Cephalometric Assessment in OSA

8/3/2019 Cephalometric Assessment in OSA

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Cephalometric assessment in obstructive sleep apnea

Nonglak Pracharktam, DDS, MSD, a Suchitra Nelson, PhD, b Mark G. Hans, DDS, M SD, B. Holly Broadbent, DDS, a Susan Redline, MD, MPH, e Carl Rosenberg, MD,' andKingman P. Strohl, MD gCleveland, Ohio

It is reported that some specific craniofacial characteristics are associated with obstructive sleepapnea syndrome (OSAS). To test this finding, the present study developed and assessed thefeasibility of a craniofacial index score (CIS) in differentiating patients with OSAS from habitualsnorers. Anthropometric measurements and lateral head radiographs were obtained on 24 maleand 4 female patients with OSAS who had physician-diagnosed OSAS (respiratory disturbanceindex (RDI) >20), and 25 male and 5 female habitual snorers (RDI


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American Journal of Orthodontics and Dentofacial Orthopedics P r a c h a r k ta m et aL4 1 1Volume 109, No. 4

i n d e v e l o p i n g O S A S . Ve r i fi c a ti o n o f c e p h a l o m e t r i cv a r i a b l e s t h a t p r e d i c t c r a n i o f a c i a l a n a t o m i c r is k sa s s o c ia t e d w i th O S A S m a y i m p a c t b o t h t h e d i a g -n o s is a n d t h e t r e a t m e n t o f t h e s e p a t i en t s . T h e

p u r p o s e o f t h is s t u d y w a s t o d e t e r m i n e t h e f e a si -b i li ty o f u s i n g a s p e c i fi c s e t o f c e p h a l o m e t r i c a n da n t h r o p o m e t r i c v a r i a b l e s t o c la s s if y p e r s o n s i n t o as n o r i n g a n d a n O S A S g r o u p w i t h a d e r i v ed c r a -n i o f a c i a l i n d e x s c o r e ( C I S ) t h a t i n c l u d e d a g e a n dw e i g h t in t h e d i s c r i m i n a n t f u n c t i o n .

M AT E R I A L S A N D M E T H O D SStudy popu la t ion

Tw e n t y - f o u r m a l e a n d f o u r f e m a l e w h i t e p a t i e n t swi th O SA S an d wi th a c l in i ca l h i s to ry o f excess ive day-t i m e s l e ep i n e ss , e p i s o d e s o f o b s t r u c t e d b r e a t h i n g d u r i n g

s leep , and loud sno r ing we re recru i t ed f rom a loca l s leepl a b o r a t o ry. Tw e n t y - s ix s u b je c t s u n d e r w e n t a s t a n d a r dp o l y s o m n o g r a p h i c s t u d y f o r e i t h e r h a l f a n i g h t o r 1 n i g h ta n d h a d a r e s p i r a t o r y d i s t u r b a n c e i n d e x ( a p n e a a n dh y p o p n e a p e r h o u r ) g r e a t e r t h a n 2 0 . Tw o s u b j e c ts w e r ee v a l u a t e d b y t h e i r p h y s i c i a n w h o u s e d o x y g e n s a t u ra t i o nm o n i t o r i n g ( C r i t i c a r e P u l s e O x i m e t e r m o d e l n o . 5 0 1p lus , Cr i t i ca re Corp . , Mi lwaukee , Wis . ) fo r 2 n igh t s , andh a d r e p e t it i v e e p i s o d e s o f a r te r i a l o x y g e n d e s a t u r a t i o nm o r e t h a n 4 % f r o m b a s e l i n e w i t h t h e c u m u l a t i v e p e r -c e n t a g e s o f ti m e s p e n t a t n o r m a l s a t u r a t i o n b e l o w 9 0 %.Al l sub jec t s rece ived con t inuous pos i t ive a i r p res su ret r e a t m e n t , a n d n o n e h a d a u v u l o p h a r y n g o p a l a t o p l a s t y o r

o t h e r s u rg i c a l t r e a t m e n t b e f o r e c e p h a l o m e t r i c r a d i o -g r a p h s w e r e t a k e n .

Twen ty - f ive male and f ive fem ale wh i t e hab i tua l snor-e r s c o m p o s e d t h e c o n t r o l g r o u p . Th i r t e e n o f t h e c o n t r o ls u b j e ct s w e r e e v a l u a t e d w i t h o x y g e n s a t u r a ti o n m o n i t o r -i n g (C r i t ic a r e P u l s e O x i m e t e r m o d e l # 5 0 1 p l u s ) f o r 2n igh t s . None o f these sub jec t s had a c l in i ca l h i s to ry o fac t ive day t ime s l eep iness . In add i t ion , t he pu l se ox imeters h o w e d n o e v i d e n c e o f r ep e t i ti v e e p i s o d e s o f d e s a t u r a t i o nind ica t ing a l ack o f subs tan t i a l apn e ic ac t iv ity. S tan dardo v e r n i g h t p o l y s o m n o g r a p h i c s tu d y w a s p e r f o r m e d o n 1 0s u b j ec t s i n th e c o n t r o l g r o u p t o e v a l u a t e h e a v y s n o r i n g a n dt o r u l e o u t O S A S . S e v e n o f t h e c o n t r o l s u b j e c ts w e r e

e v a l u a t e d f o r a b n o r m a l s l e e p - b r e a t h i n g c o n d i t io n s w i t h ap o r t a b l e h o m e m o n i t o r ( E d e n t e c M o n i t o r i n g S y s t e m ,m o d e l 4 7 0 0 S c a n n e r o r Ed e n t r a c e I I , Ed e n P r a ir ie ,Minn . ) . A l l 17 sub jec t s wi th s l eep s tud ies had a resp i ra to ryd i s tu rba nce index o f l ess than 20 an d a l ack o f c lin i ca ls y m p t o m s o f O S A S .

S t a n d a r d o v e r n i g h t p o l y s o m n o g r a p h y i n c l u d e d : o r o -nasa l a i r flow me asu red w i th thermis t e r, resp i ra to ry e ffo r ta s s e s se d b y s u r f a c e c h e s t w a l l a n d a b d o m i n a l e l e c -t romyo graphy , a r t e r i a l s a tu ra t ion as sessed by f inger pu l seox imeter (Nel l co r N-200 Pu l se Ox imeter, Nel l co r Inc . ,Ca l if .) , and s l eep s t ages eva lua ted by e l ec t roence pha log-raphy, e l ec t roocu lography, e l ec t rocard iography, and sub-m e n t a l a n d t i b i a l e l e c t r o m y o g r a p h y. R e c o r d i n g s w e r e

o b t a i n e d w i t h a p o l y g r a p h ( G r a s s M o d e l 7 8 R e s e a r c hP o l y s o m n o g r a p h , G r a s s I n s t r u m e n t C o . , M a s s . ). A r e s p i-r a t o r y e v e n t ( a p n e a o r h y p o p n e a ) w a s d e f i n e d a s acessa t ion o r d i scern ib le reduc t ion in a i r f low, l as t ing a tl eas t 10 seconds , and as soc ia t ed wi th e i ther a 4% org r e a t e r d e c r e a s e i n o x y g e n sa t u r a ti o n , o r a 2 % o r g r e a t e rd e c r e a s e i n o x y g e n s a t u r a t io n a c c o m p a n i e d b y a na r o u s a l . Th e r e s p i r a t o r y d i s t u r b a n c e i n d e x ( R D I ) w a sc a l c u l a t e d b y t h e t o ta l s u m o f a p n e a s a n d h y p o p n e a sd iv ided by to t a l s l eep t ime .

Anth ropom et r ic and cep ha lome t r ic da ta co l lec t ion

A n t h r o p o m e t r i c d a t a i n c l u d e d s ex , a g e, b o d y m a s sindex (kg/m2), as wel l as head/facial form. Class i f icat iono f h e a d f o r m s a n d f a c i al ty p e s w a s p e r f o r m e d a c c o r d i n gt o M o n t a g u . 32 C e p h a l o g r a m s w e r e o b t a i n e d w i t h t h et e e t h t o g e t h e r i n c e n t r i c o c c l u s i o n a s p r e v i o u s l y d e -scr ibed . 33 Cen t r i c occ lus ion w as u sed to min im ize var i -

a b i li ty in m a n d i b u l a r a n d s o f t t is s u e m e a s u r e m e n t s o f t e nassoc ia t ed wi th res t pos i t ion . To fu r ther min imize var i a -t ions in so f t t i s sues , t he l a t e ra l cepha logram was t akenu s i n g n a t u r a l h e a d p o s t u r e , a t t h e e n d o f t h e e x p i r a ti o np h a s e , a n d w i t h o u t s w a l l o w i n g . We h a d t h e p a t i e n tr e s p o n d t o t h e x - r a y t e c h n i c ia n b y r a is i n g t h e i n d e x f in g e ra s r a d i o g r a p h s w e r e t a k e n t o i n d i c a t e t h a t t h e p a t i e n tw a s a w a k e a n d n o t s w a ll o w in g . N a t u r a l h e a d p o s t u r e w a sf o u n d b y h a v i n g t h e p a t i e n t l o o k i n t o h i s o w n p u p i l sre f l ec t ed in a m i r ro r loca ted a t eye l eve l . To c l a r ify theou t l ine o f the o ro pha ryng ea l so f t t is sues , pa t i en t s swal -l o w e d a t a b l e s p o o n o f b a r i u m s u l f at e e s o p h a g e a l c r e a m( Es o p h o t r a s t , R o e r P h a r m a c e u t i c a l C o r p . , F o r t Wa s h -

ing ton , Pa . ) . The pa t i en t s were asked to f i r s t d i s t r ibu tet h e c r e a m w i t h i n t h e o r a l c a v it y u s i n g t h e t o n g u e f o r 1 0s e c o n d s , t h e n t h e p a t i e n t w a s a s k e d t o s w a l l o w t h er e m a i n i n g c r e a m .

A l l c e p h a l o m e t r i c l a n d m a r k s w e r e l o c a t e d a n d d i g i -t i z e d ( S u m m a g r a p h i c s , I n c . ) b y th e s a m e i n v e s ti g a t o r( N . P. ) , w i t h c u s t o m i z e d s o f t w a r e d e v e l o p e d f o r t w o -d i m e n s i o n a l m o r p h o l o g i c a n a ly s is o f a n a t o m y ( G e o C a l c ,c o u r t e s y o f D rs . J o h n B l a n k a n d R o b e r t M e n s f o r t h ,Cleve land Sta t e Un ivers i ty ) . Def in i t ion o f l andm arks ,r e f e r e n c e l i n e s , a n d c e p h a l o m e t r i c m e a s u r e m e n t s w e r ed e s c r i b e d i n o u r p r e v i o u s s t u d y ? 3 A d d i t i o n a l c e p h a l o -m e t r i c v a ri a b l es u s e d i n t h e p r e s e n t s t u d y a r e p r e s e n t e d

in Tab le I and F ig . 1 . The re l a t ionsh ip be tween ske le t a la n d s o f t t is s u e c o m p o n e n t s w a s d e t e r m i n e d b y t h e r a ti oo f th e t o n g u e a r e a t o t h e i n t er m a x i l la r y s p a c e i n t h es a g it ta l p l a n e a s p r e v i o u s ly r e p o r t e d b y Vi g a n d C o h e n 34(Fig . 2 ) . Th e cou n terp ar t ana lys is o f En low 3s was u sed toana lyze c ran ia l fos sa a l ignmen t , ramus wid th re l a t ive tot h e m i d d l e c r a n i a l f o s s a , a n d r e l a t i v e c o m p a r i s o n o fmax i l l a ry l eng th wi th mand ibu la r l eng th (F igs . 3 -4 )

Erro rs in l andmark iden t i f i ca t ion and d ig i t i z ingm e t h o d w e r e e s t i m a t e d b y e x a m i n i n g d u p l i c a t e t r a c i n g sof 25% o f the l a t e ra l he ad f i lms (n = 15 pa i r s ) . Re l i ab i l-i t y was fa i r ly accu ra te wi th p a i red t t es ts i nd ica t ing n os ign i f i can t d i ffe rences (p < 0 .05 ) in the dup l i ca t e mea-su rem en t s ( see Tab le IV) . Th e re l i ab i l it y o f a sub jec t ' s


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41 2 P r a c h a r k t a m e t a l. American Journal of Orthodontics and D entofacial O rthopedicsApril 1996

C 2 t g ~

Fig. 1. Conventional linear and angular eephalometric mea-surement s and additional soft tissue measurem ents (see Fig. 3. Counterpart analysis, as This diagram shows effects ofTable I). rotational alignment of subject' s own MCF compared with

neutral MCF on corresponding maxi llary and mandibula rplacement . Clockwise (+) alignment is shown. Relative com-parison of cumulative maxillary length f rom Ar to A point withcumulative mandibular length f rom Ar to B point is alsodemonstrated.

Fig. 2. Ratio of tong ue are a to intermaxillary area. Definition ofthe anterior intermaxillary space height (AntrMxHt), posteriormaxillary spa ce heigh t (Po strMx Ht), intermaxillary sp acelength (InMxLth). , and intermaxillary a rea was previou sly de-scr ibed by Vig and Cohen.34

natural head position tested randomly by selecting 14subjects and recording the natural head position beforeand after taking the radiograph, also revealed no signif-icant difference (p


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American ,Journal of Orthodontics and Dentofacia l Orthopedics P ra ch ar kt a m et a l . 4 1 3Volume109,No. 4

T a b l e I. A d d i t i o n a l c e p h a l o m e t r i c v a r i a b le s u s e d i n t h e p r e s e n t s t u d y

Variables Interpreta t ion

Hard t i s sues

M C FR a m/ M C FA r A - A r B

H - M P

H - Ve r

N e c k< C2C4-SN

< 2C-SNSof t t i s sues

P-PNSPhw-Psp

T1H e a d p o s tu r e

F H - H o r

R a t i oCI/FITflnMx area

Mid dle cranial fossa and posterior m axillary relat ive al ignment (Fig . 3) .Ram us width relat ive to m iddle cranial fossa horizontal d imension (Fig . 4) .Relat ive comparison of cumulative maxillary length with cumulat ive mand ibular length mea sured along

the re ference l ine Fig . 3 .Vert ical posi t ion of the hyoid relat ive to the mand ibular p lane.Vert ical posi t ion of the hyoid relat ive to a l ine which is perpendic ular to p terygomaxillary vert ical l ine

(PM) and passes sphenoethm oidal junct ion (SE).

A craniocervical angle formed by a l ine from the most po sterior-inferior point of the second cervicalverteb ra (C2) to the forth cervical verteb ra (C4) and S-N plane.

A craniocervical ang le formed by a l ine from C2 to C2 tang ent (C2tg) and S-N plane.

Soft palate length .Supe rior posterior airway space. Dis tance betw een the most superior-po sterior point of the soft palate

and p osterior pharyngeal wall , measured along a l ine paral lel to B-Go.

Tongue length . L ength of the tongue m easured from tong ue t ip ( t t ) to epig lo t t is base (Eb ).

An gle between the Frank fort horizontal l ine and the extracranial horizontal line obtained by a f luidlevel device with a metalic line.

Rat io o f the cranial index to the facial index.Rat io betw een tongue area to in termaxil lary area Fig . 2 .

t h e m e a n s b e t w e e n t h e t w o g r o up s w a s c o m p a r e d w i t ht te s t s ( e q u a l v a r i a n c e ) . B e c a u s e o f t h e h i g h n u m b e r o fc o m p a r i s o n t e s t s o f t h e m e a n s o f t h e t w o g r o u p s , a

p v a l u e o f l e s s t h a n 0 .0 0 2 , w i t h B o n f e r r o n i ' s c o r r e c t i o nw a s u s e d t o d e t e r m i n e s t a t is t i c a l s i g ni f ic a n c e .

L i n e a r c o r r e l a t i o n w a s c o m p u t e d f o r th e 2 2 c e p h a l o -m e t r i c v a r i a b l e s t o a s s e s s i n t e r d e p e n d e n c y a m o n g v a r i -a b l e s. I t w a s d e c i d e d t h a t a s u b s e t o f th e 2 2 c e p h a l o -m e t r i c v a r i a b l e s w o u l d b e c h o s e n i f s e v e r a l v a r i a b l e sw e r e v e r y h i g h l y c o r r e l a t e d w i t h e a c h o t h e r ( p - < 0 . 0 01 ) .I n a d d i t i o n , t h e f i n a l v a r i a b l e s w e r e c h o s e n i n a c c o r d a n c ew i t h r e s u l t s o f p u b l i s h e d l i t e r a tu r e .

F i n a l l y, t h e d i s c r i m i n a n t f u n c t i o n t h a t b e s t c l a s s i f i e dt h e s u b j e c t s w a s u s e d t o c a l c u l a t e t h e C I S . T h e C I S w a sd e f i n e d a s t h e m i d p o i n t o f t h e m e a n f u n c t i o n s c o r e s o ft h e t w o g r o u p s . F o r t h e d i s c r i m i n a n t m o d e l , t w o m a i n

m e t h o d s o f v a r ia b l e s e l e c t i o n w e r e u s e d . F i r s t , a l l t h ef i n al p r e d i c t o r v a r i a b l e s w e r e i n c l u d e d i n t h e m o d e l .F u r t h e r , a s t e p - w i s e p r o c e d u r e w a s a l s o c o m p u t e d t od e t e r m i n e w h e t h e r s o m e v a r i ab l e s w e r e m o r e i m p o r t a n ti n d i f f e r e n t i a t in g b e t w e e n t h e t w o g r o u p s . T h e e f f ic i e n cyo f t h e d i s c r i m i n a n t m o d e l w a s a s s e s s e d b y e x a m i n i n g t h ee i g e n v a l u e s ( r a t i o o f t h e b e t w e e n - g r o u p s v a r i a b i li t y t ow i t h i n - g r o u p s s u m s o f s q u a r e s ) 36 a n d t h e c a n o n i c a l c o r -r e l a t i o n ( d e g r e e o f a s s o c i a t io n b e t w e e n t h e d i s c r i m i n a n ts c o r e s a n d t h e g r o u p s ) ? 6 A l a r g e v a l u e o f b o t h i s a ss o -c i a t e d w i th a g o o d d i s c r i m i n a n t fu n c t i o n . A l l c o m p u t a -t i o n s w e r e p e r f o r m e d w i t h t h e S t a t i s t ic a l P a c k a g e ( S P S SI n c . , C h i c a g o , I l l. ) f o r t h e S o c i a l S c i e n c e s ( S P S S - P C + f o rw i n d o w s ) .

R E S U LT S

T h e d e m o g r a p h i c a n d a n t h r o p o m e t r i c d a t a fo rt h e s u b j e c t s i n v o lv e d in t h e s t u d y a r e p r e s e n t e d i n

T a b l e s I I a n d I I I . A s e x p e c t e d , t h e b o d y m a s s i n d e x( B M I ) o f t h e s u b j e c t s w i t h O S A S w a s s i g n i fi c a nt lyg r e a t e r t h a n t h e c o n t r o l g r o u p ( p _ 0 . 0 0 1 ). P o l y -s o m n o g r a p h i c m o n i t o r i n g o f t h e O S A S g r o u p d e m -o n s t r a t e d m o d e r a t e t o s e ve r e a p n e a ( m e a n R D I =5 2 .9 2 _+ 2 7 .5 9 ) . T h e c o n t r o l s w h o u n d e r w e n t p o l y -s o m n o g r a p h i c m o n i t o r in g h a d a m e a n R D I o f5 .1 _+ 3 . 9 2 t h a t r e p r e s e n t e d a p n e i c a c t i v i t y w i t h i nt h e n o r m a l r a n g e .

C o m p a r i s o n o f t h e 2 2 c e p h a l o m e t r ic a n a t o m i cv a r i a b l e s a r e p r e s e n t e d i n T a b l e I V. S i g n i fi c a n td i f f e r e n c e b e t w e e n g r o u p s w a s n o t e d f o r h y o i d

b o n e p o s i t i o n re l a t iv e to t h e m a n d i b u l a r p l a n e( H - M E p -< 0 .0 0 1 ). S u b j e c t s w i t h O S A S a l s o h a dm o r e o b t u s e c r a n i o c e rv i c a l a n g l e s ( < C 2 C 4 - S N ,p _< 0 . 00 2 ) t h a n t h e s n o r e r s . A l t h o u g h m a n y c e p h a -l o m e t r i c v a r i a b l e s , p a r t i c u l a r l y s o f t t i s s u e m e a s u r e -m e n t s , s h o w e d s o m e t r e n d s t o w a r d d i f f e r e n c e b e -t w e e n t h e O S A S a n d s n o r i n g g r o u p s , t h e d i f fe r -e n c e s w e r e s t a t i s ti c a l l y s i g n i fi c a n t o n l y fo r t h e h y o i db o n e p o s i t i o n a n d c r a n i o c e r v ic a l a ng l e .

L i n e a r c o r r e l a t i o n c o m p u t e d f o r ex a m i n i n g t h ei n t e r r e l a t i o n s h i p s a m o n g t h e 2 2 a n a t o m i c m e a s u r e -m e n t s i n d i c a t e d t h a t t h e r e w a s s o m e l e v el o f r e d u n -d a n c y i n u s i n g a l l o f t h e s e v a r i a b l e s i n t h e d i s c r i m i -


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4 1 4 Pr ac ha rk ta m et aL American Journal of Orthodontics and Dentofacial OrthopedicsApril1996

T a b l e II. Demographic and anthropometric data of the study population

Var~b/es

Snore

Mean I SD

O S A S

M e a n S D p Value

Male: Femal e 25:5 24:4Age 49.60 14.29 47.36 12.86 0.533BMI (kg/m 2) 31.81 4.91 42.34 13.49 0.000"**CI/FI 0.84 0.08 0.84 0.07 0.797Head position a 3.85 5.15 4.98 4.56 0.380RDI 5.10" 3.92 52.92"* 27.59 -

*For 17 subjects; **for 26 subjects; ***p -< 0.002."Head position relative to the extracranial horizontal line, recorded from a fluid level device.

T a b l e III. Percentage distribution of the head forms and facial forms

GroupsBrachycephalic

(>_81.o)

H ead fo rms Fac ia l f o rms

Mesocephalic Dolichocephalic(76-80. 9) ( 90.0)

Sno rer (%) 20 63.3 16.7 - 13.3 86.7OSAS (%) 46.2 42.9 10.7 3.6 7.1 89.3

nant model. Accordingly, the 22 anatomic variableswere redu ced to 13 predictor variables that were inaccordance with previously published results. Thediscriminant function included 13 cephalometric

( < BaSN, < C2C4-SN, A-PNS, H-M R InMxLth,MCF, P-PNS, Phw-Psp, PNS-Ba, RAM/MCF,T/InMx, T-area, T-l) and 4 anthropometric (age,BMI, CI/FI, head post) variables in the first model.The CIS computed from this model was 0.03505(Table V). On the basis of this score, the model wasable to correct ly classify 23 of the 28 OSAS subjects(82.1%) and 26 of the 30 snoring subjects (86.7%)(Table VI and Fig. 5).

For the step-wise procedure, the first variablethat entered the model was H-MP. At subsequentsteps, BMI and the soft palate length (P-PNS) were

selected in the model. These three variables alonewere successful in classifying 19 of the 28 (67.9%)OSAS subjects and 25 of the 30 (83.3%) snoringsubjects (Table VI and Fig. 6).

In addition, findings from the present studyindicated that approximately 39% (canonical cor-relati on in the stepwise procedure r = 0.63, f =0.39) o f total variance of the discriminant score wasattributabl e to between-group variability. However,approximately 52% (canonical correlation, r =0.72, r ~ = 0.52) of tota l va riance of discriminantscore was attributable to differences between thegroups when all anthropometric and cephalometric

predictor variables were included in the model.There fore inclusion of anthropometr ic and soft andhard craniofacial cephalomet ric variables improvedthe discriminant function to a considerable extent.

D I S C U S S I O N

In an attempt to test the validity of usingcephalometric radiographs to identify patients atrisk for OSAS, an index was first constructed fromanthropometric and cephalometric variables. Dis-criminant analysis was used to predict group mem-bership for new cases. The step-wise variable selec-tion model examines each variable and selectsthose with the highest predictive value. Variableselection terminates when there are no more vari-ables that meet the selection criteria. The limita-

tion of this method is that variables with lowindividual discriminant power may be ignored eventhough they may have high discriminant powerwhen considered as part of a group. Because of thislimitation, the present study examined another op-tion for selecting variables for the index. The othermethod forces all the predictor variables into themodel. When the step-wise method was used, onlythree variables met the selection criteria. Thesevariables reflected, or were related to, the softtissues (H-MP, BMI, and P-PNS). With this model,67.9% in the OSAS group and 83.3% in the snorersgroup were correctly classified. However, the clas-


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American Journal o f Orthodontics and Dentofacial Orthopedics Pr ach ar k t am e t a l. 415Volume 109,No. 4

==

LL

6

iD i s c r i m i n a n t S c o r e s

OSAS SNORERS

Fig. 5. All-groups stacked histogram: su mma ry of classification by including all pred ictor variables.

4"

3 '

2 '

1'

0

l,,,i lil,liscriminant ScoresI~10SAS

SNO~

Fig. 6. All-groups stacked histogram: summary of classification by step-wise method.

sification rate increased when we forced all thepredictor variables into the equation, with 82.1%correctly classified in the OSAS group and 86.7%in the snoring group. Further, the effectivene ss ofthis model was proved with a higher eigenvalue andcanonical correlation.

Some studies have suggested that there may besubgroups of patients with OSAS based on inter-related anatomic and functional factors. Partinenet al. 21 used eepha logra phy to study th e rela tion-ship between abnormal upper airway anatomy andbody mass in 157 OSAS patients. They found whenthe BMI is low, the severity of airway collapse, asassessed by the RDI, appears associated with ab-normal craniofacial cephalometric findings. Theyhave further stated that when BMI increases, par-ticularly in obese patients with a BMI greater than30, the RDI appears to be less dependent on thecephalometric results. Further support for the hy-

pothesis that patients with OSAS may belong to atleast two subgroups, based on the origin of thedisease, can be fou nd in the repo rt of Tsuchiya andcoworkers. = They proposed th e existence of OSASsubtypes based on the degree of obesity, the sever-ity of OSAS, and craniofacial and demographic

data. With cluster analysis the patients with OSASwere subdivided into two groups. One group had ahigh apnea index (AI) and low BMI, and the othergroup had low AI and high BMI. Each subgroupwas, then, evaluated with craniofacial and demo-graphic data by means of multiple regression anal-ysis. In the first group, a high AI was related to alarge skeletal anteroposterior discrepancy, a steepmandibular plane, and an inferoanterior position ofthe hyoid bone. In contrast, a high AI was associ-ated with a large tongue and a small upper airwayin the latter group. They concluded that in patientswith a high AI/low BMI ratio and mod erat e obesity,


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41 6 P r a c h a r k t a m e t al. American Journal of Orthodonticsand D entofacial OrthopedicsApril1996

Table IV. Compar ison of means of cephalometr ic var iables between OSAS and snor ing groups using t tests

Snore (25M, 5F)

M ean SD

OSA S (24M, 4F)

M ean SD p value Reliability (Re

Cranial baseM C F 0 . 0 4< B a S N 1 2 8 .8 6

Maxilla< S N A 8 1 .7 5< A r N - P M 5 6 . 8 1A - P N S 5 1 . 4 2P N S - B a 4 7 . 3 3

MandibleR a m / M C F 1 . 7 9< S N B 7 9 . 1 2

A r A - A r B - 0 .1 9Hyoid

H - M P 1 8 . 0 1H v e r 1 2 5 . 5 4

N eck< C 2 C 4 - S N 1 0 7 .3 9< C 2 - S N 1 0 0 .1 0

H ead postu reF H - H o r 4 . 1 7

Soft tissueP h w - P s p 7 .71P - P N S 4 1 . 0 5To n g u e l e n g t h 84 .91To n g u e a r e a 4 2 6 9. 95

RatioA n t r M x H t 7 3 . 5 2P o s t r M x H t 4 2 . 4 9

I n M x L t h 84 .41T / I n M x a r e a 0 .8 9

2 .144 .63

- 0 . 3 5 3 . 9 4 0 . 6 3 9 0 . 9 8 81 2 8 . 7 9 6 . 1 8 0 . 9 6 3 0 . 9 8 8

3 . 5 1 8 1 . 2 0 4 . 6 5 0 . 6 1 03 .47 56 .46 5 .01 0 .7604 . 0 6 5 1 . 6 2 4 . 8 4 0 . 8 6 53 . 7 3 4 6 . 6 6 3 . 9 2 0 . 5 0 4

3 .34 2 .80 4 .31 0 .3233 . 9 4 7 8 . 1 0 4 . 5 4 0 . 3 6 34 .66 0 .45 3 .93 0 .576

6 . 0 5 2 4 . 9 4 6 . 4 3 0 . 0 0 0 " * *9 .64 132 .23 9 .46 0 .010

7 . 9 3 11 4 . 3 9 8 . 3 6 0 . 0 0 2 * * *7 .63 105 .81 9 .78 0 .016

4 . 2 4 5 . 3 6 4 . 6 4 0 . 3 1 0

3 . 5 2 6 . 2 8 2 . 5 0 0 . 0 8 34 .70 44 .93 6 .77 0 .0137 . 4 7 9 0 . 5 4 6 . 7 5 0 . 0 0 4

4 5 6 . 0 6 4 6 2 9 . 0 2 4 9 4 . 2 3 0 . 0 0 6

6 . 3 0 7 3 . 3 8 5 . 0 2 0 . 9 3 16 .79 46 .36 7 .59 0 .045

5 . 6 9 8 1 . 1 4 7 . 0 8 0 . 0 5 70 .10 0 .96 0 .09 0 .008

0 . 9 8 9

0 . 9 6 7

0 . 9 9 2

0 . 9 6 0

0 . 9 8 5

0 . 9 7 60 . 9 9 2

0 . 9 4 3

***p -< 0 .002 .

Ta b l e V. Discr iminant funct ions evaluated atg roup means

M eth o d 1 M eth o d2(All predictor va ria bl es ) (Step-wise)

G r o u p 1 - 0 .981 4 - 0 .7622G r o u p 2 1 . 0 5 1 5 0 . 8 1 6 6

C I S 0 . 0 3 5 0 5 0 . 0 2 7 2

skeletal abnormal i t ies may be more imp or tant e t io-logic factors. In contrast , atypical soft t issue struc-tures (a large tongue and/or sof t palate possiblyrelated to obesi ty) may resul t in a smal l upperai rway in pat ients wi th a low AI and high BMI.These f indings may indicate that our CIS may bemore effect ive in ident i fying OSAS sufferers whohave low BMI because craniofacial anatomy maybe a more impor tant predisposing factor in th is

subgroup. We have elected to include both BMIand age in the CIS to a l low the index to begeneral ized to a larger populat ion.

W ith the step-wise procedure, the present s tudyfound tha t hyo id bone pos i t ion (H-MP) was themost important predictor variable in the discrimi-

nant funct ion. Other authors have also repor ted asimi lar re la t ionship between hyoid bone posi t ionand apnea severity. 1~'14"21-22However, the posi t ion ofthe hyoid bone is subject to a h igh degree ofvar ia t ion because of physiologic adaptat ion andchanges of the head posi t ion. 37 Recen t ly pub l ishedrepor ts suppor t the conten t ion that low hyoid boneposi t ion is a compensory response to a i rway ob-st ruct ion and not a predisposing f a c t o r. 3 s '3 9

Solo w and associates 39 assessed the effect ofai rway obst ruct ion on the posture of the head andthe cervical column in pat ients wi th OSAS. Cepha-lom etric radiographs of the subjects wer e obtained


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Am erican Journal of Orthodontics and Dentofacia l Orthopedics Pracharktam et aL 4 1 7Volume109,No. 4

T a b l e VI. Cla ss i fi ca tion re su l t s o f bo th m e tho ds o f va r iab le se lec t ion (a l l p red ic to r va r iab le s an dS t e p - w i s e m e t h o d )

A c t u a l g r o u p N u m b e r o f c a s esPe r c e n t c o r r e c t ly c l a s s i f i e d Pe r c e n t c o r r e c t ly c l a s s i f i e d

A l l p r e d i c t o r ( 1 , 2 ) S t e p w i s e ( 1 , 2 )

Snor i ng 30 26 ( 86 .7% ) 25 ( 83 .3% )OSA S 28 23 ( 82 .1% ) 19 ( 67 .9% )Eige nva lue 1 1 .0687 0 .6446Ca non i c a l c o r r e l a t i on2 0.7188 0.6261

i n n a t u r a l h e a d p o s t u r e . T h e y f o u n d t h a t t h e p a -t i e n t s w i t h O S A S s h o w e d m a r k e d l y l a rg e r c r a n i o -c e rv i c al a n g u l a ti o n ( < C 2 - S N ) t h a n r e f e r e n c e d a t af o u n d i n t h e ir p r e v i o u s s t u d y o f n o r m a l h e a l t h yadults . In teres t ingly, they d id not f ind a s ignif icant

d i f f e r e n c e i n t h e c r a n i o v e r t i c a l p o s t u r e ( S N - Tr u eVe r t ic a l ). T h u s , t h e y p o s t u l a t e d t h a t t h e s e c h a n g e smigh t be phys io log ic adap ta t ions to ma in ta in anadequa te a i rway. In con t ra s t , the head , and thusthe v isual ax is , was main ta ined in i ts or ig ina l or i -en ta t ion in r e la t ion to the t rue ve r t i ca l .

Con s i s ten t wi th the se f ind ings , sub jec t s wi thOSAS in the p re sen t s tudy showed s ign i f ican t lym o r e e x t e n d e d c r a n i o c er v i ca l a n g u l a ti o n ( < C 2 C 4 -S N ) a n d a t e n d e n c y t o w a r d d i f f e r e n c e s i n c r a n i o -ce rv ica l angu la t ion (


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4 1 8 P ra ch ar kt am et al. American Journal of Orthodontics and Dentofacial OrthopedicsApril 1996

of phys io log ic com pen sa t ion s to cl in ica l d i sease . Ont h e o t h e r h a n d , c r a n i o fa c i a l a n a t o m y m a y b e a n u n -der ly ing f ac to r tha t con t r ibu tes to the deve lopmento f c l in ica l i l l ness . C epha lom et ry i s a wide ly ava i l ab le

a n d i n e x p e n s i v e t e s t. Va l u a b l e i n f o r m a t i o n h a s b e e nd e r i v ed f r o m a n u m b e r o f s t u d ie s c o n c e r n i n g c e p h a -lomet r i c assessment in snore r s and pa t i en t s wi thOS AS. How ever, i t is e ssen t i a l t o c r i ti ca lly eva lua tethe va l id i ty o f ceph a lom et ry in iden t i fy ing sub jec t s a tr i sk fo r deve lop ing obs t ruc t ive s l eep apnea . Givent h e l i m i ta t i o n s o f t h e c e p h a l o m e t r i c t e c h n i q u e a n dt h e p o l y g e n e t i c b a s i s f or O S A S , i n o u r o p i n io n , t h eb e s t u s e o f c e p h a l o m e t r i c s w o u l d b e t o h e l p d e l i n-e a t e t h e s u b g r o u p s o f O S A S a n d t o i d e n t if y c li n ic a lcharac te r is t ic s tha t m ay cor r e l a t e wi th these c r an io -facial character is t ics . Const ruct ing the CIS is the

f ir st s t ep in t e s t ing the u t i li t y o f us ing cep ha lom et r i csas a d i agnos t i c t e s t f o r OSAS and a l a rger s tudy i sp lanned to t e s t t he va l id i ty o f t he index in the gen-e ra l popu la t ion .

C O N C L U S I O N S

These resul ts indicate that a CIS const ructedfrom cephalometr ic and anthropometr ic measure-ments can b e used to di fferent ia te habitual snorerswi th and wi thout apneas. In addi t ion, the f indingssuggest that the CIS co uld have significant value as adecision m aking tool for c l in icians t reat ing pat ients

wi th obst ruct ive sleep apnea syndrome and/or ha-bitual snoring. Further studies are planned to deter-mine the feasibi l i ty of using the index to help thecl in ician choose t reatment in tervent ions that havethe highest l ikel ihood o f success.

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American Journal of Orthodontics and Dentofacial Orthopedics P ra ch ar kt am et al .41 9Volume109,No. 4

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Cephalometric Assessment in OSA