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What is Blood Pressure?

Part 1 on blood pressure. What is blood pressure, and why is it important?

By
Rob Lamberts, MD
Episode #028

Chronic high blood pressure, or hypertension, is responsible for a huge amount of death and disease, affecting nearly 60 million people in the US. It is the #1 reason for visits to the doctor and the #1 reason people need prescription drugs. Despite all that attention, blood pressure is poorly understood and is often poorly controlled, resulting in a multitude of problems. It’s a huge topic, and (predictably) impossible for me to cover in a single article, so I will once again split it up into two. Today I’ll try to explain what blood pressure is, and next week I’ll explain the consequences of high blood pressure.

What is Blood Pressure?

Your blood pressure is the pressure used to get the blood to where it is needed. Have you ever gotten into the shower in the morning only to find out that there isn’t any water pressure?  It’s not a fun thing. It not only can make you really grumpy, it can cause those around you to be grumpy about the smell you emanate. Blood pressure is much the same. The bloodstream carries oxygen and food to cells in the body, and it carries away waste products. Insufficient blood flow, then, results in cells suffocating, starving, and not getting rid of potentially toxic waste. That not only makes the cells pretty grumpy, it can kill them.

What is Needed for Good Blood Pressure?

Two things are essential to maintain good blood pressure: good pipes and a good pump. Blood vessels are the pipes in your body. The arteries are like the water pipes, requiring higher pressure to bring the essential fluid to where it is needed. The veins are the pipes that bring back the used blood, much like the sewer system, and don’t require as much pressure. When we talk about blood pressure, we are really talking about the pressure in the arteries.

How are Your Heart and Blood Pressure Related?

The pump in your body is, of course, the heart. The heart is a hollow muscle that squeezes blood out to the body. There are two chambers, called ventricles, that do the pumping:

  • Right ventricle:  The right ventricle pumps blood to the lungs so it can get oxygen.

  • Left ventricle: The larger left ventricle pumps blood to the rest of the body.

There are two parts of the heart’s pumping cycle: the part where it relaxes and fills up with blood, called diastole, and the part where it squeezes blood out to the body, called systole.

The two parts of the heart’s pumping cycle are important because they coincide with the two important blood pressure numbers.

  • Systolic pressure:, Systolic pressure happens when the heart squeezes, and

  • Diastolic pressure: Diastolic pressure is the lowest pressure in the cycle, which happens when the heart relaxes.

So when a blood pressure cuff is inflated, the highest pressure at which the person listening with the stethoscope hears a “thunk” is the systolic pressure. The lowest pressure in the cycle, or the diastolic pressure, is signified by when the “thunk” sound goes away.  Here’s why both are important.

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About the Author

Rob Lamberts, MD
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