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Blood pressure changes over time

See how increasing resistance in the blood vessels can cause blood pressure to rise over time. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

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  • piceratops ultimate style avatar for user ∫∫ Greg Boyle  dG dB
    Is it possible to remove plaques and reduce the resistance in the circulatory system by eating a healthy diet (i.e. is it possible to reverse heart disease?)
    (26 votes)
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    • piceratops ultimate style avatar for user chi
      Unfortunately, no. We have yet to devise a method for removing plaques outside of mechanical excision and lifestyle changes can't really reverse heart disease. It's important to keep a healthy diet in order to prevent plaques from developing to a pathogenic state. Statins are a class of drugs that reduce cholesterol; in patients with more severe atherosclerosis, statins are prescribed to stabilize plaque development. :-)
      (23 votes)
  • piceratops ultimate style avatar for user ∫∫ Greg Boyle  dG dB
    [Slightly off topic] Why do smaller animals tend to have lower heart rates than larger animals (e.g. mouse = 300 bpm and a horse = 38 bpm)?) It seems that the larger animal has a lot more tissue and would need to circulate the blood more frequently to get enough oxygen to the cells.
    (13 votes)
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    • leaf green style avatar for user poisonveca
      I am not an expert but I think it applies only to warm-blooded animals and it has to do with maintaining the body temperature. It is a fact that smaller animals need more nutrients per kg of body weight then larger animals to maintain constant body temperature. It is because smaller animals lose more heat from their skin and larger animals usually are much better isolated so they give off less heat. Based on this, one can actually count the smallest possible warm-blooded animal, it is arounf 2,6g I believe. Animal smaller then this would have to eat more then 24h to keep the body warm... which is not possible :-)
      The amount of tissue that you mentions reflects in the amount of blood an animal has: for example, a smaller animal probably has 0,5l of blood and a horse has 7l (I am guessing ! I have no idea how much blood a horse has).
      Hope it was helpful.
      (10 votes)
  • male robot hal style avatar for user Tahsin
    Why is keeping our blood pressure in normal range so important for our health?
    (7 votes)
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  • leaf red style avatar for user Aron Øra Myren
    I thought the main reason for increase in BP over age was Arteriosclerosis (eg. stiffening of the arteries). What is the main cause?
    (9 votes)
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    • leaf orange style avatar for user Tanj
      More correctly, he's talking about atherosclerosis (which is arteriosclerosis due to fatty plaques) - the key is to look at the spelling of the word.
      Still, you would find more general arteriosclerotic changes over age due to less effective hormonal regulation of vessel maintenance (such as less elastin, increased collagen, calcification, etc), and other causes.
      (6 votes)
  • spunky sam green style avatar for user jgingold533
    As plaque builds up in the circulatory system and reduces the radius part of the resistance equation, can the body adjust other variables in the resistance equation to try and maintain a specific resistance? For example will the body reduce blood viscosity? Or will the body increase the radius of other capillaries or arterioles to try and offset the effects of a plaque?
    (4 votes)
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    • blobby green style avatar for user andrea.davidowitz
      Good question. Blood viscosity can't change very easily, but a doctor could put this patient on blood-thinners to try and accomplish this. The artery will try and dilate itself, but remember that the plaque doesn't really allow the walls to expand very well.

      If an artery has a lot of plaque build-up, often times tiny arterioles will branch off from below the plaque occlusion to above the plaque occlusion, in essence to bypass that diseased part of the vessel. Your body actually creates a new artery. Pretty cool, right?

      In fact, when you hear of people who get a coronary artery bypass, that's exactly what happens: the surgeon creates a little tube and connects it to the artery that is occluded so that the blood can divert around the plaque buildup. Sometimes you'll hear of a double bypass, triple bypass, etc. which means the heart surgeon had to create little artery tubes to go around plaque buildup in two places, three places, etc. Another surgical option is called an atherosclerectomy in which the surgeon kinda roto-rooters the plaque from the artery.
      (8 votes)
  • blobby green style avatar for user gail ment
    really heart rate desnt change over time ? why not ?
    (5 votes)
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    • leaf green style avatar for user Joel Sukumar
      Heart rate according to me has no relation with time (or age) because it is primarily controlled by a pacemaker (sinoatrial node) which regulates no. of beats per minute . Defects in the sinoatrial node can alter the heart rate. (Another possibility is presence of an extra pacemaker region apart from sinoatrial node which alters the heart rate)
      (3 votes)
  • female robot amelia style avatar for user phunguyenduongthien
    isn't heartbeat change toward time, so the Q have to change too, someone explain that to me please. Thank you
    (3 votes)
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  • female robot grace style avatar for user trovial
    doesnt the tissues like muscles or fat around the vessel apply pressure on ir, blocking it or increasing blood pressure?
    (3 votes)
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  • blobby green style avatar for user Kate
    How do we measure venous pressure?
    (2 votes)
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  • female robot grace style avatar for user trovial
    is the viscosity of the blood also a factor when talking about resistance, or is it irrelevant?
    (2 votes)
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Video transcript

Let's imagine that I'm here. And this is me at the age-- actually, I'll do this right now-- so let's say at the age of 31. And then I go into the future. So this is a line for the present. And then I go into the future. And this is me again. And this is now at the age of 71. So I've got 40 extra years. I've even picked up a cane to help me walk around. And finally, I go even further in the future, and I'm being very optimistic. And I'm going to go ahead and say this is at the age of 101. I live to be a centennial. And I'm sitting in a wheelchair, and I'm going to wave out at you. So that's me in a wheelchair at the age of 101. And we're going to apply that formula we've been talking about so much, delta P equals Q times R. So I said Q is cardiac output. And we've got R is resistance. So we've got this formula. And let's say I go to the doctor's office. And I go today, and I go in 40 years, and I go again when I'm 101. And today, they tell me my blood pressure is 120 over 80. And actually, I went not too long ago, and that's pretty much what they told me it was. And I go in the future, and in 40 years, they tell me it's actually gone up. My blood pressure is now 150 over 90. And in fact, I go again, when I'm 101, and they say it's 180 over, let's say, 105. So the blood pressure is rising, and that's basically what I'm told. And they say, well, you've got to make sure you eat well and exercise, and that should help your blood pressure. And I'm left wondering what the connection is between the two. So let's figure out what that connection is exactly. So my blood pressure, I just said, is 120 over 80. And if I want to figure out my mean arterial pressure, meaning the average pressure in my arteries, I can actually use my blood pressure to give me a good guess as to what it's going to be. So I know that I spend about 1/3-- my mean arterial pressure is going to equal 1/3 times my systolic, because I know I spend about 1/3 of the time-- my heart does anyway-- spends 1/3 of its time beating. And it spends 2/3 of its time relaxing. And the relaxing pressure is the diastolic pressure, that's 80. And so that works out to about 95. And so that's how I came up with that 95 number. And that's also why it's not exactly 100, which is what you'd think an average would be between two numbers. But it's because we don't spend the exact same amount of time in systole as diastole. So then if I wanted to figure out here, it would be 1/3 times 150 plus 2/3 times 90. And that works out to 110. And if I wanted to do it at the age of 101, my mean arterial pressure would be 1/3 times 180 plus 2/3 times 105. And that works out to 130. So I figured out my mean arterial pressure. Let me write that with a line. I also need my mean venous pressure, because we know we're going to have to subtract the two from one another to get the delta P, delta meaning the difference. So mean venous pressure right now is about 5. And let's assume-- this is one of a few assumptions we're going to make-- let's assume that it doesn't change, that over a few years, it really stays around the same. It's about 5. Well, then if I know that, my delta P is easy to figure out, right. I can just take 95 minus 5, and that'll get me 90. And I can take 110 minus 5, and that's 105. And I can take 130 minus 5, and that's 125. So I figured out my delta P, which is basically my mean arterial pressure minus my mean venous pressure, and that equals my delta P. OK, so far so good. Now let me change colors to figure out my Q, my flow. And right now, I have, let's say, a stroke volume-- I'll write it up here-- stroke volume, meaning each time my heart beats, about 70 milliliters of blood go out. So each time my heart beats, it sends out to the rest of the body 70 ml of blood. And that's based on the fact that I'm about 70 kilos. And my heart rate is about 70, very relaxed heart rate. And let's assume, just as we did with the mean venous pressure, that that doesn't change. So this is not going to change over time. So this works out to about 5 liters a minute because Q is simply-- let me write that here-- Q is simply SV times HR. And so I'm just multiplying those two numbers together, and you get about 5 liters a minute, and it doesn't change over time. So 5 liters a minute here, 5 liters a minute here. And I should probably mention all of my pressure units should be millimeters of mercury. I didn't write that, just to not clutter up the board. But let's just assume that-- well, it's not assuming. It is millimeters of mercury. So now using my equation, I can now say, well, delta P-- and actually maybe up here I should even change this. It should be blue so that I'm consistent. So delta P equals Q times R. So if delta P is 90 and Q is 5, my resistance equals 18. Right? It's just a bit of math that I did very quickly. But 18 times 5 is 90. And here I could figure it out. 105 divided by 5 would give me a resistance of 21. And here, I would figure out that it's going to be 25. So one thing that I've been told by my doctor is my blood pressure is rising. And two things that I've assumed are that my mean venous pressure is the same, and that my cardiac output is the same. And if I assume that, and that's definitely not true for everybody, but if I assume that for me, then that means that my resistance has gone up. Over time, my resistance has gone up. And let's now change screens and figure out how that could possibly happen. So let me draw myself out again. So I've got three versions of me. I've got the present me at the age of 31. I've got the future me with a cane at the age of 71. And I've got the really old version of myself living at a ripe, old age of 101, waving, in fact. So three versions of myself. And if I was to draw my arterial tree, let's say, a simplified version of my arterial tree. Let's say here's a vessel coming through, and I've got, let's say, another vessel, and this branches here. And I've got a third vessel, and this branches here. Right now my arterial tree looks pretty good, pretty clean. And that's why my resistance was 18. Blood is flowing through very smoothly. It's going out this way to feed the kidney and maybe to my ears and my eyes and my foot. And it's basically making its way through, no trouble. Now at the age of 71, something happens. Actually, let me just draw a little divider line. At the age of 71, something happens. I have, let's say, the same arterial tree. I'll try to draw it the same way. Except now, I've been eating, for 40 years, foods that are not the best. And I certainly haven't exercised a whole heck of a lot. I haven't gone to the gym very often. And now I've got buildup of plaque. So let's say I've got a plaque right there. And I've got a plaque, let's say, another one right there. And let's say I have a plaque right there. So I've got three little plaques. And we'll get into plaque and what it's made of exactly in a future video. But for the moment, just think of it as something that's blocking up that vessel. And it's usually made of fatty substances and macrophages and cells that have died and all sorts of basically crud that fills up the vessels. And so, because it's filled up the vessels, now here, my radius got smaller. My vessel radius in here got smaller. And over here, it got smaller. So blood, as it's flowing through, is having a tougher time getting through because the radius is smaller in these spots. And, as you know, if you calculate total resistance-- and that's what, actually, this is, total resistance-- the total resistance will start to slowly climb up. And in this case, maybe it climbs up to 21. And now years go by, let's say 30 more years go by. I'm now in a wheelchair. And I continue to not eat so well. I eat the same sort of fast food that isn't healthy for me, but I can't possibly stop because I find it tasty. And at the end of the day, my vessels look like this. I have that same one as before, let's say. And let's say this one actually grew longer. So instead of just being part of the vessel, let's say it's huge now. This one got very big. And let's say this one up here actually continued and grew a little bit as well. But I also picked up another one right here, let's say. And I also got one right here. So I have a few more blocks in the road. And so now my blood is having a real hard time getting through because it's got more obstruction to flow. All my paths have a smaller radius. And we know, and I've mentioned a number of times now, about the relationship between a radius and resistance. And that as the radius everywhere gets smaller, the resistance is going to get bigger. And so my total resistance here, let's say, is about 25. So now you can see how eating a certain way and not exercising is going to lead to potentially developing these plaques that act as roadblocks and get in the way of blood flow. And the reason that that's a problem is that, as we see now, the radius gets smaller, the resistance goes up. And in the previous slide here, we actually can see now that as the resistance goes up, assuming that the other things kind of stay the same, your blood pressure can go up. And so when you hear, in the doctor's office, that you have a blood pressure of a certain number over a certain number, that's one thing that we can measure. And what it tells you is a little bit of information about some of the things that we can't easily measure, such as resistance. So let's stop there, and we'll pick up.