Upper Airway Length Research Articles

Residents’ journal review

Residents’ journal review

Comparative study of nasopharyngeal soft-tissue characteristics in patients with Class III malocclusion

The aims of our study were to assess nasopharyngeal soft-tissue characteristics in white patients with Class III malocclusion and to compare the results with patients with ideal occlusion. A sample of 71 patients with Class III malocclusion was selected from the Dental School at the Complutense University of Madrid. None of the subjects had a history of upper airway disease, adenoidectomy, or pathology in the pharynx. Lateral cephalograms were digitized, and linear and area measures were made to define the airway characteristics. Error analysis was performed to prevent systematic or random errors. Independent means t tests and Pearson correlation analysis were used to evaluate sex differences and the correlations among the variables. A discriminant analysis was also used to identify different groups with excellent occlusion and Class III malocclusion. Nasopharyngeal soft-tissue characteristics in Class III subjects were different in male and female subjects. Adenoidal tissue and upper airway length were greater in the men. Three groups of variables tended to be related among themselves but not with others. A discriminant analysis showed that changes in cranial base length are directly related to nasopharyngeal morphology in Class III malocclusion. A discriminant equation was also obtained. This study suggests new lines of investigation about the relationship between skeletal and dental anomalies and airway obstruction, and possible specific respiratory characteristics for each type of malocclusion.

Upper airway changes in severe obstructive sleep apnea: upper airway length and volumetric analyses using 3D MDCT

Conclusion: Three-dimensional multi-detector computed tomography (3D MDCT) analysis of the upper airway suggested that the lengthening of the upper airway in the absence of volumetric change may independently contribute to the severity of obstructive sleep apnea syndrome (OSAS) in adults. Objectives: We sought to investigate the relationships among the length and volume of the upper airway to the severity of OSAS. Methods: A total of 73 subjects underwent 3D MDCT scanning and standard polysomnography. We measured the upper airway length (UAL), which was defined as the vertical distance from the hard palate to the hyoid in the mid-sagittal plane. We also used the height-adjusted UAL for analyses. Upper airway volume was measured using a 3D reconstruction of the cross-sectional area from the hard palate to the hyoid. Results: The adjusted UAL showed a significant positive correlation with the apnea hypopnea index (AHI, r = 0.523, p < 0.000) and was a significant variable for predicting the AHI of OSAS patients in multiple stepwise regression analysis. Although the severe OSAS group had a greater adjusted UAL compared with that of other groups (p = 0.001), the volume of the upper airway did not show differences among groups.

The impacts of open-mouth breathing on upper airway space in obstructive sleep apnea: 3-D MDCT analysis

Open-mouth breathing during sleep is a risk factor for obstructive sleep apnea (OSA) and is associated with increased disease severity and upper airway collapsibility. The aim of this study was to investigate the effect of open-mouth breathing on the upper airway space in patients with OSA using three-dimensional multi-detector computed tomography (3-D MDCT). The study design included a case-control study with planned data collection. The study was performed at a tertiary medical center. 3-D MDCT analysis was conducted on 52 patients with OSA under two experimental conditions: mouth closed and mouth open. Under these conditions, we measured the minimal cross-sectional area of the retropalatal and retroglossal regions (mXSA-RP, mXSA-RG), as well as the upper airway length (UAL), defined as the vertical dimension from hard palate to hyoid. We also computed the volume of the upper airway space by 3-D reconstruction of both conditions. When the mouth was open, mXSA-RP and mXSA-RG significantly decreased and the UAL significantly increased, irrespective of the severity of OSA. However, between the closed- and open-mouth states, there was no significant change in upper airway volume at any severity of OSA. Results suggest that the more elongated and narrow upper airway during open-mouth breathing may aggravate the collapsibility of the upper airway and, thus, negatively affect OSA severity.

Cephalometric Measurement of Upper Airway Length Correlates With the Presence and Severity of Obstructive Sleep Apnea

The purpose of this study was to measure upper airway length (UAL) on lateral cephalograms and to assess its relationship with the presence and severity of obstructive sleep apnea (OSA). Using a case-control study design, the investigators enrolled a sample of cases defined as adult subjects with OSA and controls who were adult patients with skeletal Class II malocclusions. The primary predictor variable was UAL. Other variables were demographic and cephalometric parameters. The respiratory disturbance index (RDI) was used to measure disease severity in cases. Bivariate analyses were computed to evaluate the associations between predictor and outcome variables. Multiple regression analyses were used to provide adjusted measures of association, controlling for the effects of confounders/effect modifiers. Diagnostic test characteristics were computed for threshold airway lengths. P ≤ .05 was considered statistically significant. The sample consisted of 96 cases with OSA (76 males) and 56 controls without OSA (36 males). OSA subjects were older, were predominately male, and had higher body mass indexes and longer and narrower airways (P < .05). After controlling for confounding variables, UALs ≥ 72 mm for males and ≥ 62 mm for females were significantly associated with the presence of OSA (P = .03). The sensitivity and specificity of UAL as a diagnostic test for OSA were ≥ 0.8. UAL was strongly correlated with RDI (disease severity) in males (r = 0.72, P < .01) and moderately correlated with RDI in females (r = 0.52, P < .01). Increased upper airway length was correlated with the presence and severity of OSA in this sample of adult patients.

Development of a Normative Data Set for the Normal Adult Airway Using 772 Cone Beam CT Scans

sized that upper airway length would be longer in patients with OSA and strongly correlated with disease severity. Methods of Investigation: This was a case-control study utilizing a sample of cases defined as adult subjects with OSA, confirmed by polysomnography, and controls who were adult patients with skeletal Class II malocclusions (non-syndromic mandibular or bimaxillary retrognathia) without history or symptoms of OSA. The primary predictor variable was UAL, which was measured as the distance along the long axis of the airway from the hyoid bone to the palatal plane. Two observers, blinded to the disease status of the subjects, independently evaluated airway length to assess the reliability of the measurement method. The technique had a high degree of inter-examiner correlation (intra-class correlation coefficient 0.96, p 0.001). Other variables were demographic (age, sex and body mass index, BMI) and cephalometric (maxillary sagittal position, SNA; mandibular sagittal position, SNB; maxillomandibular relationship, ANB; maxillary length, Co-ANS; mandibular length, CoGn; posterior airway space, PAS; hyoid-mandibular perpendicular distance, HMP; soft-palate length, PNS-SP; maxillary vertical length, S-PNS) parameters. The respiratory disturbance index (RDI) was used to measure disease severity in cases. Methods of Analysis: Bivariate and multiple regression analyses were computed to evaluate the association between predictor and outcome variables adjusted as indicated for confounders or effect modifiers. Diagnostic test characteristics were computed for threshold airway lengths. A p-value 0.05 was statistically significant. Results: Over a five-year period, we identified 96 cases with OSA (76 males) and 56 controls (36 males). OSA subjects were older, predominately male, had higher BMIs, and longer and narrower airways (P 0.05). The OSA group had a mean RDI of 51.3 31.4 events/hr. After controlling for confounding variables, UALs 72 mm for males and 62 mm for females were significantly associated with presence of OSA. Using these thresholds as a diagnostic test for the presence of OSA, the sensitivity and specificity were 0.8. UAL was strongly correlated with RDI in males (r 0.72, p 0.01) and moderately correlated with RDI in females (r 0.52, p 0.01). Conclusion: Upper airway length can be reliably measured on lateral cephalograms and is correlated with the presence and severity of OSA in adult patients.

Soft palate length and upper airway relationship in OSA and non-OSA subjects

The narrowest area of the airway between the posterior nasal opening and the epiglottis is usually located in the retro palatal area. Many consider this the most likely site of airway obstruction during an obstructive sleep apnea (OSA) event. The aim of this study was to investigate the differences in soft palate and airway length between OSA and non-OSA patients. In this study, we analyzed the ratio of the soft palate and the upper airway length in 45 consecutive patients. Twenty-five had an Apnea-Hypoapnea Index of more than five events per hour and were classified in the OSA group (male, 19; female, 6). These patients were compared with 20 normal controls (male, 12; female, 8). Controls who complained of snoring did have sleep studies (n=5). The other fifteen controls were clinically asymptomatic and did not have sleep studies. Medical computed tomography scans were taken to determine the length of the upper airway and the soft palate length measured in the midsagittal image. Soft palate length was significantly larger in OSA patients compared to controls (p=0.009), and in men compared to women (p=0.002). However, there were no differences in airway length. The soft palate length, as a percent of oropharyngeal airway length, was significantly larger in OSA patients compared to controls (p= <0.0001) and in men compared to women (p=0.02). Soft palate length increases significantly with age by 0.3 mm per year in males (after adjustment for body mass index (BMI) and OSA). Soft palate length as a percent of airway length is larger in OSA patients and increases significantly with BMI in males only after adjusting for age. In this study, OSA patients had a longer soft palate in proportion to their oropharyngeal airway compared to controls as well as men compared to women. This proportion could be used for identifying patients at risk for OSA in combination with age.

Upper airway length may be associated with the severity of obstructive sleep apnea syndrome

The exact pathophysiology leading to pharyngeal collapse in obstructive sleep apnea syndrome (OSAS) remains incompletely understood. Prior research has shown that normal men have a longer pharyngeal airway than women, and it has been hypothesized that this difference may play a role in the gender-related differences in OSAS. In the current study, we sought to study the potential relationship between the length of the collapsible pharyngeal segment, the upper airway length (UAL), and the severity of OSAS. The hospital records were searched for all patients who had had polysomnography and also had had a computed tomography of the neck. A total of 24 such patients were identified who participated (15 men and nine women). The UAL, the distance between the lower posterior part of the hard palate bone to the upper posterior part of the hyoid bone, was measured for all participants in the midsagittal plane. A correlation coefficient (Pearson r) of 0.406 was found between Respiratory Disturbance Index (RDI) and UAL (p = 0.049). When UAL was normalized to body height, a correlation coefficient (r) of 0.423 was found (p = 0.039). A gender-related difference in UAL was also found. Men with OSAS were found to have longer UAL even when normalized to body height (p = 0.003, unpaired t test) as compared with OSAS women. This study provides potential clinical relevance to prior studies in normal subjects, by demonstrating that men with OSAS have longer UAL than women with OSAS, independent of body size. In addition, the significant correlation between UAL and OSAS severity suggests that UAL may play a role in the pathophysiology of OSAS. These findings are consistent with our predictions from computational modeling studies.

Influence of Gender and Age on Upper-Airway Length During Development

Obstructive sleep apnea has a strong male predominance in adults but not in children. The collapsible portion of the upper airway is longer in adult men than in women (a property that may increase vulnerability to collapse during sleep). We sought to test the hypothesis that in prepubertal children, pharyngeal airway length is equal between genders, but after puberty boys have a longer upper airway than girls, thus potentially contributing to this change in apnea propensity. Sixty-nine healthy boys and girls who had undergone computed tomography scans of their neck for other reasons were selected from the computed tomography archives of Rambam and Carmel hospitals. The airway length was measured in the midsagittal plane and defined as the length between the lower part of the posterior hard palate and the upper limit of the hyoid bone. Airway length and normalized airway length/body height were compared between the genders in prepubertal (4- to 10-year-old) and postpubertal (14- to 19-year-old) children. In prepubertal children, airway length was similar between boys and girls (43.2 +/- 5.9 vs 46.8 +/- 7.7 mm, respectively). When normalized to body height, airway length/body height was significantly shorter in prepubertal boys than in girls (0.35 +/- 0.03 vs 0.38 +/- 0.04 mm/cm). In contrast, postpubertal boys had longer upper airways (66.5 +/- 9.2 vs 52.2 +/- 7.0 mm) and normalized airway length/body height (0.38 +/- 0.05 vs 0.33 +/- 0.05 mm/cm) than girls. Although boys have equal or shorter airway length compared with girls among prepubertal children, after puberty, airway length and airway length normalized for body height are significantly greater in boys than in girls. These data suggest that important anatomic changes at puberty occur in a gender-specific manner, which may be important in explaining the male predisposition to pharyngeal collapse in adults.

Tracheal and neck position influence upper airway airflow dynamics by altering airway length

Upper airway obstruction during sleep is characterized by inspiratory airflow limitation and reductions in maximal inspiratory airflow (VImax). To determine how mechanical factors modulate VImax, we analyzed pressure-flow relationships obtained in the isolated upper airway of paralyzed cats. VImax and its determinants, the pharyngeal critical pressure (Pcrit) and the nasal resistance (Rn) upstream to the flow-limiting site (FLS), were measured as caudal tracheal displacement, neck position, and airway length were systematically varied. As the proximal tracheal stump was displaced caudally, graded increases in VImax from 145.3 +/- 90.8 (SD) to 285.9 +/- 117.5 ml/s (P < 0.02) and decreases in Pcrit from -3.0 +/- 3.0 to -9.5 +/- 3.4 cmH2O (P < 0.002) were seen without any significant change in Rn. During neck flexion, significant decreases in VImax from 192.1 +/- 68.5 to 87.2 +/- 48.4 ml/s (P = 0.001), increases in Pcrit from -5.3 +/- 2.03 cmH2O to -1.6 +/- 1.4 cmH2O (P < 0.001), and decreases in Rn from 29.7 +/- 12.2 cmH2O.l-1.s to 16.2 +/- 8.9 cmH2O.l-1.s (P < 0.001) were noted compared with the neutral or extended neck position. Relative to the neutral airway length, upper airway length was found to decrease by 1.15 +/- 0.14 cm during neck flexion and to lengthen by 0.45 +/- 0.12 cm during neck extension. When tracheal displacement and neck position were altered, VImax and Rn correlated directly and Pcrit correlated inversely with airway length (P < 0.001). We conclude that alterations in airflow mechanics with caudal tracheal displacement and changes in neck positions are primarily due to alterations in airway length.