Stridor is caused by all except:

i. Upper airway: The airway from the nares and lips to the lower border of larynx (includes nose, pharynx, larynx). ii. Lower airway: From the lower border of the terminal bronchioles (includes various level of bronchioles up to terminal bronchioles). Stridor usually implies upper airway obstruction, so the level of obstruction is above the level of trachea (P) (from nares to the larynx). Wheezing and ronchi are signs of lower airway obstruction. Epiglottitis and laryngeal tumors are common causes of stridor . Hypocalcemia leads to tetany which causes stridor. Asthma leads to wheezing or ronchi (lower airway obstruction) Stridor is a harsh noise produced by turbulent air flow through a paially obstructed upper airway. It can be: - Inspiratory i.e. originates from supraglottis glottis and pharynx - Expiratory i.e. originates from thoracic trachea - Biphasic i.e. originates from subglottis and cervical trachea - Hence, stridor is mainly of laryngeal and tracheal origin.