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Video transcript

there's two main types of stroke ischemic strokes which is where brain tissue dies because it's not getting enough blood and therefore not getting enough oxygen to stay alive and this is often caused by some type of obstruction of a blood vessel and hemorrhagic strokes which is where a blood vessel in the brain bursts and neither of them were particularly good because they both caused brain tissue to die off so in this video we'll look at ischemic strokes which actually make up about 75% of all strokes and let me orient you to what this over here is this is an under side view of the brain just so you can get a really good look at the blood vessels that originate underneath the brain and supply it with blood so there's three major causes of ischemic strokes and we'll sort of go through each one in turns so the first one we'll talk about as an embolism or an embolic cause of stroke and let me just bring in my guy here to help us out with visualizing so we're looking at the underside an embolism is some type of traveling Mass in your bloodstream and it's most often a little blood clot so in an embolic stroke this little blood clot will travel up to one of your cerebral arteries and get stuck and cut off your blood circulation to that area so let's say it gets stuck somewhere about here let's traveled up through the internal carotid artery and is lodged here in the in the middle cerebral artery and now parts of the brain served by that MCA that middle cerebral artery are all going to start to die off so where would a clot come from well they often come from the heart and I know that sounds like a line from a boys to men song but you can literally get blood clots forming within your heart so either on the valves or within the walls of usually your left atrium or your left ventricle that then break off away from the walls of the heart travel up to your brain and then they get stuck just like you see here where else do emboli come from well you might have some cholesterol built up in one of your carotid arteries or maybe in your basilar artery as part of a process called atherosclerosis and from these collections of cholesterol that build up you can have little pieces of cholesterol that sort of flick off and just as we saw or they sort of travel up into your brain and they get stuck so this little piece of cholesterol has gotten stuck in one of our anterior cerebral arteries here and so it'll choke off blood supply to the distribution of this anterior cerebral artery so we'll have death of brain tissue on this side and remember the anterior cerebral artery supplies blood to some of the more midline parts of the brain so that's the first major type of ischemic stroke ones caused by emboli now another major type of ischemic stroke are one's called thrombotic strokes so how do those happen so it's similar to embolic strokes in that a blood vessel that supplies a part of the brain gets completely blocked but the difference is that emboli arise away from the brain whereas in a thrombosis a problem actually arises in that blood vessel and it gets blocked off at that very spot so let me show you some examples to clarify this so we talked about how you can get some carotid atherosclerosis happening here that buildup of a fatty cholesterol deposit inside your arterial wall and actually let's show it happening in the basilar artery because it's a bit easier to see on the underside picture so you get this buildup of cholesterol and this is actually the most common reason for a thrombotic stroke and eventually that cholesterol deposit is going to sort of crack open it's going to break open which actually causes a blood clot to form on top of it and that blood clot can get really really big and so as you can see in this picture it actually got so big that blood can't even get through this basilar artery anymore and so obviously no blood is being allowed to get through into the cerebral circulation from at least the basilar artery which will pretty quickly cause a stroke so that's an example of a thrombotic stroke a disruption of blood caused by a problem with that blood vessel locally and actually this this atherosclerosis commonly happens in this middle cerebral artery here and of course possibly on those sides middle cerebral artery inside these internal carotid arteries right as they sort of turn into the middle cerebral arteries and in this basilar artery here these are three key locations that atherosclerosis happens so that's a thorough sclerosis and that generally happens in larger arteries in the brain so the ones I sort of pointed out to you already but there's another sort of subtype of thrombotic strokes and this one happens in primarily smaller vessels of the brain and these are called lacunar strokes so let's actually look at these vessels here I'm going to just draw in a few tiny little vessels okay and now we'll blow one up so that's our small vessel if you have hypertension which is long-standing high blood pressure then the walls of these small blood vessels can't really handle the pressure and the force with which red blood cells travel through them with because this really high blood pressure puts a lot of strain and stress on these these blood vessel walls so what these blood vessels do in response is they sort of thicken up they get a lot thicker and so immediately you can kind of see that not very much blood is going to get through them as they start to get thicker and thicker right and that and if the high blood pressure isn't dealt with they're just going to get thicker and thicker and so you can imagine that now not very much blood is going to be able to get out of these blood vessels because it's not really that much blood can get through these blood vessels and so what do you think might happen to the piece of brain that this blood vessel serves well it's not really going to be very happy it's not going to get much oxygen and so it's going to die off so that's a lacunar stroke a small vessel stroke you can also get tiny bits of atherosclerosis happening in these small vessels which would block them off to some extent but really hypertension and this wall thickening is the major cause of these lacunar strokes so the last type of ischemic stroke I want to talk to you about is something called a watershed stroke now what does that mean well let's just go over some basics first the blood flow within your brain goes from inside to out and from outside to in so you have some redundancy there to make sure that all of this brain area is covered it's all getting enough blood but let's say that something happened to reduce total blood flow to your brain so for example if you got too large a thorough m'as or atherosclerosis in your internal carotid arteries okay so not that much blood actually really little blood is getting through up to your brain all right well the total amount of blood that's getting to your brain is going to go down right you'll be in a state of what we call hypoperfusion hypo meaning lowered and perfusion just refers to how much blood your brain is being filled with so as a result of all this you're still going to have a little bit of cerebral blood flow but you're not going to have that right so we'll make these arrows a bit smaller you know get some blood flow on this side from outside to end but you're not going to have as much because overall you're getting less blood up to your brain right because of these two blockages and so what do you notice here I'm sure you notice that there's this huge area in the middle that is not getting that blood supply from either circulation now from either the inside to out or the outside to in circulation so this area will start to die off and actually in watershed infarcts there's a classic pattern almost exactly like what I'm drawing here and so as a result of that this area is colloquially called the watershed area areas where say this part this half is normally perfused by this blood supply and this half is normally perfused by this blood supply but when you sort of scale both blood supplies back a bit this watershed area is prone to being damaged and then in this case this person has developed a watershed stroke so these are the three main causes of ischemic stroke embolism thrombosis and watershed strokes caused by hypoperfusion