Ansa Cervicalis Stimulation Increases Upper Airway Patency During Expiration in Patients With Obstructive Sleep Apnea

RATIONALE Increased phasic pharyngeal neuromuscular activity can stabilize airway patency during inspiration compared to expiration when neuromuscular activity wanes. Ansa cervicalis stimulation (ACS) of the sternothyroid muscle is a novel neurostimulation method that enhances pharyngeal patency by exerting caudal traction on the upper airway. Previous studies have shown that ACS relieves airflow obstruction during inspiration in patients with obstructive sleep apnea (OSA) during drug-induced sleep endoscopy (DISE). Studies of ACS during expiration are needed to understand caudal traction effects on passive pharyngeal mechanics. During passive expiration, the time constant (tau) is related to airway resistance and the compliance of the respiratory system. We hypothesized that isolated effects of ACS reduce tau by decreasing airflow obstruction during expiration as neuromuscular tone declines. METHODS Seventeen OSA patients (Age: 55.3±11.9 years; Male: 9; BMI: 32.4±3.1 kg/m2; AHI: 44.2±15.6 events/hour) underwent bilateral ACS of the sternothyroid muscle using hook-wire percutaneous electrodes during DISE. Airflow was measured with a pneumotachometer across a range of positive nasal pressure levels. Tau was determined by fitting the exponential decay curve from peak expiratory flow to the end of expiration in a subset of stable flow-limited breaths immediately before and during ACS (Figure 1A). Breaths with a curve fit resulting in an R² above 0.90 in expirations exceeding 0.5 second were included in the analysis. Tau was compared within breathing segments on and off ACS and assessed by univariate regression for its association with patient features, including age, gender, AHI, BMI, and oxygen nadir. A linear mixed model was performed on a per-breath basis to characterize the effect of ACS on tau, stratified by participants and nasal pressures. RESULTS Data from 186 breaths across 28 segments were analyzed. ACS significantly reduced tau in all segments, with a median decrease of 0.53 second (p<0.001, Figure 1B). Age was the only demographic factor associated with the magnitude of tau change (β=-0.017, [95% CI: -0.029, -0.004]). When stratified by participant and airway pressure, ACS led to a mean tau reduction of 0.58 second [0.38, 0.78]. Airway pressure did not significantly affect tau (p = 0.34). CONCLUSIONS Bilateral ACS significantly decreased the expiratory time constant, indicating that caudal traction influences passive pharyngeal mechanics substantially. Reductions in tau suggest that ACS stabilizes airway patency independent of phasic changes in intrinsic pharyngeal neuromotor tone.

Duke Scholars

Author Christopher Lindsell Biostatistics & Bioinformatics, Division of Biostatistics