Shinshu Med J, 69⑹：363～371, 2021

Risk Factors for Severe Obstructive Sleep Apnea Including Sleeping
Position and its Gender Difference :A Retrospective Single-institute Study in Japan
Shuhei Nozawa, Kazuhisa Urushihata＊, Ryosuke Machida and Masayuki Hanaoka
First Department of Medicine, Shinshu University School of Medicine

Purpose : Obstructive sleep apnea (OSA) is a disease characterized by sleep-disordered breathing (SDB) due toupper airway obstruction. Age, body mass index (BMI) and abnormal facial morphology which is evaluated bycephalometry have been reported as risk factors for severe OSA. In addition, the supine sleeping position worsens
SDB because it narrows the upper airway. We thought that the percentage of supine position during sleep might
be a risk factor for worsening apnea-hypopnea index (AHI) levels but it has not been verified. Therefore, we
analyzed that and its gender difference.
Methods : Between May 2008 and May 2020, 228 patients with OSA who underwent full-night polysomnography(PSG) and cephalometry at our hospital were registered retrospectively. We conducted logistic regression analysis
using their clinical background, findings on cephalometry and the percentage of supine position during sleep
recorded on full-night PSG to identify risk factors for severe AHI levels (≥30 events/h). Subsequently, subanalyses which classified them by gender were performed.
Results : The logistic regression analysis indicated that the percentage of supine position during sleep was a sig­
nificant risk factor in addition to BMI and the distance from the mandibular plane to the hyoid (MP-H) on ceph­alometry. A sub-analysis for male patients produced the same results. However, in a sub-analysis for female
patients, the risk factors were age and BMI, but not the percentage of supine position during sleep.
Conclusions : The percentage of supine position during sleep is one of the risk factors for severe OSA, but only
applies to male patients. Shinshu Med J 69 : 363―371, 2021
(Received for publication June 16, 2021 ; accepted in revised form August 26, 2021)
Key words : obstructive sleep apnea, sleeping position, gender difference, cephalometry, risk factor

Ⅰ Introduction

an increased risk of cardiovascular and metabolic
disorders1）2）. OSA was prevalent in 14 ％ of men and

Obstructive sleep apnea (OSA) is a disease caused

5 ％ of women in a review of the epidemiology3）. It isby the collapse of the upper airway during sleep anddiagnosed by the total number of SDB per hour dis­

is diagnosed through full-night polysomnography

played as the apnea-hypopnea index (AHI). A pa­(PSG). OSA causes sleep-disordered breathing (SDB),

tient with an AHI level ≥ 5 events/h is diagnosed

such as apnea and hypopnea, which can lead to in­with OSA and OSA with an AHI level ≥30 events/h

termittent hypoxemia and an increase in sympathet­is considered as severe OSA.

ic nerve activity, resulting in daytime sleepiness andHigh body mass index (BMI) is an independentrisk factor for worsening AHI levels because fat＊

Corresponding author : Kazuhisa Urushihata
First Department of Medicine,
Shinshu University School of Medicine, 3-1-1
Asahi, Matsumoto, Nagano 390-8621, Japan
E-mail : ichiju@shinshu-u.ac.jp

No. 6, 2021

deposition around the upper airway causes airway
stenosis4）.
Old age is also considered a risk factor for OSA
because muscle function, related to upper airway
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Nozawa・Urushihata・Machida et al.

patency, declines in elderly people, leading to wors­
ening of OSA

5）6）

We examined the percentage of supine position. Moreover, sex hormones also con­during sleep as a risk factor for severe OSA together

tribute to the development of OSA. The ratio of men

with the factors reported so far. In addition, theto women is 2-3 : 1, and this ratio is maintained re­gender difference was also confirmed.

gardless of race7）8）. The prevalence of OSA is lower

Ⅱin women than in men before menopause ; however,
it is similar between sexes after menopause, sug­Ａ

Materials and Methods

Participantsgesting that female hormones such as estrogen and

Between May 2008 and May 2020, 336 participants

progesterone can prevent the collapse of the upperwith suspected sleep apnea syndrome underwent

9）10）. This is consistent with the report offull-night PSG at our hospital, and 286 patients with

Bixler et al. that postmenopausal women receiving

an AHI level ≥5 events/h were diagnosed with OSA.

hormone replacement therapy had a similar preva­

Among them, 243 patients with OSA who underwent

airway11）

lence of OSA as premenopausal women . Therefore,

cephalometry were enrolled retrospectively andage can be a significant independent factor in womenpatients having allergic rhinitis, sinusitis and neuro­

especially.

muscular diseases were excluded. Finally, 228 OSA

Abnormal facial morphology is considered as a risk

patients were registered in our study (Fig. 1).

factor. Patients with OSA have a distinctive long

The patients’ clinical background, results of full-face, mandible retraction, lower hyoid bone, and lon­night PSG including the data of sleeping position, and

12）
-16）

. Sakakiba­

results of cephalometry between non-severe OSA

ra et al. analyzed the characteristics of the upper

patients (AHI＜30 events/h) and severe OSA patients

airway using cephalometry in Japanese OSA patients(AHI ≥30 events/h) were analyzed. Statistical analysis

and showed that they tended to have a longer dis­

was performed to determine the independent risk

tance from the mandibular plane to the hyoid (MP-factors for severe AHI level ( ≥ 30 events/h). The

H) on cephalometry17）, which can be a risk factor.

same analyses were performed as sub-analyses byger soft palate, tending to induce SDB

In addition to these factors reported so far, weclassifying them into male and female groups.

presume that the supine sleeping position can be

Our study was approved by the Research Ethics

related to AHI severity because it strongly affects

Committee of Shinshu University School of Medicine

AHI levels. In general, AHI levels worsen in the(approval number : 5083). The study protocols weresupine sleeping position and improves in the lateralperformed according to the principles outlined in the18）

sleeping position . This is because the supine posi­

Declaration of Helsinki of the World Medical Associa­

tion can easily narrow the upper airway as it istion.

strongly affected by gravity acting on the soft tissue

Ｂ

Cephalometry

in the anterior cervical area and tongue ; however,

The upper airway of the participants was X-rayed

the lateral position can suppress the influence offrom the side area in the standing position (Fig. 2)21）.

gravity. So, it is possible that the percentage ofSkull base length (SN), upper jaw protrusion (∠SN-

supine position during sleep contributes to AHI

A), lower jaw protrusion (∠SN-B), lower jaw retrac­levels although the fact has not been verified so far.

tion (∠ANB) and the distance from the mandibular

Moreover, it may depend on sex because there areplane to the hyoid (MP-H), which have been shown

some differences in the upper airway structure be­

to be significantly different from those in normal

tween the sexes. In a study by Whittle et al., thesubjects22）-24）, were measured manually using thetotal neck soft tissue volume was greater and there

electronic medical records system (EV Insite ; PSP

was greater overall soft tissue loading on the airway

Inc, Tokyo, Japan).

19）

in men than in women . Nashi et al. reported thatmales had heavier tongues than females20）.
364

Ｃ

Diagnosis of OSA
A PSG device was attached to the participants
Shinshu Med J. 69

Risk factors for severe obstructive sleep apnea

Fig. 1 The process of choosing patients who were registered in our study
Abbreviations : OSA, obstructive sleep apnea ; AHI, apnea-hypopnea index

Fig. 2 Cephalometric landmarks with line and area measurements [15]Abbreviations : S, sella ; N, nasion ; A, A-point, deepest point of maxilla ; B, B-point, deepest point ofmandible ; P, palate point ; PNS, posterior nasal spine ; H, superior tip of hyoid bone ; SN, skull baselength ; ∠SNA, upper jaw protrusion ; ∠SNB, lower jaw protrusion ; ∠ANB ; the length of the soft
palate ; MP-H, the distance from the mandibular plane to the hyoidfrom 9 : 30 P.M. (lights off) to 6 A.M. (lights on). Full-movement), oxygen saturation, snoring, electrocar­

night PSG examination was performed using Alice 3

diogram findings, and body position. A sleep techni­(Philips, Amsterdam, Netherlands), which collectedcian monitored the behavior or sleep position chang­data on four-channel electroencephalogram (C4/A1,

es of the patients during sleep and manually scored

C3/A2, O2/A1, O1/A2) findings, two-channel elec­

all PSG data, including airflow and respiratory effort,

trooculogram findings, submental and leg electro­

based on the American Academy of Sleep Medi‑

myogram findings, airflow (thermistor and pressure

cine Manual for the scoring of sleep and associatedtransducer), respiratory effort (chest and abdominal

events25）. Respiratory events, including apnea andNo. 6, 2021

365

Nozawa・Urushihata・Machida et al.

hypopnea, were scored according to the “alternative”

night PSG is shown in Table 4. There are differences

rule. Apnea was defined as the cessation of respira­in BMI, the percentage of supine position during sleep

tory airflow for a minimum of two breaths (10 s). Ob­

and MP-H. The logistic regression analysis for severe

structive apnea was defined as the cessation of

AHI levels indicates that the percentage of supine

airflow with continued respiratory effort (chest andposition during sleep is a significant risk factor for

abdominal movement) for the same duration. Hypo­

severe OSA, in addition to BMI and MP-H (Table 5),pnea was defined as a decrease in respiratory airflow

which are consistent with the all-gender analysis.

of ≥50 ％ with ≥3 ％ oxygen desaturation or arousal.
Ｄ

In a sub-analysis about females, a comparison be­
tween non-severe and severe OSA based on the

Data analysis
Statistical analysis was performed using SPSS

clinical background and the results of full-night PSG

statistics (version 26, IBM, USA). Measurement datais shown in Table 6. There is a difference in BMI

were expressed as mean±standard deviation values.

only. The logistic regression analysis for severe AHI

Comparison of categorical variables was performed

levels indicates that age and BMI are risk factors but

using a chi-square test. Comparison of continuous

the percentage of supine position during sleep is notvariables was first assessed using a Kolmogorov-a significant risk factor (Table 7).

Smirnov test to confirm whether they were normally
distributed. Subsequently, we confirmed that theyⅣ

Discussion

had equal or unequal variance using a Levene test. If

Although few papers show the gender difference

they were normal and equally distributed, we used aabout risk factors for severe OSA such as clinicalStudent’s t-test, but if they were normal and had an

background and cephalometry, we are able to do that.

unequal distribution, we used a Welch’s t-test. If they

The percentage of supine position during sleep waswere not normally distributed, we used a Mann-an independent significant risk factor for severe OSA.

Whitney U test.

However, this was not a risk factor for female pa­

We conducted logistic regression analysis selecting

tients. This indicates that the effect of gravity on“AHI ≥30 events/h” as the dependent variable andupper airway patency differs between the sexes.

“age,” “BMI,” and “percentage of supine position during

Marin et al. measured the upper airway dimensions

sleep,” and “MP-H” on cephalometry. Statistical sig­

using the acoustic reflection technique in 60 malenificance was set at p＜0.05.

and 54 female participants in the seated and supine

Ⅲ

Results

positions and compared the difference between thesexes in the change of the upper airway area by po­

A comparison between the non-severe and severe

sition switch26）. They found that male participants

OSA groups based on the clinical background andhad significantly larger decreases in the upper airway

the results of full-night PSG including data of sleeping

area in the supine position than female participants.

position is shown in Table 1. There are significant

Their findings were consistent with the gender dif­differences in BMI and some other data of full-night

ference in the genioglossal muscle tone strength re­

PSG. A comparison of cephalometry results between

ported by Popovic and White27）. They reported thatthem is shown in Table 2. There is a difference infemales had a greater genioglossal muscle tone than

MP-H. The logistic regression analysis for severe

males, suggesting greater defense of their upper

AHI levels indicates that the percentage of supine

airway. The usefulness of positional therapy, which

position during sleep is a significant risk factor for

prevents patients from sleeping in the supine posi­severe OSA, in addition to BMI and MP-H (Table 3).

tion, has been reported28）-30）. Although there is no

In a sub-analysis about the male group, a compari­verification that there is a sex difference in the use­

son between non-severe OSA and severe OSA based

fulness of positional therapy, the possibility that iton the clinical background and the results of full-depends on sex could not be excluded. Our study has

366

Shinshu Med J. 69

Risk factors for severe obstructive sleep apnea
Table 1 Clinical background and results of full-night PSG between non-severe OSA patients (AHI＜30
events/h) and severe OSA patients (AHI ≥30 events/h).
AHI＜30 events/h(n＝114)

Variables

AHI ≥30 events/h(n＝114)P-value59.1±13.1

59.3±13.7

0.90

BMI (kg/m )26.0±4.1

29.0±5.0＜0.001

AHI (events/h)

16.4±7.0

53.7±19.3＜0.001

TST (min)426.0±83.8

414.7±94.7

0.34

SE (％)

76.3±12.875.5±14.5

0.66

REM sleep time (％)

15.0±5.9

11.7±5.9＜0.001

Stage N1 (％)

24.4±13.1

34.2±20.3＜0.001

Stage N2 (％)

54.6±12.2

50.3±18.6

0.044

Stage N3 (％)

6.3±7.4

3.8±5.0

0.030

Supine position (％)

50.8±23.9

57.3±26.2

0.052

Left lateral position (％)

24.0±20.2

18.7±18.9

0.043

Right lateral position (％)

24.6±21.2

22.3±20.3

0.39

Mean SpO2 (％)

94.2±2.0

92.0±2.9＜0.001Lowest SpO2 (％)

80.7±6.8

68.0±13.5＜0.001

3 ％ ODI (events/h)

14.5±7.1

47.0±21.7＜0.001

CT90 (％)

4.6±11.0

22.7±18.1＜0.001

Arousal index (events/h)

22.7±9.447.6±35.3＜0.001

Snoring index (events/h)

59.4±94.0

75.1±60.4

0.33

Age (years)
2

Percentage of each position during sleep

Data are expressed as mean±standard deviation (SD)
Abbreviations : PSG, polysomnography ; BMI, body mass index ; AHI, apnea-hypopnea index ; TST, total sleep
time ; SE, sleep efficiency calculated by TST/time in bed (％) ; REM sleep time, rapid eye movement sleep time ;SpO2, oxygen saturation ; 3 ％ ODI, 3 ％ oxygen desaturation index ; CT90, total sleep time with SpO2 under 90 ％Table 2 Findings of cephalometry between non-severe OSA patients (AHI＜30 events/h) andsevere OSA patients (AHI ≥30 events/h).
Variables

AHI＜30 events/h

AHI ≥30 events/h

P-valueSN (mm)74.4±5.274.8±5.7

0.48∠SNA (°)

58.9±4.659.1±3.6

0.37∠SNB (°)

57.4±4.856.1±3.9

0.070∠ANB (°)

2.5±1.5

3.3±1.6

0.080

MP-H (mm)15.3±7.7

19.7±6.6＜0.001

Data are expressed as mean±standard deviation (SD)
Abbreviations : OSA, obstructive sleep apnea ; SN, skull base length ; ∠SNA, upper jaw protrusion; ∠SNB, lower jaw protrusion ; ∠ANB, lower jaw retraction ; MP-H, the distance from themandibular plane to the hyoid

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Nozawa・Urushihata・Machida et al.
Table 3 Results of univariate analysis and logistic regression analysis for severe OSA(AHI ≥30 events/h)
Logistic regression analysis
Variables

P-value

OR (95 ％ CI)

0.23

1.02 (0.99-1.06)

BMI (kg/m )＜0.0011.22 (1.09-1.37)

Percentage of supine position during sleep (％)

0.017

1.02 (1.01-1.04)

MP-H (mm)0.00501.09 (1.03-1.16)

Age (years)
2

Abbreviations : OR, odds ratio ; 95 ％ CI, 95 ％ confidence interval ; BMI, body mass index ;MP-H, the distance from the mandibular plane to the hyoid

Table 4 Clinical background and results of full-night PSG between non-severe OSA patients (AHI＜30
events/h) and severe OSA patients (AHI ≥30 events/h) in male group
Variables

AHI＜30 events/h(n＝79)AHI ≥30 events/h(n＝83)

Age (years)

57.6±13.558.2±14.9

0.81

BMI (kg/m2)

26.1±3.6

28.7±4.8＜0.001

AHI (events/h)

16.9±6.8

53.4±18.2＜0.001

TST (min)429.1±81.1

409.7±96.8

0.17

SE (％)

76.0±12.6

74.6±15.4

0.56

REM sleep time (％)

14.9±5.7

11.5±.7＜0.001

Stage N1 (％)

26.1±13.635.4±19.6＜0.001

Stage N2 (％)

54.1±12.7

50.0±18.5

0.010

Stage N3 (％)

5.1±5.7

3.1±4.5

0.015

Supine position (％)

47.0±21.1

56.8±23.9

0.0070

Left lateral position (％)

25.5±19.7

18.0±16.8

0.011

Right lateral position (％)

26.5±21.7

23.6±20.1

0.37

Mean SpO2 (％)

94.3±1.992.1±2.8＜0.001Lowest SpO2 (％)

80.8±7.0

67.4±13.5＜0.001

3 ％ ODI (events/h)

14.7±6.8

45.7±20.1＜0.001

CT90 (％)

4.5±11.522.7±18.4＜0.001

Arousal index (events/h)

23.4±9.7

49.0±39.7＜0.001

Snoring index (events/h)

36.0±27.880.5±70.0

0.002015.3±7.7

19.7±6.9

0.0082

P-value

Percentage of each position during sleep

Cephalometry
MP-H (mm)Data are expressed as mean±standard deviation (SD)
Abbreviations : OSA, obstructive sleep apnea ; PSG, polysomnography ; BMI, body mass index ; AHI, apneahypopnea index ; TST, total sleep time ; SE, sleep efficiency calculated by TST/time in bed (％) ; REM sleep time,
rapid eye movement sleep time ; SpO2, oxygen saturation ; 3 ％ ODI, 3 ％ oxygen desaturation index ; CT90, total

sleep time with SpO2 under 90 ％, MP-H, the distance from the mandibular plane to the hyoid

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Risk factors for severe obstructive sleep apnea
Table 5 Results of univariate analysis and logistic regression analysis for severe OSA(AHI ≥30 events/h) in male group
Logistic regression analysis
Variables

P-value

OR (95 ％ CI)

0.66

1.01 (0.97-1.06)

BMI (kg/m )0.018

1.25 (1.04-1.50)

Percentage of supine position during sleep (％)

0.00901.03 (1.01-1.06)

MP-H (mm)0.015

1.11 (1.02-1.20)

Age (years)
2

Abbreviations : OR, odds ratio ; 95 ％ CI, 95 ％ confidence interval ; BMI, body mass index, MP-H,
the distance from the mandibular plane to the hyoid

Table 6 Clinical background and results of full-night PSG between non-severe OSA patients (AHI＜30
events/h) and severe OSA patients (AHI ≥30 events/h) in female group
AHI＜30 events/h(n＝35)AHI ≥30 events/h(n＝31)

Age (years)

62.4±11.6

62.5±9.3

0.98

BMI (kg/m2)

25.9±5.2

29.8±5.4

0.005

AHI (events/h)

15.3±7.5

54.6±21.8＜0.001

TST (min)419.0±89.4

428.1±87.4

0.68

SE (％)

77.1±13.2

77.9±11.4

0.81

REM sleep time (％)

15.2±6.4

12.5±6.3

0.12

Stage N1 (％)

20.1±10.6

30.3±22.0

0.030

Stage N2 (％)

56.0±10.551.1±19.1

0.23

Stage N3 (％)

9.5±9.8

6.1±5.6

0.11

Supine position (％)

59.4±27.4

58.6±31.4

0.92

Left lateral position (％)

20.6±20.9

20.5±23.6

0.98

Right lateral position (％)

20.3±19.4

18.6±20.4

0.74

Mean SpO2 (％)

94.1±2.0

92.0±3.0＜0.001Lowest SpO2 (％)

80.4±6.0

70.5±13.0＜0.001

3 ％ ODI (events/h)

14.2±7.550.3±25.1＜0.001

CT90 (％)

4.8±9.622.7±17.3＜0.001

Arousal index (events/h)

21.2±8.644.4±21.2＜0.001

Snoring index (events/h)

97.3±139.9

63.6.±28.70.31

11.0±4.8

15.4±7.7

0.058

Variables

P-value

Percentage of each position during sleep

Cephalometry
MP-H (mm)Data are expressed as mean±standard deviation (SD)
Abbreviations : OSA, obstructive sleep apnea ; PSG, polysomnography ; BMI, body mass index ; AHI, apneahypopnea index ; TST, total sleep time ; SE, sleep efficiency calculated by TST/time in bed (％) ; REM sleep time,
rapid eye movement sleep time ; SpO2, oxygen saturation ; 3 ％ ODI, 3 ％ oxygen desaturation index ; CT90, total

sleep time with SpO2 under 90 ％, MP-H, the distance from the mandibular plane to the hyoid

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Nozawa・Urushihata・Machida et al.
Table 7 Results of univariate analysis and logistic regression analysis for severe OSA(AHI ≥30 events/h) in female group
Logistic regression analysis
Variables

P-value

OR (95 ％ CI)

Age (years)

0.036

1.11 (1.01-1.21)

BMI (kg/m2)

0.00801.32 (1.08-1.63)

Percentage of supine position during sleep (％)

0.40

1.01 (0.99-1.04)

MP-H (mm)0.21

1.09 (0.95-1.24)

Abbreviations : OR, odds ratio ; 95 ％ CI, 95 ％ confidence interval ; BMI, body mass index ;MP-H, the distance from the mandibular plane to the hyoid

the limitation that the study cohort included a rather

In conclusion, the percentage of supine position

small number of female patients (66 females vs. 162

during sleep is a risk factor for severe OSA ; howev­

males) as our study was performed at a single institute.

er, this is not the case for female patients.

References
1） Yaggi HK, Concato J, Kernan WN, Lichtman JH, Brass LM, Mohsenin V : Obstructive sleep apnea as a risk factor forstroke and death. N Engl J Med 353 : 2034-2041, 2005
2） Shaw JE, Punjabi NM, Wilding JP, Alberti KGMM, Zimmet PZ : International Diabetes Federation Taskforce on
Epidemiology and Prevention. Sleep-disordered breathing and type 2 diabetes : a report from the International
Diabetes Federation Task Force on Epidemiology and Prevention. Diabetes Res Clin Pract 81 : 2-12, 2008
3） Peppard PE, Young T, Barnet JH, Palta M, Hagen EW, Hla KM : Increased prevalence of sleep-disordered breathingin adults. Am J Epidemiol 177 : 1006-1014, 2013
4） Young T, Shahar E, Nieto FJ, et al : Predictors of sleep-disordered breathing in community-dwelling adults : theSleep Heart Health Study. Arch Intern Med 162 : 893-900, 2002
5） Peppard PE, Young T, Palta M, Dempsey J, Skatrud J : Longitudinal study of moderate weight change and sleepdisordered breathing. JAMA 284 : 3015-3021, 2000
6） Russell T, Duntley S : Sleep disordered breathing in the elderly. Am J Med 124 : 1123-1126, 2011
7） Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S : The occurrence of sleep-disordered breathing among
middle-aged adults. N Engl J Med 328 : 1230-1235, 1993
8） Tishler PV, Larkin EK, Schluchter MD, Redline S : Incidence of sleep-disordered breathing in an urban adult
population : the relative importance of risk factors in the development of sleep-disordered breathing. JAMA 289 :
2230-2237, 2003
9） Philips BA : Obstructive sleep apnea in the elderly. In : Principles and practice of sleep medicine. 5th ed. Missouri :Elsevier Saunders : 1536-1543, 2011
10） Young T, Finn L, Austin D, Peterson A : Menopausal status and sleep-disordered breathing in the Wisconsin Sleep
Cohort Study. Am J Crit Care Med 167 : 1181-1185, 2003
11） Bixler EO, Vgontzas AN, Lin HM, et al : Prevalence of sleep-disordered breathing in women : effects of gender. Am J
Respir Crit Care Med 163 : 608-613, 2001
12） Riley R, Guilleminault C, Herran J, Powell N : Cephalometric analyses and flow-volume loops in obstructive sleep
apnea patients. Sleep 6 : 303-311, 1983
13） Gungor AY, Turkkahraman H, Yilmaz HH, Yariktas M : Cephalometric comparison of obstructive sleep apnea
patients and healthy control. Eur J Dent 7 : 48-54, 2013370

Shinshu Med J. 69

Risk factors for severe obstructive sleep apnea
14） Kubota Y, Nakayama H, Takada T, et al : Facial axis angle as a risk factor for obstructive sleep apnea. Intern Med
44 : 805-810, 2005
15） Pae EK, Lowe AA, Sasaki K, Price C, Tsuchiya M, Fleetham JA : A cephalometric and electromyographic study ofupper airway structures in the upright and supine positions. Am J Orthod Dentofacial Orthop 106 : 52-59, 199416） Kikuchi M, Higurashi N, Miyazaki S, Itasaka Y : Facial patterns of obstructive sleep apnea patients using Ricketts
method. Psychiatry Clin Neurosci 54 : 336-337, 2000
17） Sakakibara H, Tong M, Matsushita M, Hirata Y, Konishi S, Suetsugu S : Cephalometric abnormalities in non-obese
and obese patients with obstructive sleep apnoea. Eur Respir J 13 : 403-410, 1999
18） Cartwright RD : Effect of sleep position on sleep apnea severity. Sleep 7 : 110-114, 198419） Whittle AT, Marshall I, Mortimore IL, Wraith PK, Sellar RJ, Douglas NJ : Neck soft tissue and fat distribution :comparison between normal men and women by magnetic resonance imaging. Thorax 54 : 323-328, 1999
20） Nashi N, Kang S, Barkdull GC, Lucas J, Davidson TM : Lingual fat at autopsy. Laryngoscope 117 : 1467-1473, 200721） Kitamura T, Sakabe A, Ueda N, et al : Usefulness of cephalometry and pharyngeal findings in the primary diagnosisof obstructive sleep apnea syndrome. Nippon Jibiinkoka Gakkai Kaiho 111 : 695-700, 200822） Pae EK, Lowe AA, Sasaki K, Price C, Tsuchiya M, Fleetham JA : A cephalometric and electromyographic study ofupper airway structures in the upright and supine positions. Am J Orthod Dentofac Orthop 106 : 52-59, 1994
23） Esaki K : Morphological analysis by lateral cephalography of sleep apnea syndrome in 53 patients. Kurume Med J
42 : 231-240, 1995
24） Yao M, Tachibana N, Okura M, et al : Relationships of craniofacial morphology and body mass index with sleepdisordered breathing in Japanese men. Laryngoscope 114 : 1838-1842, 200425） Iber C, Ancoli-Israel S, Chesson AL, Quan SF : The AASM Manual for the scoring of sleep and associated events :rules, terminology and technician specifications. American Academy of Sleep Medicine, 200726） Martin SE, Mathur R, Marshall I, Douglas NJ : The effect of age, sex, obesity and posture on upper airway size. Eur
Respir J 10 : 2087-2090, 199727） Popovic RM, White DP : Gender differences in waking genioglossal EMG (GG-EMG) and pharyngeal resistance. Am J
Respir Crit Care Med 152 : 725-731, 1995
28） De Dios JAA, Brass SD : New and unconventional treatments for obstructive sleep apnea. Neurotherapeutics 9 :702-709, 201229） McEvoy RD, Sharp DJ, Thornton AT : The effects of posture on obstructive sleep apnea. Am Rev Respir Dis 133 :662-666, 1986
30） Permut I, Diaz-Abad M, Chatila W, et al : Comparison of positional therapy to CPAP in patients with positional
obstructive sleep apnea. J Clin Sleep Med 6 : 238-243, 2010

（2021. 6. 16 received ; 2021. 8. 26 accepted）

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