The mechanism by which the spasms are triggered is not fully understood, but there is an antigen antibody complex which releases the chemical mediators of inflammation and hypersensitivity, bypassing the cellular defense mechanisms. Such chemicals include histamines, prostaglandins and a variety of other substances. This allergic response is mediated by T and B lymphocytes. The hallmark is reduction in airways diameter due to oedema, mucus plugs, and smooth muscle constriction. Air trapping occurs.
Hypoxia is a universal finding during acute attacks.
There is carbon dioxide retention and metabolic acidosis results. The disorder can be acute or chronic. An acute exacerbation of a chronic condition is also possible. They can be present singly or in varying combinations. A small amount of sputum, typically sticky, is produced.