Asthma is caused by inflammation in the airways. When an asthma attack occurs, the muscles surrounding the airways become tight and the lining of the air passages swell. This reduces the amount of air that can pass by, and can lead to wheezing sounds.

Most people with asthma have wheezing attacks separated by symptom-free periods. Some patients have long-term shortness of breath with episodes of increased shortness of breath. Still, in others, a cough may be the main symptom. Asthma attacks can last minutes to days and can become dangerous if the airflow becomes severely restricted.

In sensitive individuals, asthma symptoms can be triggered by breathing in allergy-causing substances  (called allergens or triggers). Triggers include pet dander, dust mites, cockroach allergens, molds, or pollens. Asthma symptoms can also be triggered by respiratory infections, exercise, cold air, tobacco smoke and other pollutants, stress, food, or drug allergies . Aspirin and other non-steroidal anti-inflammatory medications provoke asthma in some patients.

Approximately 20.5 million Americans currently have asthma. Many people with asthma have an individual or family history of allergies, such as hay fever or eczema. Others have no history of allergies.

Allergy testing may be helpful in identifying allergens in patients with persistent asthma. Common allergens include pet dander, dust mites, cockroach allergens, molds, and pollens. Common respiratory irritants include tobacco smoke, pollution, and fumes from burning wood or gas.

The doctor will use a stethoscope to listen to the lungs. Asthma-related sounds may be heard. However, lung sounds are usually normal between asthma episodes.

WASHINGTON — When Tom Daschle shows up for a confirmation hearing on Thursday, senators are likely to grant him all the courtesies due a former Senate majority leader.

But that does not mean Mr. Daschle should expect only softball questions. Lawmakers will most likely question him sharply about one of the most contentious aspects of President-elect Barack Obama’s domestic agenda: his call for a new public Health Insurance Plan to compete with private insurers.

No other proposal so clearly defines the political and philosophical differences between Mr. Obama and Republicans, or provokes such deep disagreements.  Mr. Daschle, the point man for Mr. Obama’s campaign to revamp the health care system, supports the concept of “a government-run insurance program modeled after Medicare.” It would, he says, give consumers, especially the uninsured, an alternative to commercial insurance offered by companies like Aetna, Humana and WellPoint.

But the proposal is anathema to many insurers, employers and Republicans. They say the government plan would have unfair advantages, like the ability to impose lower fees, and could eventually attract so many customers that private insurers would be driven from the market.

“The public plan option is a terrible idea — one of our top concerns in the health reform debate,” said James P. Gelfand, senior manager of health policy at the United States Chamber of Commerce.

The public plan, as conceived by Mr. Obama, would vie with private insurers to provide better benefits and better customer service at a lower cost. Without such competition, Democrats say, private insurers cannot be expected to control costs much better than they do now.

Jacob S. Hacker, a professor of political science at the University of California, Berkeley, said the new option was essential to the success of Mr. Obama’s effort to rein in costs and make coverage available to all Americans.