Mandibular advancement splint improves upper airway collapsibility without changing genioglossus reflex responses in people with obstructive sleep apnea during wakefulness

Rationale: Mandibular advancement splints (MAS) improve upper airway collapsibility (Pcrit) during sleep in a dose-dependent manner. We have recently shown that a simple wakefulness test, the upper airway collapsibility index (UACI), is closely related to Pcrit during sleep. Here, as a proof-of-concept, we investigated whether the UACI technique can be used to detect improvements in upper airway collapsibility with MAS during wakefulness. A secondary aim was to measure the effect of MAS on the genioglossus reflex response to brief pulses of negative airway pressure. Methods: 25 people with obstructive sleep apnea (OSA) used a custom fitted MAS device. In addition to standard polysomnography equipment, all participants were instrumented with two pressure catheters (positioned at the level of the choanae and epiglottis), a sealed nasal mask fitted with a pressure sensor, a pneumotachograph to measure airflow and two fine-wire intramuscular electrodes into the genioglossus. Approximately 30 brief negative pressure pulses were applied to the mask (∼-14cmH2O) during early inspiration while participants breathed quietly in the supine position during wakefulness to quantify the UACI: 100x(nadir choanal-epiglottic pressure)/nadir choanal pressure during negative pressure pulses.This procedure was performed with and without MAS (order randomized). Results: The UACI at baseline (41±22%, mean±SD), was significantly improved with MAS (34±26%, p=0.017). Prestimulus baseline genioglossus muscle activity immediately prior (100ms) to negative pressure pulse delivery varied between individuals but on average was 157% higher with MAS than without (p=0.006). When present in both conditions, the onset latency (17±5 vs. 16±6ms, p=0.7, n=11), peak latency (27±6 vs. 29±11ms, p=0.7, n=11) and peak amplitude (531±543% vs. 528±325%, p=0.98) of the short-latency excitatory reflex response were not different with and without MAS. However, consistent with a scaling reflex, the amplitude of the short-latency peak excitation was closely related to the pre-stimulus baseline genioglossus muscle activity with and without MAS therapy (R 2= 0.5, p<0.001, n=11). Conclusions: MAS therapy improves the upper airway collapsibility index during wakefulness. Genioglossus short-latency excitatory reflex amplitude responses vary with MAS depending on the immediate baseline EMG activity during wakefulness. These findings provide proof-of-concept support for the UACI technique and highlight its clinical potential to inform patient selection for non-CPAP therapies. This research was supported by the CRC for Alertness, Safety and Productivity