title: Physiologic differentiation of upper and lower airway obstruction.
abstract: Usual lower airway obstruction and fixed upper airway obstruction can be differentiated physiologically by means of the flow-volume curve. Normally, maximal flow decreases nearly linearly as lung volume decreases during expiration. In lower airway obstruction, this decrease is greatest at the beginning of expiration resulting in a curve that is concave upward. In fixed obstruction (stenosis) flow is constant throughout the initial part of forced maximal expiration and throughout virtually all of inspiration. This results in a plateau or flat curve which is characteristic and different from the curve in obstruction of lower airways. Cases in which this differentiation is clinically important are discussed.
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000175:diagnosis / Q000503:physiopathology*; D000403:Airway Resistance; D001249:Asthma / Q000503:physiopathology; D001980:Bronchi / Q000503:physiopathology; D003937:Diagnosis, Differential; D005260:Female; D005540:Forced Expiratory Flow Rates; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000503:physiopathology; D008176:Lung Volume Measurements; D008449:Maximal Expiratory Flow-Volume Curves; D014132:Trachea / Q000503:physiopathology; D014135:Tracheal Stenosis / Q000503:physiopathology