The XXXX upper airway in obstructive sleep apnea: role of structures and neuromuscular activity.

@entity1 @entity6841 @entity2507 @entity2421 @entity1319
The structural properties of the upper airway determine its collapsibility during periods of @entity2421 . Both @entity1319 ( @entity1319 ) sleep and increases in nasal pressure ( @entity6841 ) produce @entity2421 , which persists even after nasal pressure is abruptly reduced. To determine the factors that influence the collapsibility of the @entity2421 airway, the critical pressure (Pcrit) and nasal resistance upstream to the site of pharyngeal collapse (RN) were measured in the first three breaths after abrupt reductions in @entity6841 during non- @entity1319 and @entity1319 sleep. @entity6841 was reduced abruptly from 15.2+/-3.2 cm @entity2507 (mean +/- SD) for three breaths in 19 apneic @entity1 . Upper-airway pressure-flow relationships were analyzed to determine Pcrit for each breath in non- @entity1319 and @entity1319 sleep. We found that Pcrit rose (collapsibility increased, p < 0.001) and RN fell (p = 0.02) between the first and third breath after the decrease in @entity6841 , whereas no difference in Pcrit was detected between sleep stages. In six @entity1 , genioglossus-muscle electromyograms (EMGs) were recorded. Peak phasic activity rose between the first and third breath (p = 0.03), but tonic and peak phasic EMG activity fell in @entity1319 as compared with non- @entity1319 sleep (p < 0.001). We conclude that the @entity2421 upper airway becomes most collapsible by the third breath after an abrupt decrease in @entity6841 , regardless of sleep stage and despite an increase in genioglossus-muscle activity. Our findings suggest that predominantly mechanical rather than neuromuscular factors modulate the properties of the pharynx after abrupt reductions in nasal pressure.
