Health and medicine
- What is blood pressure?
- Learn how a stethoscope can help determine blood pressure
- Resistance in a tube
- Adding up resistance in series and in parallel
- Adding up resistance problem
- Flow and perfusion
- Putting it all together: Pressure, flow, and resistance
- Blood pressure changes over time
- Regulation of blood pressure with baroreceptors
What is blood pressure?
Find out what a systolic and diastolic blood pressure mean. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
Want to join the conversation?
- How accurate are those blood pressure meters that you can find at the pharmacy department of some stores?(54 votes)
- Good question. Sheldon G. Sheps, M.D. (emeritus hypertension specialist) has answered this on behalf of the Mayo Clinic. He writes that it is not uncommon that a wrist meter shows a very different reading from that in the doctors office. You could bring the meter to the doctor to compare. A meter of this kind is very sensitve to body position. Keep the arm at heart level when measuring blood preassure.
See http://www.mayoclinic.com/health/wrist-blood-pressure-monitors/AN01839 for more details.(45 votes)
- Why is keeping our blood pressure in normal range so important for our health?(36 votes)
- If blood pressure is too high, damage to organs and vessels will occur. It could cause vessels to become damaged which could lead to a stroke or a heart attack. Also if the blood pressure is too high the Kidneys will also not function correctly, which is a huge problem. If the blood pressure is too low, organs and tissues will not receive adequate oxygen supply. Without adequate oxygen there are severe consequences, such as death.(35 votes)
- why is doing sport so good for your blood pressure and health?(24 votes)
- Hi Fred, good question!
Regular exercise makes your heart larger and stronger, like all other muscles in your body. The heart can then pump more blood with less effort, even when not training. This reduces the force on your arteries, and thus lowering your BP. Read this for more info: http://www.mayoclinic.com/health/high-blood-pressure/HI00024
- how many times in a year does the average person go to get their blood pressure taken.(12 votes)
- what activity makes the blood pressure rise?(4 votes)
- A person can increase their blood pressure, by: yawning, moving, tensing muscles, feeling anxiety, or consuming specific drugs/foods. A person can lower blood pressure in the short-term by managing that above list. In the long-term, reducing blood pressure requires dietary/lifestyle changes or biofeedback / careful practice.(6 votes)
- what diseases does bad blood pressure cause?(2 votes)
- The most common things we attribute to hypertension are: strokes, retinal damage of the eye, heart attack, heart failure, and renal failure.(6 votes)
- Can bloodpressure make you angry like as if you feel like exploding or destroying something.(2 votes)
- I think you're mixing up cause and effect. If you're angry or tense, your blood pressure would increase. Your mental state is what impacts your blood pressure and heart rate, not the other way around.(6 votes)
- Why we take blood pressure from arm??(4 votes)
- And measuring in the neck would also risk airway. Can you imagine strapping the blood pressure cuff on your neck and pumping it up?(2 votes)
- I've heard that the difference between the systolic and diastolic blood pressure is just as important, or more important, than the two readings. Can you explain this?(4 votes)
- that is important in terms of seeing a disorder in the heart's function such as cardiomyopathy. If there is a big discrepancy, it can mean that the heart is not filling or pumping right.(1 vote)
- Lets just say, I have a high blood pressure. I don't know that and start my daily exercise/workout. Is it bad for my health since exercising means increase of the blood pressure?(3 votes)
- Exercise actually helps in lowering the blood pressure in the long run, so a doctor would not prevent a patient from being active in most circumstances.
For more information:
So recently I went into my doctor's office, and I was told that my blood pressure was 115/75. So I thought we would talk about exactly what this means and try to figure out how to think about blood pressure in general, using these numbers and this experience as kind of a launching point. So the way I think about blood pressure is I always imagine kind of a tube and I imagine blood going through that tube. And this tube is like a blood vessel. So there's blood trying to get its way from one side to the other. And on its way, the neat thing that it's doing is as it flows, it's pushing out. So it's forcing against these walls, and specifically what I mean by that is there are cells and there's plasma, and all that stuff is pushing out against the walls of the blood vessels. So you've got a force, and that force is being exerted on the surface area of the blood vessel. So it's force over a surface area. And any time you see force over an area, you know that equals a pressure. And in this case, it's a blood pressure because it's the blood that's doing that work. So this is how I think of blood pressure, specifically as those little blue arrows. And the two questions that kind of pop into my mind anytime I'm thinking about blood pressure are where is the blood pressure being taken, and when are you taking it? So let's start with the first question, where? And by that I mean where in the circulatory system. So you've got the heart-- and this is my Valentine's Day heart-- and you've got the aorta coming off of the heart. And it's got lots of branches, but I'm going to just draw one branch, which is the artery leading off to my arms. This is called the brachial artery going off to my arm. And usually, I'd say 90% of the time, maybe even more, the blood pressure that you're getting recorded, or the number that's being told to you, is being checked at this point. I marked it with a little x because that's kind of the upper arm. So that's usually where they're checking the blood pressure. And again, they're checking the force that the blood is putting on the vessel walls. So these little blue arrows. So that answers the where question. And certainly, you can imagine if I checked blood pressure let's say at some other spot, let's say over here or over here, you might get a different blood pressure reading than if I checked it at the yellow x. So really were just talking about that one spot. Now the other question is when are you checking it? So for this, let me show you a little table or a figure, rather. So imagine that over time, time is this way, you have different recordings for blood pressure. So this will be blood pressure. And blood pressure is usually measured in millimeters of mercury. So I'll write millimeters of mercury here. And let's go from 200 all the way down to 0. And I'll use my numbers that I got from the doctor the other day to illustrate what I'm trying to say. So right at that yellow x, at the bottom, let's say of my reading I've got 75. So let's start at 75, which is about here. As the heart is pumping, the pressure starts building up. And it gets up to about 115. So really what is happening is blood is making its way from the heart as it squeezes towards that x. And as it gets there, the force that it's putting on the walls is going up, up, up. And as it goes up, it goes from 75 all the way to 115. So that all happens during the squeezing part of the heart cycle. We call that systole. So this is all happening during systole, which is when the heart is squeezing down, and we know the heart is a pump. Now from that point forward, the heart begins to relax. So at this point, at 115, the heart is now relaxing slowly. And as it relaxes, the pressure begins to fall. And it continues to fall all the way out here. And the pressure gets down to about 75 again. And this is diastole. So this is when the heart is actually taking a break from squeezing and is now refilling, and we call that diastole. So I'll call that refilling. And so during systole, you spend about 1/3 of the time. And in diastole, you spend about 2/3 of the time. And I'm talking about one heartbeat here. So this would be one heartbeat. So it's not 50-50. And the easy way to remember this is in a given day, 24 hour day, I spend about 8 hours working and about 16 hours relaxing, or not working. And so I think of the heart doing its squeezing, its work, for eight out of 24 would be about 1/3. Kind of the same as me. About 1/3 of the time, the heart is squeezing. So that's how the heart is spending its time, in systole and diastole. And the pressure is ranging between 115 and 75. So really it's never just 115 or just 75. It's somewhere between the two. And for example, if I checked right here in time, it might be let's say 85, or here it might be 102, or here it might be 87. So it's somewhere between 115 and 75. So this number I wrote up here becomes the range. This is the range of blood pressure. So when I talk about when, it really depends on when in the cycle you're at and you're somewhere in that range. And when I talk about the where, we know that we're talking about a reading that's taken in the upper arm. So those are the two thoughts that should cross your mind every time you hear a blood pressure recording. And of course, the top number, 115 again, is the systolic blood pressure. And 75 is the diastolic blood pressure.