"Saw-tooth sign" in upper airway disorders—a case report.

Spirometry flow-volume loop measurement is the screening test of choice to rule out obstructive lung diseases. Flow oscillations occasionally seen on flow volume loops, referred to as a "saw-tooth" sign, are thought to be due to an upper airway obstructive processes associated with upper airway collapsibility. Widely described in obstructive sleep apnea syndrome, flow oscillations have also been linked to many other upper airway pathologies. The mechanism by which flow oscillations occur is centered on the inspiratory and expiratory flow of air. It has been theorized that the mechanism of flow oscillations result from rapid intermittent changes in driving pressure or airway resistance. Since visual inspection of the flow volume loop can reveal presence of flow oscillations clinicians should be aware of this phenomenon and the presence of flow loop oscillations should clue physicians to rule out upper airway pathology.