Alan A. Lowe

Facial morphology and obstructive sleep apnea.

In a sample of 25 adult male subjects with moderate to severe obstructive sleep apnea, the interaction among craniofacial, airway, tongue, and hyoid variables was quantified by means of a canonical correlation analysis. One lateral cephalometric radiograph with the teeth in occlusion was obtained for each subject together with overnight polysomnographic measurements before the initiation of therapy. A principal component analysis reduced the data base and one significant canonical correlation (r1 = 0.994) was identified for the 22 variables. Sleep apnea subjects showed a posteriorly positioned maxilla and mandible, a steep occlusal plane, overerupted maxillary and mandibular teeth, proclined incisors, a steep mandibular plane, a large gonial angle, high upper and lower facial heights, and an anterior open bite in association with a long tongue and a posteriorly placed pharyngeal wall. A multivariate statistical analysis extracted clinically significant associations among craniofacial, tongue, and airway variables. Subjects with sleep apnea demonstrated several alterations in craniofacial form that may reduce the upper airway dimensions and subsequently impair upper airway stability.

Cephalometric and computed tomographic predictors of obstructive sleep apnea severity.

The interaction between craniofacial structure assessed by lateral cephalometry, and tongue, soft palate, and upper airway size determined from computed tomography (CT) scans was examined in 25 control subjects and 80 patients with obstructive sleep apnea (OSA). On the basis of the cephalometric analyses, the patients with OSA had retruded mandibles with larger ANB angle differences, elongated maxillary and mandibular incisors and mandibular molars, and high total upper and lower face heights The computed tomographic evaluations revealed that patients with OSA also had larger tongue, soft palate, and upper airway volumes. Men with OSA and skeletal Class I malocclusions had significantly larger soft palates than comparable controls. Both tongue and soft palate volumes were positively correlated with body mass index. A principal component analysis reduced the database, and one significant correlation was identified. Subjects with high total, upper and lower face heights, elongated maxillary and mandibular teeth, and proclined lower incisors were observed to have large tongue, soft palate, and upper airway volumes, to have a higher apnea index and to be obese. Linear regression analysis indicated that a high apnea index was seen in association with large tongue and soft palate volumes, a retrognathic mandible, an anteroposterior discrepancy between the maxilla and mandible, an open bite tendency between the incisors, and obesity.

Mandibular advancement oral appliance therapy for obstructive sleep apnoea: effect on awake calibre of the velopharynx

BACKGROUND The mechanisms of action of oral appliance therapy in obstructive sleep apnoea are poorly understood. Videoendoscopy of the upper airway was used during wakefulness to examine whether the changes in pharyngeal dimensions produced by a mandibular advancement oral appliance are related to the improvement in the severity of obstructive sleep apnoea. METHODS Fifteen patients with mild to moderate obstructive sleep apnoea (median (range) apnoea index (AI) 4(0–38)/h, apnoea-hypopnoea index (AHI) 28(9–45)/h) underwent overnight polysomnography and imaging of the upper airway before and after insertion of the oral appliance. Images were obtained in the hypopharynx, oropharynx, and velopharynx at end tidal expiration during quiet nasal breathing in the supine position. The cross sectional area and diameters of the upper airway were measured using image processing software with an intraluminal catheter as a linear calibration. RESULTS AI decreased to a median (range) value of 0 (0–6)/h (p<0.01) and AHI to 8 (1–28)/h (p<0.001) following insertion of the oral appliance. The median (95% confidence interval) cross sectional area of the upper airway increased by 18% (3 to 35) (p<0.02) in the hypopharynx and by 25% (11 to 69) (p<0.005) in the velopharynx, but not significantly in the oropharynx. Although in general the shape of the pharynx did not change following insertion of the oral appliance, the lateral diameter of the velopharynx increased to a greater extent than the anteroposterior diameter. Following insertion of the oral appliance the reduction in AHI was related to the increase in cross sectional area of the velopharynx (p = 0.01). CONCLUSIONS A mandibular advancement oral appliance increases the cross sectional area of the upper airway during wakefulness, particularly in the velopharynx. Assuming this effect on upper airway calibre is not eliminated by sleep, mandibular advancement oral appliances may reduce the severity of obstructive sleep apnoea by maintaining patency of the velopharynx, particularly in its lateral dimension.

Three-dimensional CT reconstructions of tongue and airway in adult subjects with obstructive sleep apnea

The interaction between airway and tongue structures in a sample of 25 adult men with obstructive sleep apnea was quantified on the basis of a series of preoperative CT slices obtained for each subject. Tracings were completed for tongue, and right and left nasal, nasopharynx, oropharynx, and hypopharynx structures; computer graphics were used to obtain superior and lateral three-dimensional reconstructions of all structures for each subject. In addition, cross-sectional areas of specific sites of airway constriction, surface area, volume, and ratio calculations were completed. The majority of the constrictions occurred in the oropharynx (0.52 +/- 0.18 cm2), but six subjects had two constrictions--one in the oropharynx and one in the hypopharynx. The airway had a mean volume of 13.89 +/- 5.33 cm3, whereas tongue volume ranged from 44.03 to 99.56 cm3 with a mean of 71.96 +/- 13.41 cm3. Subjects with more severe obstructive sleep apnea tended to have larger tongue and smaller airway volumes. The more obese subjects showed larger tongue surface areas and smaller airway surface areas. To determine the structural relationships between airway and tongue variables, a series of logarithmic plots was determined. An isometric relationship characterized tongue surface area and tongue volume. A logarithmic plot of oropharyngeal airway vs. tongue volume showed a negative allometric relationship. Tongue volume increased more rapidly than airway volume in subjects with obstructive sleep apnea. Subjects with large tongue volumes were observed to experience significant complications at the time of surgical treatment. Quantification of the volume of the oropharynx and its relationship to tongue volume provide an overview of the interaction between these structures.

A cephalometric and electromyographic study of upper airway structures in the upright and supine positions

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway obstruction during sleep, usually in the supine position. To investigate the relationship between upper airway size and genioglossus (GG) muscle activity, upright and supine cephalograms were obtained in 20 OSA patients and 10 symptom-free control subjects. Tongue electromyographic (EMG) recordings were obtained with surface electrodes, and pressure transducers were placed in the 10 symptom-free controls. The tongue cross-sectional area increased 4.3% (p < 0.05), and the oropharyngeal area decreased 36.5% (p < 0.01) when the OSA patients changed their body position from upright to supine. No changes were observed in the tongue area, but soft palate thickness increased (p < 0.01) when the control subjects changed from the upright to the supine position. Furthermore, the oropharyngeal cross-sectional area decreased 28.8% (p < 0.01) despite a 34% increase (p < 0.05) in resting GG EMG activity. Posterior tongue pressure increased 17% (p < 0.05) with the change from upright to supine. On the basis of these findings, we propose that body posture has a substantial effect on upper airway structure and muscle activity. This postural effect should be taken into account when assessing upper airway size in the erect posture (conventional cephalography) and in the supine position (computed tomography). The vertical and anteroposterior position of the tongue and its relationship to airway size may be more important than soft palate size in the pathogenesis of OSA.

Cephalometric comparisons of craniofacial and upper airway structure by skeletal subtype and gender in patients with obstructive sleep apnea

To investigate whether patients with obstructive sleep apnea (OSA) have abnormalities in their craniofacial and upper airway (UA) structures compared with normal subjects, cephalometric comparisons were systematically performed in both the upright and the supine positions in subjects with and without OSA, who were then grouped according to their craniofacial skeletal type and gender. A total of 347 patients with OSA and 101 control subjects were divided into male and female groups and then classified into Class I (CI), Class II, Division 1 (CII/1), Class II, Division 2 (CII/2), and Class III (CIII) skeletal subtypes. In the upright position, the most atypical craniofacial and UA structure was shown in male patients with CI OSA. In patients with OSA, the degree of UA abnormalities was less in the supine position regardless of skeletal subtype. In the supine position, the most atypical craniofacial and UA structure was also shown in male patients with CI OSA; there were no significant differences between male patients with CII/2 OSA and control subjects or between female patients with CI OSA and control subjects. With a change in body position from upright to supine, distinctive changes in the UA structure in both patients with OSA and control subjects occurred, according to skeletal subtype and gender. We conclude that there are a series of characteristics of craniofacial and UA structure that differ between patients with OSA and control subjects matched for skeletal subtype and gender. These differences may predispose to UA obstruction during sleep in patients with OSA.

Sleep bruxism in patients with sleep-disordered breathing

The aim was to test the hypothesis of a direct association between sleep-disordered breathing and sleep bruxism. The frequency of masseter contraction (MC) episodes and rhythmic jaw movements (RJM) was measured in patients with mild and moderate obstructive sleep apnoea (OSA). The diagnosis of sleep bruxism was made from a combination of questionnaire, clinical observation and all-night polysomnographic recording which included masseter electromyography. A total of 21 patients (19 males/two females, mean age 40.0 years+/-9.2 SD) were randomly selected from a provisional diagnosis of snoring and OSA by a sleep physician. In the patients with mild OSA [n=11, mean apnoea hypopnoea index (AHI)=8.0+/-4.1 SD, body mass index (BMI)=29.1+/-5.0], the diagnosis of sleep bruxism was made in six out of 11 patients (54%); similarly, four out of 10 patients (40%) with moderate OSA (n=10, mean AHI=34.7+/-19.1, BMI=30.6+/-5.0) were identified as bruxists. Although the combination of clinical, subjective estimation and nocturnal electromyographic recording of masseter muscle might provide a more solid base for the diagnosis of sleep bruxism, the result is biased by the variation in the bruxing activity. MC episodes were associated with the termination of apnoea or hypopnoea episodes in only 3.5% of the mild group and 14.4% of the moderate group (p<0.05). It appears that sleep bruxism is rarely directly associated with apnoeic events, but is rather related to the disturbed sleep of OSA patients.

Relationship Between Jaw Muscle Volume and Craniofacial Form

To study the relationship between craniofacial form and jaw muscle function, we evaluated 25 adult male subjects with Obstructive Sleep Apnea (age, 30-61 years; weight, 58-122 kg) on the basis of CT scans obtained for routine diagnostic purposes. All scans were obtained with the Frankfort horizontal plane at right angles to the floor; each CT slice was 8 mm thick. Masseter and medial pterygoid muscle outlines were traced, digitized, and stored, and three-dimensional reconstructions were made for calculation of muscle volume. Lateral cephalometric radiographs were analyzed for quantification of selected craniofacial variables. Significant correlations could not be identified between physiological apnea variables and jaw muscle volume. An intersubject variability in masseter muscle volume was identified (range, 22.4 - 38.1 cm3). Medial pterygoid muscle volume revealed more variability (range, 7.4 - 15.2 cm3). Masseter muscle volume had a negative correlation with mandibular plane and gonial angle, and a positive correlation with posterior face height, ramus height, posterior face length, condylar center to first molar point length, gonion to pterygomaxillary fissure length, and the ramus height/ anterior face height ratio. Medial pterygoid muscle volume showed a positive correlation with posterior face height, ramus height, posterior face length, and the lengths between condylar center to first molar contact point, gonion to pterygomaxillary fissure, and antegonion to key ridge. Subjects with large masseter and medial pterygoid muscle volumes had flat mandibular and occlusal planes, and small gonial angles.

Obstructive sleep apnea subtypes by cluster analysis.

A sample of 84 adult male patients with obstructive sleep apnea (OSA) were classified by a cluster analysis on the basis of apnea index (AI) and body mass index (BMI). Demographic, cephalometric, tongue, soft palate, and upper airway-size data were evaluated for the two subgroups of OSA patients and for 18 control subjects. One OSA group consisted of 43 patients with a high AI and low BMI ratio, the other group was comprised of 41 patients with a low AI and high BMI ratio. The patients with a high AI and low BMI ratio had retruded mandibles with high mandibular plane angles and proclined lower incisors. The patients with a low AI and high BMI ratio had inferior hyoid bones and large soft palates. A multiple regression analysis was performed between AI (the dependent variable) and the other variables (independent variables) for each of the subgroups. In the patients with a high AI and low BMI ratio, a high AI was related to a large skeletal anteroposterior discrepancy, a steep mandibular plane, and an inferoanterior position of the hyoid bone. In the patients with a low AI and high BMI ratio, a high AI was related to a large tongue and a small upper airway. In both groups, BMI was the major contributor to AI. In conclusion, these two groups may represent distinct subgroups of OSA patients and provide some insight into the contribution of obesity to the pathogenesis of OSA. The patients with a high AI and low BMI ratio have a skeletal mismatch, whereas the patients with a low AI and high BMI have atypical soft tissue structures.

Cephalometric and demographic characteristics of obstructive sleep apnea: An evaluation with partial least squares analysis

Obstructive sleep apnea (OSA) is caused by repeated obstruction of the upper airway during sleep. The purpose of this study was to test the relative contributions of specific demographic and cephalometric measurements to OSA severity. Demographic, cephalometric, and overnight polysomnographic records of 291 male OSA patients and 49 male nonapneic snorers were evaluated. A partial least squares (PLS) analysis was used for statistical evaluation. The results revealed that the predictive powers of obesity and neck size variables for OSA severity were higher than the cephalometric variables used in this study. Compared with other cephalometric characteristics, an extended and forward natural head posture, lower hyoid bone position, increased soft palate and tongue dimensions, and decreased nasopharyngeal and velopharyngeal airway dimensions had relatively higher associations with OSA severity. The respiratory disturbance index (RDI) was the OSA outcome variable that was best explained by the demographic and cephalometric predictor variables. We conclude that the PLS analysis can successfully summarize the correlations between a large number of variables, and that obesity, neck size, and certain cephalometric measurements may be used together to evaluate OSA severity.