Upper Airway Narrowing of Retropalatal Region Significant in Obesity With OSA

Obese patients with obstructive sleep apnea (OSA) have a significantly narrower upper airway, specifically of the retropalatal region, compared with obese individuals without OSA, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

Researchers of this case-control study sought to characterize structural differences in the upper airway anatomy and airway compliance (distensibility) in obese patients with OSA and whether these differences are also present in obese patients without sleep apnea.

The study included 157 obese patients with OSA and 46 obese controls. Patient with OSA were recruited from the Center for Sleep and Circadian Neurobiology in Philadelphia, Pennsylvania, and had an apnea-hyponea index ≥15 events/h. Of the study participants, 97% had a body mass index ≥30 kg/m². Polysomnograms were performed in the laboratory setting using both thermal sensor and nasal pressure monitors to measure airflow during sleep. Dynamic magnetic resonance imaging was performed during wakefulness to measure the dimensions of the upper airway, obtaining 1 set of sagittal and 3 sets of axial slices from the midsagittal, retropalatal, retroglossal, and epiglottal regions. Measurements were taken of the maximum, minimum, and average airway area in each region during respiration.

The study results showed that the mean apnea-hyponea index in the OSA group was 42.4±27.3 events/h compared with 2.7±1.4 events/h in the control group. Midsagittal measurements were significantly larger in patients with OSA, specifically for airway length in both maximum (P =.0066) and minimum (P =.0088) areas. However, measurements of the retropalatal airway area overall were significantly smaller in the OSA group compared with the control group; the anterior-posterior distance was smaller in both maximum (P =.0371) and minimum (P =.0010) areas, although lateral distance was only smaller in the minimum (P =.0205) area. The only difference in the retroglossal and epiglottal regions was the anterior-posterior distance of the maximum airway area, which was significantly larger in patients with OSA, indicating increased airway compliance. 

Limitations of the study included potentially unreliable measurements. Although most of the dynamic measurements were found to be at least moderately reproducible, some measures demonstrated only slight reproducibility. Additionally, the study population was not well-matched for age and body mass index between groups; however, age differences should not have affected the airway measurements as the study groups were composed of middle-aged adults.

In obese patients with OSA, a significant correlation was found between apnea-hyponea index and dynamic airway measures in the retropalatal and retroglossal regions. A significantly narrower retropalatal region was a distinguishing feature in patients with OSA compared with obese controls, especially in anterior-posterior and lateral dimensions, suggesting it plays an important role in the pathogenesis of OSA.

Reference

Feng Y, Keenan BT, Wang S, et al. Dynamic upper airway imaging during wakefulness in obese subjects with and without sleep apnea [published online July 24, 2018]. Am J Respir Crit Care Med. doi:10.1164/rccm.201711-2171OC