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?

Question

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

Answer 1

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.)