A new nasal acoustic reflection technique to estimate pharyngeal cross-sectional area during sleep

The conventional acoustic reflection technique in which acoustic waves are launched through the mouth cannot be applied during sleep, nor can it be ap plied to the nasopharynx, which is the major site of occlusion in patients with obstructive sleep apnea syndrome. We propose a new technique of nasal acoustic reflection to measure pharyngeal cross-sectional areas including t he nasopharynx. The acoustic waves are introduced simultaneously to both no strils during spontaneous nasal breathing. A new algorithm takes into accou nt the nasal septum with asymmetric nasal cavities on both sides and assume s prior knowledge of the cross-sectional area of the nasal cavities and the position of the nasal septum. This method was tested on an airway model wi th a septum and on healthy human subjects. The conventional technique gave inaccurate measurements for pharyngeal cross-sectional areas for an airway model with asymmetric branching, whereas the new technique measured them al most perfectly. The oro- and hypopharyngeal cross-sectional area measuremen ts acquired by the new method were not different from those obtained by the conventional method in normal subjects. This new method can be used as a m onitor of upper airway dimensions in nocturnal polysomnography.