Correlation Between the Severity of Sleep Apnea and Upper Airway Morphology
Correlation Between the Severity of Sleep Apnea and Upper Airway Morphology
Purpose of review Recent advances in upper airway imaging allow a better analysis of the upper airway morphology. With the increased accuracy of computed tomography, MRI and other imaging techniques, it becomes possible to identify very local changes in bony structure, soft tissues and lumen of the pharyngeal airway. These advances are able to provide new insights into obstructive sleep apnea (OSA) evaluation and treatment.
Recent findings The present review intends to capture the current status of the research on the correlation between OSA severity and upper airway morphology. Morphological abnormalities that are responsible for OSA differ with age. Therefore, correlations between morphology and OSA in children and adults and the effects of puberty are discussed in different chapters. Literature provides several anatomical correlates that correlate with the severity of OSA but are not able to differentiate healthy individuals from OSA patients.
Summary As anatomical correlates are not able to identify OSA in an individual, their main importance might lie in the selection of the ideal treatment on a patient-specific basis. Several sources report promising results in this use of morphological biomarkers. These, in combination with the new insights gained by the advances in imaging, should be the bases for additional research in the domain of treatment selection and result prediction.
Obstructive sleep apnea (OSA) is a disease that had been described clinically for the first time 30 years ago by Guilleminault et al. and is characterized by repetitive episodes of upper airway obstruction during sleep. OSA is common in the general population with an estimated prevalence of 0.3–5% in adult men, 1–3% in adult women and 1–4% in the pediatric population.
The collapsibility of the pharyngeal airway is increased by a deformed upper airway lumen. Normal individuals have an elliptical shape pharyngeal airway lumen with the long axis in the lateral dimension. For adult OSA patients, the shape becomes more circular or even elliptical with the long axis in the anterior–posterior dimension. It has also been shown with computed tomography (CT) and magnetic resonance imaging (MRI) that OSA patients have an anatomically small pharyngeal airway. This small airway may be due to bony structures; enlarged soft tissues, for example, tonsils, adenoids or tongue; or obesity.
To prevent the airway from collapsing during sleep, several treatment methods have been described. The standard treatment for moderate-to-severe OSA in adults is the application of nasal continuous positive airway pressure (nCPAP). By increasing the pressure inside the airway, the collapse is less likely to happen. Mandibular repositioning appliances (MRAs) are indicated for patients with mild-to-moderate OSA. These appliances alter the position of the mandible in order to increase the pharyngeal airway dimensions. Other devices used for the same purpose include soft palate lifters and tongue retaining devices. The indications for upper airway surgery are controversial and its role in treatment of OSA in obese patients is not well established. Different soft tissues, for example, tonsils, adenoids, uvula or soft palate, are surgically removed to increase again the pharyngeal airway volume. In addition to general surgical measures, also a number of treatments that combine surgery with devices have been reported.
Although CPAP has a high effectiveness in preventing pharyngeal collapse, its limitations include a relatively poor acceptance and compliance. Therefore, an actual effectiveness of only 50% is observed. Similarly, an effectiveness of around 50% for MRAs has also been reported. Sher et al. investigated 37 studies that described the results of an uvulopalatopharyngoplasty (UPPP) to treat OSA surgically. They have reported a combined effectiveness of UPPP in OSA patients of only 40%. Identical issues are faced in the treatment of OSA in children, in whom adenotonsillectomy – the first-line treatment – has an effectiveness of approximately 80% in the general population, but 50% or less in obese children.
As most OSA treatments have a low-to-moderate success rate and the interpatient responses are very inhomogeneous, the great challenge in treating children, adolescents and adults with this disorder is identifying the optimal treatment for each individual patient. Treatment results of OSA largely depend on an individual's morphological status of the pharyngeal airway and its surrounding tissues and bony structures. The aim of this review is, therefore, to give an overview of the morphological parameters that have been reported to correlate with the severity of OSA. Because OSA in children and that in adults are often considered as two separate diseases, the review also focuses on the age differences and the influence of puberty on the upper airway. The review ends with a discussion on new techniques, which could identify the exact morphologic characteristics that are responsible for OSA and which might guide the clinician in the search for the optimal patient-specific treatment.
Abstract and Introduction
Abstract
Purpose of review Recent advances in upper airway imaging allow a better analysis of the upper airway morphology. With the increased accuracy of computed tomography, MRI and other imaging techniques, it becomes possible to identify very local changes in bony structure, soft tissues and lumen of the pharyngeal airway. These advances are able to provide new insights into obstructive sleep apnea (OSA) evaluation and treatment.
Recent findings The present review intends to capture the current status of the research on the correlation between OSA severity and upper airway morphology. Morphological abnormalities that are responsible for OSA differ with age. Therefore, correlations between morphology and OSA in children and adults and the effects of puberty are discussed in different chapters. Literature provides several anatomical correlates that correlate with the severity of OSA but are not able to differentiate healthy individuals from OSA patients.
Summary As anatomical correlates are not able to identify OSA in an individual, their main importance might lie in the selection of the ideal treatment on a patient-specific basis. Several sources report promising results in this use of morphological biomarkers. These, in combination with the new insights gained by the advances in imaging, should be the bases for additional research in the domain of treatment selection and result prediction.
Introduction
Obstructive sleep apnea (OSA) is a disease that had been described clinically for the first time 30 years ago by Guilleminault et al. and is characterized by repetitive episodes of upper airway obstruction during sleep. OSA is common in the general population with an estimated prevalence of 0.3–5% in adult men, 1–3% in adult women and 1–4% in the pediatric population.
The collapsibility of the pharyngeal airway is increased by a deformed upper airway lumen. Normal individuals have an elliptical shape pharyngeal airway lumen with the long axis in the lateral dimension. For adult OSA patients, the shape becomes more circular or even elliptical with the long axis in the anterior–posterior dimension. It has also been shown with computed tomography (CT) and magnetic resonance imaging (MRI) that OSA patients have an anatomically small pharyngeal airway. This small airway may be due to bony structures; enlarged soft tissues, for example, tonsils, adenoids or tongue; or obesity.
To prevent the airway from collapsing during sleep, several treatment methods have been described. The standard treatment for moderate-to-severe OSA in adults is the application of nasal continuous positive airway pressure (nCPAP). By increasing the pressure inside the airway, the collapse is less likely to happen. Mandibular repositioning appliances (MRAs) are indicated for patients with mild-to-moderate OSA. These appliances alter the position of the mandible in order to increase the pharyngeal airway dimensions. Other devices used for the same purpose include soft palate lifters and tongue retaining devices. The indications for upper airway surgery are controversial and its role in treatment of OSA in obese patients is not well established. Different soft tissues, for example, tonsils, adenoids, uvula or soft palate, are surgically removed to increase again the pharyngeal airway volume. In addition to general surgical measures, also a number of treatments that combine surgery with devices have been reported.
Although CPAP has a high effectiveness in preventing pharyngeal collapse, its limitations include a relatively poor acceptance and compliance. Therefore, an actual effectiveness of only 50% is observed. Similarly, an effectiveness of around 50% for MRAs has also been reported. Sher et al. investigated 37 studies that described the results of an uvulopalatopharyngoplasty (UPPP) to treat OSA surgically. They have reported a combined effectiveness of UPPP in OSA patients of only 40%. Identical issues are faced in the treatment of OSA in children, in whom adenotonsillectomy – the first-line treatment – has an effectiveness of approximately 80% in the general population, but 50% or less in obese children.
As most OSA treatments have a low-to-moderate success rate and the interpatient responses are very inhomogeneous, the great challenge in treating children, adolescents and adults with this disorder is identifying the optimal treatment for each individual patient. Treatment results of OSA largely depend on an individual's morphological status of the pharyngeal airway and its surrounding tissues and bony structures. The aim of this review is, therefore, to give an overview of the morphological parameters that have been reported to correlate with the severity of OSA. Because OSA in children and that in adults are often considered as two separate diseases, the review also focuses on the age differences and the influence of puberty on the upper airway. The review ends with a discussion on new techniques, which could identify the exact morphologic characteristics that are responsible for OSA and which might guide the clinician in the search for the optimal patient-specific treatment.