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A Predictive Morphometric Model for the Obstructive Sleep Apnea Syndrome

Clete A. Kushida, MD, PhD; Bradley Efron, PhD; and Christian Guilleminault, MD
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From Stanford University, Stanford, California. Acknowledgments: The authors thank Rolfe LaForge, PhD, for his contribution to the statistical analyses; Anstella Robinson, MD, for her contribution to the interrater reliability measurements; and Ann Mack, Julianne Lemons, Evangeline Roldan-Fong, Ray Kubisiak, Mike Bilberry, Doug Yost, Lars Black, and Angela Giacomini for technical assistance. Grant Support: In part by grants NIA AG07772 and NIA AG00164-07 from the National Institutes of Health. Requests for Reprints: Clete A. Kushida, MD, PhD, Stanford University Sleep Disorders Clinic and Research Center, 401 Quarry Road, Suite 3301-A, Stanford, CA 94305-5730. Current Author Addresses: Drs. Kushida and Guilleminault: Stanford University Sleep Disorders Clinic and Research Center, 401 Quarry Road, Suite 3301-A, Stanford, CA 94305-5730. Dr. Efron: Sequoia Hall, Room 106, Stanford University, Stanford, CA 94305.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1997;127(8_Part_1):581-587. doi:10.7326/0003-4819-127-8_Part_1-199710150-00001
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Background: Mathematical formulas have been used to clinically predict whether patients will develop the obstructive sleep apnea syndrome (OSAS). However, these models do not take into account the disproportionate craniofacial anatomy that accompanies OSAS independently of obesity.

Objective: To determine the accuracy of a morphometric model, which combines measurements of the oral cavity with body mass index and neck circumference, in predicting whether a patient has OSAS.

Design: 6-month prospective study.

Setting: University-based tertiary referral sleep clinic and research center.

Participants: 300 consecutive patients evaluated for sleep disorders for the first time.

Measurements: Body mass index, neck circumference, and oral cavity measurements were obtained, and a model value was calculated for each patient. Polysomnography was used to determine the number of abnormal respiratory events that occurred during sleep. Sleep apnea was defined as more than five episodes of apnea or hypopnea per hour of sleep.

Results: The morphometric model had a sensitivity of 97.6% (95% CI, 95% to 98.9%), a specificity of 100% (CI, 92% to 100%), a positive predictive value of 100% (CI, 98.5% to 100%), and a negative predictive value of 88.5% (CI, 77% to 96%). No significant discrepancies were revealed in tests of intermeasurer and test-retest reliability.

Conclusions: The morphometric model provides a rapid, accurate, and reproducible method for predicting whether patients in an ambulatory setting have OSAS. The model may be clinically useful as a screening tool for OSAS rather than as a replacement for polysomnography.


Grahic Jump Location
Figure 1.
Oral cavity measurements for the morphometric model. Top.Bottom left.Bottom right.

Measurement of the palatal height by two separate calipers, labeled ABC and DEF. Angle ABC is a 20-degree angle between the maxillary and mandibular incisor tips with the vertex (B) of an externally placed caliper at the mandibular condyle. Angle DEF represents a caliper placed inside the oral cavity. The vertical distance DF is equal to P (palatal height) in millimeters. Measurement from the mesial surfaces of the crowns of the second molars to obtain either Mx (maxillary intermolar distance) or Mn (mandibular intermolar distance) in millimeters. Measurement of OJ (overjet), or the horizontal overlap of the crowns of the maxillary and mandibular right central incisors in millimeters.

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Figure 2.
Frequency histogram of morphometric model values for the study groups with and without the obstructive sleep apnea syndrome (OSAS).

The white bars represent the OSAS group; the striped bars represent the non-OSAS group. The dashed vertical line indicates the model cutoff value of 70. The OSAS group has 254 patients with a mean morphometric value of 95.3 ± 21.2 and an age range of 24 to 77 years. The non-OSAS group has 46 patients with a mean morphometric value of 61.6 ± 6.2 and an age range of 15 to 71 years.

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Figure 3.
Comparisons of receiver-operating characteristic curves.

Different discriminant capacities to distinguish patients with the obstructive sleep apnea syndrome (OSAS) from patients without OSAS by using the morphometric model (MM) (a), body mass index (BMI) (b), and neck circumference (NC) (c) are shown. The true-positive and false-positive rates for the entire locus of possible points for the selected discriminant capacity are shown in each graph. The area under the curve values are 0.996 for the morphometric model, 0.938 for BMI, and 0.898 for neck circumference.

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Figure 4.
The craniofacial versus the obesity component of the model.

This scatterplot shows the craniofacial component (P + [Mx − Mn] + 3 x OJ) in the abscissa compared with the obesity component (3 x [Max (BMI −25, 0)] x [NC ÷ BMI]) in the ordinate. Plus signs indicate patients with a diagnosis of the obstructive sleep apnea syndrome (OSAS); circles indicate patients without OSAS. The solid line indicates the decision boundary at a craniofacial component cutoff value of 70, revealing the contribution of the craniofacial component of the model to nonobese patients. BMI = body mass index; Mx = maxillary intermolar distance; Mn = mandibular intermolar distance; NC = neck circumference; OJ = overjet.

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