When measuring the blood pressure nurses often say numbers like”120 on 80″. What exactly do those numbers mean and why do you die when they coincide?
In: Biology
When you pump up a blood pressure cuff to the degree that it completely cuts off circulation, no blood is moving through the brachial artery. When you listen through your stethoscope, you hear nothing.
As you let the air out of the cuff, the pressure drops low enough so that the blood being pushed through the brachial artery forces its way through past the cuff, and then once the heart relaxes the blood vessel slams shut again. You suddenly hear a thump in the stethoscope every time the blood forces its way through. The highest number you hear this noise at is called the systolic pressure, which is the maximum force the blood is pushing against the walls of the artery while the heart is beating.
As you continue to let the pressure drop, the blood vessel will continue to pop open with each heart beat and slam shut as the heart relaxes. Eventually, the cuff pressure drops so low that it can’t squeeze the vessel shut even when it relaxes. At this point, the noise in the stethoscope goes away. This is called the diastolic pressure, which is the resting pressure in the artery when the heart is fully relaxed.
This is written as “systolic/diastolic” and said as “systolic over diastolic.” For example, 120/80. The values of these numbers over time are used by doctors to predict your likelihood of future cardiovascular diseases like heart attacks, strokes, or heart failure.
The only ways your systolic and diastolic could become equal are if your heart isn’t beating or if you have a massive bleed in that limb such that no blood is actually coming down your artery. In case of the former, you’d be in cardiac arrest and actively dying, while in the case of the latter you would very obviously have blood squirting everywhere. And in either case, you wouldn’t actually say the systolic and diastolic were equal, you would say that you’re unable to obtain a blood pressure at all as you will not actually be able to detect the blood sound (or the fluid wave for automated cuffs.)
OP asked what it means if the BP is the same, not what happens when your BP is the high. In short, if the pressure in your blood vessels is the same when the heart is contracted from when it isn’t (basically the pump vs the non pump) then blood isn’t moving through the blood vessels.
You need positive pressure to move any liquid through any tube, if the pressure in the tube is the same when the pump is on from when the pump is off then you can conclude that while the pump is in the “ON” position it isn’t actually moving any liquid.
Systolic pressure (120) must be greater than diastolic pressure (80) in order to move blood through vessels. The closer those numbers become, the less blood flow you’re getting. If they’re both too high (so, in excess of normal ranges), you’ve got some stress on your cardiovascular system that could be dangerous if they become too high.
No one has stated what the numbers actually mean. 120/80 refers to the distance a column of mercury will be pushed up (in millimetres). They used mercury because its denser and you could read the movement easier. They used a tube of it and the high number pushed it up 120mm. Then they allow it to drop to the lower number, which only pushed it up to 80mm.
That why they initially squeeze the cuff hard (to see how high it reaches) and slowly release the pressure until the lower number is reached.
Edit: the chemical sign for mercury is Hg, so the unit for blood pressure (at least in Canada) is mmHg
Children and adults have different blood pressure numbers that are considered normal. The numbers also change with different age groups, gender and size
The first number is the systolic pressure (when the heart is actively pumping), and the second number is diastolic (when the heart is resting).
120 over 80 is the a borderline healthy measurement on the high side.
High blood pressure is bad because it puts an undue strain on your heart, and comparing systolic and diastolic numbers can help determine exactly what the problem is.
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