**5. Risk factors and systemic complications**

The incidence of OSA is different between men and women; most epidemiological studies reports male predominance with 5-8:1 ratio [11]. Male predominance is due to the sex related differences in upper airway anatomy and function, plus the differences in ventilator response to arousals from sleep [12]. But menopause women show a similar incidence to men because hormonal influences which play an important role in pathogenesis of OSA [13]. The other important risk factor is body mass index (BMI); the Wisconsin Sleep Cohort Study shows that one standard deviation difference in body mass index (BMI) was associated with a four-fold increase in disease prevalence [14] [15]. Partial or complete airway obstruction for more than

10 seconds will lead to decrease oxygen supply to vital organs such as the heart and brain which result in many sign and symptoms. Excessive daytime sleepiness, memory loss, impaired concentration, morning headache, decreased manual dexterity, libido and decrease sexual performance [16].

Systemic complications of OSA includes cardiovascular and neurocognitive disorders and death. Periods of apnea, prevent effective gaseous exchange at the alveoli which lead to hypoxia and hypercapnia. Apnea dependent hypoxia and hypercapnia increase sympathetic neural tone, which in turn cause vasoconstriction and increase in sympathetic nerve activity. Sympathetic nerve function rises progressively during apnea and is enhanced further by arousal. Increase in the sympathetic tone is the major cause of cardiovascular complications. OSA is associated with hypertension [16-18], arrhythmia, myocardial infarction [16, 19, 20], and congestive heart failure [16]. During the obstruction episodes there are marked changes in blood flow in cerebral arteries. Netzer et al reported 80% changes in cerebral blood flow in cerebral arteries [21]. During periods of apnea there is rapid increase in cerebral blood flow followed by rapid fall to below baseline levels after apnea periods. Fluctuation in cerebral blood flow along with many physiologic changes may lead to stroke [16]. Mortality rate of OSA can reach up to 30% in 15 years if left untreated [22]. Excessive daytime sleepiness could contribute to high rates of road traffic accidents. Studies show RTA among OSA patients is 1.3 to 7 times higher than the general population [23, 24].
