Asthma is a disorder that intermittently causes shortness of breath and difficulty breathing, although the exact type and severity of symptoms vary from person to person. Some people with asthma cough, wheeze, and have trouble breathing nearly every day. Others feel perfectly well in between occasional attacks of chest congestion and wheezing. Some Olympic athletes with asthma experience only a tightness in the chest during world-class athletic competition. Other people have such severe asthma attacks from exercising that they require emergency treatment. All people with asthma share something in common, however: breathing passageways that periodically become abnormally narrow.
More than 20 million people in the United States — almost 7% of the population — have asthma (see "Asthma in America"). Most people tend to think of asthma as a childhood disease, for good reason: Most cases of asthma are diagnosed by age 5. Nonetheless, adults of any age may develop asthma, although the likelihood of developing it becomes increasingly rare the older you get. Studies indicate that as many as 10% of people over 65 have asthma, higher than the prevalence of asthma in childhood. If you are an adult with asthma, it is likely that you have had the disorder for a long time and will continue to deal with it for the rest of your life.
For reasons that are unclear, children with asthma often grow out of their illness, usually around adolescence. If the condition develops or persists into adulthood, though, it is rare that asthma just goes away. But the condition can be managed. In fact, if you have asthma that is properly controlled, you can anticipate being free of symptoms and fully active almost all the time.
Asthma in America
Normally when you inhale, air passes easily from your nose and mouth into the trachea, which branches into the two bronchial tubes, or bronchi, that feed the right and left lungs. These primary bronchi divide into smaller and smaller branches, ultimately narrowing into small stems called bronchioles that terminate in microscopic sacs, or alveoli. These tiny sacs cluster around the bronchioles in a configuration that resembles bunches of grapes (see Figure 1).
Figure 1: How you breathe
When you take a breath, air travels through a system of increasingly smaller airways from the trachea, to the bronchi, and ultimately to tiny sacs known as alveoli (see inset). A system of tiny capillaries absorbs the oxygen from the alveoli and delivers it throughout the body.
With each intake of breath, your airways dilate and the alveoli expand to admit air, providing oxygen to networks of tiny blood vessels in the alveolar walls. Exhale, and the alveoli shrink, forcing exhaled gas — and with it, carbon dioxide — into the bronchioles, back through the bronchi and trachea, and out of your body.
If you have asthma, much of the time your airways are fully open, and at those times you can breathe normally. At other times, however, your airways become constricted and breathing becomes difficult, so bad at times that you may feel as though you are trying to breathe through a straw while a gorilla sits on your chest.
The variable narrowing of the breathing tubes that can come and go over a period of minutes, hours, or days is one of the hallmarks of asthma. This variability distinguishes asthma from other lung diseases, such as emphysema and chronic bronchitis (together known as chronic obstructive pulmonary disease, or COPD), which cause permanent breathing problems that occur day in and day out (see "Asthma or something else?").
Airways narrow in asthma because they are hypersensitive, or — to use a less medical-sounding term — "twitchy." Having twitchy airways doesn't mean that they feel twitchy; it means that there is an underlying tendency for the airways to react by narrowing when they encounter certain stimuli, such as cat dander or cold air. These stimuli are known as asthma triggers, because they cause symptoms to flare up (see "Asthma triggers"). If you have asthma, the potential for airway narrowing is always there: Your airways remain hypersensitive or "twitchy" even when you feel well. Asthma thus involves intermittent airway narrowing and persistent vulnerability to that narrowing — a concept that is central to both the understanding of this disorder and its treatment.