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Stages of hypertension

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Tanner Marshall.

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Video transcript

- (Voiceover) If you've ever gotten your blood pressure measured before, I'm sure you've heard a number like 120 over 80, right. Well, what do those two numbers mean? Well, let's start with the units cause these aren't just numbers, right. Usually, it comes along with units like mmHg which mean millimeters of mercury, where the Hg is what's used to abbreviate mercury. I know, why Hg, right? Well, it's named after this Latin word for liquid silver, so it's essentially Latin. And so, millimeters of mercury is the standard unit used to present somebody's blood pressure. Okay, so this first number, this top number is known as your systolic blood pressure. Remember that systole is the phase of the heart cycle where the heart contracts and pumps out blood or simply during a heart beat. So, you've got your two ventricles, your left and your right ventricles, and when those squeeze and get smaller, they actually eject blood out to your circulatory system, right. And when this happens, when the blood is forced through the blood vessels, pressure is going to be generated in those blood vessels, and this is what we call your systolic blood pressure. The lower number, in this case 80 millimeters of mercury is called the diastolic pressure. Now, we can figure out what that is by its name. It's the pressure in the blood vessels during diastole. Again, remember that diastole is when the heart is relaxing. So this is the pressure in the blood vessels between beats when the heart's relaxing. So, it's like contraction systolic pressure, and then relaxation diastolic pressure. Pretty easy. So I'm going to draw out these two gauges. One's for systolic pressure, and the other's for diastolic pressure. So let's say that my blood pressure was measured at 115 over 75 millimeters of mercury. So I'm right about here on our gauge. Really anything sort of below 120 in the systolic range, we're just going to draw as like this green zone. So your sort of safe from hypertension in this zone. Now, that's not to say that like a pressure of 15 millimeters of mercury is a good thing. What I mean is that you wouldn't have hypertension or you wouldn't have high blood pressure. So usually around 120 is considered an average systolic blood pressure. Along the same lines, right around 80 millimeters of mercury on the diastolic side, while the heart is relaxing, is considered average on the diastolic side. And so, if it's below 80 millimeters of mercury, then we'd say that there would be no hypertension. So this again is in kind of the green zone for hypertension. So now let's say that my pressure was a little higher, maybe 130 over 85. So over here on the systolic side, we're above the green zone now. So in this zone, up to about 140 millimeters of mercury, it's still not hypertension, but it's like it's getting close. It's like we're getting there. So let's make that zone yellow, and this zone actually is referred to as prehypertension. So it's like before hypertension. And so the same goes for diastolic pressure. Our yellow prehypertensive zone or stage is between 80 and 90 millimeters of mercury. Now, it's important to note that these yellow zones aren't like this hard and fast rule. It's more based on averages and is like this sort of warning sign that the blood pressure is maybe slightly elevated, and it's possible it could lead to hypertension in the future especially if this is combined with unhealthy lifestyle like no exercise or poor diet. Okay, so with that said, in general, hypertension is defined as a blood pressure greater than 140 over 90. So let's draw that as this kind of reddish zone above 140. So if my blood pressure was 150 over 100 which is right here on the systolic and right here on the diastolic, we see that, that would be considered hypertension, right. So to be more specific, though, that would be considered stage one hypertension, which is this zone on the systolic side from 140 to 160 and then, over here on the diastolic side from about 90 to 100. Now there are only two stages, so stage two is really anything above 160 on the systolic side and 100 on the diastolic side. So for example, again, my blood pressure was 170 over 110. That would be stage two hypertension. Now, let's say my blood pressure is measured at 150 over 85. Okay, I can figure that out. Looks like over here it's 150 so that falls in to stage one hypertension, but then over on the diastolic side 85 is in the prehypertension stage. What gives? Is that possible? Yeah, absolutely, we even have a special name for this, and it's called isolated systolic hypertension. That sort of makes sense though, right, because the hypertension is isolated to the systolic blood pressure. Usually, this is described as systolic blood pressure in the stage one or above zones, so above 140, and then a diastolic pressure below the hypertension zone. This sort of isolated systolic hypertension is more common in the elderly and is actually associated with an increased risk of cardiovascular complications. I'm sure you can see where I'm going next, right. What if my blood pressure is measured at 130 over 105? So I'm in the prehypertension range for systolic and stage two hypertension for diastolic. As you probably guess, this is known as isolated diastolic hypertension. So the hypertension is limited to the diastolic pressure only. This one is actually more common in younger patients that tend to be obese or overweight. However, it's not typically associated with underlying cardiovascular complications like isolated systolic hypertension is.