Changes in upper airway size during tidal breathing in children with obstructive sleep apnea syndrome

Abstract

We performed respiratory-gated magnetic resonance imaging to evaluate airway dynamics during tidal breathing in 10 children with obstructive sleep apnea syndrome (OSAS; age, 4.3 +/- 2.3 years) and 10 matched control subjects (age, 5.0 +/- 2.0 years). We hypothesized that respiratory cycle fluctuations in upper airway cross-sectional area would be larger in children with OSAS.

Methods: Studies were performed under sedation. Respiratory gating was performed automatically at 10, 30, 50, 70, and 90% of inspiratory and expiratory volume. Airway cross-sectional area was measured at four ascending oropharyngeal levels at each increment of the respiratory cycle.

Results: We noted the following in subjects with OSAS compared with control subjects: (1) a smaller upper airway cross-sectional area, particularly during inspiration; (2) airway narrowing occurred during inspiration without evidence of complete airway collapse; (3) airway dilatation occurred during expiration, particularly early in the phase; and (4) magnitude of cross-sectional areas fluctuations during tidal breathing noted in OSAS at levels 1 through 4 were 317, 422, 785, and 922%, compared with 19, 15 17, and 24% in control subjects (p < 0.001, p < 0.005, p < 0.001, and p < 0.001, respectively).

Conclusions: Fluctuations in airway area during tidal breathing are significantly greater in subjects with OSAS compared with control subjects. Resistive pressure loading is a probable explanation, although increased airway compliance may be a contributing factor.

Figure 1.

Midsagittal magnetic resonance image demonstrating the four ascending levels for analysis (thick dotted lines). Level 1 is 4 mm above tip of epiglottis.

Figure 2.

Mean upper airway cross-sectional area at 5-vol increments of inspiration and 5-vol increments of expiration as percentage of VT. Subjects with obstructive sleep apnea syndrome (OSAS) are shown in red, control subjects in blue. Inspiration: open triangles/squares; expiration: closed triangles/squares. Dashed segments represent estimated changes. *p < 0.05; **p < 0.001; ***p < 0.0001.

Figure 3.

Dynamic changes in cross-sectional area at midtonsillar level (level 2) during tidal breathing (5-vol increments of inspiration [Ins], 5-vol increments of expiration [Exp]) of control subjects (top panels) and subjects with OSAS (bottom panels). Note differences in anteroposterior (A-P) and lateral airway dimension.

Figure 4.

Mean and SD of minimal upper airway cross-sectional area at four oropharyngeal levels (detailed in Figure 1) during inspiration. There are highly significant differences between subjects with OSAS and control subjects at all levels (p < 0.0001).

Figure 5.

Mean and SD of maximal upper airway cross-sectional area at four oropharyngeal levels (detailed in Figure 1) during expiration. There is no significant difference between subjects with OSAS and control subjects.

Figure 6.

Maximal percentage of change in upper airway cross-sectional area at the four oropharyngeal levels (detailed in Figure 1) during tidal breathing. *p < 0.005; **p < 0.001.

Figure 7.

Shape analysis: average A-P and lateral (LAT) dimension for all percentages of VT levels for both groups. Lines link segmental volume levels. Subjects with OSAS are shown in red; control subjects in blue. Open triangles: inspiratory A-P and lateral dimension in OSAS; closed triangles: expiratory A-P and lateral dimension in OSAS; open squares: inspiratory A-P and lateral dimension in control subjects; closed squares: expiratory A-P and lateral dimension in control subjects. Ellipses illustrate relative differences in A-P and lateral dimensions in OSAS and control subjects. Ellipses are shown for minimum during inspiration (filled ellipses) and maximum during expiration (open ellipses).