ABSTRACT
Patency of the upper airway during sleep is integrally related to craniofacial
morphology, but craniofacial structure is only one element that defines airway
patency. If a tube is narrow enough, its walls collapsible enough, and the
transluminal pressure differential great enough, the tube will fail as a conduit.
This happens in the obstructive sleep apnea syndrome (OSAS). This tube, the
upper airway, has daunting structural complexity and variability. There are two
main intake ports in this tube; internally, it has recesses, multiple valves,
movable baffles, and glands that can swell or fill parts of the tube with mucus.
The rigidity of the tube can change very quickly secondary to both internal and
external control factors; parts of this tube can grow into the lumen (e.g., tonsils).
The tube carries multiple fluids, and it works better in certain positions than
others. This is the normal human upper airway and functions beautifully most of
the time.
