Polysomnography (PSG) is a sleep study where several parameters are tested for diagnostic purposes in people with sleeping disorders. This process yields a polysomnogram. The tests records all the biological and physiological changes that take place in your body during sleep. The changes/activities recorded while sleeping include brain waves/ activity, eye movement, muscle movement, heart rhythm, breathing function, and pulse oximetry. The recording can be done at night or during the day for people with circadian rhythm sleep disorders and shift workers. The latter two are very important in diagnosing obstructive sleep apnea.
Which sleeping disorders are diagnosed using polysomnography?
Polysomnography is a very good study to diagnose circadian rhythm sleep disorders, narcolepsy, idiopathic hypersomnia, periodic limb movement disorder (PLMD), Rapid eye movement behavior disorder (RBD), parasomnias, and sleep apnea. The study analyses all the sleeping behaviors and rules out the disorders to give the right diagnosis. However, polysomnography should not be frequently used for people with shift related sleep disorders.
On which people is polysomnography done?
It should only be used in persons with indications requiring polysomnography including sleep apnea, obesity, risky neck circumference and others. Sleep apnea is one of the sleeping disorders best diagnosed using polysomnography. The sleep apnea symptoms include:
- Daytime sleepiness even after sleeping well at night.
- Having frequent and excessive snoring. This may be a complaint from you partner that you produce loud snoring sounds.
- Frequently waking up at night while gasping for air.
- Being restless as you sleep.
- Periodically having a feeling that you can’t breathe while you sleep.
How is polysomnography done?
The study is done using wire channels that are attached to the body and the polysomnography machine. The channels are a minimum of 12 where a minimum of 22 wires are attached to the body. Each of the body changes/activity being investigated uses at least one channel to record and interpolate the change/activity.
The polysomnography machine contains the wires which are connected to a central box which is then connected to a computer. The computer records, stores and displays the resulting data forming the polysomnogram.
The brain activity investigation (electroencephalogram, EEG) utilizes several electrodes where 6 or more are used to investigate any seizures that may occur during sleep. Attached to the scalp the electrodes provide an insight into the brain activity and sorted into the several stages of sleep.
The eye movement study also known as electrooculogram (EOG) has 2 electrodes placed around the right and left eye on the canthus. This checks for rapid eye movements by noting the eye activity.
The muscle movement or skeletal muscle activation investigation (Electromyogram, EMG) is used to check PMLD (periodic limb movement disorder). This is done by checking the excess legs movements as you sleep using 4 or more electrodes. Muscle tension is the indicator checked by these electrodes and during sleep the muscles are supposed to relax thus reducing the muscle tension.
The heart rhythm is investigated by an electrocardiogram (ECG) using two or more electrodes. The electrodes measure the heart’s electrical activity during diastole and systole. The investigation when analyzed can indicate any abnormalities occurring during heath pathology.
The nasal and oral airflow are also measured using either a thermocouple or pressure transducers. The latter is more sensitive. The two are placed inside or around the nostrils. Interruption in breathing is an indicator for obstructive sleep apnea and is as essential as the rate of respiration. Hypopnea which is diminished airflow is sometimes given wrongly as the diagnosis during sleep apnea.
Snoring in some cases is recorded with a sound probe over the neck but the results are recorded as mild snoring, moderate snoring or loud snoring. The level of snoring depends on the snoring sounds produced during sleep. Snoring sounds can also be recorded on a numerical scale of 1 to 10.
How does one prepare for a polysomnography?
The doctor recommending you for a PSG they always give the patients some do’s and don’t’s during the day of the study. These include:
- The patient should not caffeine in the afternoon leading to the study.
- No alcohol too for that day’s afternoon.
- One should not take a nap during the day of the study
- Sedatives are also not recommended during the study day
When is the polysomnography done?
Polysomnography is done in periods where the patient, a partner or the clinician suspects a case of sleep disorder. To ensure that the clinician gets the right diagnosis the study is done. It is done for both adults and children. For children especially it is very important because simple symptoms like snoring can be indicative of a serious underlying problem. The study is done in a lab, at a hotel, at a medical office or at home.
Polysomnography is done in the evening where a period of setting up and sleeping is advised. The home setup is recommended these days for the study to show the sleeping patterns and conditions in the natural setup. It increases the comfort and reduces the cost of the study.
How is the polysomnogram interpreted?
The interpretation is done by a sleep medicine physician. The medical history, drugs and alcohol taken are used for interpretation together with the main sleeping patterns investigated which include:
Sleep onset latency.
This is the period between wakefulness and sleep after lights are put off. The EEG is useful in determining this.
In sleep efficiency an investigation of the ratio of minutes slept in bed sleeping vs the minutes spent in bed is calculated. It is normally supposed to be a minimum of 0.85.
This utilizes data from EEG, EOG and chin EMG. All these data sources are analyzed for every 30 seconds to indicate of the person being investigated is in any of the four stages of sleep (stage 1, 2, 3, and rapid eye movement sleep). The results thus show if the individual is awake, has non-REM sleep (Stage 1, 2 and 3) or has rapid eye movement. The sleep depth increases relatively from stage 1 to stage 3 where stage three is deep sleep. It should be noted that with increase in age the stage 3 and REM decrease. Also most of the time spent during sleep the individual has stage 2 sleep except in infants. Most individuals experience REM for 20 to 25 percent of the sleeping time. Alcohol, anti-depressants and most analgesics among other factors can affect the sleep stages too.
Sleep apneas and hypopneas.
These breathing irregularities affect the airflow to the lungs. The two are reported as a sleeping disorder if a 4 % oxygen desaturation occurs. The difference between the two is that in the apnea there is a complete or near complete cessation of breathing for at least 10 seconds whereas hypopnea is the reduction by 30% or more of airflow for 10 seconds or more. The two are followed by moments of arousal.
Cardiac rhythm abnormalities.
The cardiac rhythm abnormalities recorded are not as much as when a full cardio investigation is being done. These abnormalities are useful in diagnosing the sleep disorder when analyzed with other factors recorded.
PLMD (periodic leg movement disorder).
Legs movements are recorded in the polysomnogram to enable the sleep medicine physician to interpret the movement relative to other factors recorded.
Sudden changes in brain wave activity also known as arousals.
Arousals constitute sleep interruptions. Arousals are caused by many intrinsic and extrinsic factors. The intrinsic ones include apnea, hypopnea and PLMD while extrinsic factors are for example noises in the surroundings.
Oxygenation during sleep.
This is also an indication of breathing problems during sleep. If oxygenation is very low it indicates hypopnea or sleep apnea may be the cause.
Body positioning during sleep.
Most of the time, people snore or get insomnia because of the body position taken during sleep. Having this noted goes a long way in resolving sleeping disorders.
Snoring sounds during sleep.
Snoring sounds are recorded as you sleep. These sounds when interpreted relative to the other factors above are useful in the management of snoring.
What does the sleep medicine physician deduce?
The sleep medicine physician rules out the sleep disorders and offers the right diagnosis. The physician can rule out the conditions below:
- Obstructive sleep apnea. In this case the physician may recommend a CPAP titration study. This CPAP study can also be done in the same night to ensure the patient visits the lab only once cost effectively. This combination is called split night. Polysomnography is also very effective in checking the severity of the apnea.
- Central sleep apnea.
All these conditions diagnosed by polysomnography can be managed using either natural methods, behavior changes or medication. These methods are as described Here
What are the risks associated with conducting a polysomnography?
The procedure is noninvasive and uses electrodes attached to the body. It is therefore painless. It also has almost no complications. The only side effect that is commonly experienced is skin irritation in the areas where the electrodes / test sensors are attached.