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Sleep disordered breathing, snoring, and the sleep apnoea/hypopnoea syndrome (SAHS) are 2-8 times more common in men than in women in all adult age groups. 1 2 In men these conditions are associated with obesity, increased neck circumference, and reduced cross sectional area of the upper airway, 3-6 all factors which predispose to the partial or complete obstruction of the upper airway.
The male predominance in SAHS has not been fully explained and is in some respects paradoxical. Compared with men, a greater proportion of total body soft tissue in normal women is fat and obesity is more frequent in women. 7 8 A condition strongly associated with obesity might therefore be predicted to show a higher frequency in women. Similarly, pharyngeal airway cross sectional area has been reported to be less in women when matched for body mass index (BMI), 9 which would be expected to predispose to airway obstruction. However, women do have a smaller neck circumference when matched for BMI and so overall mass loading on the upper airway may be less. 10 Dynamic factors are also relevant; the upper airway when seated is smaller in women, but there is no difference between supine men and women. 10 This suggests that women have a greater ability to defend the airway against posture related changes, and a higher waking upper airway dilating muscle tone in women may provide a physiological basis for this. 11
Magnetic resonance imaging (MRI) has become an established method for the in vivo quantification of fat tissue. 12 13 Fat has a relatively short T1 relaxation time, so fatty tissue has a higher intensity than other soft tissues in T1 weighted spin echo MRI images. The availability of this technique has prompted a number of studies which have attempted to clarify the relationship between obesity and upper airway obstruction at a detailed anatomical level. Although there is a clear relationship between overall neck size and airway obstruction in men, 3 there is still controversy about the significance of the precise anatomical distribution of fat deposition in the neck. Horner et al observed fat pads lateral to the airway which were larger in obese SAHS patients than in weight matched controls, 14 and our group made similar findings in...