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. 2025 Jan 16;65(1):2400901.
doi: 10.1183/13993003.00901-2024. Print 2025 Jan.

Ansa cervicalis stimulation effects on upper airway patency: a structure-based analysis

Yike Li  1 , Alan R Schwartz  1   2   3 , David Zealear  1 , Matthew S Shotwell  4 , Megan E Hall  4 , Christopher J Lindsell  5 , Holly A Budnick  1 , Silvana Bellotto  6 , David T Kent  7
Affiliations

Ansa cervicalis stimulation effects on upper airway patency: a structure-based analysis

Yike Li et al. Eur Respir J. .

Abstract

Rationale: Ansa cervicalis stimulation (ACS) of the infrahyoid muscles has been proposed as a neurostimulation therapy for obstructive sleep apnoea (OSA). ACS stabilises the pharynx by pulling it caudally, but its specific effects on flow limitation caused by palatal, oropharyngeal lateral wall, tongue base, or epiglottis collapse remains unclear.

Objectives: To quantify the effect of ACS on collapsibility of different pharyngeal flow-limiting structures.

Methods: Participants with OSA underwent bilateral ACS during drug-induced sleep endoscopy. Maximum inspiratory airflow was assessed over a range of positive airway pressures while ACS was applied. The flow-limiting structure for each breath was classified based on manometric and endoscopic findings and a linear mixed-effects model characterised their response to ACS. The influence of patient characteristics was explored with univariate models.

Measurements and main results: 41 participants yielded 1761 breaths for analysis. On average, bilateral ACS decreased the observed pharyngeal critical closing (P CRIT) and opening (P OPEN) pressures by -3.0 (95% CI -3.6--2.3) and -3.7 (-4.4--3.0) cmH2O, respectively (p<0.001). During tongue base obstruction, modelled ACS effects for P CRIT and P OPEN were -2.0 (-2.7--1.4) and -3.1 (-3.8--2.4) cmH2O, respectively (p<0.001). Greater reductions were generally observed for other flow-limiting structures. A lower apnoea-hypopnea index was associated with a greater decrease in P OPEN (p<0.01). Other patient characteristics, including body mass index, did not influence P CRIT or P OPEN (p>0.05).

Conclusions: Bilateral ACS decreased collapsibility of all airway flow-limiting structures. ACS generally had greater effects on palatal, oropharyngeal lateral wall and epiglottic collapse than the tongue base.

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Conflict of interest statement

Conflict of interest: A.R. Schwartz is a scientific advisor for Apnimed, HuMannity Foundation, Invicta Medical, Itamar/Zoll, LivaNova, Lunair, Nyxoah SA, Periodic Breathing LLC, Respicardia/Zoll and Sonosa. C.J. Lindsell reports grants from NIH and Department of Defense and research funds from the CDC, biomeme, Novartis, bioMerieux, AstraZeneca, AbbVie, Entegrion Inc. and Endpoint Health, outside the submitted work, patents for risk stratification in sepsis and septic shock issued to Cincinnati Children's Hospital Medical Center, service on data safety monitoring board or advisory boards unrelated to the current work, stock options in Bioscape Digital unrelated to the current work, and is editor in chief of the Journal of Clinical and Translational Science. D.T. Kent has received research support from Invicta Medical, Inspire Medical System, and Nyxoah SA, is a consultant to Invicta Medical and Nyxoah SA, is a scientific advisory board member with Nyxoah SA, and is an inventor on patent pending PCT/US2020/021359 and related work licensed by Nyxoah SA that is relevant to this work. The remaining authors have no potential conflicts of interest to disclose.

Figures

None
Overview of the study. OSA: obstructive sleep apnoea; stim: stimulation voltage; RIP: sum of thoracic and abdominal respiratory impedance plethysmography belts; VImax: peak inspiratory airflow; ACS: ansa cervicalis stimulation; PCRIT: critical closing pressure; POPEN: opening pressure; VOTE: velum, oropharynx, tongue base, epiglottis; BMI: body mass index.
FIGURE 1
FIGURE 1
An illustrative example of combined airflow, pharyngeal manometry and endoscopy data for each pharyngeal flow-limiting structure. The flow-limiting segment of the pharynx (i.e. velo-, oro- or hypopharynx) was localised by placing one manometry catheter caudal to the faucial arch of the soft palate and another one in the vallecula. Soft palate obstruction caused the velopharyngeal and epiglottic pressures to track increasingly negative downstream pressure, tongue base or oropharyngeal lateral wall obstruction caused only the velopharyngeal pressure to return to nasal pressure, and epiglottic obstruction resulted in both catheters returning toward nasal pressure. The flow-limiting structure within a relevant segment was subsequently identified endoscopically as either the soft palate (velopharynx), oropharyngeal lateral walls or tongue base (oropharynx), or epiglottis (hypopharynx). The manometry depictions have different y-scales to enable easier visualisation of the changes in the pressure curves.
FIGURE 2
FIGURE 2
Changes in observed pharyngeal critical closing (PCRIT) and opening pressure (POPEN) with bilateral ansa cervicalis stimulation (ACS). Data are depicted as median, interquartile range (IQR) and 1.5×IQR. Each point represents the per-trial PCRIT or POPEN calculated from a regression line through the plotted points (supplementary figure S1).
FIGURE 3
FIGURE 3
Change in linear mixed-effect model pressure–flow curves with application of bilateral ansa cervicalis stimulation (ACS), stratified by pharyngeal flow-limiting structures. The pharyngeal critical closing (PCRIT) and critical opening pressures (POPEN) were calculated for each condition (table 2). Data are presented with 95% CI. VImax: peak inspiratory airflow.
FIGURE 4
FIGURE 4
Proposed mechanical effects of ansa cervicalis stimulation of the sternothyroid trunk on pharyngeal patency. a) Loss of caudal traction increases pharyngeal collapsibility. b) We postulate that infrahyoid muscle contraction 1) pulls down on palatopharyngeus muscle insertions into the oropharyngeal lateral walls; 2) increases longitudinal strain in the oropharyngeal lateral walls, reducing their compliance; 3) reduces tongue pressure against the soft palate; and 4) tips the hyolaryngeal complex anteriorly, displacing the tongue base and epiglottis anteriorly via ligamentous attachments.
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