O057 The Impact of Surgical Weight Loss on the Physiological Endotypes causing Obstructive Sleep Apnea

BACKGROUND: Weight loss improves upper airway collapsibility in people with obstructive sleep apnoea (OSA). However, it’s unclear how weight loss affects the other endotypes responsible for OSA (loop gain, arousal threshold and muscle compensation). We investigated the effect surgical weight loss has on the OSA endotypes and whether the baseline endotypes predict response to surgery. METHODS: Endotypes were measured using non-invasive methods in 43 OSA patients who had a clinical polysomnogram before and after (~6-18 months) receiving weight loss surgery. Linear regression was used to assess whether the baseline endotypes predicted improvement in OSA severity defined by the apnoea-hypopnoea index (AHI). RESULTS: Weight loss surgery was associated with significant improvements in AHI (43.4[28.6-64.8]events/hr vs. 16.9[11.6-33.3]events/hr, p<0.001), body mass index (42.1 ±5.5kg/m2 vs. 32.8 ±4.5kg/m2, p<0.001), upper airway collapsibility (73.8[65.2-78.5]%eupnea vs. 77.1[71.7-81.3]%eupnea, p=0.034) and loop gain (0.62[0.53-0.71] vs. 0.54[0.44-0.72], p=0.012). Weight loss surgery was also associated with a reduced arousal threshold (144.5[130.1-160.5] vs.136.9[121.9-156.4], p=0.007). A greater reduction in OSA severity was associated with greater improvements in upper airway collapsibility (p=0.001, r2 =0.23) and reductions in the arousal threshold (p<0.001, r2=0.27). Poor upper airway collapsibility at baseline was weakly predictive of a greater improvement in OSA severity (p=0.018, r2 =0.13). No other endotype was predictive of OSA improvement. DISCUSSION: Weight loss surgery is associated with improvements in weight, OSA severity, upper airway collapsibility and loop gain. There was a paradoxical worsening of arousal threshold. Furthermore, weight loss surgery may be particularly effective in improving OSA in those with poor upper airway collapsibility.