Asthma is an obstructive airway disease that is reversible. It is characterized by hyper-responsiveness of the airways, resulting in chronic inflammation and bronchospasm. Chronic bronchitis and emphysema are other examples of obstructive airway diseases that are reversible. (CH, 2011)

Asthma can either be extrinsic, also known as atopic asthma, or intrinsic, which is also called non-atopic asthma. Extrinsic asthma is the more common variety, comprising of about seventy percent of all cases. This type of asthma is actually an allergic response to a stimulus. The stimulus can vary from person to person. The allergic response can have two phases, namely, an acute response and a late response. The acute response occurs immediately and is mediated through sub-epithelial vagal receptors that cause bronchospasm. This results in a narrow airway through which air must pass to reach the terminal alveoli. The resulting obstruction can worsen with the late response. The late response...
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