Effect of oxygen in obstructive sleep apnea: Role of loop gain

We compared the effect of oxygen on the apnea–hypopnea index (AHI) in six obstructive sleep apnea patients with a relatively high loop gain (LG) and six with a low LG. LG is a measure of ventilatory control stability. In the high LG group (unstable ventilatory control system), oxygen reduced the LG from 0.69 ± 0.18 to 0.34 ± 0.04 (p < 0.001) and lowered the AHI by 53 ± 33% (p = 0.04 compared to the percent reduction in the low LG group). In the low LG group (stable ventilatory control system), oxygen had no effect on LG (0.24 ± 0.04 on room air, 0.29 ± 0.07 on oxygen, p = 0.73) and very little effect on AHI (8 ± 27% reduction with oxygen). These data suggest that ventilatory instability is an important mechanism causing obstructive sleep apnea in some patients (those with a relatively high LG), since lowering LG with oxygen in these patients significantly reduces AHI.