A polysomnogram is a sleep study conducted in a facility in which the patients stay overnight under the supervision of a trained sleep technologist. Many lines of data are collected, and this is probably the most reliable sleep study.
Sensors or electrodes collect information from the brain, producing an EEG (electroencephalogram). From the EEG, it may be determined whether the patient is asleep or awake. If asleep, the stage of sleep is then determined and whether REM (Rapid Eye Movement) is present, which is when dreaming usually occurs. Clearly, sleep apnea refers to events during sleep, not wakefulness, and sleep apnea is usually worse during REM. The EEG can also detect seizures that may be confused with other sleep events such as REM Behavior Disorder that also has a characteristic EEG pattern. Other illnesses such as Fibromyalgia have a recognizable pattern. It is best to collect EEG data in a facility, since portable or home testing is often not adequate and overall not cost-effective. A trained sleep technologist must apply the sensors or electrodes and maintain them throughout the night.
Sensors are placed slightly in the nose (like oxygen cannulas) and partly over the mouth (to detect mouth breathers). In this way, airflow or air passing in and out of the nose and mouth is recorded. This data is combined with information from belts around the chest and abdomen that indicate air moving in and out of the lungs or effort of breathing. If there is no air flow at the nose/mouth (apnea) but the belts indicate chest and abdominal effort, then this is an obstructive apnea, or obstruction in the back of the throat. If there is no airflow and no belt motion or lack of any breathing effort then this is a central apnea, or the brain did not give an adequate command to breathe. It is important to distinguish between these two apneas, since they are treated differently. Obstructive apneas characteristically involve snoring, while central apneas usually do not.
A very important sensor, an oximeter, is placed over a finger to detect oxygen saturation and pulse. Apneas (by definition, lack of breathing ) can lower oxygen if they last long enough, usually more than 10 seconds. A patient with obstructive sleep apnea will intermittently lower his or her oxygen saturation during the night, especially during REM and while supine (lying on his or her back).
An electrocardiogram (EKG or ECG) is also recorded, since apneas can lead to arrhythmias, in particular Atrial Fibrillation, which needs to be treated.
Sensors are placed over the legs to detect leg movements that can disturb the patient's sleep. The wires from these sensors are all placed on a jack box and this in turn is plugged into an amplifier. Then the signals are transmitted to a computer. If a patient has to go to the bathroom, it takes only a few seconds to unplug the jack box and place it around the patient’s neck like a large necklace, and the patient can go to the bathroom.
Usually the patient arrives at the sleep lab in the early evening and leaves in the early morning. Sensor paste in the hair and body can easily be removed with water. In our laboratory we do not use oil-based glues to hold sensors or electrodes in place.
Some patients worry about not being able to sleep at the lab, but more than 90% do, since sleepiness is one of their main complaints to begin with. Rarely, a mild, short-acting, modern sleeping pill that minimally affects the sleep information obtained is used to induce sleep.
Polysomnograms can be done to diagnose sleep problems, treat them, or follow up and monitor them. Often, a diagnostic study is done to document sleep apnea and its severity, and then a titration (therapeutic study) is done, whereby PAP (either CPAP, continuous positive airway pressure, or "BIPAP," bilevel positive airway pressure) is used to control the sleep apnea. Sometimes, both may be accomplished in one night using a split night study. In a split night study, half of the study is diagnostic and the other half is therapeutic, but the study is performed in a single night. The right conditions must be present in order to be able to conduct a split night study.
Portable or Home Testing:
Testing at home can be done using oximetry alone or oximetry with airflow (sensors at nose or mouth) and effort (belts around chest and abdomen) information. Other data can be gathered at home, but the information becomes progressively more expensive to obtain, more prone to problems, and more difficult to interpret. Usually, EEG (brain) data is not collected, so it’s not clear when the patient is asleep or awake or how the data correlates with the sleep state.
Patients must be carefully screened for home sleep testing. The elderly, children/teenagers, patients with cardiopulmonary or neurological problems, those with little if any snoring, uncooperative patients, and patients with other potential sleep problems (parasomnias, narcolepsy, periodic leg movements) are not good candidates for home testing. Patients who have had prior problems with testing or treatment of sleep apnea are also not good candidates for home sleep testing.
Portable home testing is more for the young or middle-aged obese patient who snores loudly, stops breathing at night, and is inappropriately sleepy during the day. Thus, there is a strong suspicion of “pure” obstructive sleep apnea. If this patient is otherwise healthy (no cardiopulmonary or neurological disease, no use of alcohol or drugs, and no suspicion of other sleep problems), then Obesity Hypoventilation Syndrome (shallow breathing) and severe hypoxemia (low oxygen) should be ruled out, and the patient is a candidate for portable testing to diagnose sleep apnea. Home sleep testing does not rule out sleep apnea (though some insurances misinterpret this), but can rule it in. It is also problematic to rule out sleep apnea using home testing in a symptomatic patient with a "critical occupation" (pilots, truck or bus drivers, etc.). If sleep apnea is found, then documented treatment can follow. But if the test is negative, then many authorities would still want a polysomnogram monitored by a sleep technologist in a sleep lab setting. The same line of thinking applies to a dangerously symptomatic (obese, loud snoring, stops breathing, fell asleep while driving) patient with a negative home test. With home sleep testing, patients usually need to apply the sensors themselves and keep them on the whole night, so it is not rare to end up with inadequate data collection.
Treatment is another matter, Here, the physician can make an educated guess as to the PAP (positive airway pressure) settings or whether an “auto-PAP” can be used. An auto-PAP is a “smarter” (technologically advanced) machine that decides its own settings within a range prescribed by the physician. Close follow-up is necessary. Also, the physician needs to guess which mask (nasal pillows, nasal mask, or full face mask — covering nose and mouth) should be used. In the overnight polysomnogram, both the settings on the PAP machine and the mask are carefully selected and proven to work.
Many patients refuse to go to a facility to undergo an overnight study, while others may not have the proper insurance or financial resources. However, given the number and types of available tests, more expertise in the field of sleep medicine is required, not less. The physician must know which test to use, under which circumstances, and in which patient, and then weigh the validity of the results.
An abnormal overnight oximetry (assuming the patient was mostly asleep) by itself only means that the patient’s oxygen saturation dropped during the night. This could be due to obstructive or central sleep apnea (or a mixture of the two), or to lung disease, heart disease, neurological disease, drugs, obesity itself, infection, or technical problems with the study creating artifacts. There are certain characteristic desaturation patterns of sleep apnea, but these aren't specific without data also showing the airflow obstruction causing these oxygen desaturations. Clearly, the study itself is not as important as the physician interpreting the study, who should have considerable experience and knowledge about sleep medicine. (See Instructions for Oximetry under the FORMS tab)
Sleepiness during the day (EDS or excessive daytime sleepiness) is one of the hallmark symptoms of sleep apnea. It is documented by a Sleepiness Questionnaire. The questionnaire most commonly used is called the Epworth Sleepiness Scale, which most patients fill out (or the provider does). It’s very helpful if the patient is quite sleepy, but many patients underestimate their sleepiness or are very good at covering it up. Sometimes they confuse it with fatigue. Often, the spouse or another person is a more reliable source of information and can describe the sleepiness better than the patient. With treatment, the sleepiness usually improves, though this may take days to months.
Lack of daytime sleepiness does not rule out sleep apnea, and patients may deny sleepiness altogether — particularly those patients with heart or lung disease or active lifestyles. Often it is only after treatment when the patients are able to compare the difference that they finally acknowledge their sleepiness and fatigue before treatment.
It is sometimes very difficult to distinguish sleepiness from fatigue or just being plain tired. If patients actually fall asleep when they are relaxed and passive (after lunch in their recliner, for example), then sleepiness is indeed involved. Otherwise, it can be difficult to distinguish.
Daytime sleepiness can be caused by many disorders, including sleep apnea, insomnia of any cause, Restless Legs Syndrome/Periodic Leg Movement Disorder, drugs and medications, psychiatric (depression) and psychological (boredom) conditions, sleep deprivation, neurological conditions (narcolepsy), and circadian rhythm disorders (shift work, sleep phase disorders). It is the responsibility of the physician to tease out the cause, prove it (diagnose), manage it, and improve the patient.
Snoring is the second hallmark symptom of obstructive sleep apnea when it arises in the back of the throat. Snoring can also arise in the nose. It is usually worsened by alcohol, colds, allergies, sleeping on the back (supine), gaining weight, and aging. Women snore less loudly than men and admit it less, but are more prone to it during pregnancy and after menopause. It should be emphasized that snoring is not a major symptom of central sleep apnea. Using PAP therapy usually completely eliminates the snoring in obstructive sleep apnea, and thus the bed partner is very thankful. Throat surgery ameliorates the snoring but does not necessarily treat the sleep apnea. Snoring is difficult to document, but in the lab snoring sensors are used.
General medical and sleep questionnaires are also necessary for the patient with suspected sleep disorders. (See the FORMS tab). As noted above, there are multiple causes of sleepiness and snoring, while almost any disease and drug can impact sleep and its disorders.
(See also www.sleepeducation.com).