Upper airway obstruction: the culprits are the arytenoids.

The rapid accumulation of data on sleep apnoea syndrome recently drew the attention of investigators to the upper extrathoracic airways (UEA). These airways include the nasal and buccal airway, the pharynx (divided into naso-, oroand hypopharynx), the larynx, and the extrathoracic trachea. These structures conduct air from the atmosphere to the alveoli. Their peculiar shape accounts for their capacity to modify the temperature and humidity of inspir".d air. Their involvement in the defence mechanism of the respiratory tract is well-known. UEA also serve for the initial part of digestion: biting, chewing and swallowing of food. The co-existence, at this level, of air, liquids and solids may explain the complexity of the physiological mechanisms involved. The trachea possesses a rigid cartilagineous structure, which maintains the airway open. By contrast, the pharynx has a muscular structure. Its calibre, therefore, depends on the tone of the pharyngeal muscles. This is probably the weakest part in the chain, but not the only one. Indeed, the larynx shares with the trachea a cartilagineous supporting structure, but also ha<: rapidly moving parts, the vocal cords, which can narrow or close the glottic orifice. To get air from the atmosphere to the alveoli a negative pressure must be created inside the alveoli and, therefore, inside the respiratory tract. A negative canalicular pressure, i.e. a negative transmural pressure, may collapse a compliant airway, such as the pharynx. A fine neuromuscular mechanism maintains this airway open. Impairment of the mechanism during sleep might be responsible for the sleep apnoea syndrome. During wakefulness, narrowing or closure of the UEA can occur at diffe.rent levels. The aetiology might be either functional or structural. Recently, several authors have reported acute narrowing, or closure, of the upper airways (especially the glottis) of psychological origin, occurring in both children and adults, during either rest or exercise (111]. Narrowing of the glottic orifice, but also of the pharynx, has also been described following topical anaesthesia of upper airways, resulting in stridor and decrease of inspiratory flow (12, 13]. These findings reflect an impairment of the reflex regulation of upper airways calibre. Upper airway obstruction during sleep has previously been reported during negative pressure ventilation with an "iron lung" (14]. Recently, it has been shown that, during these conditions, obstruction can occur either at the glottic or supraglottic level, and results from an uncoupling of upper airway muscles and diaphragm