A wheeze is the sound generated when air travels though a breathing passage (airway) that has become narrowed. The narrowing can be due to mucus secretions trapped within the airway or to the airway muscles’ constriction or tightening around the airway. The airway narrowing due to asthma is reversible. Medications prescribed for asthma help the narrowed airway return to its normal state. A wheeze is best described as a high-pitched whistling sound. Wheezing can occur while breathing in (inspiratory wheezing, during the inspiratory phase of the breath), while breathing out (expiratory wheezing, during the expiratory phase of the breath), or during the entire breath.
Asthma is one of several conditions that can cause wheezing, as detailed further in the following question. If wheezing is severe, it can be heard without a stethoscope. Wheezing in asthma reflects ongoing lung inflammation and airway narrowing, or bronchoconstriction. The sound is generated by turbulent flow through constricted air-ways. The presence of wheezing in asthma indicates that the asthma is active, and that more intensive and efficacious treatment is warranted. Wheezing is never normal and should never be ignored. If airway narrowing and inflammation are left untreated, there is a real risk of the disease worsening, which can become potentially life threatening.