Flow–volume loops. A. Normal flow–volume loop Flow–volume loops. A. Normal flow–volume loop. During expiration (E), the normal loop can be straight or slightly convex to the volume (x-) axis. B. Obstructive flow–volume curve. During expiration, the expiratory loop is concave toward the volume axis. A normal peak flow (as in this case) does not preclude an obstructive process. C. Restrictive flow–volume curve. The flows are normal when corrected for low lung volumes. D. Variable extrathoracic obstruction. The expiratory loop remains normal, but there is flattening of the inspiratory loop. E. Fixed obstruction. Both the expiratory and inspiratory loops reach a plateau at low flows. Source: Pulmonology, The Philadelphia Guide: Inpatient Pediatrics, 2e Citation: Shah SS, Zaoutis LB, Catallozzi M, Frank G. The Philadelphia Guide: Inpatient Pediatrics, 2e; 2016 Available at: http://accesspediatrics.mhmedical.com/DownloadImage.aspx?image=/data/books/1698/shah_c27_f002.png&sec=112042780&BookID=1698&ChapterSecID=112042624&imagename= Accessed: October 24, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved