Reduced tone of pharyngeal muscles can cause trapping of the upper airway during inspiration. Causes of upper airway trapping during inspiration: The basal tone of upper airway muscles decreases during the normal sleep phase, the caliber of the upper airway decreases, and airway resistance increases, but the firing phase of upper airway muscles and the rhythmic contraction of intercostal muscles remain intact. The basal tone of the upper airway muscles, intercostal muscles, and most skeletal muscles is further suppressed during sleep. Reduced pharyngeal muscle tone can cause trapped closure of the upper airway during inspiration. Normal breathing requires a high degree of coordination of respiratory muscle contraction. The upper airway muscles have some basal tone to keep the airway open. Each diaphragm contraction is preceded by a nerve discharge that causes contraction of the upper airway muscles. The contraction of the chin-lingual muscle pulls the tongue forward to fix the pharyngeal wall, which further keeps the upper airway open and resists the trapping effect of negative pressure in the pharyngeal cavity on the upper airway during inspiration. Subsequently, the intercostal muscles contract to stabilize the chest wall, and the diaphragm contracts to generate negative thoracic pressure to complete inspiration. The diseases caused by the trapping of the upper airway during inspiration include pediatric obstructive sleep apnea, cricopharyngeal muscle dystonia, pediatric paroxysmal sleep hemoglobinuria, cricopharyngeal muscle dysfunction in the elderly, and sleep apnea syndrome in the elderly. Pharyngeal muscle paralysis: The pharyngeal muscles are mainly innervated by motor nerve fibers coming from the pharyngeal plexus, with soft palate paralysis being common, and the causes can be divided into two categories: central and peripheral paralysis. Central is seen in various causes of medullary lesions, such as medullary palsy, encephalitis, and auditory neuroma invading the medulla oblongata. Sleep apnea syndrome in the elderly: sleep apnea syndrome (SAS) is the second major sleep disorder after insomnia, which can cause severe hypoxemia and sleep disorders, and is closely related to the occurrence of hypertension, cardiac arrhythmia, cardiovascular and cerebrovascular diseases and respiratory failure. In addition, due to daytime sleepiness, memory and reaction ability are impaired, and the patient’s working ability is reduced and the incidence of accidents is increased. Because of this, SAS has become an important part of sleep medicine, an emerging fringe discipline, and has received increasing attention from the medical community at home and abroad. In recent years, with the widespread application of non-invasive ventilation technology, breakthroughs have been made in the treatment of SAS.