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