Asthma, or Reactive Airway Disease, is a disease of inflammation. The bronchioles, or breathing tubes, deep inside the lungs, get irritated and inflamed, usually due to an allergic or immunologic response to irritants.
When the inflammation (and concomitant excess mucus production) is severe enough, or when another irritant just pushes someone over the threshold, the muscles which line the bronchioles go into spasm, and cause the characteristic severe shortness of breath and wheezing. This can be life-threatening, and in the US, 5000 people each year die from acute asthma attacks.
Some folks can go from normal to severe attack in a few seconds, some folks decline slowly, some folks do both at different times.
Rescue treatment is generally based on drugs which relax the spasming bronchiole muscles. Albuterol in inhaled form is the most common rescue drug. Rescue medicines should generally be taken only when an acute attack is occurring.
Maintenance treatment is designed to be taken chronically, and it reduces the amount of inflammation in the bronchioles, and helps keep down the production of mucus. Drugs like inhaled steroids (flovent, Qvar), steroid/long-acting dilator combinations (advair), leukotriene inhibitors (singulair, accolate), or even prednisone, fall into this category. Proper use of maintenance medication reduces the number of acute attacks.
The proper diagnosis of asthma depends on taking a good medical history and doing a good physical exam, along with doing some basic tests like lung spirometry (both before and after using rescue inhalers) and having the patient take their own peak flow measurements, both when feeling short of breath, and when in their normal state.
Doing the above helps a doc confirm or rule out a diagnosis of asthma, and if needed, tailor-make a control plan to suit the needs of the individual.