obstructive sleep apnea - hypopnea syndrome ( osahs ) is a disorder characterized by recurrent episodes of partial or total upper airway obstruction during sleep . the apnea - hypopnea index ( ahi ) refers to the number of episodes of apnea and hypopnea that occur per hour of sleep1 . owing to its current prevalence , it is considered a major public health concern , which can manifest serious physical and social consequences if not managed properly2 
 3 . this disorder mainly affects middle - aged economically active patients , resulting in high costs and lost workdays4 . the diagnosis of osahs is based on a combination of the laboratory findings of apnea and hypopnea with clinical symptoms6 . radiographic imaging of the upper airways allows for the study of bone and soft tissue anatomy , in addition to the determination of the site of obstruction and the choice of appropriate treatment for osahs patients7 . cephalometry has been used since 1983 and was initially applied in patients with sleep - related breathing disorders . the aim of the test is to study the facial , maxillary , and mandibular skeleton and any relationships with the soft tissues that may cause pharyngeal obstruction8 . cephalometry is an easy , low - cost , non - invasive , and widely available modality in the majority of hospitals . radiation use is minimal , readily accessible to clinicians , and not uncomfortable for the patient . it has proved to be useful for the evaluation of the upper airways and bone structure in normal subjects and osahs patients9 
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 11 . a complete cephalometric analysis should be performed in patients with osahs to identify associated maxillofacial abnormalities12 . from this perspective , it has been used in several sleep disorder centers , with the purpose of diagnosing the site of obstruction in patients with obstructive sleep apnea . in some centers , this test is part of a service protocol that is important for the decision as to which type of surgery should be performed . therefore , it is recommended in all patients with osahs undergoing surgery8 
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 15 . it is also used with mandibular advancement devices to assess therapeutic efficacy in patients with mild to moderate osahs15 
 16 . obesity , in particular the presence of visceral fat , is considered a predictive factor for osahs17 . several studies have been performed using anthropometric measurements of obesity in patients with osahs , e.g. , body mass index ( bmi ) , neck circumference ( nc ) , waist circumference ( wc ) , and hip circumference ( hc)18 
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 21 . these measurements may be used both to assess the need for patient referral to polysomnographic evaluation and to anticipate treatment in high - risk patients , since this disorder may cause severe consequences in untreated patients2 
 21 . it is expensive and easier , more affordable tests with less technological density , such as cephalometry9 
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 23 to screen for osahs . anthropometric measurements are easily obtained and fundamental for the preparatory study of a patient with suspected osahs . therefore , the number of patients referred for polysomnography could be greatly reduced , lowering healthcare expenses , with simple measurement of cervical , waist , and hip circumferences . the use of these measurements in patients with snoring and those clinically suspected of having osahs would thus prioritize complementary polysomnography testing in patients with higher suspicion of disease24 . the aim of this study was to correlate cephalometric and anthropometric measurements with the ahi , in order to assess if these measurements can be used as predictors of osahs severity . data obtained from the medical charts of 93 male and female patients with osahs , ranging in age from 19 to 80 years , were studied . these patients had been examined from july 2010 to july 2012 in a specialist private clinic in teresina . the medical charts of patients who had undergone previous surgical treatment for osahs , including use of continuous positive airway pressure devices or intraoral devices , in addition to patients with craniofacial deformities and upper airway tumors , were excluded from the study . patients were considered to have osahs if , in addition to clinical complaints , they had an ahi    5 upon overnight polysomnography testing1 . the following cephalometric traces were considered , since they are the most commonly used cephalometric measures : retroglossal posterior airway space ( pas ) , defined as the space between the base of the tongue and the posterior pharyngeal wall ; the distance between the mandibular plane and the hyoid bone ( mp - h ) ; the sna angle , formed by the junction between the sellar point ( s , midpoint of the sella turcica ) , nasion ( n , junction between the frontal and nasal bones ) , and point a ( deepest concavity on the anterior profile of the maxilla ) ; the snb angle , formed by the junction between the sellar point ( s ) , nasion ( n ) , and point b ( deepest concavity on the anterior profile of the mandibular symphysis ) ; the distance between the posterior nasal spine and the tip of the soft palate ( pns - p ) ; and the difference between sna and snb ( anb ) ( figure 1)8 
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 description of cephalometric parameters ( source : the author ) . bmi was calculated as the weight of the subject ( in kilograms ) divided by their height ( in meters ) squared . obesity is defined as a bmi    30 kg / m 
 25 . wc was measured between the last rib and the iliac crest and hc was measured as the maximum circumference at the level of the border of the trochanter . data was entered into the statistical package for the social sciences ( spss ) version 16.0 program for calculation of simple descriptive statistics , e.g. , percentage distribution , mean , and standard deviation . a normality test ( kolmogorov - smirnov ) was applied and the adequate statistical test was chosen for each type of variable ( parametric or nonparametric ) . pearson 's correlation coefficients were examined between ahi and the following variables : age , bmi , nc , wc , hc , and cephalometric measurements ( sna , snb , anb , mp - h , pas , and pns - p ) . sex differences were compared by the student 's t test . statistical significance was set at p  <  0.05 . the project was approved by the research ethics committee of the universidade federal do piau , under caae number 0047.0.045.000 - 10 . the mean bmi was 27.68    3.83 kg / m ( women , 27.41    4.50 kg / m ) and 24 ( 25.81% ) obese ( bmi , 32.81    2.50 the mean age of the patients was 46.70    15.46 years ( range , 19 to 80 years ) . table 2 describes the sample characteristics and variables studied , including their variations and means . note : ahi  =  apnea - hypopnea index ; bmi  =  body mass index ; nc  =  neck circumference ; wc  =  waist circumference ; hc  =  hip circumference ; sna  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point a ; snb  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point b ; anb  =  difference between sna and snb ; mp h  =  distance between the mandibular plane and the hyoid bone ; pas  =  space between the base of the tongue and the posterior pharyngeal wall ; pns p  =  distance between the posterior nasal spine and the tip of the soft palate . table 3 shows an analysis of the pearson correlation coefficients used to evaluate the relationship between ahi , age , and anthropometric / cephalometric measurements . analyzing the relationship between age and osahs severity by ahi showed a positive correlation between these 2 data series , indicating that osahs was more severe in older patients . similarly , there was also a positive correlation between bmi and ahi , which allowed us to infer that the higher the bmi , the greater the ahi . regarding body circumference measurements , both nc and wc showed a statistically significant positive correlation with osahs severity . concerning the relationship between cephalometric data and ahi , a statistically significant positive correlation for mp - h and pns - p was observed ( table 3 ) . note : ahi = apnea - hypopnea index ; bmi = body mass index ; nc = neck circumference ; wc = waist circumference ; hc = hip circumference ; sna = angle formed by the junction of the sella ( s ) , nasion ( n ) , and point a ; snb = angle formed by the junction of the sella ( s ) , nasion ( n ) , and point b ; anb = difference between sna and snb ; mp h = distance between the mandibular plane and the hyoid bone ; pas = space between the base of the tongue and the posterior pharyngeal wall ; pns p = distance between the posterior nasal spine and the tip of the soft palate   comparing anthropometric parameters between men and women indicated a statistically significant difference for nc and wc , but not for hc . regarding cephalometry , mp - h and pns - p were significantly different between men and women ( table 4 ) . 
 note : ahi  =  apnea - hypopnea index ; bmi  =  body mass index ; nc  =  neck circumference ; wc  =  waist circumference ; hc  =  hip circumference ; sna  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point a ; snb  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point b ; anb  =  difference between sna and snb ; mp h  =  distance between the mandibular plane and the hyoid bone ; pas  =  space between the base of the tongue and the posterior pharyngeal wall ; pns p  =  distance between the posterior nasal spine and the tip of the soft palate  
 tables 5 and 6 show an analysis of the pearson correlation coefficients used to assess the relationship between ahi and age as well as anthropometric / cephalometric measurements for males and females . note : ahi  =  apnea - hypopnea index ; m  =  males ; f  =  females ; bmi  =  body mass index ; nc  =  neck circumference ; wc  =  waist circumference ; hc  =  hip circumference ; * * p  <  0.01 ; * p  <  0.05 . note : ahi  =  apnea - hypopnea index ; m  =  males ; f  =  females ; sna  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point a ; snb  =  angle formed by the junction of the sella ( s ) , nasion ( n ) , and point b ; anb  =  difference between sna and snb ; mp h  =  distance between the mandibular plane and the hyoid bone ; pas  =  space between the base of the tongue and the posterior pharyngeal wall ; pns p  =  distance between the posterior nasal spine and the tip of the soft palate ; * p  <  0.05 . for anthropometric measurements , ahi showed a statistically significant correlation with age , bmi , nc , and wc in males . regarding cephalometric measurements , the only correlation found was that of ahi with pns - p measurement in males ( table 6 ) . obesity may increase susceptibility to osahs by causing fat deposition in the upper airway tissues , narrowing the nasopharyngeal caliber and/or leading to hypoventilation in association with reduced wall complacency27 . assessment of craniofacial morphology in osahs patients not only aids specialists concerned with recognizing morphologic changes induced by altered sleep patterns , but also provides the patient with adequate treatment11 . there is a vast amount of scientific literature on cephalometric and anthropometric measures , which compares control groups and snorers to osahs patients and aims at using these measurements as predictors of this condition7 
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 32 . some studies have been performed to assess appropriate treatments , surgical treatment plans , and the indications of intraoral devices11 
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 45 . in the current study , there was a significant correlation between age and ahi ( table 3 ) , indicating that osahs is more severe in older patients . this is in agreement with the majority of previous studies17 
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 46 , with the exception of those by mayer et al42 and schellenberg , maisline , and schwab37 . it was observed that bmi was correlated with ahi , allowing us to infer that more severe osahs occurs in subjects with a higher bmi , which is concordant with most published studies17 
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 47 . nevertheless , this fact was not observed by yucel et al41 and martinez - rivera et al24 . findings in the present study point to a positive correlation between nc and ahi , which is in agreement with other studies19 
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 46 . a correlation with bmi was also observed previously17 
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 44 , suggesting that obesity affects patients with osahs through fat deposition in the neck20 
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 30 . in contrast to the majority of studies , ogretmenoglu et al17 stated that nc was more weakly correlated with ahi than bmi . wc also showed a positive correlation with ahi , in agreement with other studies19 
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 46.this correlation was weaker than that observed with nc , supporting the existing literature19 
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 32 showing that the correlation of ahi with wc is greater than that with bmi . however , davidson and patel32 observed that wc was more predictive than bmi as well as nc . analyzing the relationship between cephalometric data and ahi showed a statistically significant correlation for mp - h and pns - p , indicating an increased palatal length and an increased distance between the hyoid bone and the mandibular plane , which was consistent with other studies29 
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 48 . according to yucel et al41 , the position of the hyoid bone , which has an impact on the shape and position of the tongue , affects hypopharyngeal airway patency41 . a study by bharadwaj , ravikumar , and krishnaswamy conducted in india compared 10 osahs patients to a control group of 10 healthy subjects ( mean age , 34.9 years ) . these authors concluded that upright cephalometry demonstrated mandibular retrognathism , increased anb angle , increased pns - p length and increased soft palate thickness , increased tongue length , and decreased pas in the group of osahs patients when compared to the control group11 . other studies have shown that pns - p and mp - h measurements are increased , while pas is decreased , in patients with osahs , and these measurements were considered predictive of osahs7 
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 15 . a study conducted in strasbourg ( france ) in 1990 , comparing 43 osahs patients to a control group of 40 asymptomatic individuals , showed that pns - p measurement was increased in patients with osahs , while sna , snb , and anb measurements did not demonstrate any alterations in either group28 . other studies have shown increased mp - h measurement and decreased pas measurement in comparisons between osahs groups and control groups13 
 40 . however , mayer et al42 found no correlation between pas measurement and ahi . in a comparison between male and female patients in the present study , these results are partially in agreement with findings by millman et al49 , who described a higher nc for males , but no difference between the genders for bmi and wc . this fact reflects well - known characteristics concerning body fat distribution in men and women49 . in the current study , nc was more closely correlated with ahi than wc and bmi , both in the overall population and in male and female subjects , indicating that nc is the best anthropometric measurement for prediction of osahs severity , especially in males18 
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 44 . comparing cephalometry between male and female subjects showed a statistically significant difference in mp - h and pns - p measurements , which were higher in male subjects . pns - p measurement was correlated with ahi in males , while there were no significant correlations in females . in conclusion , the results of this study show a correlation of anthropometric ( bmi , nc , and wc ) and cephalometric ( mp - h and pns - p ) measurements with the ahi , reinforcing their preparatory role and use as predictors of osahs .
summary 
 introduction :  patients with obstructive sleep apnea - hypopnea syndrome ( osahs ) often have associated changes in craniofacial morphology and distribution of body fat , either alone or in combination . 
 aim :  to correlate cephalometric and anthropometric measures with osahs severity by using the apnea - hypopnea index ( ahi ) . 
 method :  a retrospective cephalometry study of 93 patients with osahs was conducted from july 2010 to july 2012 . 
 the following measurements were evaluated : body mass index ( bmi ) , neck circumference ( nc ) , waist circumference ( wc ) , hip circumference ( hc ) , the angles formed by the cranial base and the maxilla ( sna ) and the mandible ( snb ) , the difference between sna and snb ( anb ) , the distance from the mandibular plane to the hyoid bone ( mp - h ) , the space between the base of the tongue and the posterior pharyngeal wall ( pas ) , and the distance between the posterior nasal spine and the tip of the uvula ( pns - p ) . 
 means , standard deviations , and pearson 's correlation coefficients were calculated and analyzed . 
 results :  ahi correlated significantly with bmi ( r  =  0.207 , p  =  0.047 ) , nc ( r  =  0.365 , p  =  0.000 ) , wc ( r  =  0.337 , p  =  0.001 ) , pns - p ( r  =  0.282 , p  =  0.006 ) , and mp - h ( r  =  0.235 , p  =  0.023 ) . 
 conclusion :  anthropometric measurements ( bmi , nc , and wc ) and cephalometric measurements ( mp - h and pns - p ) can be used as predictors of osahs severity .