Sleep Apnea (cont.)
How is obstructive sleep apnea diagnosed and evaluated?
History and physical examination
Obstructive sleep apnea can be diagnosed and evaluated
by subjective (perceived or biased) and objective (factual, based on empirical
data) methods. An example of a subjective method that measures the effects
of obstructive sleep apnea on patients is the Epworth Sleepiness Scale.
The Epworth Sleepiness Scale is a self-report test that establishes the severity of sleepiness. A person rates the likelihood of falling asleep during specific activities. Using the scale from 0-3 below, the risk of dozing can be ranked from the chart below.
| 0 = Unlikely to fall asleep |
| 1 = Slight risk of falling asleep |
| 2 = Moderate risk of falling asleep |
| 3 = High likelihood of falling asleep |
| Situation |
Risk of Dozing |
| Sitting and reading |
|
| Watching television |
|
| Sitting inactive in a pubic place |
|
| As a passenger in a car riding for an hour with no breaks |
|
| Lying down to rest in the afternoon |
|
| Sitting and talking with someone |
|
| Sitting quietly after lunch without alcohol |
|
| In a car while stopped for a few minutes in traffic |
|
After ranking each category, the total score is calculated. The range is 0-24, with higher scores suggesting greater sleepiness.
Scoring:
- 0-9 = Average daytime sleepiness
- 10-15 = Excessive daytime sleepiness
- 16-24 = Moderate to severe daytime sleepiness
Breaking it down further, excessive daytime sleepiness is greater than 10.
Primary snorers usually have a score less than 10, and individuals with moderate to severe sleep apnea usually have a score greater than 16. Self reported, subjective measures such as the Epworth Sleepiness Scale usually are combined with a thorough medical history. The history includes questions about:
- work performance,
- daytime sleepiness,
- driving and accident history,
- napping,
- falling asleep during meetings, and
- decreased memory.
Next a physical examination is performed to examine the
areas of possible airway collapse.
- In the nose, this includes the septum,
turbinates, nasal polyps, adenoid hypertrophy, and
nasopharynx (back of
the nose).
- In the mouth, the
palate, tonsils, uvula, pharyngeal
walls, and neck circumference are all examined.
- A flexible nasopharyngoscopy is usually
performed to examine the airway during active breathing and simulated snoring
maneuvers. (The nasopharyngoscope is a fiber-optic, flexible tube approximately
18 inches in length and an eighth of an inch in diameter with a camera on its end. The camera end is inserted through
the nasal passage to the upper throat or
pharynx where the actions of the tongue
and palate can be observed.)
Polysomnography
The primary objective test for obstructive sleep apnea
is polysomnography, also referred to as a sleep study. This test measures
different physical and physiological parameters while a subject is asleep.
During attended polysomnography, a technician observes a person sleeping and
monitors recording equipment in the setting of a sleep laboratory. A typical
polysomnography test includes:
- an electroencephalogram
(EEG) monitors brain waves,
- an electro-oculogram (EOG)
monitors eye movements,
- an electromyogram
(EMG) monitors muscle activity,
- measurement of oral and nasal airflow,
- measurement of chest and abdominal movement,
- audio recording of the loudness of snoring,
- blood oxygen levels (oximetry), and
- video monitoring of the
subject during the study.
The EEG (electroencephalogram) monitors brain waves and
can be used to determine the level of sleep or wakefulness. It is helpful for
determining if an event (respiratory or limb movement) disrupts the level of sleep.
An EOG (electro-oculogram) measures eye movements using sticker electrodes placed next to each eye. During
REM sleep (dreaming sleep), the eyes typically move from side-to-side. This
measurement can help determine the duration of REM sleep.
An EMG (electromyogram) measures muscle movements.
Frequently, an additional monitor is placed on the chin to measure muscle
relaxation (tone). During stage 1-4 sleep there is a baseline muscle tone;
however, during REM sleep all muscles relax. The EMG also helps to determine the
duration of REM sleep. An EMG of the legs can be used to detect "restless legs
syndrome" or periodic leg movements during sleep.
Oral and nasal
airflow can be measured by several different methods to help determine the size
and frequency of breaths during sleep. Chest and abdominal movements occur with
each attempt to breathe and can be used to distinguish between central sleep
apnea and obstructive sleep apnea.
(During central sleep apnea, the signal to take a breath is not given, so the muscles
do not attempt to take a breath. During obstructive sleep apnea, the muscles
attempt to take a breath, but no air moves.)
Measurement of the loudness of
snoring can be used to quantify snoring. (Sometimes a measurement is needed to
convince someone that they have a snoring problem.) It can also be used to
measure changes after treatments for snoring.
Oximetry is used to measure the decreases in oxygen in
the blood during apneas and hypopneas.
The video monitor is most helpful for
detecting movement disorders, parasomnias, or
seizures during sleep. (Often a
patient will not remember sleepwalking, sleep talking,
or other parasomnias, so a video is helpful to review the events with the
patient.)
After polysomnography is completed the data are
analyzed by a board certified sleep specialist. The number of apneas, hypopneas,
leg movements, and desaturations as well as sleep levels are all recorded in a formal
report, and a diagnosis is made.
Although the primary objective test for obstructive sleep apnea is the sleep study (polysomnography);
other tests for obstructive sleep apnea include the:
- Multiple Sleep Latency Test (MSLT) and
- Maintenance
of Wakefulness Test (MWT)
Multiple Sleep Latency Test
For someone who reports being sleepy during the day, it
is sometimes helpful to measure how sleepy they are. Also, after treatment of
sleep problems the doctor may want to measure improvement in daytime sleepiness.
Sleepiness can be measured with a Multiple Sleep Latency Test (MSLT).
Basically,
the MSLT measures how fast someone falls asleep during the day. It must be done
after an overnight sleep study (polysomnography), which documents adequate opportunity
for sleep the night before. The test is composed of four to five naps that last 20
minutes and are spaced two hours apart. The person is instructed to try and fall
asleep. The average time to fall asleep is calculated for all four or five tests.
Normal time would be greater than 10 minutes to fall asleep. Excessive
sleepiness is less than five minutes to fall asleep.
Maintenance of Wakefulness Test
The Maintenance of Wakefulness Test (MWT) also measures daytime sleepiness.
The person in this test is instructed to try to stay awake. This is repeated
for four 40 minute sessions two hours apart. Not falling asleep in all four tests is
the strongest objective measure of no daytime sleepiness.
Some agencies use these tests to ensure that their employees are not
excessively sleepy while at work. Specifically, airline pilots and truck drivers
who have sleepiness need to be tested. This is done for public safety and
work productivity. Unfortunately, there is no test that will guarantee that
someone will not fall asleep at his or her job or while driving.
Severity levels in obstructive sleep apnea
Obstructive sleep apnea can be categorized as mild, moderate, or severe. This
stratification assists in determining the direction of treatment. For example, some
treatments that are excellent for mild sleep apnea nearly always will fail for
severe sleep apnea.
The severity level is measured with polysomnography. In
one grading scale using the apnea-hypopnea index, mild obstructive sleep apnea is 5-15 events
per hour, moderate obstructive sleep apnea is
15-30 events per hour, and severe obstructive sleep apnea is more than 30 events
per hour.
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