Effect of Hypopnea Scoring Criteria on Noninvasive Assessment of Loop Gain and Surgical Outcome Prediction

Rationale: Unstable ventilatory control (high loop gain) is a causal factor in the development of obstructive sleep apnea. Methods for quantifying loop gain using polysomnography have been developed that predict favorable responses to upper airway surgery. However, this method is reliant on respiratory event scoring and hence may be affected by hypopnea scoring criteria. Objectives: To determine to what extent differences in hypopnea scoring influence loop gain measurement. Methods: We performed a retrospective analysis of 46 polysomnograms before and after upper airway surgery. Polysomnograms were rescored according to three different American Academy of Sleep Medicine hypopnea definitions (2007 Alternative, 2012 Recommended, and 2012 Acceptable criteria). Loop gain and apnea-hypopnea indexes (AHIs) were compared between criteria using linear regression and Bland-Altman limits of agreement (LOA). Responders to surgery were classified by a 50% or greater reduction in AHI and AHIpostsurgery less than 10 events per hour. Responders were determined separately for each American Academy of Sleep Medicine criterion. Receiver operating characteristic curve analysis predicting surgical outcome was performed for each loop gain measurement derived from each criterion. Results: A near-perfect agreement was found between loop gains derived using the 2007 Alternative and 2012 Recommended criteria (r 2 = 0.99; bias =20.003; LOA, 20.016 to 0.010). Greater variability was found for 2012 Acceptable compared to the 2007 Alternative (r 2 = 0.70; bias = 20.015; LOA, 20.099 to 0.070) and 2012 Recommended (r 2 = 0.69; bias =10.018; LOA, 20.068 to 0.104) criteria. Both 2007 Alternative and 2012 Recommended loop gains significantly predicted surgical response with similar areas under the curve (AUCs; 2007 Alternative AUC= 0.86 [95% confidence interval (CI), 0.75-0.97]; 2012 Recommended AUC= 0.84 [95% CI, 0.71-0.97]). 2012 Acceptable loop gains were a poor predictor of surgical response (AUC = 0.62 [95% CI, 0.43-0.80]). Conclusions: Loop gain measured noninvasively by polysomnography can be influenced by respiratory event scoring. We recommend caution when using the 2012 Acceptable criteria with this method, because such findings may not be directly generalizable to other loop gain values derived from other scoring criteria.