What is Blood Pressure?

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

Rob Lamberts, MD
5-minute read
Episode #28

What Happens When Systolic Blood Pressure Gets too Low?

The systolic pressure is essential to get blood to the brain. Just like the shower upstairs, a low pressure in the pipes will make the pressure to a person’s upstairs inadequate. It’s pretty important that the brain doesn’t stop functioning, so inadequate blood flow to the brain is not tolerated. If the pressure in the pipes isn’t adequate, the body takes drastic measures to make sure the brain gets enough blood: it passes out. The exchange goes something like this:

Your brain says, “Hey, I need more blood!  I am starving and can’t breathe!”

“I am trying as hard as I can!” the heart responds. I’m even beating faster!” 

“It’s not enough,” gasps the brain. “I need food and oxygen. I need it now!”

“I just can’t get blood up there. You are too high up!  Can you make my job easier?” the heart begs.

“No problem” says the brain, and passes out, causing the body to lie on the ground.

“Much better!” responds the heart. Now I can get you all the blood you need.

Pretty cool isn’t it?  You don’t get that kind of drama on the Grammar Girl podcast.

Low systolic blood pressure is an immediate problem; if it gets too low, you can’t live. A high systolic pressure isn’t that big of a deal in the short run, in fact, it’s the diastolic number we focus on more for treatment.  That’s because the diastolic pressure causes more harm in the long-run.

What Should Your Blood Pressure Be?

What’s a good blood pressure?  It depends on the age and size of the individual. Little kids don’t have as much gravity to deal with, so they don’t require as high of a blood pressure. For adults, the normal range for systolic blood pressure (which is the first number in the reading) is between 100 and 130 millimeters of mercury. Millimeters mercury expresses the amount of pressure in terms of how high it can push a column of mercury – which is a real heavy liquid.  You probably noticed that silver stuff in some blood pressure measuring devices?  That’s mercury. 

Systolic pressures in the 90’s are OK as long as there is no fainting or dizziness, but below that is usually the sign of trouble.

The diastolic pressure should ideally be below 80. There is no official number for a low diastolic blood pressure and there are few conditions that cause it to be low without also bringing down the systolic.

Quick and Dirty Tips for Blood Pressure

I’ll stop here now, giving you a few quick and dirty tips regarding your blood pressure. My next article will specifically cover the issue of high blood pressure.

Tip 1: Get your blood pressure checked.

A good goal to shoot for is 120/70. Since high blood pressure doesn’t usually have symptoms, you need to get it checked regularly.

Tip 2:  If you want to know when to worry about your blood pressure, read my next article.

If you have questions you want answered, send them to housecalldoctor@quickanddirtytips.com. You can find me on Twitter as @housecalldoc and on Facebook under “House Call Doctor.”

Let me remind you that this article is for informational purposes only. My goal is to add to your medical knowledge and translate some of the weird medical stuff you hear, so when you do go to your doctor, your visits will be more fruitful. I don’t intend to replace your doctor; he or she is the one you should always consult about your own medical condition.

Catch you next time!  Stay Healthy!

Blood Pressure image courtesy Shutterstock


Please note that all content here is strictly for informational purposes only. This content does not substitute any medical advice, and does not replace any medical judgment or reasoning by your own personal health provider. Please always seek a licensed physician in your area regarding all health related questions and issues.