The Effect of Upper Airway Surgery on Loop Gain in Obstructive Sleep Apnea

Abstract

Study objectives: Controversy exists as to whether elevated loop gain is a cause or consequence of obstructive sleep apnea (OSA). Upper airway surgery is commonly performed in Asian patients with OSA who have failed positive airway pressure therapy and who are thought to have anatomical predisposition to OSA. We hypothesized that high loop gain would decrease following surgical treatment of OSA due to reduced sleep apnea severity.

Methods: Polysomnography was performed preoperatively and postoperatively to assess OSA severity in 30 Chinese participants who underwent upper airway surgery. Loop gain was calculated using a validated clinically-applicable method by fitting a feedback control model to airflow.

Results: Patients were followed up for a median (interquartile range) of 130 (62, 224) days after surgery. Apnea-hypopnea index (AHI) changed from 60.8 (33.7, 71.7) to 18.4 (9.9, 42.5) events/h (P < .001). Preoperative and postoperative loop gain was 0.70 (0.58, 0.80) and 0.53 (0.46, 0.63) respectively (P < .001). There was a positive association between the decrease in loop gain and the improvement of AHI (P = .025).

Conclusions: High loop gain was reduced by surgical treatment of OSA in our cohort. These data suggest that elevated loop gain may be acquired in OSA and may provide mechanistic insight into improvement in OSA with upper airway surgery.

Clinical trial registration: Registry: ClinicalTrials.gov, Title: The Impact of Sleep Apnea Treatment on Physiology Traits in Chinese Patients With Obstructive Sleep Apnea, Identifier: NCT02696629, URL: https://ichgcp.net/clinical-trials-registry/NCT02696629.

Keywords: hypoxemia; loop gain; lung; obstructive sleep apnea; upper airway surgery; ventilatory control.

© 2019 American Academy of Sleep Medicine.

Figures

Figure 1. Preoperative and postoperative AHI.

The distribution of group AHI values are shown in the box-and-whiskers plots (group median, upper and lower quartile, upper and lower extreme, and outliers). (A) Preoperative and postoperative AHI in the whole group. (B) Individual preoperative and postoperative AHI in responders (n = 15). (C) Preoperative and postoperative AHI in nonresponders (n = 15). AHI = apnea-hypopnea index.

Figure 2. Preoperative and postoperative loop gain

The distribution of group loop gain values are shown in the box-and-whiskers plots (group median, upper and lower quartile, upper and lower extreme, and outliers). (A) Individual preoperative and postoperative loop gain. (B) Individual preoperative and postoperative loop gain in responders (n = 15). (C) Preoperative and postoperative loop gain in nonresponders (n = 15).