TABLE IV.C.1b.

Reasons for sex differences in OSA

Study	LOE	Study design	Study groups	Clinical end-point	Conclusion
Anatomy and anthropometric traits
Polesel184	3b	Cross-sectional	Brazil N = 552 women N = 450 men	Anthropometrics	Waist circumference and waist-to-height best predicted OSA in women Waist-to-height ratio and neck circumferences best predicted mild OSA in men, while BMI was associated with severe OSA
Cho168	3b	Cross-sectional	Korea Suspected OSA N = 2016	Anthropometrics Cephalometry	Men with OSA had increased soft palate length compared to controls Women with OSA had increased soft palate thickness and nasion angle than controls
Sutherland169	3b	Cross-sectional	Chinese and Australian sleep clinic N = 363 200 Chinese 163 Caucasian	Craniofacial features by face photography ethnicity	Women with OSA had different facial features compared to controls, such as greater face width to eye width ratio, and reduced mandibular plane Men with OSA had increased mandibular plane angle relative to controls
Perri185	3b	Cross-sectional	Caucasian of European origin Sleep clinic N = 104 OSA N = 85 healthy	Surface cephalometry	OSA patients had anthropometric and surface cephalometric phenotypes that differed in comparison with healthy subjects, however, sexual dimorphism levels (i.e., male–female ratios) were broadly similar in the two groups
Lim176	3b	Cross-sectional	Korean Clinic N = 151	Anthropometrics	Neck circumference predicted OSA in men only, while waist-to-hip ratio predicted OSA in both men and women
Dancey186	3b	Cross-sectional	Canada sleep clinic N = 3942	Neck circumference	Neck-to-height ratio predicted AHI, accounting for 19% of the variability, more significantly in men
Upper airway anatomy and function
Brooks173	3b	Cross-sectional	Healthy volunteers N = 77 men N = 98 women	Pharyngeal cross-sectional area during quiet breathing using the acoustic pulse technique	The men had a larger change in pharyngeal area with changing lung volume than the women
Segal172	2b	Cross-sectional	Chart review for those who have had PSG and CT neck N = 24 (15 men, nine women)	Upper airway length	Men with OSA were found to have longer upper airway length even when normalized to body height compared with OSA women Correlation between upper airway length and AHI
Mohsenin171	3b	Cross-sectional	Sleep Clinic AHI ≥ 5 N = 71	Upper airway dimensions using acoustic reflectance while lower jaw was in the resting and retrusive posture	Men tend to have a larger but more collapsible airway during mandibular movement than women
Eckert187	3b	Cross-sectional	12 healthy, eight OSA	Genioglossus electromyogram (GGEMG)	Reductions in GGEMG during REM sleep were not different between OSA patients and control subjects or between sexes
Malhotra170	3b	Case–control	Healthy volunteers age and BMI matched 19 men, 20 women	MRI	Pharyngeal airway length and cross-sectional area, soft palate area, and airway volume were greater in men compared with women
Obesity and fat distribution
Simpson188	3b	Cross-sectional	Western Australian Sleep Health Study Sleep clinic OSA patients (60 men, 36 women)	Obesity measures using dual-energy absorptiometry	In women, percentage of fat in the neck region and body mass index together explained 33% of the variance in AHI In men, percentage of fat in the abdominal region and neck-to-waist ratio together accounted for 37% of the variance in AHI
Huang174	3b	Cross-sectional	Taiwanese Sleep center >18 years N = 2345 patients (339 females)	BMI	AHI was associated with BMI more strongly in men
Harada175	3b	Cross-sectional	Japanese Sleep Clinic 271 men, 100 women with OSA	CT scan measured visceral fat area	AHI was independently associated with visceral fat area only in men
Ventilatory control
Sin177	3b	Cross-sectional	Canadian sleep center N = 219 (43 women, 176 men; 104 OSA, 115 no-OSA)	Hypercapnic ventilatory response test (HCVR)	Elevated carbon dioxide and older age were significantly correlated with low HCVR in men, while BMI was associated with HCVR in women
Jordan179	3b	Cross-sectional	Healthy volunteers12 men, 11 women at both their luteal and follicular phases	Post-stimulus ventilatory decline (PSVD)	There were no significant differences in PSVD between men and women in either luteal or follicular phases
Syed178	2b	RCT	10 men and seven women with OSA, with control 10 healthy men and 10 healthy women	Hypoxic ventilator response augmentation (HVRA) Ventilatory long-term facilitation (vLTF)	HVRA and vLTF were enhanced in the OSA group compared with control Sex did not impact any measures Exposure to intermittent hypoxia during sleep led to a corresponding increase in respiratory events compared with sham exposure, irrespective of sex
Pillar181	3b	Cross-sectional	8 normal women and eight age and BMI-matched men, during stable NREM	Upper airway mechanics Ventilation Activation of two dilator muscles, genioglossus and tensor palatini were monitored during loading	Men developed more severe hypopnea in response to identical applied external loads than did women Men and women had near identical minute ventilation responses to total load, implying no differences in central drive or load response There were no significant increases in genioglossus or tensor palatini activation in response to loading in either sex
Zhou182	3b	Cross-sectional	8 men (25–35 years) and 8 women in the midluteal phase of the menstrual cycle (21–43 years) Repeated studies in 6 women during the midfollicular phase	Apneic threshold	In women, induction of a central apnea required an increase in tidal volume by 155% ± 29%, compared to men with an increase in tidal volume by 142% ± 13% Similarly, women required greater reduction in PETCO2 compared to men, to general a central sleep apnea There was no difference in the apneic threshold between the follicular and the luteal phase in women
Jordan180	3b	Cross-sectional	11 men and 11 women were matched for severe OSA severity Second group of 12 men and 12 women were matched for body mass index	Loop gain (LG) measured using proportional assist ventilator Critical closing pressure of upper airway (Pcrit) by progressive CPAP drop technique	In the BMI-matched subgroup, women had less severe OSA during NREM sleep and lower Pcrit, but similar LG compared to men