Pharyngeal Narrowing Ratio-Its significance
Snoring is associated with greater pharyngeal narrowing. In OSA Surgery, it is important to know the structure responsible for pharyngeal narrowing and subsequent snoring and Olathe soft palate, mainly its lower half always is the most narrow pharyngeal airway cross-section, even in cases of enlarged tonsils or root of the tongue. The enlarged tonsil, adenoid and base of tongue displace the soft palate backwards. There is air turbulence, Venturi tube effect and the physics based on Bernoulli principle all are responsible for vibration of soft palate.
The muscular hypotonia of striated muscles around the upper airway (see the anatomical basis of OSA) also contribute to cause of snoring mechanism.
How important is Sagital CT/MRI PN ratio in OSA surgery?
Very helpful for the OSA surgeon, even more helpful than a PSG study as far as planning the surgical procedure. To identify upper-airway narrowing in snoring apart from Sagital CT scanning, a flexible direct endoscopy of the retro palatal area gives lot of information.
Soft palate-tongue contact and automatically calculated pharyngeal narrowing ratio (PNR), defined as a ratio between the airway cross-section at the hard palate level and the narrowest cross-section from the hard palate to the epiglottis, could assist in earlier identification of potential obstructive sleep apnea syndrome (OSA) patients even on awake individuals.
From Sagital CT images, measurements of spaces and structures at different pharyngeal levels can be taken, impaired nasal breathing was noted and the pharyngeal narrowing (ratio between the area at the hard palate level and the narrowest one) calculated. In snoring persons pharyngeal narrowing will be greater and also proportional to the loudness of snoring. Also the length of soft palate with uvula will be longer in comparison to non-snoring persons.
The key structure is soft palate: it defines the constriction and is sucked into vibrating by negative pressure which develops at that site. Constriction presents also an obstruction to breathing. Soft palate should therefore be the target for causal treatment of snoring, LAUP, CAUP, RF somnoplasty all aimed at the soft palate in OSA surgery.
(Please see the gallery for pictures- CT/MRI PN ratio)
Dr Paulose is an ENT Consultant Plastic and Laser Surgeon with over 35 years of experience covering in Ear, Nose and Throat procedures, specializing in Laser Surgery and conventional medicine across India, U.K. and Middle East. He is currently engaged with the Jubilee Hospital, in Kerala, India.
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