Effect of body posture on pharyngeal shape and size in adults with and without obstructive sleep apnea

Abstract

Study objectives: In patients with obstructive sleep apnea (OSA), the severity and frequency of respiratory events is increased in the supine body posture compared with the lateral recumbent posture. The mechanism responsible is not clear but may relate to the effect of posture on upper airway shape and size. This study compared the effect of body posture on upper airway shape and size in individuals with OSA with control subjects matched for age, BMI, and gender.

Participants: 11 males with OSA and 11 age- and BMI-matched male control subjects.

Results: Anatomical optical coherence tomography was used to scan the upper airway of all subjects while awake and breathing quietly, initially when supine, and then in the lateral recumbent posture. A standard head, neck, and tongue position was maintained during scanning. Airway cross-sectional area (CSA) and anteroposterior (A-P) and lateral diameters were obtained in the oropharyngeal and velopharyngeal regions in both postures. A-P to lateral diameter ratios provided an index of regional airway shape. In equivalent postures, the ratio of A-P to lateral diameter in the velopharynx was similar in OSA and control subjects. In both groups, this ratio was significantly less for the supine than for the lateral recumbent posture. CSA was smaller in OSA subjects than in controls but was unaffected by posture.

Conclusions: The upper airway changes from a more transversely oriented elliptical shape when supine to a more circular shape when in the lateral recumbent posture but without altering CSA. Increased circularity decreases propensity to tube collapse and may account for the postural dependency of OSA.

Figure 1

Representative aOCT images of the velopharynx and oropharynx from one healthy control subject and one OSA subject in the supine and lateral recumbent postures. All scans were obtained when the airway was at its minimum cross-sectional area during the respiratory cycle. The inner and outer walls of the imaging catheter are visible within each airway. All images have been rotated to align the anterior pharyngeal wall with the top of the page.

Figure 2

Maximum (closed symbols) and minimum (open symbols) cross-sectional area (CSA) in the oropharynx (left panel) and velopharynx (right panel) in healthy control (circles) and OSA subjects (triangles) in the supine and lateral recumbent postures. n = 11 per group; mean ± SE; * significantly different from control group; P < 0.05.

Figure 3

Lateral (upper) and anteroposterior (A-P) (lower) diameter at maximum (closed symbols) and minimum (open symbols) cross-sectional area (CSA) in the oropharynx (left panel) and velopharynx (right panel) in healthy control (circles) and OSA subjects (triangles) in the supine and lateral recumbent postures. n = 11 per group; mean ± SE; * significantly different from control group; P < 0.05; †significantly different from supine posture; P < 0.05.

Figure 4

Ratio of anteroposterior (A-P):lateral diameter at maximum (closed symbols) and minimum (open symbols) cross-sectional area (CSA) in the oropharynx (left panel) and velopharynx (right panel) in healthy control (circles) and OSA subjects (triangles) in the supine and lateral recumbent postures. n = 11 per group; mean ± SE; † significantly different from supine posture; P < 0.05

Figure 5

Schematic representation of the compartmental tissue arrangement surrounding the pharyngeal airway when in the supine and lateral recumbent postures. BE, bony enclosure; PA, pharyngeal airway; A, anterior soft tissue mass; P, posterior soft tissue mass; L, lateral soft tissue mass. Note (i) the increased circularity of the airway in the lateral recumbent posture, (ii) greater radius of curvature of the anterior and posterior airway walls in the supine posture, and (iii) the relatively greater mass on the anterior pharyngeal airway when supine (shaded region, A) than the mass on the lateral pharyngeal airway when lateral recumbent (shaded region, L). Modified from Isono’s bony enclosure model.