Around 50% of patients with the sleep apnea/hypopnea syndrome (SAHS) are not obese: body mass index (BMI) < 30 kg/m2. We hypothesized that local fat deposition around the upper airway may be different in nonobese patients with SAHS from that in normal subjects with the same body mass. We therefore examined the relationship between indices of general obesity; BMI, neck circumference (NC), and percentage total body fat with neck fat deposition measured by magnetic resonance imaging in three matched subject groups. Nine nonobese, nonsnoring control subjects (BMI, 25 SE 0.7 kg/m2; NC, 38.1 SE 0.5 cm; age, 37.5 SE 2.5 yr), nine nonobese patients with SAHS (BMI, 25.7 SE 0.4 kg/m2; NC, 39.8 SE 0.8 cm; age, 40 SE 4.2 yr), and nine obese patients with SAHS matched to the other groups for age (BMI, 34 SE 1.1 kg/m2; NC, 43.9 SE 0.6 cm; age, 40 SE 2.7 yr). Neck volume and fat content were assessed from the hard palate to the vocal cords using T1-weighted images. Percentage total body fat was 30 and 44% greater in nonobese and obese patients with SAHS, respectively, than in control subjects. Neck tissue volume was 10% greater in nonobese and 28% greater in obese patients with SAHS than in control subjects. The percentage of neck tissue volume attributed to fat was 27% greater in nonobese and 67% greater in obese patients with SAHS than in control subjects. The excess fat in both the nonobese and obese patients with SAHS compared with that in control subjects was localized to areas anterolateral to the upper airway, the differences were 52 and 88%, respectively. There were no significant differences between nonobese patients with SAHS and control subjects with respect to fat located in other areas of the neck; obese patients with SAHS had 42% more fat than control subjects (p < 0.05). We conclude that even relatively nonobese patients with SAHS have excess fat deposition, especially anterolateral to the upper airway when compared with control subjects with the same level of obesity assessed using BMI and NC. This may contribute to their predisposition to SAHS.

Most patients with sleep apnoea/hypopnoea syndrome (SAHS) are middle-aged men. As there are conflicting data on the effects of age and gender on upper airway calibre, we tested the hypothesis that increasing age and the male sex predispose to upper airway narrowing in normal subjects.We measured upper airway calibre using acoustic reflection in 60 men and 54 women (median 35, range 16-74 yrs) both seated and supine.All upper airway dimensions, except oropharyngeal junction (OPJ), decreased with increasing age in both men and women (r>-0.24, p≤0.05) while supine (r 2 >0.06). Men had greater changes in airway area at OPJ on lying down (mean (SEM) 0.5 (0.1), 0.2 (0.1) cm 2 ; p<0.02). Men had greater body mass indices (mean (SD) 26 (4), 24 (4) kg·m -2 ; p=0.04), and larger neck circumferences (mean (SD) 38 (3), 33 (2) cm; p<0.0001) than women. For any body mass index, neck circumference was larger in men than women (p<0.001).This study shows that upper airway size decreases with increasing age in both men and women, and that men have greater upper airway collapsibility on lying down at oropharyngeal junction than women. Eur Respir J 1997; 10: 2087-2090 The effects of age and gender on upper airway calibre are unclear. Clarification of their influences is important because the clinical condition associated with upper airway narrowing, the sleep apnoea/hypopnoea syndrome (SAHS), is predominantly a condition of middle-aged men [1]. BROOKS and STROHL [2] reported men to have larger upper airway calibre than women when seated and awake. Studies performed in the sitting position have indicated that upper airways resistance increases, and pharyngeal area decreases [3] with age in men but not in women. In contrast, computed tomography (CT) scan studies in supine men have shown no age-related increase in upper airway collapsibility in men [4]. In order to clarify this, we tested the hypothesis that increasing age and the male sex predispose to upper airway narrowing in the normal population. Methods SubjectsWe aimed to select a cross section of the local population and therefore recruited 60 male and 54 female subjects from the hospital workforce using an advertisement that did not refer to sleep. Their height, weight and neck circumference at the cricothyroid membrane were measured (table 1). Subjects were asked whether they snored and in which position, and whether they suffered from uncontrollable daytime sleepiness. Responses were noted but no one was excluded from the analysis as this was a population-based study. However, subjects with gross retrognathia were assessed clinically and excluded from the analysis. The study was approved by the local Ethics Advisory Committee.

Background-Obesity and increased neck circumference are risk factors for the obstructive sleep apnoea/hypopnoea syndrome (SAHS). SAHS is more common in men than in women, despite the fact that women have higher rates of obesity and greater overall body fat. One factor in this apparently paradoxical sex distribution may be the diVering patterns of fat deposition adjacent to the upper airway in men and women. A study was therefore undertaken to compare neck fat deposition in normal men and women. Methods-Using T1 weighted magnetic resonance imaging, the fat and tissue volumes in the necks of 10 non-obese men and 10 women matched for age (men mean (SE) 36 ( Conclusions-There are diVerences in neck fat deposition between the sexes which, together with the greater overall soft tissue loading on the airway in men, may be factors in the sex distribution of SAHS. (Thorax 1999;54:323-328) Keywords: sleep apnoea; neck fat; sex diVerences; magnetic resonance imaging 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 diVerence 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. 11Magnetic 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. Ho...