Objective: Obstructive sleep apnea (OSA) is far more common in males than females. The discrepancy between the lower prevalence of OSA, the greater frequency of obesity and the smaller airway size in women compared to men suggests that a gender difference underlies this condition. We hypothesized that due to differences in tissue linkage women have more stable and less mobile upper airway structures than men, providing protection against severe forms of OSA.
Methods: Seventy-one consecutive patients with OSA, defined as having apnea-hypopnea index > or =5 events per hour, were enrolled into the study. The median (range) apnea-hypopnea index was 20 (5-132) events/h. In addition, measurements of upper airway dimensions were made, using an acoustic reflectance method, while the lower jaw was in the resting position and during retrusive posture. Measurements of upper airway dimensions were used during wakefulness to examine whether changes in pharyngeal dimensions, resulting from retrusive movement of the mandible commonly occurring during sleep, would explain the gender differences in the characteristics of OSA.
Results: OSA was much more positional and severe in men than women as indicated by the higher apnea-hypopnea index in supine position compared with sleeping on the side (difference between supine and side apnea-hypopnea index: 43.7+/-5.2 (SEM) events/h in men versus 10.7+/-7.6 events/h in women, P=0.0015). The position dependency of OSA was most pronounced in those patients who demonstrated the largest decrease in pharyngeal cross-sectional area with retrusive movement of the mandible. There was no significant change in pharyngeal cross-sectional area as a result of retrusive movement of the mandible in women.
Conclusions: Men tend to have a larger but more collapsible airway during mandibular movement than women and this, in part, may play a role in the positional dependency and severity of OSA in men.