodes of increased nervous tension, frustration, or anger.
Experts theorize that the rapid and shallow breathing pattern (hyperventilation) that characterizes anxiety problems may be responsible for promoting bronchospasm in asthma-prone individuals. It has likewise been proposed that the alterations in this pattern brought about by biofeedback and behavior modification techniques, such as meditation and deep breathing exercises, may account for the benefits sometimes obtained from these modalities. But whatever the success of these measures, there is no scientific support for the notion that asthma is directly caused by emotional stress. What we can say for sure is that the condition itself has been the cause of a good deal of stress.
Exercise is another important factor in many asthmatics, acting as a trigger. The phenomenon is referred to as exercise-induced bronchospasm (EIB) or exercise-induced asthma (EIA). Attacks typically begin between five and ten minutes after the start of a workout. During exercise your lungs work harder, and you breathe in and out more rapidly. As a consequence the inspired and expired air becomes drier, cooler, more irritating, and more likely to precipitate an asthma attack in a susceptible person. It remains unclear whether it is the dryness, the coolness, or a combination of these factors that is responsible for triggering the attack. Nevertheless, in response the respiratory system releases the same kinds of mediators as seen in true allergic reactions.
Since exercise-induced attacks do not begin immediately, those sports that require only short bursts of energy rather than constant activity are generally better tolerated by most asthmatics. These include baseball, bowling, golf, lightweight training, tennis (especially doubles), and sprinting. Although swimming requires more constant activity and is generally more demanding on the respiratory system, its untoward effects appear to be offset by the moistened air that is inhaled.
Sex is another physical activity that may aggravate asthma. Even mild asthmatics may notice an increase in wheezing during lovemak-ing. A history of sex-related asthma may be the first clue to the physician that a patient suffers from a previously ignored mild case of the condition. Fortunately, sex-induced asthma generally responds quite well to various medications, particularly sprays, and need not be an impediment to romance.
Problems in the upper gastrointestinal system, especially hiatal hernias, may also trigger asthma attacks. Regurgitation of the stomach contents back into the esophagus, a process doctors call gastroesophageal reflux and that often occurs at night when the individual with a hiatus hernia is recumbent in bed, can precipitate a severe attack. Coughing can be fitful in these cases. Older individuals with hiatus hernias are especially prone. Investigators believe that in asthmatics the reflux within the gastrointestinal system sets off a reflex in the respiratory system, leading to an attack. Naturally, the gastrointestinal problem must be dealt with if the asthma is to improve.
Nocturnal asthma, another form of acute asthma that, as its name suggests, begins in the middle of the night, is unrelated to reflux but is a particular problem for a small percentage of asthmatics. Current thinking suggests that attacks are the result of the effects of normal hormonal fluctuations on asthmatic airways, and several explanations have been given for this phenomenon. For one thing, the body's natural levels of epinephrine and Cortisol, two important asthma-controlling agents, are ordinarily at their lowest levels during the night; at the same time, histamine, which can worsen asthma, is at its highest level. Other explanations for nocturnal asthma include the effects of the body temperature drop that ordinarily occurs during the night, as well as the physiologic nighttime increase in the activity of the vagus nerve, which is responsible for airway constriction known as bron-chostriction.
Viral respiratory infections are troublemakers for everyone, but they are especially worrisome for asthmatics, who tend also to be more susceptible to them. The increased inflammation, swelling, and thickened mucus production that these infections cause add to the already overburdened respiratory apparatus of the sufferer. The common cold, the flu, and sinus infections are particular problems for asthmatics; although equally problematic when present, bacterial infections are much less frequently responsible for triggering or aggravating asthma symptoms.
In young children, viral bronchiolitis and croup have actually been linked in some instances to the subsequent development of asthma. And in one large study of adult-onset asthmatics, nearly half of them attributed the start of their illness to a prior respiratory infection. Investigators speculate that these infectious processes sensitize the lining of the respiratory system with allergy-related IgE antibodies, setting the stage for future allergic asthma attacks.
Environmental irritants and pollutants are other well-known asthma aggravators. Atmospheric pollutants, such as ozone and sulfur dioxide, top the list, which also includes such common irritants as cigarette smoke, chimney fumes, gasoline vapor, and automotive exhaust.
It is perhaps less well known that strong odors of various kinds can also precipitate attacks. In this category, insecticides and roach sprays head the list, followed by ammonia-containing household cleansers. Nearly 75 percent of asthmatics point to colognes, perfumes, and fresh paint as other problem odors, and approximately a third of sufferers claim to be irritated by ordinary cooking smells.
