ORLANDO, FL-More is being learned about sleep and how it relates to otolaryngology. At the recent Combined Otolaryngology Spring Meeting, attendees heard details about how the different stages of sleep affect obstructive sleep apnea (OSA), as well as intriguing findings showing how airway anatomy changes can actually be seen during sleep with use of real-time CT imaging.
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July 2008To set the stage, at the Triological Society section at the conference, Andrew Kleinberger, BA, a fourth-year medical student at New York University School of Medicine, described details about sleep stages, and presented details of a study that provides some clinical predictors of impaired sleep architecture.
When patients present with sleep-related complaints, and there is a low suspicion of obstructive events, should a sleep study be ordered? This is a common issue in the otolaryngologist’s office, and one that can be resolved if there are some clinical predictors on hand to watch for.
First, Mr. Kleinberger explained that sleep architecture refers to the overall structure of sleep. A standard hypnogram will show that sleep is broken up into stages, alternating between REM and non-REM (stages 1 and 2, or light) [light]) sleep, and stages 3 and 4, or slow-wave sleep. Impaired sleep architecture has less slow-wave sleep and REM sleep-thereby becoming a lighter, less restorative sleep.
In severe obstructive sleep apnea, the length of the slow-wave sleep can actually be completely obliterated, and the REM is decreased, with a compensatory increase in stage 2 and light sleep, he said.
Implications for the Otolaryngologist
For the otolaryngologist, sleep issues are important because sleep-related complaints are common, plus sleep architecture has been shown to be associated with sleep-disordered breathing.
But not all sleepiness indicates obstruction. Impaired sleep architecture can be a marker for non-sleep-disordered breathing conditions such as smoking and alcohol use, comorbid psychiatric and system illnesses, or other stressors, Mr. Kleinberger said.
When Should Sleep Studies Be Done?
To help resolve the question of when patients should be sent for sleep studies, a prospective study was done of 211 consecutive patients who underwent overnight polysomnography at a university sleep disorders center. Patients were excluded if a sleep study was ordered for suspicion of either a central sleep disorder, such as insomnia or narcolepsy, or periodic limb movement disorder. They were also excluded if they had a known diagnosis of OSA, or were undergoing polysomnography for the purposes of conducting a continuous positive airway pressure (CPAP) titration.
The patients had a mean age of 47.5 years, 70% were male, and the population had a mean body mass index (BMI) of 30.2. The sleep study showed the patients had a mean Epworth score of 10.6; a mean apnea-hypopnea index (AHI) of 21.4, and a mean respiratory disturbance index (RDI) of 33.4. The mean snoring severity score was 4.9.
Of this cohort, 70 percent went on to receive a diagnosis of obstructive sleep apnea, Kleinberger said. Sleep architecture was impaired in this group, too. Compared to normative data from the Sleep Heart Health Study, our cohort experienced significantly more light sleep, less slow-wave sleep, and less REM sleep. These differences were highly significant, he said.
In brief, age, Epworth score, and snoring score were the most significant predictors of impaired sleep architecture. Not surprisingly, AHI and RDI also correlated with impaired sleep architecture.
If a clinician encounters a patient in the office with vague sleep complaints, he or she should consider ordering a sleep study if [any of] the following is present: older age, high Epworth score, or high snoring severity score. It’s these patients who will be more likely to display impaired sleep architecture, he said.
Mr. Kleinberger noted (this was not part of the study), Seventy-two patients with obstructive sleep apnea underwent UPPP [uvulopalatoplasty], and sleep studies before and after that. And they were found to have improved sleep architecture after UPPP.
Real-Time MRI Shows Obstruction in Action
When it comes to knowing just how severe a patient’s apnea is and what happens during an event, it is always good to be able to see the anatomy. Even better is being able to measure arousals and relating that to what is happening at the site of obstruction. Combining real-time (RT) MRI (which is excellent at showing soft tissue dynamic obstruction) with peripheral arterial tone (PAT) may be the answer. Watch-PAT detects and records arousals from sleep, and RT-MRI is a real-time imaging acquisition program using MRI to acquire up to 33 frames per second.
Jose Barrera, MD, an instructor of sleep surgery and facial plastic surgery at Stanford University, presented findings from a preliminary study to determine just how well RT-MRI combined with autonomic measures during natural sleep could predict the precise site of obstruction in OSA patients.
A prospective study of 17 OSA patients was performed to demonstrate the feasibility of this technique. They were all OSA patients with a mean BMI of 27.5, and had a mean AHI of 36.8 events per hour. For the study, patients underwent continuous RT-MRI monitoring during a 90-minute nap without sedation, their upper airways were visualized in real-time, and Watch-PAT measurements were attained at the same time.
Autonomic measures showed the patients had mean respiratory events of 31.9 per hour per subject, and had mean desaturation of 19.4 per hour per subject. The RT-MRI showed the specific location of airway obstructions with a high degree of precision, Dr. Barrera said.
During an obstructive event, the real-time MRI coincided with the real respiratory event, he said. The obstruction coincided with respiratory and desaturation events. Importantly, sleep MRI during natural sleep targets the actual site of obstruction and the potential of predicting successful surgical outcomes, he said.
The advantage of this approach is that by seeing dynamic obstruction in real time, the etiology of obstruction is elucidated. Static MRI is performed in an awake patient and doesn’t show movement, while sleep MRI is performed in a sleeping patient showing movement in real time. The site of obstruction is clearly seen, he said.
Surgeons would know exactly what happens when an obstructive event occurs, and this would help with planning the surgery. There could well be a role for sleep MRI in OSA patients.
©2008 The Triological Society
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