Role of surgical hyoid bone repositioning in modifying upper airway collapsibility

Abstract

Background: Surgical hyoid bone repositioning procedures are being performed to treat obstructive sleep apnea (OSA), though outcomes are highly variable. This is likely due to lack of knowledge regarding the precise influence of hyoid bone position on upper airway patency. The aim of this study is to determine the effect of surgical hyoid bone repositioning on upper airway collapsibility. Methods: Seven anaesthetized, male, New Zealand White rabbits were positioned supine with head/neck position controlled. The rabbit's upper airway was surgically isolated and hyoid bone exposed to allow manipulation of its position using a custom-made device. A sealed facemask was fitted over the rabbit's snout, and mask/upper airway pressures were monitored. Collapsibility was quantified using upper airway closing pressure (Pclose). The hyoid bone was repositioned within the mid-sagittal plane from 0 to 5 mm (1 mm increments) in anterior, cranial, caudal, anterior-cranial (45°) and anterior-caudal (45°) directions. Results: Anterior displacement of the hyoid bone resulted in the greatest decrease in Pclose amongst all directions (p = 0.002). Pclose decreased progressively with each increment of anterior hyoid bone displacement, and down by -4.0 ± 1.3 cmH₂O at 5 mm. Cranial and caudal hyoid bone displacement did not alter Pclose (p > 0.35). Anterior-cranial and anterior-caudal hyoid bone displacements decreased Pclose significantly (p < 0.004) and at similar magnitudes to the anterior direction (p > 0.68). Conclusion: Changes in upper airway collapsibility following hyoid bone repositioning are both direction and magnitude dependent. Anterior-based repositioning directions have the greatest impact on reducing upper airway collapsibility, with no effect on collapsibility by cranial and caudal directions. Findings may have implications for guiding and improving the outcomes of surgical hyoid interventions for the treatment of OSA.

Keywords: OSA; closing pressure; obstructive sleep apnea; pharynx; rabbit model; sleep-disordered breathing; upper airway patency; upper airway surgery.

FIGURE 1

Schematic of the experimental setup with upper airway negative pressure application. The upper airway was isolated at the level of the trachea. A syringe is connected to the cranial tracheal segment and pulled to create a negative pressure in the upper airway, which is detected at the level of the mask. Pmask, mask pressure. Pua, pressure at the cranial end of the trachea. Adapted and modified from Amatoury, 2012 (Amatoury, 2012).

FIGURE 2

Schematic of the hyoid bone (lateral view) showing the different directions of hyoid bone displacement applied, including cranial, caudal, anterior, anterior-caudal 45° (ant-caudal) and anterior-cranial 45 (ant-cranial). The hyoid bone was displaced from 0 to 5 mm at 1 mm increments in all the directions.

FIGURE 3

Representative raw data example showing Pmask (mask pressure) and Pua (upper airway pressure) during application of negative intraluminal pressure for Pclose (closing pressure) determination. Initially, Pmask and Pua decrease at the same rate as increasing negative pressure is being applied to the upper airway, indicating an open airway. Eventually there is a deviation in Pua and Pmask, with a sudden drop in Pua while Pmask stabilizes, indicating that the upper airway has closed (i.e., Pclose = −3.25 cmH₂O in this example). Pmask and Pua were later retuned to 0 cmH₂O when the system was opened to atmosphere.

FIGURE 4

Individual rabbit (n = 7; open symbols, dashed interpolated line) and group mean ± SD (closed dark circles with error bars representing standard deviation, solid interpolated line) ΔPclose vs increasing hyoid displacement for each displacement direction: (A) anterior, (B) caudal, (C) cranial, (D) ant-caudal, and (E) ant-cranial. ΔPclose progressively decreased with hyoid displacement in all anterior based directions (A,D,E), while there was no significant change in ΔPclose for cranial and caudal directions.

FIGURE 5

Schematic model of the upper airway demonstrating the potential effect of cranial and caudal hyoid repositioning on supra-hyoid and infra-hyoid upper airway regions to aide in explaining study outcomes. When the hyoid is at its baseline position (A), the upper airway is patent. Displacement of the thyroid cartilage and hyoid caudally with caudal tracheal displacement (B), stretches upper airway soft tissues in both supra- and infra-hyoid regions, hence stiffening the airway’s walls along its length (Amatoury et al., 2014; Amatoury et al., 2016; Tong et al., 2019). Unfolding of the upper airway wall may also occur (Amatoury et al., 2010; Kairaitis et al., 2015). Following direct application of caudal hyoid bone displacement (C), supra-hyoid tissues are stretched, however infra-hyoid tissue (e.g., thyrohyoid, sternohyoid and omohyoid muscles) strains are likely reduced (unlike with tracheal displacement), leading to a “floppier” and more collapsible airway segment in this region. The balance between regions along the length the upper airway of increased and decreased stiffness, overall gives way to no change in upper airway collapsibility. Following cranial displacement of the hyoid bone (D), the soft tissues in the supra-hyoid region (e.g., hyoglossus, styloglossus, palatoglossus) become “floppier” and the airway narrowed, while the infrahyoid region is stretch and stiffened. Similar to caudal hyoid displacement, this likely results in the overall zero change in upper airway collapsibility with cranial hyoid displacement.