Loop gain measured noninvasively from polysomnography can be influenced by respiratory event scoring in obstructive sleep apnea (OSA), according to study results published in the Annals of the American Thoracic Society.

Methods for quantifying loop gain in OSA using polysomnography have been developed that predict favorable responses to upper airway surgery; however, these methods are dependent on respiratory event scoring and may be affected by hypopnea scoring criteria. Thus, researchers conducted a retrospective analysis of 46 polysomnographys performed before and after upper airway surgery to determine to what extent differences in hypopnea scoring affect loop gain measurement. Polysomnographys were rescored according to 3 definitions of hypopnea, according to the American Academy of Sleep Medicine (2007Alternative, 2012Recommended, and 2012Acceptable criteria). Individuals were considered responders to surgery by a ≥50% reduction in apnea hypopnea index and apnea hypopnea index post-surgery <10 events/h.

The researchers found a near perfect agreement between loop gains derived using the 2007Alternative and 2012Recommended criteria. Greater variability was seen in the 2012Acceptable compared with the 2007Alternative and 2012Recommended criteria. Both 2007Alternative and 2012Recommended loop gains significantly predicted surgical response, with similar area under the curve. However, 2012Acceptable loop gains were a poor predictor of surgical response.

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“We recommend caution when using the 2012Acceptable criteria with this method, as such findings may not be directly generalizable to other loop gain values derived from other scoring criteria,” the authors noted.

Further work is required to more accurately define normative ranges of loop gain in patients with OSA and to define what constitutes a clinically/physiologically significant difference in loop gain.


Landry SA, Joosten SA, Thomson LDJ, et al. Effect of hypopnea scoring criteria on non-invasive assessment of loop gain and surgical outcome prediction [published online December 10, 2019]. Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201906-436OC