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The idea of someone watching you while you sleep can be more than creepy. What if this person would be wearing a white coat and he’d be in the next room because his profession demands it? The visual is nonetheless unnerving.
The idea of sleeping on a strange bed, in a sterilized environment, possibly with monitors surrounding you, and electrodes on various parts of the body. You might wonder what good such a simulated sleeping process might bring. However, that is the standard setup for polysomnography.
What are Polysomnography and Polysomnogram?
Polysomnography translates to the observation of various stages of sleep as the subject transitions from one to another during sleep. The report of this study is a polysomnogram. It is necessary for anyone suffering from sleep-related issues to participate in one since it gives the sleep expert and your doctor a keen look at the abnormalities in brainwaves, breathing or movements during sleep. During a PSG a doctor measures the following.
- Skeletal muscle activity
- Oxygen levels in the blood
- Rate of breathing
- Palpitation levels
- Eye movement during REM
The objective of PSG is to measure the changes in the body and the brain of a subject during the transition from NREM to REM. More specifically, between the slow wave (deep) sleep and REM stage.
The Mechanics of sleep and Decoding it with Polysomnography
Polysomnography or PSG includes a complete study of biophysiological changes of sleep. Although the classic PSG study happens during the night, some laboratories accommodate shift workers, delayed sleep onset syndrome patients, and people with circadian rhythm disorders during other times of the day to study their sleep patterns.
It is a comprehensive process that considers many studies including electroencephalogram or EEG (brain activity measurement), eye movement (EOG), muscle activation and activity (EMG), and heart rhythm (ECG). After the scientific discovery of sleep apnea, breathing function tests, and respiratory effort indicators also became an integral part of the PSG test.
The Anatomy of Dreaming
Typically, REM is responsible for most of our vivid and bizarre dreams. We also experience rapid random eye movements in coordination with the visuals. The average sleeper, without any sleep-related problems, should experience about six REM cycles per night. They can switch between NREM and REM seamlessly.
It would be wrong to state that people do not dream during the NREM cycles. However, during this period, our body does not experience atonia or complete loss of muscle control. It is albeit rare. You have most likely experienced NREM dreams more than once. It is not a deep sleep state, and the sleeper wakes up easily upon slight noise or external movements.
The EEG of the brain during the Stage 2 of NREM sleep is intriguing since it shows K-complexes and high-frequency brainwaves, in short bursts. Sleep experts show increasing interest in Stage 3 of NREM sleep. In this stage, people are more likely to dream and experience parasomnias. Since this stage does not impose atonia, there is a chance that people who suffer from parasomnia move about, talk, walk, or grind their teeth while dreaming.
Earlier two distinct stages comprised stage 3, but right now the slow wave sleep and delta wave sleep occur back to back. However, people are less likely to remember their episodes of parasomnia including night terrors, sleepwalking, and sleep talking since the dreams are disjointed and less memorable.
Multi-phasic Sleep and Brainwave Studies
The vividness of dreams during the REM cycle enables us to remember them to the finest detail. The frequency of recollection of such dreams shows that most people tend to dream more during REM phases. Dreaming during the NREM stage usually occurs during the morning hours.
A comprehensive study on healthy subjects without parasomnia involved the segregation of sleep into only REM and only NREM stages. Using polysomnography and EEG, it was clear that when the subjects entered the forced NREM stage, they experienced a sub-cortical activation similar to that experienced during REM stages. That event leads to the genesis of dreams during the wee hours in the morning during regular NREM sleep as well.
Even though we have kept the explanation of NREM and REM stages brief, it is enough to understand that there are several interlinked factors at play here. Sleep is anything but the sweet release and escape into the dream world we thought it would be.
Several idiopathic disorders, secondary diseases, and external factors disrupt the quality of our nightly slumber. In fact, there are people out there, who have not experienced a good night’s sleep in years. Nightmares, night terrors, somnambulism or dream-induced movements plague their nights and keep their co-sleepers annoyed as well.
Why does Insomnia not Warrant Polysomnography?
You must remember that insomnia is the term that describes the gross lack of sleep. In cases of insomnia, people are unable to fall asleep and staying asleep. It is a complex disorder that can increase fatigue-related symptoms, decrease energy, reduce cognitive abilities and induce mood swings.
All in all, people suffering from this disorder are highly likely to feel unsatisfied with their sleep duration and quality. However, sleep experts have not noticed any kind of sleep-related abnormal behavior among insomniacs. Sometimes, the symptoms of insomnia disappear just as unannounced as they arrived. That is a classic case of acute insomnia. In other cases, the disorder persists for days, weeks and even years at times.
Once a person experiences sleepless nights for longer than three months, a doctor pronounces him an insomniac. The usual treatment can be as simple as sleeping medications, or as complex as sleeping behavior therapy, psychological counseling, and supportive medicines, depending on the cause of the disease.
In most cases, chronic insomnia is comorbid, i.e., it occurs as a side effect of other disorders like high blood pressure, hyperthyroidism, dyspepsia, depression, and bipolar disorders. Therefore, the treatment of it is more complicated than acute insomnia. Your sleep specialist will need to speak with you in detail about your sleeping habits, recurrence of sleeplessness, history of insomnia in the family, and discuss the treatment plan in detail.
What is the Necessity of Polysomnography?
As you can understand from this, the inability to fall asleep at a socially acceptable time, remain asleep for the desired duration and waking up earlier than desirable can qualify as insomnia. The signs of insomnia are quite visible, and doctors can find out if you have it once they start learning about your daily habits, including bouts of sleeplessness and sudden awakenings during the night. Diagnosis of it usually does not require sophisticated, comprehensive testing like PSG. Even the usual complaint of fatigue does not demand a PSG.
A comprehensive set of tests like the ones that make up PSG are typically used for the detection of the more complex interlink of disorders including restless legs syndrome (RLS) or periodic limb movement disorder (PLMD), narcolepsy, idiopathic hypersomnia, idiopathic parasomnia, REM sleep behavior disorder (RBD), and sleep apnea. These disorders are quite complicated since they involve multiple stages of sleep, or they are the result of the discomfort caused by secondary diseases of the body.
Although doctors do not run PSGs on people complaining about circadian rhythm disorders, this test can rule out the ones as mentioned earlier. That is a method of detection by the rule of elimination.
What is the Mechanism of a Standard Polysomnogram Test?
The setup and mechanism of the process are quite complicated. A polysomnogram will include the recording of minimum 12 channels. That would require a 22-wire attachment to the patient. The number of channels and wires will vary between two laboratories.
The preference of the doctors will determine the nature of the channels and the placement of the wires. Here’s a brief idea about the minimum number of channel requirements and their purposes.
- Three channels for EEG.
- Two channels measure the eye movements during the EOG.
- The number of channels can vary between one and two for the airflow measurement.
- A doctor may recommend one or two channels for the study of chin muscle tone.
- At least one muscle measures the leg tone.
- Minimum one lead measures the heart rate and palpitation.
- The belts require one channel each since they measure the chest wall and upper abdominal wall movement.
- One channel measures the saturation of oxygen.
All of them accounts for the minimum 12 channel requirements in every sleep clinic.
In most cases, the piezoelectric sensors measure the movement of the belts. Sometimes, respiratory inductance plethysmography replaces these sensors for the same purpose. The action produces low-frequency waveforms as per the inhalation and exhalation. It is possible for this method to give rise to artifacts, especially during the study of obstructive apnea cases.
What are the Critical Parts of a Polysomnogram?
Each channel has multiple connecting wires that lead to the central box. The central box has a direct connection with the computer that displays, records, analyses, and stores relevant patient sleep data. When the subject is asleep, the monitor displays data sets from several channels simultaneously.
Most sleep clinics and laboratories have small video cameras in the sleeping chamber that can observe the patient’s movements and convey their dialogs during sleep-talking to the next room. It is a wholesome system that accounts for all sorts of physical and physiological changes during the patient’s slumber.
Measurement of Brain Activity with EEG
The standard EEG process uses six exploring electrodes. It also employs two reference electrodes, unless the doctors suspect a seizure disorder. In the event of a seizure during sleep, more wires are necessary to monitor brainwave activity. These exploring electrodes go on the possible frontal, central , and occipital regions of the skull. The paste that holds these electrodes in place will conduct the electric impulses that originate from the neurons of the cranial cortex.
These exploring electrodes send the signal according to brain activity that represents different stages of sleep. An expert can easily tell these signals apart depending on which stages they belong. EEG helps in studying the brain activity of the different N1, N2, N3 (NREM) and REM stages of sleep.
EOG Measures the Electric impulses of the Eye Movements
The electrooculogram (EOG) measures the extent of eye movement during the REM sleep. This process uses two electrodes. The expert places them about 1 cm above the outer corner and 1 cm below the lower edge of the right and left eyes respectively. Each electrode picks up on ocular activity. It is possible to detect something as minute and delicate due to the subtle potential difference between the retina and cornea (the latter has a positive charge).
When REM sleep occurs, there is rapid eye movement that alters the potential difference and sends electric signals across through these leads. Therefore, the observers can quickly tell when REM sleep begins and how long it extends.
EMG monitors the Skeleton-muscular Activity
While studying the quality and quantity of sleep, there is no way one can miss out on the study of muscle activation. The classic definition of REM states that during this period, there is a complete loss of muscle activity or the onset of atonia.
NREM period does not have atonia, and it is possible for people to move their body during the N1, N2, and N3 stages. However, people with periodic limb movement disorders and RLS can move their legs even when they are fast asleep. There are several instances when a person has been able to move his or her legs (and sometimes their hands) during sleep.
Such situations indicate abnormal muscle tension that should not have been present during this stage of sleep in the first place. Ever since we were children, we have associated rest with relaxation. It is not wrong to believe that sleep involves complete relaxation of muscles. In fact, when you dream of running behind another person, the only reason we do not run in our real life is that we lose complete control of our muscular activity. You could think of it as partial paralysis unless the person suffers from REM behavior disorder (RBD). In RBD, a person can talk, sit up, walk around, eat and even hit others during his or her sleep.
ECG or EKG Observes the Heart Activity During a PSG
A standard ECG procedure involves ten electrodes. Polysomnogram uses only about two or three for the entire process. The medical professionals usually place one wire under the collarbone, on each side, and one about six inches above the waist on the left and one on the right.
As the heart goes through its systolic and diastolic motions, these electrodes measure the movement. The result is in the form of a graphic wave that has distinguishing features like the P wave, QRS complex, and the T wave. The duration of each motion translates as the troughs and crests on the electrocardiogram.
Any abnormalities in the structure of the wave corresponds to the irregularity in the heart function. Since each node denotes a particular feature of the heart, doctors can figure out the underlying pathology from the ECG.
Measurement of Respiratory Factors
The analysis of oral and nasal airflow is crucial during sleep. People, who sleep soundly, usually do not snore much. On the other hand, people suffering from breathing obstruction can feel discomfort that results in snoring and vocalization (groaning) during sleep.
A pressure transducer usually measures the rate of oral and nasal airflow. The clinician can easily estimate the rates of respiration from this data. Sometimes, patients resort to mouth breathing when there is an obstruction in their nasal airway. It can produce false negatives and often leads to misdiagnosis. When the condition is obstructive apnea, clinicians can identify it as hypopnea.
What do the Experts Record During a PSG?
Video and audio recording serve as sound sources of information about the patient’s breathing and respiration. It is especially useful in studying sleep apnea among patients. A sleep technician can note the snoring problem as moderate, mild, or loud depending on the loudness and frequency of snoring. They usually use a numerical scale of 1 to 10 to do so. Snoring results from blockage of airflow and it can state whether the hypopnea can be obstructive sleep apnea (OSA).
A combination of the results from the numerable tests that form the cohesive PSG process eliminates the possibility of artifacts in the outcome. Misdiagnosis is a distant possibility when there is not enough data from the personal observation of the doctors from videos and audios of the sleeper.
What should I Prepare for During my first Polysomnogram?
In general, the patient needs to come to the sleep clinic. It can be a private clinic or a hospital. The patient needs to go in early (preferably the same evening), so the doctors and clinicians can hook up the channels and wires. Sometimes, the clinicians will recommend a hotel that has facilities to set up sleep studies and allow cameras in the room so that the experts next door can keep an eye on the patient’s sleeping habits.
It takes some time for the patient to get used to the wires and channels. However, you must remember that sleep apnea studies are also typical among children as young as 3 years old. Therefore, it is a safe procedure, and the location only serves the purpose of comfort and not health or safety.
Sometimes, in critical cases, when the patient has shown several artifacts in previous test results, the clinicians may agree to set up the entire mechanism at the home of the patient, where he or she can be a little more comfortable than inside an artificial environment.
Typically, a person sleeps through the night with the wires hooked on to the monitors that generate regular graphs and data. Additionally, the clinicians observe the movements and listen to the snoring tendencies of the participant every second. The patient can usually go home the next morning. However, if the clinician recommends a sleep latency test or excessive daytime sleepiness (EDS) test for the patient, he or she might have to stay another day.
What Does a typical PSG report State?
Once the test is over, the scorer completes data analysis by converting the data into 30-second periods. You can get the following data from any such score.
- Sleep onset latency. It is the time a person takes to fall asleep after the lights go out. The average sleep latency is around 20 minutes or less for the ordinary person. The interpretation of their sleep-wake state depends upon the patient’s EEG results and not on their personal encounters.
- The efficiency of sleep. How well did the patient sleep? The usual method of determining it is through dividing the number of minutes of rest by the minutes in bed. The efficiency score usually lies between 85% and 90%. For some sound sleepers, it is even higher than 90%.
- The different stages of sleep. We know by now that rest has four main stages – N1, N2, N3, and REM. The information on the sleep stages of a patient comes from the seven channels connecting EEG, EOG, and EMG. This data is enough to determine how a person transitions from NREM to REM stages. It will show how long a person spends in light sleep, delta sleep, slow wave sleep, and REM. While the fraction of time in each stage depends on the age, there are other factors like health, obesity, blood glucose, anti-depressants, pain medication, and antipsychotics that can contribute to aberrations in the result.
- Breathing difficulties during sleep. Breathing irregularities can arise from many factors. Smokers, people prone to allergic rhinitis, simple cough and cold, and bronchitis can all contribute to breathing difficulties. Sleep apnea is different from any of those. It is the complete blockage of breathing for at least 10 seconds that lead to desaturation of oxygen from the lungs. The previous cases we have discussed result in 30% or lesser airflow that can lead to awakening.
- Sudden awakenings or arousals. We have all experienced this at least once. We have found ourselves wide awake in the middle of the night with no idea what woke us up, or we have woken up confused and gone back to sleep. These can happen due to many reasons including sudden limb movements, environmental noises, and breathing difficulties.
The other information comes from the movement of the subject in his sleep, the levels of oxygen saturation in his lungs, the cardiac function and rhythms, and the preferred position of the patient.
Once the data is complete and the clinician has scored it based on his observations, they go to the sleep expert. The diagnosis is a complicated process since the medical professional has to take account of the previous medical history, current medication, history of drug and alcohol abuse, family history of insomnia and other health-related information.
Do I Need Polysomnography?
The only person fit to answer that question is your GP and sleep specialist. Sometimes, problems like abnormal movements during sleep that range from pure kicking and punching to the more complex sleep-sex can disrupt regular rest. Apart from lowering the quality of sleep, these symptoms also disturb the life of a couple and disrupt the relationship between roommates.
If you are experiencing any of the following symptoms below, you should speak with your medical expert immediately.
- Restlessness during sleep.
- Holding your breath during sleep and waking up for large gasps of air.
- Excessive sleepiness during the daytime followed by poor quality sleep at night.
- Loud snoring that occurs throughout the night.
- Waking up multiple times during the night with or without valid cause.
These signs can be of narcolepsy, parasomnia, REM behavior disorder, sleep-related seizure disorders, and “sleep attacks” during the day, and continuing discomfort during the day. The latter can prompt the patient to move their legs frequently to reduce the tingling, crawling and burning sensation in their legs.
Sometimes, this kind of discomfort can also attack the upper limbs. RLS occurs in males more commonly than females, although it usually begins in the late middle-ages. Consumption of alcohol, regular intake of anti-depressants and antipsychotic medication, and a history of drug abuse increase the propensity of sleeping disorders. If you identify with one or multiple of these signs and symptoms, you need to seek counsel of a sleep expert.
What are the Risks Associated with PSG?
Children and adults have to undergo PSG from time to time if they complain about recurrent sleep-related issues. It is a non-invasive process that is painless. The nodes attach to various parts of the forehead, neck, chest, and face via a conductive adhesive. The only risk is irritation from the adhesive. However, that goes away quickly with soothing ointments and anti-histamines topically.
What can be the Possible Interpretations of the Result?
Interpreting a PSG report is not a layman’s job. Even if you are curious and you absolutely need to Google the findings, do not rely on your understanding or interpretation skills completely to start treatment or stop the ongoing medication. A team of medical experts including physiologists, sleep experts, and psychologists need to work hand-in-hand to interpret the results of the PSG.
In case you find an abnormality in the results, you might see the following;
- Breathing disorders that can be the early signs of sleep apnea.
- Abnormal daytime sleepiness that can lead up to narcolepsy.
- Movement disorders that can be a secondary pathological condition or complex idiopathic RLS or PLMD.
- Seizures during sleep that are otherwise hidden and not felt by the patient.
The medical experts need to take a look at your complete breathing and hypopnea profile to determine the chances of you having sleep apnea. The data helps them measure the apnea-hypopnea index (AHI).
What’s the next step After Receiving a PSG Report?
After you get a PSG report, your doctor might state that you have sleep apnea. Since the inference relies on several inclusive and exclusive studies including the AHI studies, there is a reason to believe that you might require a sleeping aid regularly.
Something like a continuous positive airway pressure (CPAP) machine can help you maintain proper pressure in the airway. It will provide complete air supply to your mouth or nose. Even when you are asleep, the CPAP machine will continue to supply positive air pressure to your respiratory tract, so your breathing remains smooth.
To find the correct CPAP setting, another polysomnography might be necessary. The recommendation depends on your adjustment to the initial CPAP settings, the prognosis, level of improvement and the recommendations of the doctor.
What Should I Remember About Polysomnography?
Just like every other medical test and procedure, you need to learn and remember a few facts about PSG.
- It is a test that will generally happen in a clinic or hospital setting. However, upon special request, some professionals set up their machinery and monitors at hotels and homes.
- PSG is undoubtedly non-invasive and entirely painless, but for the first timers, falling asleep with uncountable leads on their body can be uncomfortable.
- You should refrain from drugs, alcohol, and smoke for 24 hours before your PSG.
- The sleep doctors will monitor your brain activity, heart rate, eye movement rate, and muscle activation rate and blood oxygen while you sleep. It is necessary that you go in at least an hour before your appointment to assist them with the preparation.
- You should focus on packing things that define your bedtime routines like your favorite set of pajamas, your eye mask, maybe a snuggie too. Each clinic has its prerequisites and rule. You need to speak with the doctors about what is permitted and what is necessary.
- Remember not to drink caffeine for a couple of hours before the surgery. It can interfere with the slow wave and delta wave readings.
PSG is anything but a simple procedure for the doctors and clinicians to run, but it is indeed simple on the part of the patient. The person needs to act normal and go the sleep at his regular bedtime, so the experts can sit and monitor the different sleep indicators from the next room.