Asthma is  Reversible Obstructive Airway Disease

Air reaches the lung by passing through the windpipe (trachea), which divides into two large tubes (bronchi), one for each lung. Each bronchi further divides into many little tubes (bronchioles), which eventually lead to tiny air sacs (alveoli), in which oxygen from the air is transferred to the bloodstream, and carbon dioxide from the bloodstream is transferred to the air.

Asthma involves only the airways (bronchi and bronchioles), and not the air sacs. The airways trap airborne particles in a thin layer of mucus which covers their surface. The mucus is either coughed-up or swept up into the trachea by cilia, tiny hairs on the lining of the airways. Once the mucus reaches the throat, it can again be coughed up or swallowed.

The asthmatic's airways are hyper-reactive. In response to stimuli, the airways may become obstructed by:

• constriction of the muscles in bronchi and bronchioles, narrowing the airway
• inflammation and swelling of the airway with obstruction of air flow
• increased mucus production which can obstruct the airway.

Once the airways have become obstructed, it takes more effort to force air through them; breathing becomes labored. Forcing air through constricted airways can make whistling or rattling sounds, called wheezing. Exhaling through obstructed airways is difficult and stale air remains in the lungs after each breath. This decreases the amount of fresh air which can be taken in with each new breath, and less oxygen is available. This decreased supply of oxygen makes an uncontrolled asthma attack a potentially life-threatening affair.

Air Sources:  The spring or summer wheezing attacks of pollen sensitive patients is a form of extrinsic asthma, usually obvious to patients and allergists alike. Indoor allergens often play a role in maintaining year-round asthma and may present as "intrinsic" asthma. Allergy to house dust mites is a leading cause of winter asthma. Cigarette smoke is always a major problem for asthmatics. Air pollution is a growing concern, although rates of asthma are equal or higher in rural residents compared with urban residents. People living in rural areas do not automatically breath cleaner air.

Food Sources: Food allergy can cause both immediate and delayed patterns of asthma. Immediate food reactions can cause sudden, dramatic and life-threatening asthma is one of the consequences of anaphylaxis reactions to food. Delayed patterns of food allergy can cause chronic asthma and/or bronchitis and are among the most neglected causes of chronic "intrinsic" asthma.

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