If your physician recommends that you undergo an overnight sleep study, also known as nocturnal polysomnography (NPSG), you might be curious what it involves and what you can expect from it. You might also wonder what are the wires used in the sleep study are for.
An NPSG records your heart rate, brain activity, oxygen levels, eye movements, airflow, respiratory effort, body movement, and more. During an overnight sleep study, sleep technicians monitor you inside a sleep clinic through the use of various medical equipment that records simultaneously on a digital sleep diagnostic system.
Registered Polysomnographic Technologists (RPSGT), also known as sleep technologists, are trained specifically to conduct a sleep study test in order to diagnose and treat sleep and arousal disorders. They work together with a doctor who also practices in the field of sleep disorder medicine. Together, they ensure the patient receives an accurate diagnosis, proper management, and thorough education of their sleep disorder, in addition to said sleep disorder.
The sleep technologist prepares the equipment for the sleep study and monitors the recording. They are specially trained to handle multiple medical and technical monitors and have expertise in abnormal and normal sleep patterns.
Possible Disorders Diagnosed Through a Sleep Study
Overnight sleep studies are performed for the purpose of determining if you have a sleep disorder. Some sleep disorders it can help diagnose include:
Obesity Hypoventilation Syndrome
Other Sleep-Related Respiratory Disorders
Sleep Study Wires and Sensors
The sensors that the technologist places on your body for the sleep study are used to record your bodily functions in order for the physician to come up with a sleep disorder diagnosis (if you have one).
Generally speaking, channels relate to the number of electrodes attached to you via wires during your sleep study and that transmit your body function’s data. The polysomnogram records at least 12 channels that require at least 22 sleep study wires that would be attached to you. Each sleep clinic will vary in the number of channels it uses, but the number used typically follows your physician's request.
At least three channels are used for the EEG (to measure your brain activity), two for the chin muscle tone, one or two to measure airflow, two for eye movements, one or more for leg movements, one for oxygen saturation, one or two for heart rhythm and rate, and for each belt that measures abdominal wall and chest wall movement.
A more detailed look at some of these sensors follow:
1. Electrocardiogram (EKG). This sensor uses potential electrical waveforms and is used for measuring your heart rhythm and rate.
2. Electro-encephalogram (EEG). This sensor is used for measuring your electrical brain activity. These
electrodes are typically attached to your scalp close to the top (central), back (occipital) and frontal areas of your brain. These channels are used to identify if you are awake, asleep, and the different stages of sleep your progress through.
3. Electrooculography (EOG). This sensor is typically placed on the outer edges of each of your eyes and is used for measuring electrical eye movement activity. This channel is typically used to help identify sleep onset with slow rolling eye movements correlated with the EEG and Rapid Eye Movement (REM) sleep.
4. Electromyography (EMG). This sensor is used for measuring electrical muscle activity that your skeletal muscles produce. There is a lack of muscle tone (atonia) during REM sleep which is measured by the chin EMG channel. It is also used to test for medical abnormalities and sleep disorders such as Periodic Leg Movements of Sleep (PLMS).
Other sensors used to monitor:
Snore Volume. Often uses a piezoelectric sensor, an acoustic sensor and a cannula (nasal pressure transducer) in patients with sleep apnea.
Respiratory Airflow. This sensor uses a thread that is flexible and can fit behind your ears along with a couple prongs that the doctor places in your nostrils. It monitors your breathing to see if you require respiratory help.
Body Position. This sensor can be attached to abdominal belts or directly to your chest. It is very versatile and can help the technician monitor your sleep positions including: left, right, supine, prone or upright. It is helpful in identifying positional dependent events.
Respiratory Effort. This sensor typically comes in the form of thoracoabdominal belts. These belts measure the effort to breathe.
Blood Oxygen Saturation. Placed on your finger to detect any blood oxygen level changes. It is often used for checking for respiratory problems and sleep apnea.
- Video. Its important that the sleep technologistrecord the video for purposes of verifying body positions and to document possible movement disorders or seizure activity during the NPSG.
These sensors are connected to a jackbox that is connected to the polysomnogram recording device. Although you will be hooked up to many wires and sensors, they are fairly inconspicuous and shouldn't intrude that much on your sleep. You should still have the ability to move around in the bed and get into a position that is comfortable enough for you to sleep. As soon as all the sensors and wires are set up, the only thing left for you to do is go to sleep.
During the study, the belts and sensors attached to you will enable the sleep technicians to monitor you and record all channels of information. This information assists them in preparing a report for your doctor so they can then determine if you do have a sleep disorder diagnosis or not.
Different Stages of Sleep Studied During an Overnight Sleep Study
During your overnight sleep study and through the use of the aforementioned sensors and channels, your
sleep technology technicians and physicians gain a better understanding of the quality and stages of your sleep. There are four sleep stages that a person typically goes through and each is important individually to the process.
Sleep Stage 1
This stage is where you transition from being awake to falling asleep. It's considered the dozing stage where you will display some slow eye rolling movements. You spend around two to five percent of your total sleeping time in this stage.
Sleep Stage 2
You begin to display larger brain waves in this stage and a lack of eye movement. This is the stage that is believed to be the beginning of consolidated sleep. The brain waves you form during this stage are known as K-complexes and sleep spindles with both showing a certain pattern of EEG activity. You spend around 45 to 55 percent of your total sleeping time in this stage.
Sleep Stage 3
During this stage, it will be hard to arouse you. You will display slow and large delta waves on the PSG. You may feel disoriented and groggy if woken. Around 20-25 percent of your total sleeping time is spent in this stage.
Sleep Stage REM
This is the stage where you drift into your REM sleep. Your breathing will become shallow, rapid and more irregular. Your eyes will jerk around in different directions rapidly and the muscles in your limbs become paralyzed temporarily. It is during this stage that you begin to 'dream'. Your blood pressure and heart rate increases. You spend around 25 percent of your total sleeping time in the REM stage.
After you have completed your sleep study, your physician needs to review the collected information and analyze it before you get your results. The sleep specialist will analyze the data and come up with a diagnosis based on your sleep study test results, medical history and sleep history. You will then be asked to schedule a follow-up appointment where you will sit down with the physician to go over your results and determine a treatment plan if you are diagnosed with a sleep disorder.
If you feel that you or a loved one might need a sleep study, or just want to learn more about the process, just click the link below!