One of the recognized abnormalities of a flow-volume loop is a sawtooth profile due to flow oscillations that are superimposed on either the maximal expiratory or inspiratory flow curve, or the tidal loop.
Sawtooth pattern on a flow-volume loop
The sawtooth pattern occurs in only a small fraction of patients but it is quite noticeable when you see it. Estimates of the number of individuals with flow oscillation range from 1.4% to 13.4% with the higher estimates being observed primarily with inspiratory loops. Since many spirometry efforts are concentrated solely on exhalation this means that it may frequently go unrecognized. Recently, I had several reports with distinct sawtooth flow-volume loops come across my desk within a short time period and for this reason thought it might be interesting to re-visit this old subject. I call it old only because most of the research on sawtooth profiles was done in the 1970’s and 1980’s and not much has been published since then.