**4. Pathogenesis of obstructive sleep apnea**

Upper airway has a great tendency to obstruction. Any pathological change that narrows the airway leads to OSAS. The pharynx is the site of upper airway obstruction during sleep. The size of the pharyngeal lumen depends on the balance between the forces that narrows and dilates the airway. The force that narrows the upper airway is the suction type, negative air pressure occurring during inspiration, and personal anatomical factors. The force that dilates the upper airway is the tension of the genioglossus and tensor veli palatini muscles surrounding the airway and tension of other small muscles attached to the pharynx. The difference between the narrowing and dilating forces are called transmural pressure. During sleep the tension of the muscles surrounding the airway decreases. The tongue and soft palate displace to the posterior wall of the oropharynx and narrows the upper airway. The airflow rate increases due to the narrowing airway dimension. The increased airflow applies more negative, suction-type pressure to the airway lumen. The increased negative airway pressure, decreased muscle activity, and airway lumen diameter lead to upper airway obstruction and apnea. During apnea the blood oxygen desaturation decreases, carbon dioxide saturation increases, and pH decreases. This change leads to the stimulation of central nervous system chemoreceptors, and awakening occurs to end up in apneic process. When the patient awakens, the tension of the muscles increases, which ends up in the obstruction of the upper airway. Blood oxygen saturation increases, carbon dioxide saturation decreases, pH increases, and the patient falls asleep again. This sleeping, apnea, awakening cycle continues during total sleep time [3, 5, 6, 8].

**5.3. Anatomical factors**

may cause OSA.

greater, respectively.

configuration [1–12].

esophageal reflux [1–21].

[10–12, 22].

**7. Classification of OSAS**

**6. Symptoms of obstructive sleep apnea**

Major symptoms: Snoring, apnea, excessive daytime sleepiness.

palate.

**1.** Lesions and anatomical variations: Changes in craniofacial form, inadequate muscle activity, soft tissue anomalies, micrognathia, retrognathia, macroglossia, enlarged soft palate, steep mandibular plane angle, nasal obstruction, adenotonsillar hypertrophy, reduced airway lumen, vocal cord dysfunction, edema of the epiglottis, polyps, tumors, acromegaly, nasal obstruction, juvenile temporomandibular ankylosis, and syndromes (Franceschetti-Treacher Collins, Apert, Crouzon, Pierre Robin, and Down syndromes)

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**2.** Neck circumference: Neck circumference is a significant predictor of OSA. Men and women have a greater risk for OSA if they have neck circumferences of 17 and 16 inch or

**3.** Head and neck position: When a patient changes from upright to supine position, the thickness of the soft palate increases, and the anteroposterior oropharyngeal cross-sectional area decreases. The decrease in cross-sectional area is most evident in posterior of the soft

**4.** Airway lumen diameter and shape: The investigations have shown that the OSAS patients have narrower airway area even they are awake and upright position. The airway has an anteroposterior configuration in normal people, but OSAS patients' airway has horizontal

Cardiopulmonary symptoms: Systemic hypertension, pulmonary hypertension, nocturnal

Neurobehavioral and social: Restlessness and headache in the morning, insomnia, depres-

Other symptoms: Dry mouth, night transpiration, nocturnal cough, hearing loss, gastro-

The severity of OSAS can be classified into three groups according to the apnea-hypopnea index (AHI). An AHI score smaller than 5 is considered normal. An AHI score between 10 and 20 represents mild obstructive sleep apnea, AHI score of 21–40 represents moderate obstructive sleep apnea, and AHI score greater than 40 represents severe obstructive sleep apnea

arrhythmia, atypical breath ache, acute pulmonary edema, reversible proteinuria.

sion, anxiety, mood disturbances, tendency to accidents, nervousness, forgetfulness.
