PHARYNGEAL DYNAMICS IN OBSTRUCTIVE SLEEP-APNEA SYNDROME

Pharyngeal dynamics in obstructive sleep apnea syndrome. Obstructive sleep apnea results from a pharyngeal collapse. Upper airway call be investigated using either static or dynamic methods during wakefulness or when the patient is sleeping. Somnofluoroscopy is one of the dynamic methods allowing a visualization of the upper airway during sleep. A lateral projection of the pharynx is obtained during fluoroscopic examination which allows visualization of the upper airway dimensions and the bone structures (hyoid bone, cervical spine, mandible). Standard polygraphic parameters (EEG, EGG, flow rate, thoracic and abdominal movements) and fluoroscopic image are simultaneously acquired on the same videotape. Using this technique, we have described the typical pattern of events occuring during an episode of apnea: 1-beginning of airway occlusion in the oropharynx with anterior or posterior hooking of the soft palate, 2-suction on the uvula downwards and complete occlusion of the oropharynx with further extension to the hypopharynx, 3-active movements of the cervical spine and hyoid bone as if the patient is choking, 4-overcoming of the occlusion usually accompanied by opening of the jaw and occuring either as a sudden event throughout the length of the pharyngeal airway or as a progressive reopening from the hypopharynx. In a recent study, we have investigated upper airway dynamics when a continuous positive pressure with one level (CPAP) or two levels of pressure (BiPAP) was applied. When using CPAP with pressure below the optimal pressure, uvula movements were the first changes we observed, preceding the pharyngeal collapse. Lowering the expiratory pressure alone leed to a significant reduction in pharyngeal dimensions starting at expiration and extending also to inspiration when the expiratory pressure is further reduced. Using BiPAP may lead to upper airway instability. The frequency and the variability of this phenomenon need further studies to be established.