Gender differences in the expression of sleep-disordered breathing - Role of upper airway dimensions

Study objectives: Obstructive sleep apnea (OSA) is a common disorder that i s characterized by repetitive episodes of upper airway narrowing and collap se. Obesity is a major risk factor for OSA. Compared with men, women have g reater 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 to ne are important determinants of upper airway patency during sleep. The dis crepancy between greater frequency of obesity and lower prevalence of OSA i n women has not been explained and suggests a different pathogenetic mechan ism underlying this condition. Most clinical studies in OSA have either com bined 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 dimen sions in the expression of sleep-disordered breathing (SDB) and its relatio nship to gender. Design: Prospective study of subjects referred for evaluation of SDB. Setting: University-based sleep center. 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 polysomnogra phy with measurement of upper airway size using the acoustic reflectance me thod. Although the two groups were similar in age, the female patients were slightly heavier than the male patients (body mass index [BMI], 38.0 +/-1. 7 kg/m(2) vs 33.3 +/-0.8 kg/m(2), respectively; p<0.0001). Despite similar clinical presentation of snoring and excessive daytime sleepiness, women ha d mild OSA (respiratory disturbance index [RDI], 9.2<plus/minus>2.7 events per hour) or increased upper airway resistance syndrome compared with men w ith more severe OSA (RDI, 28.0 +/-3.5 events per hour; p<0.0001). In contra st, women had a significantly smaller oropharyngeal junction and pharynx th an men (p<0.02). Upper airway size correlated significantly with the severi ty of sleep apnea in men only. There was no correlation between BMI and pha ryngeal size in either gender. Conclusions: This study demonstrates that the static properties of upper ai rway in awake men but not women correlate with the severity of sleep apnea. This suggests inherent structural and functional differences in upper airw ay during sleep between men and women with more favorable airway mechanics in women.