Structure and severity of pharyngeal obstruction determine oral appliance efficacy in sleep apnoea

Abstract

Key points: •Some patients with obstructive sleep apnoea (OSA) respond well to oral appliance therapy, whereas others do not for reasons that are unclear. •In the present study, we used gold-standard measurements to demonstrate that patients with a posteriorly-located tongue (natural sleep endoscopy) exhibit a preferential improvement in collapsibility (lowered critical closing pressure) with oral appliances. •We also show that patients with both posteriorly-located tongue and less severe collapsibility (predicted responder phenotype) exhibit greater improvements in severity of obstructive sleep apnoea (i.e. reduction in event frequency by 83%, in contrast to 48% in predicted non-responders). •The present study suggests that the structure and severity of pharyngeal obstruction determine the phenotype of sleep apnoea patients who benefit maximally from oral appliance efficacy.

Abstract: A major limitation to the administration of oral appliance therapy for obstructive sleep apnoea (OSA) is that therapeutic responses remain unpredictable. In the present study, we tested the hypotheses that oral appliance therapy (i) reduces pharyngeal collapsibility preferentially in patients with posteriorly-located tongue and (ii) is most efficacious (reduction in apnoea-hypopnea index; AHI) in patients with a posteriorly-located tongue and less-severe baseline pharyngeal collapsibility. Twenty-five OSA patients underwent upper airway endoscopy during natural sleep to assess tongue position (type I: vallecula entirely visible; type II: vallecula obscured; type III: vallecula and glottis obscured), as well as obstruction as a result of other pharyngeal structures (e.g. epiglottis). Additional sleep studies with and without oral appliance were performed to measure collapsibility (critical closing pressure; Pcrit) and assess treatment efficacy. Overall, oral appliance therapy reduced Pcrit by 3.9 ± 2.4 cmH₂ O (mean ± SD) and AHI by 69 ± 19%. Therapy lowered Pcrit by an additional 2.7 ± 0.9 cmH₂ O in patients with posteriorly-located tongue (types II and III) compared to those without (type I) (P < 0.008). Posteriorly-located tongue (p = 0.03) and lower collapsibility (p = 0.04) at baseline were significant determinants of (greater-than-average) treatment efficacy. Predicted responders (type II and III and Pcrit < 1 cmH₂ O) exhibited a greater reduction in the AHI (83 ± 9 vs. 48 ± 8% baseline, P < 0.001) and a lower treatment AHI (9 ± 6 vs. 32 ± 15 events h^-1 , P < 0.001) than predicted non-responders. The site and severity of pharyngeal collapse combine to determine oral appliance efficacy. Specifically, patients with a posteriorly-located tongue plus less-severe collapsibility are the strongest candidates for oral appliance therapy.

Figure 1.. Examples of endoscopic views of two representative patients without and with oral appliance

The patient who did not respond to therapy was classified (off oral appliance) with tongue type I; Pcrit decreased from −1.7 to −5.2 cmH₂O, and the AHI reduced from 54 to 30 events h⁻¹ with oral appliance. The patient who responded to therapy was classified with tongue type II, Pcrit decreased from −1.0 to −9.0 cmH₂O, and the AHI reduced from 64 to 6 events h⁻¹ with oral appliance.

Figure 2.. AHI reduction

Differences in AHI reduction between tongue groups.

Figure 3.. Individual data illustrating the effect of oral appliances on collapsibility (Pcrit) by tongue type

Presence of additional sites of collapse (P, palate; L, lateral walls; E, epiglottis) is marked along the corresponding patient circle. Open circles correspond to the patients with baseline AHI < 20 events h⁻¹. Responders to oral appliance therapy are represented in green and non-responders are represented in red. The shaded box indicates the ‘predicted responders’ to oral appliance therapy (tongue type II or III and baseline Pcrit < 1 cmH₂O).