Unusual breath sounds can sometimes be heard when a person is breathing in or breathing out. Stridor is the abnormal whistling or wheezing sound heard when a person inhales. Alexander Leung and Helen Cho, authors of the 1999 "American Family Physician" paper "Diagnosis of Stridor in Children," report that stridor with inspiratory wheezing, which occurs when breathing in, is caused by a blockage in the throat, most often an obstruction above the glottis, or upper section of the windpipe.
Infection
The authors of the paper "Diagnosis of Stridor in Children" note that many infectious agents can cause inspiratory wheezing, or stridor. The flu, respiratory and cold virus can all cause viral croup, the most common cause of stridor in children. Symptoms of viral croup include fever, barking cough, stridor and hoarse voice.
A pocket of infection, or abscess, on the tonsils can be large enough to block the airway and cause stridor. A type-B flu virus called Hemophilus influenzae can cause epiglottis, a swelling of the glottis located above the vocal cords. Leung and Cho note that symptoms of both tonsil abscess and epiglottis include fever, trouble swallowing, shortness of breath and drooling. A child may also extend her neck in an unusual way due to pain.
Allergy
The National Institutes of Health (NIH) note that allergies can cause swelling in the neck and throat, causing inspiratory wheezing and difficulty breathing. Spasmodic croup, unlike viral croup, occurs without an infection. Symptoms include a barking cough and stridor. According to NIH, spasmodic croup may be triggered by an allergy, emotional conditions or refluxed acid from the stomach. Spasmodic croup typically occurs at night and can recur.
Choking
Authors Leung and Cho report that choking on a foreign body, most often food, is a common cause of sudden inspiratory wheezing. Other symptoms include cough and trouble breathing. Sometimes the person appears to recover; however, the food sticks in the throat and causes delayed swelling or infection that results in stridor.
Cancer
The NIH notes that cancer of the throat or larynx can cause inspiratory wheezing. Other symptoms may include cough, persistent hoarse voice, neck or throat pain, trouble swallowing or weight loss. Examination by an otolaryngologist, a head and neck surgeon, can properly diagnose the condition. The NIH observes that throat cancer affects men 10 times more often than women, and a history of excessive alcohol use and smoking increases the risk.
