What’s involved in having a sleep study?

A sleep study is a commonly used diagnostic test to help diagnose sleep disorders or problems with sleep. It is usually used in conjunction with seeing a sleep physician who will then use information from a clinical interview and examination, together with the data from a sleep study to diagnose sleep disorders and put together a treatment plan. Part of a sleep study is recording data while you sleep, but an equally important part is then analysing and interpreting that data. This video discusses the process of having a sleep study and the steps involved in analysing and interpreting the data.

Sleep studies can be done in a sleep-laboratory, as described in this video, or can be done in the home. Laboratory-based sleep studies are standardised and the measurements taken are similar in most laboratories, though they are often analysed and interpreted differently depending on the expertise and interest of the interpreting sleep physician. Home-based sleep studies are usually simpler, with less leads, and more focussed on the diagnosis of sleep apnea in people felt to be at high risk of sleep apnea.

Another term for performing a sleep study is polysomnography or PSG. The term polysomnography comes from ‘poly’ for many, and ‘somnography’ for measurement of sleep. That is using many signals or types of data to measure sleep. The standard measurements used in a sleep study or PSG  are:

  • Electroencephalography (EEG): is the measurement of electrical signals from the brain. Usually this is recorded from 6 sites across both sides of the brain. It is used to determine whether people are awake or asleep, what type of sleep people are in and gives insights in to sleep quality.
  • Electromyography (EMG): is the measurement of muscle activity. This is recorded from just under the chin and sometimes over the jaw muscles involved in clenching or teeth grinding (bruxism). It is used to detect bruxism and also to look at muscle tone in the tongue and other upper airway muscles.
  • Electrooculography (EOG): is the measurement of electrical signals from muscles around the eyes. These signals are recorded from over muscles that are responsible for eye movements. Patterns of eye movements help to differentiate between different types of sleep. In rapid-eye movement (REM) sleep, the eyeballs move around underneath the eyelids.
  • Electrocardiography (ECG): is the measurement of electrical signals from the heart to determine heart rate and rhythm.
  • Airflow: is measured using a nasal cannula and looking at pressure changes across the breathing cycle. A second measure using temperature (thermistor or thermocouple) can also be used and is the red sensor seen in this video at 1min30sec just outside my nose and mouth.
  • Chest and abdominal movement: are measured by using bands around the chest and abdomen to determine whether people are making an effort to breath. If chest and abdominal movements are out of sync it can indicate that the airway is partially or completely blocked.
  • Leg movements: are measured using electrical sensors such as EMG or piezo-electric sensors on the legs.
  • Body position: is measured using a small device usually taped on the chest to look at the effect of body position on things like breathing during sleep.
  • Oxygen saturation: is measured using a sensor on the finger or less commonly the earlobe. This uses a light shone through the tissue of the finger (or earlobe) to determine how much oxygen is being transported to the tissues and whether it is adequate.
  • Noise sensor: A sensor measuring sound intensity in decibels (dB) is used to measure the volume of noises such as snoring. The background noise in a quiet bedroom is around 40dB. Snoring can be as loud as 70dB.
  • Video: Infrared video is used to look at movements during sleep such as leg movements or other behaviours such as sleepwalking or other parasomnias.

Video Timeline:

  • 00:00 – 00:55 Typical bedroom in a sleep laboratory
  • 00:55 – 02:30 Wired up ready for sleep
  • 02:30 – 04:35 Looking at the data

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People often ask me what’s involved in having a sleep study. So I’m going to try and show you the sleep laboratory and some of the wiring and leads that we use and then how we look at the data.

This is an example of one of the rooms where we do a sleep study. So a typical sleep laboratory. One of the things we do try to control is light. So we will generally use heavy curtains. We’re also going to try and control noise, so double glazing on the windows. Again, heavy curtains to control the noise.

One of the things we record during a sleep study is videos. So we use infrared video often positioned above the bed and an infrared video camera to record video and then positioned behind the head of the bed is a digital amplifier and there’s a lot of electrodes that run into that. I’m going to get wired up for a sleep study and I will come back to you and tell you what all those leads are.

Now I’ve been wired up to have my sleep study and I’m going talk you through what the leads are and what they actually measure. So there are lots of leads but it’s all pretty manageable once you’re all wired up. It does look a bit uncomfortable but in actual fact, I can move around pretty freely.

We have leads on the scalp and they measure what the brain is doing during sleep called EEG or electroencephalography, some leads on the side of the eyes to measure eye movements and some leads under the chin to measure muscle tone in the upper airway and then a lead to act as a reference and another one is a ground that cuts out a lot of the electrical magnetic interference and we get nice, clean signals.

We also have something in the nose that measures air flow and that’s a good way of us detecting whether there’s a problem with the airflow during sleep. A temperature sensor that sits just outside the nose and mouth that also measures air flow. It’s a bit of a backup signal and what we used to use until about five years ago.

I have a band around the chest that measures how much the chest is moving in and out as a measure of breathing. The band around the abdomen that measures the same thing and if those things are in sync, the breathing is usually pretty good. When they go out of sync, it can be a sign that there’s sleep apnea. There are some ECG leads that you can’t see. There are leads on my legs to measure muscle activity in the legs and something on the finger to measure oxygen saturation. Lots of leads but they all go off into a digital head box and that’s connected into the network and goes back to the control room where the staff are watching what’s going on during sleep.

If you do need to get up and go to the bathroom during the night, you can let the staff know and they can disconnect the box and you can head off to the bathroom and then back to bed and they will plug you back in ready to go.

Once we’ve recorded all the data, that’s often where the hard work begins and we actually get a lot of data from the sleep study. We record about 16 channels of data, 8 hours of data and we look at it in – up to 30-second pages or it can be 1000 pages worth of data.

The things that we look at is looking at the brain wave activity, so the top leads is where we look up what the brain is actually doing. So it gives us an idea about what type of sleep people are having. As we scroll across the screen, the lower amplitude is where people are asleep and then there are the sudden disruptions of higher amplitude and faster frequencies and that’s when someone has been disturbed from sleep or had their sleep disrupted.

The whole screen is five minutes of data, so you can see within that five minutes there are lots of disruption of sleep. The channels towards the bottom of the screen tell us about what’s going on with breathing during sleep.

The blue line is signalling the nose that measures air flow and each time that goes up and down is a single breath and there would be a sequence of three or four breaths but then a period of about 45 seconds when no air is getting in.

The brown leads below, those are the bands around the chest and the abdomen and they show us that someone is still trying to breathe and making an effort to breathe and trying harder and harder as time goes on and eventually it gets to a point where the brain senses it’s difficult to breathe. The muscles in the upper airway contract. People take a much bigger breath and often there is snoring or a gasping noise.

The oxygen levels come back up and then the whole cycle starts again, drift back into sleep, upper airway muscles relaxing, the airway closing over completely again for another 45 seconds.

That’s an example of severe obstructive sleep apnea and an example of how we use the data from the sleep study and try and integrate it to look at what’s happening both when you sleep, the cardiovascular system and breathing and that’s something that’s very useful for me in how I manage patients clinically.

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