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Sleep and consciousness
- [Voiceover] When we think about breathing problems at night, we could think about the problem coming from three key areas. The first one being a problem arising from the brain and the brain being a key central organ that controls the respiratory centers that help regulate the lungs so the brain is really important here. The second one being a problem with upper airways so if there's any obstruction to the airways from the mouth and the nose to the lungs, that can cause a problem. And last, but not least, we can also have a problem with the lungs themselves or the chest wall. Anything that stops the lungs from being able to expand out. So let us take each one of these things step by step and let us start by looking at the airways. So the main issue with the airways is that obstruction to the airways causes a significant problem in terms of breathing at night. And if we consider the air that goes in through our nose and in through our mouth reaches our lungs, we have points at which the soft tissues around our neck may potentially relax at night and they may potentially block this airflow intermittently. They may potentially cause an obstruction to this airflow. And when they cause an obstruction to this airflow, you may notice some snoring or gasping and this suggests that airflow is being stopped. That term is, for lack of effort, is called apnea, and all that apnea really means is that there is an absence of airflow. So if the airways are obstructed, we can have something called obstructive sleep apnea. And this condition obstructive sleep apnea is actually very common. It gets worse as people get older. These soft tissues block this airflow that we have and this condition actually results in a variety of daytime and nighttime symptoms. So we actually mentioned some of the nighttime symptoms, right? We mentioned this can have snoring, gasping for air, and these kind of apneas, these kind of pauses, breaks in the breathing where there's a lack of airflow. This condition also poses problems during the daytime, because during the daytime people can feel very tired and sleepy and they may particularly comment that their sleep is never refreshing so they wake up feeling unrefreshed. So that's a little bit about this obstructive sleep apnea and the way that we diagnose it, we do a sleep study or a polysomnography and what we're looking for is 15 or more of these apneas, that not only are pauses in the breathing, but you can also demonstrate evidence that the person is having obstruction in their airways per hour, and that's done on the sleep study, on the polysomnography. So that's a little bit about obstructive sleep apnea. That's a very important cause of breathing related sleep disorders. Alrighty, so we've got obstructive sleep apnea, but what happens if there's something that is wrong with the actual brain. Now the brain is part of the central nervous system, right? So this is actually termed something different. This is termed central sleep apnea. So the way that we could think about it, again, we have this apnea, which is this lack of complete stop in airflow. We have sleep because it's going to happen at night, the breathing is going to be effected at night, and we have central because the brain is part of the central nervous system and that's where there's a malfunction of the central, kind of centers that help control breathing. And what we're looking for here is the presence of these apneas, but there is no obstruction. Again, on the polysomnography, we're only looking for five or more. The arbitrary criteria that I used, we're looking for five or more of these apneas per hour to be happening during sleep. And really when we think about these apneas, we believe that the central sleep apnea that there's a problem with the brain's control system for ventilation. So basically, the parts of the brain that help control the breathing, they are malfunctioning. Now I'm just going to talk to you about a particular type of breathing malfunctioning that happens in the central sleep apnea. I'm just going to spend a second on that. If we consider our normal breathing to be in and out, inhale, exhale, inhale, exhale, on this graph, there's a particular type of breathing that we see sometimes in central sleep apnea and it looks something like this. It's a crescendo/decrescendo apnea type display. So let me show you. So we have the crescendo, decrescendo, then we have apnea, no breathing, and then again it starts crescendo, decrescendo, apnea, and it carries on like that. And this is actually something that's called Cheyne-Stokes breathing. And with this Cheyne-Stokes breathing, we believe that this is particularly related to central sleep apnea, that's as a result of heart failure, strokes, and renal disease, renal failure I should say. Okay, so we talked a little bit about the brain being a site of malfunctioning and we talked a little bit about the airways being a site of obstruction. Now finally the lungs. The lungs need to inflate and deflate when we breathe in and out. So any process that stops the lungs from inflating or deflating appropriately, is going to cause us a problem. So when we think about the lungs, we can actually have something called hypoventilation disorder. Disorders of sleep associated hypoventilation. And when we say hypoventilation, normally when we breathe in and out we get rid of carbon dioxide, but unfortunately when we don't breathe in and out enough, when we don't ventilate our lungs enough, we can get a buildup of carbon dioxide and in some cases we can also not have enough oxygen. Now these kind of hypoventilation problems with our breathing can occur because there's a problem with the lungs, the chest wall, if we're using some medications that depress our respiratory function like narcotic pain killers for example. If somebody is very obese and just the shear amount of obesity reduces their ability to breathe in and out and ventilate their lungs. And the problem here is that this chronically elevated carbon dioxide poses a problem because it can actually result in right-sided heart failure and never mind our low oxygen because one of the things that we know is that our brain, our heart, pretty much all the organs in our body need oxygen to function. So if we have a low oxygen, we're going to have problems with our brain over time, especially chronically we can have a degree of cognitive impairment. We may have problems with our heart. Some people may develop arrhythmias, abnormal heart rhythms again over time, and also our blood as well. So we can develop polycythemia, which is a very elevated amount of red blood cells in our blood, and this can also be a problem. That can cause it's own huge range of complications. So as we can see here, breathing related sleep disorders, we can really break them down into these three big categories. Are they related to the airways, obstructive sleep apnea? Are they related to the brain, central sleep apnea, or are they related to the chest wall, the lungs, this kind of sleep associated hypoventilation conditions or disorders?