0566 Assessment of Soft Palate Muscle Fatigue and its Effect on Velopharyngeal Upper Airway (UA) Mechanical Properties

Abstract Introduction Soft palate muscles are crucial in the maintenance of UA patency. This study aimed to investigate the fatigability of soft palate muscles and to quantify its effects on velopharyngeal UA dynamic properties in OSA patients and control subjects. Methods 8 control (AHI ≤ 10 /h), 21 OSA patients (13 with mild/moderate disease: 10 /h < AHI ≤ 20 /h and 8 with moderate/severe: AHI > 20/h) were included in the study. Subjects were asked to develop repetitive intra-oral positive pressure during cheek-bulging maneuvers while wearing a mouth piece to keep the jaw opened. Subjects were asked to develop sustained maximal bulging pressure for 5 sec every 10 sec until the peak pressure could not reach 85% of baseline maximal pressure for 2 consecutive times. UA dynamic properties were assessed by measuring instantaneous airflow and velopharyngeal pressure in response to phrenic nerve magnetic stimulation (PNMS) performed before, immediately and every 3 minutes after the fatiguing protocol for a maximum of 30 minutes’ recovery time. UA closing pressure (Pcrit) was estimated by modeling the flow/pressure relationship in response to PNMS. Results The sex, age, BMI and the soft palate mechanical properties (including the baseline strength, endurance time, total muscle work) did not significantly differ between the 3 groups. Maximal peak bulging pressure measured using cheek-bulging maneuver significantly changed following the fatigue task (p < 0.05). Baseline velopharyngeal Pcrit were less negative in moderate/severe OSA group compared to mild/moderate OSA (-6.5±2.6 vs. -11.9±3.2, p < 0.05). In mild/moderate OSA patients, PNMS-induced drop in maximal instantaneous airflow tend to increase 3 mins after the fatiguing trial compared to baseline (22.7±21.1 l.s-1vs. 9.6±5.8 l.s-1, p < 0.1), and their Velopharyngeal linear resistance 3 mins after the fatiguing trial tend to be higher than the moderate/severe OSA group (3.9 ± 5.0 cmH2O·l−1·s−1 vs. 1.8 ± 1.1 cmH2O·l−1·s−1, p< 0.1). Conclusion The cheek-bulging maneuver could induce soft palate muscle fatigue, with no difference observed in soft palate mechanical performances among patients with different OSA severity. The fatiguing maneuver could further alter velopharyngeal UA mechanical properties in patients with mild/moderate OSA. Support SBD from IUCPQ Foundation