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Sleep Disordered Breathing and Sleepiness in Patients with Chiari Type I Malformation

Nathaniel F. Watson, MD

Dr. Watson is an Assistant Professor of Neurology at the University of Washington (UW) and Co-director of the UW Sleep Disorders Center at Harborview.

Portions of 2007 ASAP Conference Presentation

When I’m talking about sleep disordered breathing, I’m talking about sleep apnea mostly, which is a term that you all may be familiar with.  Sleep apnea is basically having problems with breathing during sleep at night.  There are multiple types of sleep apnea.  There is obstructive sleep apnea - where there’s a blockage of tissue keeping you from breathing effectively.  There’s central sleep apnea - where your brain is not telling the body to breath in your sleep.  Then there are milder forms of obstructive sleep apnea which are similarly a result of blockages in breathing, what we call ‘respiratory effort-related arousals’.  I’ll talk more about that and give you more background.   
 
The relationship between Chiari Malformations and respirations is actually fairly complex.  The way that we breathe is our brain samples carbon dioxide and oxygen from the blood as it goes through our brain stem and it adjusts our breathing level accordingly.  When we’re awake we have a wakefulness drive to breathe, so we can remember to breath and we can cause ourselves to breathe when we’re awake.  When we’re asleep our breathing is totally dependent on our brain stem measuring specific carbon dioxide levels and oxygen levels.
These areas here, [see Figure 4] you can see in the brain stem, the Dorsal and Ventral Respiratory Group and the Pontine Respiratory Group.  These are the areas that have these cells or these chemo-receptors that take these measurements and then tell the body to breath.  You can imagine that all the pressure that’s going on in this region in patients with Chiari Malformations that this affects the functioning of these cells.  So that’s what happens.  They don’t measure these blood gases as well as they should and therefore breathing is affected.
There are some other things going on as well.  [see Figure 5] Cranial nerves that are coming out of this region that sub-serve muscles of the tongue and the throat can be stretched and affected.  That can cause your throat to become floppy and collapse in on itself also causing problems breathing in your sleep.  Lastly there are nerves that send signals from the lung stretch receptors and also what’s called the carotid body and the aorta that are also monitoring these blood gases.  So those nerves can be affected as they’re feeding information to this area.  The signals that come out of here to the diaphragm and the other muscles that breathe can also be affected, particularly by people that have co-morbid syringomyelia.  So it’s really a problem with blood gas sampling, it’s a problem with the output of these centers to control breathing and a problem of the sensory input that tells the brain what’s going on with the rest of the body as far as breathing is concerned.  

This is a diagram [see Figure 5] that is showing you the nerves that would be involved that would be stretched and causing problems.  We have 9, 10 and 12.  The Glossopharyngeal nerve sends motor output to the upper pharyngeal muscles here and what’s called the Stylopharyngeus muscle which also helps keep the airway open.  The Vagus nerve, the tenth nerve, sends motor output to the lungs so it helps control breathing and also the pharynx and larynx; so again here in the throat region.  Then the Hypoglossal nerve, the twelfth nerve, controls motor activity in the tongue.  That’s important because people with obstructive sleep apnea will often have a tongue that can fall back into your airway when you lie on your back and block air flow.  Stretching and damage to these nerves can cause problems.

Let me talk a little bit more about the two different kinds of sleep apnea, the obstructive sleep apnea and the central sleep apnea.  Obstructive sleep apnea as a sleep position is by far the most common type of sleep apnea that we see.  What we have here is 120 seconds of an overnight polysomnogram, [see Figure 6] which is a sleep study which some of you may or may not have had.  Just to go through these channels to let you know what we’re looking at in this colorful picture.  This is measuring brain waves to tell you what stages of sleep you’ll be in during the night.  Then you have this, measuring eye movements, which helps us stage sleep as well.  A chin tone, which is muscular tone in the chin, helps us tell what sleep stage you’re in.  We look at snoring; we look at chest and abdominal movement.  This is very important because this is telling us whether or not a person is trying to breathe.

 If you’re having central apnea, your chest and abdomen aren’t moving because your brain’s not telling your body to try to breathe.  When you have an obstructive apnea, as a result of an obstruction in the throat and the nose and everything, your chest and abdomen are trying to suck in and create negative pressure to breathe. It’s just that air can’t get through that area.  Here you can see that this is the pressure flow transducer at the nose (which measures air flow at the nose) and we just have these repetitive apneas over and over again.  There’s no air flow going on here, there’s a drop in the oxygen saturation level that’s pretty severe in this patient, in each one of these.  That’s the amount of oxygen in the blood which is obviously important for your body functioning. 

Then there’s an arousal - so there’s kind of a snort and a wake up here that opens the airway back up, allows a little bit of breathing, and then the patient falls back asleep and this happens again.  This is very insidious, the patient doesn’t usually know that it’s happening unless their bed partner tells them about it or they’re noticing they’re sleepy during the day.  Those are the reasons that these people end up coming to see me.

The important relationship between this and Chiari is that some people that have this can elevate because they’re not breathing well, they’re carbon dioxide levels can go up.  When that happens, the blood vessels in the brain can dilate and so more blood can go into the blood.  That has a tendency to increase intracranial pressure and increasing intracranial pressure is bad for people with Chiari Malformations.  So it can make the Chiari Malformations worse so that’s a vicious cycle.  The Chiari Malformation is making the sleep apnea worse, and then the sleep apnea with the CO2 and so that’s a concern. 

The obstruction in obstructive sleep apnea can be multiple areas, large tonsils, large uvula, which is that thing that dangles down in the back of your throat, blockages in the nose, septal deviations and things like that.  Large tongues can also contribute to this.  And then also muscle tone in the throat, as I mentioned, those three nerves that can be stretched.  When we all fall asleep we actually have about twenty muscles in our throat that have to increase their tone to keep your airway open.  If they don’t do that very well you get a collapsible floppy airway which is a real problem for people.

 For obstructive sleep apnea the prevalence is actually pretty high, it’s one of the most common diseases known to man.  If you just took a random sampling of people off the street and did a sleep study on them and you said that those that had apneas or hyponeas (which are like apneas but not as severe) if they had more than five of those an hour you would diagnose them with this.  You would find that about 9% of women and 24% of men would have an apnea/hyponea mix higher than 5.  If you ask a second question where you say you also need to have symptoms in order for this to be a disorder; then it’s about 2-4% of the population that has this problem.  That’s in the general population, not in Chiari folks and we’ll talk about Chiari specifically in a minute.

The risk factors are, [see Figure 7] in the general population being a man, being older, being overweight, those are the most common ones.  Smoking can contribute, having a large neck size.  In men, if the neck size is 17 inches or greater you’re at risk for this.  In women, if the neck size is 16 inches or greater.  The treatments for it are really three - this is for the run of the mill patient, not the patient with the Chiari.  CPAP, continuous positive airway pressure, which is a little mask, you can see this gentleman wearing it over his nose. It’s connected by a tube to a small box that pushes pressurized humidified room air.  So there’s no additional oxygen or anything like that being put in there, and it’s usually between 5 and 20cm of water pressure and it works like a pneumatic splint to sort of pop the airway open and keep it open when you sleep.  In people that have trouble with that or if they have really big anatomic obstructions, large tonsils for instance, we can do different types of surgeries.  This is an example of a uvula palatal pharyngoplasty or a UPPP.  We trim out the uvula which dangles down here and part of the soft palate.  This is not usually curative but helpful and definitely helpful for snoring.  Lastly, dental appliances that can be worn at night that move the lower jaw forward can pull the tongue forward and open up this air space.

Central sleep apnea, which only makes up about 5% of the people with sleep apnea that we see [see Figure 8] is shown here with this polysomnogram fragment.  This is similar to what I showed you before but what I want you to focus on down here is these chest and abdomen measurements of movement.  You can see here, when we have these cessations in air flow right here, now we’re not having any respiratory effort here.  This patient is just not trying to breathe when they’re asleep.  This is often complicated as to what’s causing this.  We divided it into whether or not CO2 levels are up or not.  Some people have it, it’s called idiopathic, we don’t know why.  Some people can have problems with this because they’re very, very obese.  Other people that have neuromuscular diseases can have problems with this.  Heart failure can often result in this type of picture.  For those people that have central sleep apnea, here are all the different causes. 

It’s complicated but here in the red box [see Figure 9] is probably the most common reasons why people with Chiari Malformations will have this. One is this sort of “won’t breathe” factor, so the pressure being put on those dorsal and ventral respiratory groups in the brain stem that I showed you earlier, pressure’s being put on that and those receptors that measure CO2 and Oxygen don’t function like they should.  That causes problems.  Also the output to the muscles that sub-serve respiration can also be affected, more so by co-morbid Syringomyelia but also by the Chiari Malformation itself, and then of course everybody that’s asleep has a loss of the wakefulness stimulus to breathe. 

Let’s talk about a couple of the studies that have been done that have looked at Chiari I Malformations and sleep disordered breathing.  This one here, [see Figure 10] looked at 46 Chiari Malformation patients, 20 were children and 26 were adults. Here they did have 5 with Chiari II Malformations.   What they found was a very high prevalence of sleep disordered breathing, 73% of adults had sleep disordered breathing.  And that would be defined as an apnea, hypopneas, which is more than five per hour.  As you can see, the majority had obstructive sleep apnea but a pretty high number also had central sleep apnea.  This is much higher central sleep apnea than we would expect to see in the general population.  As far as the children are concerned the numbers were still quite high.  There was a little bit more central sleep apnea in this group and this was due to the Chiari II group which had more severe central sleep apnea.  There’s something about the Chiari II that’s causing more problems with the respiratory control. 

I’ve talked about this prevalence of 2-4% in adults.  The prevalence is 1-3% in children; these numbers are much, much higher than that!  so this kind of thing to me just tells me that we need to move sleep disordered breathing up the list of symptoms that people with Chiari Malformations are having because it seems to be so common. 

This study [see Figure 11] looked at 13 Chiari I patients and they’d had a control group that did not have Chiari Malformations, and you can see again the apnea, hyperpnoea index was higher. On average it was 13 compared to 3 for control.  So if the cut off is 5, the average in the Chiari’s is abnormal, the average in the control is normal.  You can see that also when you look at just who was above 5, 59%, again a very high number had clinically significant sleep disordered breathing compared to the controls.  Not only that but it also affected the level of oxygen in these individual’s blood so the lowest oxygen level went down to 80% in the Chiari group as opposed to 90% in the normal group.  The Chiari group then also spent 24% of the night with an oxygen level below 90%.  Generally speaking we like to keep the oxygen level in the 90s, so this is of concern to us. 

They looked at Epworth Sleepiness Scale, and I’ll talk more about this in a minute but the bottom line is that there was no major difference in the amount of sleepiness that was being endorsed between the two groups.  So this was kind of interesting and contrary to what we might think.  Central apneas were more common in the Chiari group and then the basilar invagination that Dr. Oro was talking about in the Syringomyelia is also more commonly associated with these central apneas.

Let’s talk about the research that Dr. Ellenbogen and myself have been involved in.  We recruited Chiari I patients from Rich’s specialty clinic and then we got health age matched controls from the Seattle area.  All the subjects in our study were female because all of Chiari subjects happened to be female.  We did MRI of the brain including this cardiac gated phase contrast CINE MRI on all subjects.  Then we administered some questionnaires that were related to sleep.  The Berlin Questionnaire is a validated questionnaire that measures risk of sleep apnea.  The Epworth Sleepiness Scale which measures propensity to fall asleep.  We looked at how long these individuals sleep and how long it takes them to fall asleep.  Then we had a few other miscellaneous sleep disordered breathing questions. 

The Berlin Questionnaire is a ten item questionnaire where we assess three categories; snoring, sleepiness and then whether or not obesity or hypertension is present.  In order to be considered high risk for sleep apnea you have to basically be high risk in two out of these three categories.  You have to have snoring or breathing pauses greater than three to four times a week; sleepiness greater than three to four times a week or drowsy driving; or a body mass index greater than 30 or a history of hypertension.  So if you’re high risk, which is what this is here in two of these three, then you’re high risk for sleep disordered breathing. 
 
The Epworth Sleepiness Scale is an interesting eight item scale that measures a propensity for an individual to dose or fall asleep in these eight different situations.  The lowest score you can get is zero.  The highest score is 24 and you can score from zero to three on any of these items.  So you can see some of these items here you may have a greater propensity to fall asleep during that than others, lying down to rest in the afternoon, hopefully more so than in a car while stopped in traffic.  But you’d be surprised, this is the scary part of sleep apnea and in fact people with sleep apnea are at much higher risk for motor vehicle accidents than those that don’t have it.  An abnormal score is greater than or equal to eleven on this sleepiness scale.

The two groups were in their mid to late 30s. [see Figure 12] You can see that the healthy control group was slightly more educated.  Most of our subjects were Caucasian which is reflective of our population of inference.  You can see that the control group was more likely to be employed and the Chiari group was more likely to be married, or living with someone.  The Berlin Questionnaire, we had a higher risk of snoring in almost half of the Chiari group compared to 6% of the controls and this was significantly different.  Sleepiness, almost three quarters compared to about half of the controls.  Then obesity or hypertension was twice as common in the Chiari group compared to the controls.  Overall when we looked at sleep disordered breathing risk we found that 69% of the Chiari I group were at high risk for sleep disordered breathing compared to 20% of the controls.  And so our numbers are pretty close to the three quarters that we were quoting earlier in the other stories that have been done. 

We also looked at the Epworth Sleepiness Scale [see Figure 13] and our summary scores were almost twice as high in the Chiari group, so we did find a pretty big difference in the level of sleepiness between these two groups.  And this is on average almost abnormal.  When you look at the percentage of people that had a score greater than or equal to eleven, almost half the Chiari group had an abnormal range Epworth Sleepiness Scale score, compared to about 9% of the controls.  This is interesting and hadn’t been reported before but the self reported sleep duration is a little more than an hour less in the Chiari group than it is in the healthy controls; and it also takes the Chiari group about three times longer to fall asleep, about an hour on average to fall asleep compared to the healthy controls. Real big effects on what would be thought of as sleep quality in these individuals. 

There has been one study that has looked at the effect of surgical decompression on Chiari Malformations and the effect that has on sleep apnea.  [see Figure 14] That’s a study that I’m showing you here.  Again, in this group of Chiari subjects, sixteen patients, three quarters had sleep disordered breathing.  So we’ve seen multiple studies now showing that about three quarters of people will have significant sleep disordered breathing; again a lot more central sleep apnea than what we would expect.  Sleepiness is defined a little more liberally than we do, but nonetheless, again, in about 50% of people.  Eight of the twelve that had sleep disordered breathing underwent surgical decompression and they got a post-op sleep study on six of them.  What they found was the biggest impact the surgery had was by reducing the central sleep apnea index.  Those are the apnea that happen when a patient doesn’t breathe, their brain doesn’t tell them to breathe.  The obstructive apnea index from blockage was also reduced but not significantly in this study.  The arousal index was reduced, so you would imagine if you’re reducing the apneas, you’re reducing the arousals that would happen at the end of it and that is what was seen. Overall the apnea hypopnea index was reduced, not to normal, but significantly reduced.  But not quite significantly. You might imagine if there were more patients in this study that you would find a significant difference here.  And then again they found no change in the Epworth following surgery.  So this deserves more investigation. You would expect that if you’re resolving the apnea the sleepiness would get better. But you know perhaps, a lot of times people can confuse sleepiness and fatigue.  It’s really hard to know.  Sleepiness is obviously being a propensity to fall asleep, fatigue maybe being more of a muscular or brain kind of fatigue and so there might be some issues with that. 

In conclusion, from our work [see Figure 15] and the other work that I’ve presented here, Chiari I subjects are at much higher risk for sleep disordered breathing than controls of similar sex and age.  I think we need to move this farther up the symptom scale that we get concerned about, in people that have Chiari Malformation, particularly considering that sleep disordered breathing could make the Chiari Malformations worse over time.  In addition, sleep apnea is associated with cardiovascular diseases and hypertension and those are really important reasons to get it identified and taken care of.  Chiari patients are sleepier than controls even though the surgery didn’t seem to necessarily improve that, but they are sleepier.  The Chiari subjects sleep less and take longer to fall asleep so there is some insomnia issues going on here and there really aren’t any studies that have looked specifically at insomnia in this disorder. 

I think that we need to do a lot more research in this area.  We need to focus on these objective measures of these various symptoms.  For instance, sleepiness can be measured subjectively with a questionnaire but a better way would be to do what’s called a multiple sleep latency test where we let an individual have between four and five opportunities to nap during the day and we measure how quickly they fall asleep.  I think that we should do that test before and after decompression and get a better idea of whether or not we’re improving sleepiness in these folks.  The one study that was done did show that surgical decompression can improve sleep disordered breathing and so I think that we need to think about this as part of the symptom complex that might drive the physician towards whether or not they want to proceed with surgery for this disorder. 

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