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View a Sleep Study

From the Stanford University Sleep Disorders Clinic

Talk About Sleep, in conjunction with the Stanford University Sleep Disorders Clinic, is pleased to bring you a photo essay and personal tour to demystify the Sleep Study that your doctor has prescribed for you. To see a detailed view of any of the photos shown below, simply click on the photo.

The Polysomnogram (PSG)

A Sleep Study or Polysomnogram (PSG) is a multiple-component test, which electronically transmits and records specific physical activities while you sleep. The recordings become data, which will be “read” or analyzed by a qualified physician to determine whether or not you have a sleep disorder.

Throughout the tour, we will discuss the many components of a PSG and explain the 4 types of Polysomnographic Studies. They are:

  • Diagnostic Overnight PSG – General monitoring and evaluation.
  • Diagnostic Daytime Multiple Sleep Latency Test (MSLT) – Used to diagnose Narcolepsy and measure the degree of daytime sleepiness. To ensure accurate results, it is performed on the morning following a Diagnostic Overnight PSG.
  • Two Night PSG with CPAP Titration – General monitoring and diagnostic evaluation is conducted on the first night. If Sleep Apnea is discovered, the patient returns for a second night to determine the necessary CPAP pressure required to alleviate apnea.
  • Split Night PSG with CPAP Titration – Split Night PSG is conducted when moderate or severe Sleep Apnea has been discovered or strongly suspected during the first part of the nights study. The second half of the night is used for CPAP Titration.

Let’s Get Started

It’s the night of your sleep study. Hopefully, you have followed the directions given to you by the sleep center regarding meals, medication and other issues, so that they don’t interfere with the sleep study results. For example, alcohol or caffeine can interfere with your sleep and should be avoided.

Pack a small bag with your pajamas, toothbrush and any other items you will need the next morning. Many patients like to bring their own pillow for better sleep. You will usually have a private bathroom available so you will be able to shower, dress and go straight to work if necessary. Let’s go to the sleep center, they are waiting for you!


 You will be escorted to your private bedroom. Along the way, you are likely to see the central monitoring area, where the technicians monitor as many as six sleeping patients. It is done by means of computers, video, and print-outs of your recorded activity. The technicians will be able to react quickly if you need help or have a question while in your room.


 This technician is paying close attention to the activity of a sleeping patient.


 You have arrived at your private bedroom. It may resemble a hospital room, a hotel room, or your bedroom at home. You will be asked to slip into your pajamas before the process of hooking up the surface electrodes (leads) begins. The hook-up process may take place in your bedroom or an outer work area.


 Once you are hooked up and the preparation is over, you may have some time to relax before dropping off to sleep. Most clinics allow the patient to choose their bedtime, within reason. Televisions may be provided, but you may want to bring a book or magazine. Also, the technician can adjust your bedroom’s temperature to suit your personal preference.


Setup can take 30-45 minutes or more in order to get everything connected properly. There are a large number of supplies that are used in the process, as you can see in the photo. The two blue belts are placed around your chest and abdomen to measure your respiratory efforts, and the band-aid like oximeter probe on your finger measures the amount of oxygen in your blood. The electrodes are temporarily “glued” to your skin and scalp. Don’t worry, the glue comes off easily the next morning!


 This set up tray contains additional items for a patient hookup including: paper tissues, electrode wires, marking pencils, tape measure, gauze pads, hair clips, cotton swabs, alcohol pads, safety razor, glue bottles and a needle-less syringe containing the liquid adhesive that will help secure the electrodes


A key part of a sleep study is understanding what is happening while you sleep. By attaching the electrodes to your body, the recorded electrical signals generated by your brain and muscle activity are sent back through the wires and recorded digitally and on continuous strips of paper. The pattern of this activity can be recognized by a sleep specialist who “reads” or interprets the study. These valuable clues reveal whether or not you have a sleep disorder, and if present, how severe it is.


 This is a close up of the gold plated surface electrodes that will be glued to the skin and scalp during the PSG. They will record the extremely low levels of electrical energy present during any muscle or brain activity.


 Before the electrodes can be glued onto the scalp, cranial dimensions are taken with a tape measure to ensure their precise placement. During placement the patient usually sits in a comfortable chair.


The EEG or electroencephalogram, is a major part of a sleep study. It measures and records four forms of brain wave activity – alpha, beta, delta and theta waves. Alpha waves are usually found during relaxed wakefulness, particularly when your eyes are closed. Theta waves are seen during the lighter sleep stages 1 and 2, while delta waves occur chiefly in deep sleep, the so-called “slow wave sleep” found in sleep stages 3 and 4.


The EMG or electromyogram, records muscle activity such as face twitches, teeth grinding, and leg movements. It also helps in determining the presence of REM stage sleep. The amount and duration of these activities provides the doctor important information about your sleep.

The EOG or electro-oculogram, records eye movements. These movements are important in determining the different sleep stages, particularly REM stage sleep. The electrodes are usually placed on the outer aspect of your right eyebrow and along the outer aspect below or beneath your left eye.

EKG or electrocardiogram, records heart activities, such as rate and rhythm. Electrodes are placed on your chest.

Nasal Airflow Sensor: Records breath temperature, airflow, apnea and hypopnea events. A sensor is placed near your nose and mouth.

Chest/Abdomen Belts: Records breathing depth, apnea and hypopnea events. Elastic belts are placed around your chest and abdomen.

Oximeter: Records blood oxygen saturation. A band-aid like clip is placed on a finger.

Video: Records body positioning and movements.

Snore Microphone: Records snoring. An electrode is placed over your trachea, on your lower neck.

Sleeping is a complex activity that must occur for a successful polysomnographic study. During sleep, our brain and body cycle between NREM and REM sleep approximately every 90 minutes.

During these transitions, major changes occur in our EEG, EOG, EMG, heartrate and respiration that are necessary for healthy sleep. If abnormal changes are observed during a particular sleep stage, then we are able to define this problem as it occurs during the night.

Some sleep disorders are generally worse in a particular sleep stage, such as sleep apnea during REM sleep and PLMD in NREM sleep. Your PSG technician and sleep specialist are well aware of these facts and want you to get as good a night’s sleep as possible in order to make your test experience as fruitful as possible.


  Here you can see EMG electrodes on the chin, jaw, cheeks, and lower leg. EEG electrodes on the scalp and forehead, EOG electrodes above the eyebrow, and the snore microphone on the lower neck.


 Elastic belts are placed around the chest and abdomen to record breathing rate and effort from the diaphragm, as well as apnea and hypopnea events.


 The hookup is complete! The electrodes and all other components are in place. The data they collect and record is what makes a polysomnographic study. Once the sleep specialist reads the “book” of data, they will know if you have a sleep problem or a sleep disorder. Following a diagnosis, the sleep specialist will work with you and your doctor to plan appropriate treatment.


 Although being hooked up may look uncomfortable and sleeping through the night seems impossible, most patients fall asleep with little difficulty.

CPAP Titration is required if sleep apnea is diagnosed or strongly suspected. Typically, this is a full night of study performed during a second night, but is sometimes performed during the last few hours of a split-night study.

CPAP (Continuous Positive Airway Pressure) therapy is the first line of treatment for sleep apnea. The CPAP device delivers pressurized air through tubing to a nasal mask or nasal pillows, which are fitted around the head. The pressurized air acts as an airway splint. It gently opens the patient’s throat and breathing passages, allowing them to breathe normally while asleep, but only through their nose!


 This is a CPAP machine, with humidifier and hose. The mask is not shown.

To properly treat sleep apnea, the correct CPAP air pressure setting must be determined by titration. Titration is done for each patient – there is no “one size fits all” solution.

During a titration study, the patient will sleep all wired up, just like a normal sleep study, but they will also wear a nasal mask which is connected to a CPAP machine. Since the pressurized air can be irritating to a nose that hasn’t been used much at night, many sleep labs also connect the CPAP device to a heated humidifier during the titration procedure. This adds moisture to the air after it leaves the CPAP and before it enters the patient’s nose, easing the drying effect of the pressurized air.


 To ensure effectiveness and optimal comfort, the nasal mask is properly fitted prior to application. This patient drifted right to sleep!

During the titration study, the technician will set the air pressure on the CPAP at a certain level and then watch the resulting measurements. If that pressure does not reduce the number of apnea and hypopnea events, or eliminate the snoring, the technician will adjust the air pressure and continue observation. This process continues throughout the night until the optimum pressure is reached.

Multiple Sleep Latency Test or MSLT, is designed to measure the degree of sleep tendency or sleepiness in a given patient. This test is conducted during the day following a routine PSG and features a series of up to 5 naps, each lasting usually less than 30 minutes that are timed to start every two hours during the day. For example, 10 am, 12(noon), 2 pm, 4 pm and 6 pm represent a possible nap schedule.

It is important prior to having an MSLT study that a 1-2 week sleep diary be completed and your doctor be aware of any medications (OTC or otherwise) that you are taking, since many medications can effect the results of this test.

The purpose of the MSLT is two fold: first, to average the number of minutes that it takes to fall asleep (sleep onset latency) during all the naps and second, to record if REM stage sleep occurs during any of these scheduled napping periods.

The testing procedure includes essentially the same PSG leads as for a diagnostic overnight study. During the periods between naps, the patient must stay awake and not fall asleep.

This test is particularly useful in helping people with Narcolepsy adjust their medication, diagnose Narcolepsy, objectively quantify the degree of sleepiness in a particular patient, such as an OSA (obstructive sleep apnea) patient who is still sleepy despite CPAP treatment and in diagnosing Idiopathic Hypersomnolence.

We hope this article has helped to better prepare you for your sleep study.

The Talk About Sleep Mission: to be a world leader in the sleep field by providing quality information, support and resources to sleep disorder patients, their family, friends and healthcare professionals.

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