HomeHealthcare AccessPatient Advocacy

Understanding and Measuring Systolic and Diastolic Blood Pressure

Timothy Aungst, PharmD
Published on June 12, 2019

It’s estimated that over 40% of the U.S. population has hypertension, and most of those people don’t know it. Why? One reason is that it’s tricky to confirm if you have hypertension, especially if you’re only getting your blood pressure read at occasional doctors’ visits. That’s why recent guidelines recommend that patients also learn how to measure their blood pressure at home.

Here, we’ll talk about what your blood pressure numbers mean and how you can choose a proper, at-home monitor to keep track of them on your own.

02:47

First, what are systolic and diastolic blood pressures?

To know if your blood pressure is “good” or “bad”, you’ll first need to know about systolic and diastolic blood pressure. The top number of your blood pressure reading is your systolic blood pressure. That’s how much pressure is pushing on your blood vessel walls as your heart contracts and pumps out blood to your body. The bottom number is your diastolic blood pressure. That tells you the pressure on your blood vessel walls when your heart relaxes between contractions.

For example, 128/82 would be interpreted as a systolic blood pressure of 128 mmHg and a diastolic blood pressure of 82 mmHg. If your blood vessels are healthy, they will stretch to make room for the blood that is pumped through them. However, if your blood vessels are stiff, the blood flowing through them will be under greater pressure, and that means your blood pressure numbers will be higher.

What is a “good” blood pressure?

It’s important to emphasize that a “good” blood pressure reading depends on your own individual health. Your provider will be able to tell you what’s healthy and safe given your personal health circumstances.

Nonetheless, below are guidelines from the American Heart Association for people in general. Remember: Your blood can be temporarily high or low at times (like with exercise, stress, or caffeine). This chart applies to how your blood pressure is normally, which is why you may want to take an average of several readings before seeing where you fall.

Blood pressure category Systolic blood pressure Diastolic blood pressure
Normal Below 120 mmHg and Below 80 mmHg
Elevated 120-129 mmHg and Below 80 mmHg
High blood pressure (stage 1) 130-139 mmHg or 80-89 mmHg
High blood pressure (stage 2) Above 140 mmHg or Above 90 mmHg
Hypertensive crisis (call your doctor immediately) Above 180 mmHg and/or Above 120 mmHg

*Adapted from the American Heart Association

Why should I monitor my blood pressure at home?

Even if your doctor takes your blood pressure in the clinic, monitoring your blood pressure at home can be useful whether or not you have hypertension.

  • It can tell you if your blood pressure is changing over time, which is important because your risk for hypertension increases as you age.

  • It can come in handy while you’re exercising, and tell you if you’re exercising at a healthy and safe intensity level.

  • If your doctor suspects that you have hypertension, it can give them a better sense of what your blood pressure is like on a normal basis.

  • If you have hypertension, it can help your doctor see if your treatment plan is working. Current guidelines recommend that patients with hypertension aim for a blood pressure lower than 130/80 mmHg, with the help of lifestyle changes and medications.

  • If you take blood pressure medications, it can be especially helpful if you experience symptoms like headaches or dizziness. Low blood pressure readings during those times can alert your doctor to adjust the dose of your medication or give you a different drug to try. No matter what, do not change how you’re taking your medications without talking to your doctor. Call your doctor immediately if you find that your blood pressure is too high or too low, or if you experience symptoms like headaches, dizziness, or fainting.

How do I choose a blood pressure monitor?

The first step in measuring your blood pressure at home is getting a blood pressure monitor—one that is accurate, fitted, validated, and works for your lifestyle. These are some things you should consider:

  • Get an arm cuff – Devices come in many styles these days, including ones that attach to your arm (above the elbow) and ones that attach at your wrist. Wrist cuffs can be attractive because you don’t need to roll up your sleeves to use them, but they tend to give inaccurate measurements. Go with an arm cuff instead.

  • Choose the right cuff size – The wrong cuff size can lead to inaccurate blood pressure readings. Larger cuffs are better for larger arms, and smaller cuffs are better for smaller arms. Make sure you get a size that fits you.

  • Make sure the device is right for your age – Devices are specific to age. Some are meant for older people, and some are meant for children. As an aside, some are even meant for women who are pregnant. Make sure to get one that’s right for you.

  • Make sure the device is validated – It may be tempting to just buy the cheapest device on the internet, but you may end up with a blood pressure device that isn’t approved or validated for taking an accurate measurement. Make sure yours is validated.

  • Decide if you want Bluetooth features – Newer blood pressure devices with Bluetooth integration allow you to conveniently track your blood pressure measurements through an app. This feature makes it easy to share your records with your doctor (by email or by printing it out), but it usually comes at a price.

How do I get an accurate blood pressure reading?

Once you’ve chosen a validated blood pressure monitor that fits your needs, you’ll still need to take an accurate reading with it. The best way to learn is to bring it with you to your next doctor’s visit, so your doctor can show you how to use it correctly. In general, these are good things to keep in mind when measuring your blood pressure at home:

  • Sit in a chair with a firm back, keeping your back straight and your legs flat on the ground and uncrossed.

  • Rest for 5 minutes or more before measuring your blood pressure.

  • Keep your arm at heart level and on a flat surface such as a table.

  • Place the blood pressure cuff around your arm so that it’s touching your skin. Do not put the cuff over clothing.

  • Take two measurements at least 1 minute apart in the morning before taking medications, and take two measurements at least 1 minute apart in the evening before supper. Be sure to do this at the same times each day. Your doctor may also ask you to take additional measurements depending on your specific health concerns.

  • If you’ve been exercising and need a measurement of your “normal” blood pressure, rest for at least 30 minutes before taking your reading.

  • Do not smoke or drink caffeinated beverages like coffee, soda, or tea if you’re planning to take a blood pressure reading in the next 30 minutes.

Other helpful resources

The American Heart Association has a lot of helpful resources for people with hypertension, including a guide for measuring blood pressure at home, a tool to track your blood pressure online, and a journal for tracking blood pressure that you can print out.

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