Year : 2009 | Volume
: 20 | Issue : 4 | Page : 487--491
Obstructive sleep apnea: Clinical and diagnostic features
C Sunitha, S Aravindkumar
Department of Orthodontics, Saveetha Dental College and Hospitals, Saveetha University, Chennai, India
Department of Orthodontics, Saveetha Dental College and Hospitals, Saveetha University, Chennai
Obstructive sleep apnea (OSA) is an increasingly common disorder. It is characterized by frequent episodes of airway obstruction associated with a reduced caliber of the upper airway and is vulnerable to further narrowing and collapse. Acute and repetitive effects of apnea and hypopnea include oxygen desaturation, reduction in intrathoracic pressure, excessive daytime sleepiness, impaired executive function and central nervous system arousals.
The apnea-hypopnea index and respiratory distress index help quantify the severity of the condition. The condition is associated with several clinical symptoms of which daytime sleepiness is considered the cardinal symptom. Obesity is one of the major predisposing factors. Three types of apneas have been recognized -obstructive, central and mixed; OSA is the commonest. This review will cover aspects of their radiologic features, diagnosis and management.
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Sunitha C, Aravindkumar S. Obstructive sleep apnea: Clinical and diagnostic features.Indian J Dent Res 2009;20:487-491
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Sunitha C, Aravindkumar S. Obstructive sleep apnea: Clinical and diagnostic features. Indian J Dent Res [serial online] 2009 [cited 2019 Nov 12 ];20:487-491
Available from: http://www.ijdr.in/text.asp?2009/20/4/487/59457
Obstructive sleep apnea (OSA) syndrome is characterized by repetitive episodes of upper airway obstruction that occur during sleep, usually associated with a reduction in blood oxygen saturation.  People with sleep apnea literally stop breathing repeatedly during their sleep, often for a minute or longer and as many as hundreds of times during a single night. 
The severity of the OSA can be assessed using apnea-hypopnea index and respiratory distress index. The apnea-hypopnea index measures the frequency of disordered breathing events but does not quantify other processes that may be operative in the pathophysiology of OSA such as the degree of oxygen desaturation. ,
Apnea is defined as cessation of airflow that lasts for at least 10 seconds. Apnea index is the average number of apneas per hour.  Hypopnea is defined as a significant reduction in airflow lasting at least 10 seconds. Hypopnea is a 30% or greater reduction in flow associated with a four per cent drop in oxygen saturation. Hypopnea index is the average number of hypopneas per hour. 
The American Academy of Sleep Medicine (AASM) rates the average number of obstructive sleep apnea events per hour as respiratory distress index (RDI). , An RDI of 0 to 5 is normal; 5 to 20 is mild; 20 to 40 is moderate and over 40 is considered severe.
The various clinical symptoms observed in patients with OSA presented in [Table 1]. ,,,,,,, The factors that could predispose for the occurrence of OSA are presented in [Table 2]. ,
Types of Apnea
The different types of apnea are obstructive, central and mixed. 
Obstructive sleep apnea occurs due to obstruction caused by collapse of soft tissue structures in the oropharynx or hypopharynx.  These include the base of the tongue, soft palate with uvula, tonsils, epiglottis and pyriform sinuses. The base of the tongue is a common site of hypopharyngeal obstruction in sleep apnea. The possible causes of obstruction in this type of apnea are 
Nose: Deviated septum, enlarged turbinates, polyps.Nasopharynx: Enlarged adenoids.Pharynx: Enlarged tonsils, enlarged uvula or soft palate, enlarged base of the tongue, tongue base falling into pharyngeal airway, submucosal fat or redundant mucosa.Larynx: Laryngopharyngeal reflux changes with severe posterior commissural swelling.
Central sleep apnea occurs when the brain fails to send appropriate signals to the breathing muscles to initiate respiration.  It is often secondary to central nervous system diseases such as infarction and infection involving the brain stem or due to neuromuscular diseases involving respiratory muscles.
Mixed apnea starts as unobstructed apnea which is quickly followed by thoracoabdominal movements with upper airway obstruction.  Mixed apnea occurs more often than central but less often than obstructive apnea.
The common radiographic of OSA are present in [Table 3]. , The other characteristics that may be seen in these patients are nasal airway obstruction  and oropharyngeal abnormalities  (elongated soft palate, medially and posteriorly positioned posterior faucial pillars, enlarged adenoids, hyperplastic tonsils, macroglossia). Apneic children have been found to have longer hyoid- mandibular plane distance. A descending position of the hyoid with increasing age is thought to be caused by the tongue's increase in bulk and becoming larger in relation to the intermaxillary space, a trend that is pronounced in males. ,,,,,,,,
Physical examination is frequently normal in OSA other than the presence of obesity (defined as a body mass index greater than 28 kg/m 2 ) and neck diameter greater than 16 inches.  The upper airway should be evaluated in all patients, particularly in nonobese adults, for features associated with the presence of OSA such as: 
Narrowing of the lateral airway walls, which is an independent predictor of the presence of OSA in men but not womenEnlarged tonsilsRetrognathia or micrognathiaSoft palate edemaHigh, arched hard palate
These patients may have an enlarged uvula or tonsillar hypertrophy. An elongated soft palate that rests on the base of the tongue is another cause of airway obstruction sometimes seen in patients with sleep apnea.  Professional groups recommend that patients with suspected OSA undergo a complete physical and otolaryngologic examination including medical history and determination of body mass index (BMI). 
The chances of dozing off is assessed in each of the eight situations presented in [Table 4] and [Table 5]. The Epworth sleepiness scale (ESS) is calculated as the sum of the chances of dozing off scores in each of the eight situations. 
A score of more than 10 on the Epworth scale is considered pathological and indicates that a sleep specialist should be consulted. ESS score in various conditions is presented in [Table 5]. ESS is also useful in evaluating response to treatment. The score in ESS should decrease with effective treatment.
Overnight polysomnography (PSG) is considered the gold standard in diagnosis of sleep apnea.  Sleep polysomnography features electrocardiography, brainwave electroencephalography (EEG) measurements, motor activity extremity measurements, diaphragmatic/chest movement, eye movement, pulse oximetry for oxygen desaturation measurement, and inhalation/exhalation oro-nasal flow characteristics. 
All the information collected provides a detailed account of the number and severity of the apneas/hypopneas occurring during sleep and their effects on the body's oxygen level, sleep stages as well as arousals. An individual is diagnosed to be sleep apneic if there is cessation of air flow for 10 seconds, five or more episodes of apnea per hour, and/or decrease in oxygen saturation of at least 4% during episodes.
However, polysomnography does not provide data for patients who have mild OSA but do not experience any episodes during the sleep study. Therefore, a polysomnogram must be interpreted with the entire clinical picture in mind. It is also expensive and labor intensive.
The only alternative to polysomnography at present is a procedure called overnight oximetry which measures a patient's oxygen saturations throughout the night. , Home studies may be useful in patients who have more severe sleep apnea with significant oxyhemoglobin desaturation which is easy to document with fewer parameters. Home evaluation is useful when the results are clearly positive. However, negative results do not rule out the presence of a sleep disorder. Oximetry is not valid in those receiving oxygen therapy. It can be used to screen before ordering a sleep study since it has a high negative predictive value and is inexpensive.
Multiple sleep latency test
Multiple sleep latency test (MSLT) measures the speed of falling asleep.  A multiple sleep latency test may also be performed to assess the level of daytime sleepiness. The average adult requires 10 or more minutes to fall asleep during the day. A mean sleep latency of less than five minutes is considered abnormal. The MSLT may be useful to measure the degree of excessive daytime sleepiness and to rule out other types of sleep disorders.
MSLT consists of four to five naps of 20 minutes duration every two hours during the day. The latency to sleep onset for each nap is averaged to determine the daytime sleep latency. Normal daytime sleep latency is greater than 10-15 minutes. OSA is generally associated with latencies of less than 10 minutes.
Radiographs that have been found to be useful include lateral neck films that can demonstrate adenotonsillar hypertrophy and other airway lesions. ,,
Computed tomography (CT) scans have high spatial resolution and provide tomographic images often used to diagnose pharyngeal obstruction. However, CT scan provides only axial images and cannot image the entire pharyngeal airway in a single plane. It has been reported that on CT examination, reduced pharyngeal size is correlated with increased sleep disordered breathing rates and more severe nocturnal desaturations. The drawbacks include radiation exposure, expense and that it is a non-dynamic study. In 1987, Stein et al.  reported that CT scan may be a useful tool to determine the obstructive site.
In 1992, ultrafast MRI was reported to have the advantages of being noninvasive with high contrast resolution and allows scanning in multiple planes, allowing the whole airway to be visualized at one time.  It is a non-invasive modality that allows examination of the entire pharynx in multiple planes and in a short time with no radiation exposure as compared to CT. It provides good temporal and high contrast resolution. If the pharyngeal cavity is seen to be disappearing in trans-axial and sagittal planes, obstruction is diagnosed. Narrowing is said to be present if the pharyngeal cavity disappears only in one of the images and if there is more than 50% reduction in the pharyngeal space during sleep as compared to maximum area seen in wakeful state.  Reduction in airspace of up to 50% is considered normal.  The sites of obstruction during sleep are identical to those of narrowing during wakefulness in only 31% of cases. , In other patients, obstruction occurs only after sleep. As the functional factor is different during sleep and wakefulness, imaging should be done in both states. MRI is the best non-invasive modality for evaluation and follow-up of patients with obstructive sleep apnea.
Flexible fiberoptics provide a dynamic examination of the upper airway.  Rigid bronchoscopy and laryngoscopy under general anesthesia with spontaneous respiration may be necessary in children where the site of obstruction cannot be determined by physical examination or radiographic studies. The use of fluoroscopy in awake and sleeping children has also been reported and is a useful and non-invasive technique to evaluate the airway.
Upper Airway Resistance Syndrome
Upper airway resistance syndrome (UARS) is characterized by repetitive arousals from sleep that probably result from increasing respiratory effort during narrowing of the upper airway.  These patients suffer the same sleep disruption and deprivation as other sleep apnea patients. In such cases, the only abnormality that appears on the polysomnogram is recurrent arousals. It is possible to measure an increase in the negative pressure exerted by the patient in an effort to breathe against increasing resistance as the airway narrows. This measurement of inspiratory pressure is not usually done during a standard polysomnogram. Patients with upper airway resistance syndrome, therefore, constitute a group whose OSA could be easily missed by the polysomnogram. Patients with UARS have arousals during sleep related to the abnormally increased work of breathing and increased upper airway resistance. Yet their number of disturbances per unit time, may remain normal.
As dental professionals, we have a significant role to play in the early diagnosis, management and care of patients suffering from sleep apnea. Many treatment approaches have been used in the management of this condition. The success rates of these procedures are, however, relatively low. Oral appliances play a major role in the non surgical management of OSA and have become the first line of treatment in almost all patients suffering from OSA. Of all the oral modalities of treatment, continuous positive airway pressure (CPAP) is considered to be the most effective for management of OSA.
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