During intense aerobic exercise, a person often breathes through the mouth and the humidification of the inhaled air by the nasal passages and the sinuses is lost. This results in thermal cooling of the air that reaches the distal airways, causing wheezing. Occupational factors like exposure to strong smells, leather, cotton, etc., are all well-known agents that provoke wheezing. Virtually any agent can cause wheezing. Infections cause wheezing and this is due more to viruses than to bacteria.
Emotional stress increases the parasympathetic tone and provokes wheezing.
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.