What is asthma?
Asthma one of the leading caused of visits to the doctor's office. It is responsible for more absences from work and school than any other chronic illness. What's more, it's on the rise.
Asthma is a chronic disease of the lungs in which the airways overreact to certain factors, called asthma triggers, by becoming inflamed or obstructed, making it difficult to breathe comfortably. Experts refer to these oversensitive airways as "twitchy." The good news is that while asthma can't be cured, it is reversible. That means it doesn't get worse on its own, and the inflammation can be treated. People with asthma periodically have breathing troubles, called "attacks," but between these bouts, the airways and lung function usually return to normal.
The asthma attack
To understand what happens during an asthma attack, you first have to know some basics about breathing. Normally, air enters the body through the mouth and nose. Fresh air, high in oxygen, flows through the windpipe into all the airways, until it reaches the tiny air sacs in the lungs, where oxygen and carbon dioxide are exchanged. The air that's breathed out is stale, meaning it's high in carbon dioxide, the body's waste gas.
During an asthma attack, the branches of the windpipe, called bronchi, react in three ways: Their linings swell; their surrounding muscles tighten; and mucus glands in the walls produce excess mucus. All of this blocks the flow of air.
Symptoms may be as subtle as a hacking cough or chest tightness -- or as severe as a life-threatening inability to breathe. Typically, symptoms include:
- Wheezing -- the whistling sound caused by air moving through the narrowed airway.
- Breathlessness -- the result of too many swollen, plugged-up airways.
- Coughing -- the lungs' attempt to dislodge the mucus. People with asthma often feel that if they could just cough up enough mucus, their symptoms would subside, but rarely is it possible to clear the airways completely.
Asthma attacks can strike without warning and last from minutes to days. People experiencing an attack feel as though they can't get enough air into their lungs. But what's really happening is their airways are too constricted to let stale air out of their lungs. This trapped air blocks fresh air from entering the lungs. During a severe asthma attack, emergency room doctors will take a blood sample to check on the blood's oxygen and carbon dioxide levels.
It's important that asthma be controlled: Severe cases that are left untreated can be fatal. Fortunately, this doesn't happen too often, but as asthma cases are rising, the number of asthma deaths are rising as well. According to a study by Drs. Robert Strunk and David Mrazek at the National Jewish Center for Immunology and Respiratory Medicine in Denver, people who have died from serious asthma attacks share a number of characteristics:
- Previous hospitalization for an attack that required respiratory support (a tube put in the airway or windpipe and connected to a mechanical ventilator or respirator)
- Discharge from a hospital while still wheezing
- Disregard of the seriousness of asthma symptoms
- A recent reduction in dosage of prednisone
- Asthma-related seizures in the past
- Signs of depression
- Serious family problems
- Non-compliance with treatment program for any number of reasons, such as hostility, psychological problems, poor personal care
Anyone who falls into one or more of these categories may be at high-risk for experiencing a severe asthma attack and needs to be evaluated by a specialist. Symptoms will not improve on their own, so it's important not to ignore them.
No one knows what causes asthma, but there are definitely things that make it worse. Asthma is often divided into two types: allergic and non-allergic asthma. Not everyone with asthma has allergies, but a tendency to get allergies is the strongest identifiable risk factor for developing asthma. At least 80 percent of asthmatic children have allergies, and 50 percent of asthmatic adults.
People who have allergic asthma experience attacks when exposed to whatever they're allergic to. An allergic reaction results when the body's defenses, which are controlled by the immune system, react to the presence of otherwise harmless substances in the environment, such as grass and tree pollen, mold spores, animal dander, and dust. These substances are called allergens.
Normally, when the body is attacked by a foreign invader, such as a virus, the immune system leaps into action by sending out antibodies to fight the intruder. Unfortunately, some people's immune systems overreact to harmless allergens. The first time they're exposed to an allergen, their body may produce a special antibody called immunoglobulin E -- or IgE. Afterwards, every time they're exposed to this same allergen, these IgE antibodies, ever vigilant against foreign invaders, poke holes in the immune system's white cells, releasing the chemicals stored inside.
One of these chemicals is called histamine, which is responsible for the runny nose, watery eyes, and itchy skin that plague allergy sufferers. Other chemicals called leukotrienes cause the muscles of the airways to constrict. The immune system also releases cells called eosinophils, which inflame the airways -- an obvious problem for people with asthma. Allergies can be diagnosed by skin tests or food challenge tests.
People with non-allergic asthma are sensitive to other environmental triggers, such as strenuous exercise, perfumes, cigarette smoke, certain drugs, weather changes, cold or flu infections, stress, aspirin, and certain food additives. These triggers can mimic allergies -- they may inflame the airways, for example -- but they don't provoke a true immune response, the kind that involves IgE antibodies and histamine release. Non-allergic triggers can usually be identified because they so consistently provoke an asthma attack.
Both types of asthma can be controlled by taking medications and avoiding triggers.
Who gets asthma?
Nearly 15 million Americans have asthma. You can get asthma at any age, but it's most likely to occur in children by age five, and in adults by age 40. Still, one in ten new asthma cases is diagnosed in persons over 65.
Even without understanding the cause of asthma, researchers have identified certain factors that can raise a person's risk. One factor is a family history of the disease. For example, a child with one parent with asthma has a 20 percent chance of getting it himself. This rises to 63 percent if both parents have asthma. A recent Italian study found that 15 percent of current asthma cases among children and 11 percent of wheezing cases among adolescents are attributable to parental smoking. It is believed that some people have a predisposition to manufacture large quantities of IgE antibodies, putting them at higher risk of allergies, and possibly, asthma. There are also racial differences in asthma rates, with African-Americans experiencing a much higher rate of severe asthma than whites.
Asthma is the most common chronic disease of childhood. It can begin as early as infancy, though it's difficult to diagnose at that age. An infant may have a softer, shorter cry or show difficulty in feeding. In children, asthma symptoms may appear as rapid or noisy breathing and chest congestion -- symptoms that sometimes get mistakenly treated as infections. No one knows why, but asthma is more common in young boys than young girls. After puberty the rates for both sexes even out. Children don't outgrow their asthma -- their lungs remain "twitchy" for life -- but their symptoms may disappear as their lungs get bigger, allowing more room for air flow. In some children, symptoms disappear around puberty only to resurface again in adulthood. When asthma first strikes in adolescence, it's likely to be the non-allergic type with less chance of remission.
People who develop asthma in their twenties and thirties often had asthma as a child, or had asthma symptoms that never were correctly diagnosed. After age 40, asthma is more likely to be the non-allergic type. It is often more difficult to manage than childhood asthma -- but it can be controlled. After age 65, asthma is triggered more by pollution and respiratory infections than by allergies.