Loop Gain Predicts the Response to Upper Airway Surgery in Patients With Obstructive Sleep Apnea

Abstract

Study Objectives: Upper airway surgery is often recommended to treat patients with obstructive sleep apnea (OSA) who cannot tolerate continuous positive airways pressure. However, the response to surgery is variable, potentially because it does not improve the nonanatomical factors (ie, loop gain [LG] and arousal threshold) causing OSA. Measuring these traits clinically might predict responses to surgery. Our primary objective was to test the value of LG and arousal threshold to predict surgical success defined as 50% reduction in apnea-hypopnea index (AHI) and AHI <10 events/hour post surgery. LG remained a significant predictor of surgical success after controlling for covariates (logistic regression p = .018; receiver operating characteristic area under curve = 0.80). Conclusions: Our study provides proof-of-principle that upper airway surgery most effectively resolves OSA in patients with lower LG. Predicting the failure of surgical treatment, consequent to less stable ventilatory control (elevated LG), can be achieved in the clinic and may facilitate avoidance of surgical failures.

Exposure to mild intermittent hypoxia increases loop gain and the arousal threshold in participants with obstructive sleep apnoea

“…Loop gain and arousal threshold analysis. A customized MATLAB (Mathworks, Natick, MA, USA) program, that has been previously described, was used to measure loop gain (see next paragraph for list of components) and the arousal threshold (Terrill et al 2015;Joosten et al 2017;Landry et al 2018). Seven-minute windows of NREM or REM sleep were identified by the program.…”

“…Given these findings, we postulated that loop gain would increase during NREM sleep, because of exposure to mild intermittent hypoxia during wakefulness immediately prior to sleep. Our hypothesis was based on the understanding that loop gain is in part dependent on controller gain, an indicator of chemoreflex sensitivity (Terrill et al 2015;Joosten et al 2017;Landry et al 2018). Our postulation was supported by our results, since loop gain was increased during NREM sleep following exposure to mild intermittent hypoxia on both Day 1 and Day 10, but not following exposure to the sham protocol.…”

“…hypoxia and/or hypercapnia) that initiated the response and is the result of two components, controller gain and plant gain (Terrill et al 2015;Joosten et al 2017;Deacon et al 2018;Landry et al 2018). Controller gain primarily reflects chemoreflex sensitivity, while plant gain reflects the ability of gas stores in the lung to minimize changes in blood gases influenced by ventilation (Terrill et al 2015;Joosten et al 2017;Deacon et al 2018;Landry et al 2018). Thus, modifications in chemoreflex sensitivity following exposure to intermittent hypoxia should be accompanied by increases in loop gain during NREM sleep.…”

Assessing ventilatory control stability in children with and without an elevated central apnoea index

“…We suggest that knowledge of the underlying LG in such children could also be used to aid decision‐making by helping to stratify which children would be most likely to benefit from supplementary oxygen, an intervention that is known to stabilize respiratory control by reducing LG . Certainly, knowledge of an individual's LG in adults with either OSA or central sleep apnoea associated with congestive heart failure has been shown to be useful in predicting response to different therapies . If the children with an elevated LG were non‐responsive to supplemental oxygen (i.e.…”

Time for Surgeons to Think Outside the Anatomical Box

“…Earlier this year, Joosten et al 6 produced similar findings in which low loop gain predicted favorable response to upper airway surgery. As we begin to look beyond the anatomy of our sleep surgery patients, we will further our understanding and ability to quantify other metrics of importance such as loop gain, arousal threshold, and airway collapsibility.…”