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Current time:0:00Total duration:11:41

Video transcript

what you see here is an anterior view of a guy with his brain showing and you can see all these blood vessels that are supplying his brain here and if anything happened to any of these blood vessels they would deliver less blood to parts of the brain which would likely result in a loss of brain function which is what a stroke is so we don't want him to have a stroke so let's look at a few things that that predispose one to developing a stroke things called risk factors and I think the easiest and sort of most intuitive way to do this is to pick a vessel so we'll pick this one here and the in the brain and we'll look at the different things that can happen to that vessel that might predispose you to developing a stroke so let's just zoom in on that area there so we've zoomed in quite a bit here so you can see the artery here this is a cerebral artery and this is all just sort of surrounding brain tissue all this stuff in pink here and all these wavy lines these are all the grooves and ridges that sort of cover your brain so what sort of things might affect your blood vessel inand predispose you to having a stroke well young blood vessels are usually nice and healthy so the walls of the arteries are pretty strong and have a lot of tensile strength whereas when you get older these walls sort of almost get a little bit weaker so that sort of causes two issues the first one is that if this blood vessel wall is a little bit weaker then it's more likely to rupture and if it ruptures then blood traveling within your arteries can more easily leak out and cause a hemorrhagic stroke so that's the first thing the second thing is that as you get older your arteries the walls of them also get a bit stiffer and stiffer blood vessels put you at a higher risk for developing high blood pressure and that in itself is a risk factor for stroke and we'll talk about that in a few minutes here so age age is a risk factor and actually your risk is the greatest after about 65 years old although strokes can happen in younger people as well and actually risk factors can be sort of separated or thought of in two groups things you can do something about it and things you can't do something about so we'll call the things you can't do anything about non-modifiable or risk factors and we'll call the things you can do something about modifiable risk factors so so age is obviously one of those things you can't do anything about unfortunately for people like me so let's just keep our running list up there in the corner so what are some other non-modifiable risk factors well men are more likely than women to have a stroke and it's not exactly clear why people of African descent are at a higher risk of having a stroke and that's thought to be because they have high blood pressure more often and again we'll talk about blood pressure in a minute and the last one I'll mention is that if you've had a prior stroke before you'd have a higher risk of having another stroke so those are the major non-modifiable risk factors the things that we can't do anything about but what can we do something about well the biggest modifiable risk factor for stroke is hypertension or high blood pressure let me show you two ways in which hypertension predisposes you to stroke so let's say you have another little vessel here a little blood vessel coming off one of the bigger arteries in your brain so this is our little blood vessel well when you have normal blood pressure all your little red blood cells they sort of travel through your cerebral vessels at a at a at a normal speed right so they're not really going too fast they're going just at the right speed to not damage your blood vessels to not sort of bump into your blood vessel walls enough to damage them but what happens when you have really high blood pressure is that these blood cells move a lot faster and when they move a lot faster they do two things the first way that's a problem is because they're moving a lot faster and they tend to bump into the walls of the blood vessel a lot more and so while that's not a huge problem in bigger blood vessels when they get into sort of these smaller blood vessels like this one that high pressure is a little bit too much for the smaller blood vessel to handle and so the walls of these smaller blood vessels start to get a bit thicker to try to compensate for the the extra pressure that they're feeling so this process of the smaller blood vessel undergoing thickening is called hyaline arteriolosclerosis so that's quite a mouthful so let's actually break that down so we remember what it means hyaline just refers to how a cross-section of the vessel would look under a microscope it looks kind of glassy and Highland is derived from the Greek word for something that's glassy or crystal like arteriole oh just refers to the fact that it's happening a smaller artery so an arterial and sclerosis just refers to hardening so hyaline arteriolosclerosis well why is this bad well you can imagine that if the hypertension is long-standing then this vessel will just continue to get smaller in diameter until not very much blood and sometimes no blood at all can get out the other end of the arterial so what do you think is going to happen to the brain tissue that that arteriole serves well it's going to die off and you're going to have a stroke in that area so that's the first way that hypertension is is bad for your cerebral blood vessels what's the other way well as your blood cells rush past this Junction here they're going to continuously sort of bang into this little edge here and if they continue to do that over time they cause a ballooning out and aneurysm of the artery wall so here's our aneurysm and the problem with aneurysms is that as they're sort of a weakening of a vessel wall they have this tendency to rupture and spill blood out of the circulation so will hypertension can cause aneurysms which can then cause hemorrhagic strokes now these next three risk factors sort of work together so I'll talk about them all together I'm referring to diabetes smoking and high blood cholesterol so what happens in diabetes is that you get lots and lots of blood sugar floating around in your blood vessels and this glucose what it does at high concentrations is it damages blood vessel walls and makes them hard and stiff and we all know that smoking right so here the toxins from smoking tobacco smoking these toxins go ahead and damage your blood vessels as well now our third player cholesterol these little particles called LDL cholesterol what they do when they see these damaged blood vessel walls is they sort of hop into the damaged blood vessel walls because they think it's a really cool comfortable place to hang out and they sort of build up so I'll draw it over here but let's say they built up to a really really significant extent and I'm not sure if it looks like it but just to be clear this cholesterol is actually building up within the blood vessel wall and by the way this cholesterol building up within blood vessel walls is called atherosclerosis from here two things can happen either this big cholesterol formation can sort of crack open cause a clot to form on top of it and block off the entire blood vessel that way or or a piece of this cholesterol collection can sort of break off and float downstream to block off a smaller vessel but either way you deprive downstream brain tissue of blood and the stroke would develop that way so diabetes smoking and cholesterol can all work together to increase your risk of having a stroke and I just want to clarify that they all independently increase your risk of having a stroke but here I've just shown you them all working together just for simplicity sake so now let's zoom out a little bit to look at some other risk factors so that atherosclerosis we talked about that can actually affect these internal carotid arteries and in fact they often are affected by atherosclerosis so these are the internal carotid arteries and you can get that fatty buildup of atherosclerosis within them so if that happened you're effectively reducing blood supply to large parts almost all of your brain and you could end up having a massive stroke because although there are sort of redundancy mechanisms in place to provide collateral blood flow to the brain like the Circle of Willis here if you get blockages say in your internal carotid still the internal carotid provide the majority of blood to the brain so if you block one of these off you're really really going to increase your risk for having a stroke and having a lot of your brain tissue die off so the next set of risk factors I want to talk about are ones caused by heart conditions so here's your heart just quickly here's your left atrium your left ventricle your right ventricle and your right atrium now the heart condition that most strongly predisposed is you two having a stroke is called atrial fibrillation so what happens in atrial fibrillation well let's actually just look at the left atrium here because that's the one that's relevant for stroke so in atrial fibrillation your your atria don't contract properly and they actually sort of just quiver instead of properly contracting and so because they're sort of quivering blood is allowed to stick around in them for a little bit longer than it normally is and that blood that sticks around can start to clot because when blood isn't moving it starts to clot just spontaneously and these clots they can break off travel into the left ventricle and then out of the left ventricle where they can head up to the brain and they can get lodged in blood vessels in the brain and therefore they cut off blood supply to parts of the brain and cause an ischemic stroke atrial fibrillation another heart condition that predisposes you to stroke is a myocardial infarct or a heart attack so let's say for example you had a heart attack that affected this part of your left ventricle here normally this left ventricle pumps blood and contracts really really nicely and strongly but after you've had a heart attack it doesn't really contract properly so again you can get this blood sort of sitting around in the left ventricle with nothing to do but clot and again this blood clot can sort of break away from the wall and follow the same route as the clot that developed earlier one more risk factor that has to do with the heart is heart failure so in heart failure your heart muscle actually fails to pump properly it fails to contract properly and if you had a really really bad heart failure you wouldn't get enough blood ejected out of your heart to supply the brain with enough blood that it needs so in this case you would get global ischemia of your brain tissue in other words your entire brain wouldn't be getting enough oxygen so you'd have a pretty big ischemic stroke so the last risk factor I want to touch on is something called the T IA a transient ischemic attack or a mini stroke so I mentioned that some heart conditions can cause clots to travel up to the brain and get stuck in cerebral blood vessels and I also mentioned that you can get some carotid are atherosclerosis here that might embolize right so peace might break off and travel up into the brain and get stuck in an artery now if either of these types of clots goes away on its own within 24 hours so if they dissolve or if the body's own mechanisms break them down and they go away within 24 hours then you've had something called a T ia or a mini stroke simply having had one or more of these mini strokes greatly increases your risk of having a proper stroke so that was an overview of some of the non-modifiable and some of the modifiable risk factors for stroke