Two weeks after doing your sleep test, your sleep report should be ready for your review. Depending on the type of sleep study you did, the amount of detail shown on your report will vary. This is the time when lots of patients I met are extremely anxious, they usually do not know what to expect, nor do they know which are the right questions to ask.
During the result discussion, a sleep therapist, or your family doctor/ physician may go through the report with you, but which sections of the report must we pay most attention to? What are the correct questions to ask?
Let’s talk about it!
1. “What is my AHI?”
AHI stands for Apnea Hypopnea Index. In a sleep test report, this is always the number one thing physicians refer to. It gives them an idea of how severe your sleep apnea is. AHI also refers to how many times you stop breathing per hour, the higher the number, the more severe your sleep apnea is. Every time you stop breathing for 10 seconds, it will be considered as “one apnea”.
See following table for a guide:
|30 and above||Severe|
Now you have understood what AHI refers to, you may realise the report sometime mentions another acronym “RDI”. RDI stands for Respiratory Disturbance Index. In general, your RDI would usually be a number higher than your AHI. While your AHI represents how many apnea episodes (stopping breathing) you have in an hour, the RDI is a combination of all your apnea, plus any respiratory disturbances in your airway.
For example, if there is a big difference in your AHI and RDI, you may be a chronic sufferer of hay fever or allergies, or you might just have a case of deviated septum. With an obstruction in your upper airway, your airways will naturally be narrower, creating a higher resistance in your airway; this will have an effect of how well you are breathing while sleeping.
Take note there is no universal consensus exists on whether the AHI or the RDI should be the standard index used to determine how severe your sleep apnea is. Some doctors may like to use the RDI index to obtain your worse case scenario, while most physicians stick to the general AHI number.
2. “What is my SpO2 Nadir?”
Firstly, lets put some definition into the question above.
SpO2 stands for “arterial oxygen saturation”, and Nadir means “the lowest point”. Combine them together, it pretty much means the “lowest amount of oxygen in your arterial blood”. The units for these are always by percentages. Remember the little finger clip thing you had when you did your sleep study? That’s exactly what it is recording.
To give you a reference, a healthy, conscious person would usually have their blood oxygen level sitting around the 95-96% mark. When we go to sleep and relax, it is natural for our blood oxygen level to drop down to maybe 92%, or 90% minimum. When it drops below 90%, this sometimes can be a concern, especially when it happens during one of your apneas. Oxygen level dropping more than 4% at one time will activate your body’s’ “flight or fight” response, causing your heart to beat faster to compensate for the oxygen lost, resulting in you overworking the heart and waking up tired and groggy. So if you feel groggy or have a case of daytime sleepiness, understanding the level of your oxygen level while sleeping may answer some of your questions.
Well, those are pretty much the two main questions I would like you to ask your physicians. Even if you chose to do the simplest pulse oximeter sleep test, should still be able to give you your rough AHI and SpO2 Nadir.
Now, if you did a more comprehensive test, say, a home based sleep study or an In-lab/ Hospital Polysomnography Test (PSG), your sleep test report should consist of about 3 pages. With the first page showing a full summary of your report, including a few recommended treatment options, second page giving you numbers and data such as amount of time spent sleeping and sleep efficiency, and on the last page, you may see a page similar to this:
The image above gives you a very detailed overview of exactly what is happening during the night, with the X-Axis showing the time, and Y-Axis giving you different parameters.
Let us break down each parameter and talk about it in more detail:
The graph above represents a healthy representation of which stage of sleep you are supposed to be in during the night. We go through about three to four sleep cycles a night, and spend different amounts of time in each cycle too. Sometimes, by stopping breathing or having apneas at night, this may impede on how well you are sleeping and may mess up your sleep cycle.
The graph above shows a sample of what the report may look like for someone whose sleep cycle is very disturbed. As you can see, there are red bolded horizontal lines, and those represent your REM cycle. Ideally, we like to have about 3-4 cycles of unbroken REM sleep. From the diagram above, we can see 4 cycles of sleep, the second and fourth cycle occurring at approximately 11:50pm and 3:00am are very disturbed and broken up, this is possibly due to a disturbance from the patients’ apneas. The second cycle occurring at 1:23am is also being shortened by arousal/ disturbing episodes.
See below for a reference of how long we should stay in each cycle of sleep.
Stage 1: 1-5%
Stage 2: 40-55%
Stage 3+4: 20-35%
A persons’ resting heart rate depends on your age and fitness level. On average, our resting heart rate should be sitting at around 70 beats per minute. If you are an experienced marathon runner, you may have a resting heart rate of 50 beats per minute. Overall, what the sleep test looks out for is a big jumps or fluctuation of heart rate. There is always a reason why your heart rate will spike in the middle of the night.
The graph above represents heart rate. It might be a little bit hard to see, but the graph is showing a resting heart rate averaging around 60 beats per minute (see Y-Axis). Every now and then, you will see a spike or two, this is most likely happening when you are having any apneas or a result of a drop in your blood oxygen level.
Your sleep test will also show which sleeping position you are in, with the terms “supine” meaning you are lying on your back, left side, right side, and “prone”, which means you are sleeping on your stomach. By comparing your sleeping position with the amount of apneas you have, it may suggest which sleeping position is the best for you. In general, sleeping on the side is always better than sleeping in the supine position, as your muscles at the back of the throat does not collapse directly onto your airway.
The graph above is showing the sleeping position of this patient. With the patient starting out sleeping on their back (supine), flipping onto the left side at around 11:03pm, turned onto their belly between 11:15pm and 1:00am, briefly sleeping on their left side again at 1:15am, then sleeping on their belly for the rest of the night.
With a sleep test, it will tell you your intensity of snoring. Some people have very intense sessions of snoring during the night, but it may not cause any damage or a drop in oxygen level at all.
On the graph above, it represents your snoring index. Every one of those black lines means you snored once. The longer the line, the more intense your snoring is.
This is probably the most crucial part of the report. It tells us how much oxygen we are deprived of during the night, and how many times it is occurring. The more times it occurs, chances are your heart rate will be elevated more often.
On the graph above, the Y-Axis has a value of between 80% to 100%, and as you can see, the average blood oxygen level across the graph is sitting above the 90% mark, however you can notice there is a drop in oxygen level in a few places here and there, chances are these drop are due to the patients’ apneas. Ideally, we will like our blood oxygen level to maintain above 90%. If it drops below 90%, the patient may feel symptoms such as migraines or headaches upon waking up.
This type of sleep apnea is the most common amongst all patients, it is when your airways are partially closed, but enough to cause a desaturation of your oxygen level. Shallow or slow breathing because of a partial obstruction in the airway causes hypopnea.
2) Obstructive Sleep Apnea
This kind of apnea is a little bit more severe than hypopneas. It is when your airway is fully shut down for more than 10 seconds. This is more common in patient who are overweight or obese.
3) Central Sleep Apnea
Central Apnea occurs due to a communication fault in the nervous system. This is when your nervous system is telling you to breathe, but your muscles are not responding to its’ command. This type of apnea is not as common as hypopneas or obstructive sleep apnea, but by using the right treatment option, it is as easy to treat as hypopneas and obstructive sleep apneas.
4) Mixed Sleep Apnea
Mixed Apnea is a combination of obstructive and central sleep apnea. It typically starts with central apnea episodes for about 10 seconds, followed by obstructive apnea events. (Brain telling body to breathe but it is not following instructions, followed by a complete shut down of the airway.) A majority of patients with mixed sleep apnea have both obstructive and central sleep apneas.
To see which kind of apnea you have from a sleep test, a graph similar to this one may be shown on your sleep test report:
The graph above represents a patient with severe hypopnea events with Central Apneas. With each respective vertical line showing one apnea event.
OA: Obstructive Sleep Apnea
CA: Central Sleep Apnea
MA: Mixed Apnea
Arousals are also known as “wake events”. This occurs when your body enters a “fight or flight” mode due to your apneas. It is a self defence mechanism in the human body where it tries to wake us up so we can start breathing properly again. Arousals can both be conscious or unconscious to the patient. Some people may experience events such as waking up in the middle of the night feeling “panicky”.
In the figure above, you can see multiple blue vertical lines. Each and every one of those lines represents one wake event. This patient is constantly being aroused during the night, not getting enough good quality sleep. The patient will most likely experience symptoms such as daytime sleepiness.
The sleep test also checks out for Periodic Limb Movement Syndrome (PLMS). PLMS is when your legs or arms move involuntarily when you are asleep. If you have PLMS, this may happen every 10 to 60 seconds and is out of your control. There are various ways this can happen such as flexing of the toe or foot, bending of the ankle or knee, or twitching of the hip. Patients who has restless leg syndrome may experience more of these compared to a healthy individual. These are all involuntary movements, and can disrupt your sleep quality. Patients with numerous amounts of these events may wake up feeling groggy or tired.
This parameter only exists for people who were previously diagnosed with sleep apnea, and this is another additional study used to assist with their treatment. The purpose of this parameter is to find out the perfect amount of pressure needed to open up an airway for a patient. You do not need to do this study if you are tested negative for sleep apnea.
With the assistance of a sleep technician, the patient will be wearing a mask during the night (instead of nasal cannula and oral thermistor), which will be hooked up to a CPAP (Continuous Positive Airway Pressure) machine. During the night, the sleep technician will manually regulate the amount and intensity of air pressure pumping into the mask. The general rule of thumb is, if the patient is snoring, the pressure should be increased, and vice versa. The pressure is constantly being fluctuated up and down to get the most comfortable and perfect pressure for the patient.
The graph above represents a titration study. As you can see, the horizontal blue line represents the amount of pressure with the unit of cmH20 (centimetre of water), the pressure always starts at the lowest setting, to allow the patient to fall asleep before it is increased. The vertical red line on top represents the type of Apnea.
The sleep technician slowly increases the pressure up to a point where all the apneas are eliminated, and then slowly titrate up and down as needed during the night to get the perfect pressure.
In the morning, they would have achieved the most suitable pressure for the patient, and this gives the physician an idea of what settings the CPAP treatment machine needs to be set at. Depending on the sleeping position, the amount of pressure you need may be different too. It is up to the sleep technician to find out the perfect pressure for the patient.
This parameter may seem confusing or hard to understand for some people, we have not gone into detail as much, but we will explore more about CPAP machines in the next article.
It may take some time to interpret your sleep study report, but it will definitely help you stay aware of what is going on during your daily sleeping routine and work on ways to fall asleep.
On the next article, we will talk about the various types of treatment option for different severities of sleep apnea, as well as their pros and cons.