Study objectives: Obstructive sleep apnea (OSA) is a
common disorder that is characterized by repetitive episodes of upper
airway narrowing and collapse. Obesity is a major risk factor for OSA.
Compared with men, women have greater total body fat and are more
obese, and yet the prevalence of OSA is much higher in men. The airway
size and compliance and pharyngeal muscle tone are important
determinants of upper airway patency during sleep. The discrepancy
between greater frequency of obesity and lower prevalence of OSA in
women has not been explained and suggests a different pathogenetic
mechanism underlying this condition. Most clinical studies in OSA have
either combined the sexes or have described results from men only. The
object of this study was twofold: (1) to examine the effect of obesity
on pharyngeal size in both men and women, and (2) to determine the role
of upper airway dimensions in the expression of sleep-disordered
breathing (SDB) and its relationship to gender.
Design: Prospective study of subjects referred for
evaluation of SDB.
Setting: University-based sleep
Subjects: Seventy-eight male patients
(mean ± SE age, 49.2 ± 1.5 years) and 52 female patients (mean
age, 47.4 ± 1.5 years).
Measurements and results:
All subjects underwent in-laboratory polysomnography with measurement
of upper airway size using the acoustic reflectance method. Although
the two groups were similar in age, the female patients were slightly
heavier than the male patients (body mass index [BMI], 36.0 ± 1.7
kg/m2 vs 33.3 ± 0.8 kg/m2, respectively;
p < 0.0001). Despite similar clinical presentation of snoring and
excessive daytime sleepiness, women had mild OSA (respiratory
disturbance index [RDI], 9.2 ± 2.7 events per hour) or increased
upper airway resistance syndrome compared with men with more severe OSA
(RDI, 28.0 ± 3.5 events per hour; p < 0.0001). In contrast, women
had a significantly smaller oropharyngeal junction and pharynx than men
(p < 0.02). Upper airway size correlated significantly with the
severity of sleep apnea in men only. There was no correlation between
BMI and pharyngeal size in either gender.
This study demonstrates that the static properties of upper airway in
awake men but not women correlate with the severity of sleep apnea.
This suggests inherent structural and functional differences in upper
airway during sleep between men and women with more favorable airway
mechanics in women.