Systolic blood pressure is the first number on your reading and measures the force of blood as your heart pushes it out. Diastolic blood pressure, the second number, is the force of blood as your heart relaxes and refills.
When you visit your doctor, the first thing they often do is check your blood pressure. This is important because your blood pressure is a measure of how hard your heart is working.
Blood pressure readings comprise two numbers: your systolic and diastolic blood pressures. But what do those values mean, and how should you interpret the results? Keep reading to learn more.
Your heart is a muscle about the size of your fist. It’s made up of four chambers and contains four valves. The valves open and close to let blood move through the chambers and into and out of your heart.
Your heart beats around
Systolic blood pressure
Your systolic blood pressure is the top number of your blood pressure reading. It measures the force of blood against your artery walls while your ventricles — the lower two chambers of your heart — squeeze, pushing blood out to the rest of your body. This period is called “systole.”
Your systolic blood pressure reading is a
Diastolic blood pressure
Your diastolic blood pressure is the bottom number on your reading. It measures the force of blood against your artery walls as your heart relaxes and the ventricles are allowed to refill with blood. Diastole — this period of time when your heart relaxes between beats — is also the time that your coronary artery is able to supply blood to your heart.
Your diastolic blood pressure reading is a minimum value — the lowest blood pressure during diastole.
Pulse pressure is the difference between your systolic and diastolic blood pressure.
Your blood pressure may be normal, high, or low. High blood pressure is also known as hypertension, while low blood pressure is called hypotension.
Blood pressure is measured in millimeters of mercury (mm Hg). In writing, people usually separate the numbers with a slash — for example, 120/80, which means a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg. People will often speak this as “120 over 80.”
The American Heart Association describes the different blood pressure ranges for adults as:
| Systolic pressure (mm Hg) | Diastolic pressure (mm Hg) | ||
|---|---|---|---|
| Normal | lower than 120 | and | lower than 80 |
| Elevated | 120 to 129 | and | lower than 80 |
| Stage 1 hypertension | 130 to 139 | or | 80 to 89 |
| Stage 2 hypertension | 140 or higher | or | 90 or higher |
| Hypertensive crisis | higher than 180 | and/or | higher than 120 |
There are different ways doctors determine whether your blood pressure is low, but they generally consider hypotension to be a systolic pressure of
Both systolic and diastolic blood pressure are important, but doctors may pay more attention to your systolic pressure. That’s because research links high systolic blood pressure to a higher risk of cardiovascular events, such as heart attack and stroke. High diastolic pressure can also affect your risk, but not as much.
However,
It’s much more common to have high blood pressure than low blood pressure. According to the Centers for Disease Control and Prevention (CDC),
Causes and risk factors for high blood pressure
Some risk factors for hypertension, like age, genetics, and family history, are beyond your control. For example, people assigned male at birth are more likely to develop high blood pressure at an early age. The
Other risk factors include lifestyle habits and other health conditions, including:
- diabetes
- high cholesterol
- kidney disease
- sleep apnea
- lack of physical activity
- smoking
- drinking too much alcohol
- chronic stress
- a diet high in salt, sugar, and fat
Causes and risk factors for low blood pressure
Causes of low blood pressure
- arrhythmia
- autonomic dysfunction
- blood loss
- dehydration
- pregnancy
- certain medications, such as those for hypertension, depression, or Parkinson’s
If you’re older than 65, you may be at risk of orthostatic hypotension, a condition in which your blood pressure drops when you move from sitting to standing.
Can one blood pressure value be high and the other low?
It would be unusual to have one reading in the elevated or high range and another in the low range. However, some people do have high readings of one type of blood pressure while the other type remains in a typical range.
Isolated systolic hypertension occurs when your systolic blood pressure is high, but your diastolic blood pressure is not. It’s the
Likewise, isolated diastolic hypertension occurs when your diastolic blood pressure is high, but your systolic blood pressure is not.
Isolated diastolic hypotension is the term for low diastolic blood pressure with typical systolic pressure. It’s often caused by aging or taking blood pressure medications.
You can also have isolated systolic hypotension, which is low systolic blood pressure with typical diastolic pressure.
High blood pressure doesn’t cause symptoms unless you’re in a hypertensive crisis. It’s known as a “silent killer” because it quietly damages your blood vessels and organs, and you may not realize you have it until the damage is done.
Unmanaged high blood pressure can lead to cardiovascular events like heart attack, heart failure, or stroke. It can also affect other systems, like your eyes and kidneys.
On the other hand, blood pressure that’s too low will cause symptoms. Symptoms or complications that may occur from low blood pressure can include:
- dizziness
- fainting
- seizures
- chest pain
- loss of balance
- nausea
- thirst
- inability to concentrate
- headaches
- blurred vision
- fatigue
- breathing difficulties
- clammy or bluish-tinged skin
Medications can often treat both high and low blood pressure. Lifestyle strategies that help you manage these conditions can also help prevent them.
Managing and preventing high blood pressure
In addition to medications, certain lifestyle changes can help you manage high blood pressure or prevent it before it starts. Experts recommend:
- eliminating excess sugar, salt, and saturated fats from your diet
- eating more heart-healthy foods such as lean meats, fish, fruits, vegetables, and whole grains
- following the Dietary Approaches to Stop Hypertension (DASH) diet
- drinking more water
- getting daily physical activity
- quitting smoking if you smoke
- maintaining a moderate weight
- reducing alcohol consumption
- managing stress
- monitoring your blood pressure regularly
- managing underlying conditions like diabetes and sleep apnea
Managing and preventing low blood pressure
Treatment for low blood pressure depends on the cause of the condition.
If a medication is causing your low blood pressure, your doctor may change your dosage or stop that treatment. If an infection is at fault, they may provide an antibiotic. If anemia is causing your low bow blood pressure, they may suggest iron or vitamin B-12 supplements.
Drinking plenty of fluids can help you prevent hypotension. Also, talk with a doctor about any underlying conditions or medications you’re taking that may cause low blood pressure. They can discuss which symptoms to look for and how best to monitor your condition.
If you often experience orthostatic hypotension, standing up slowly can help prevent symptoms.
Systole refers to the period when your heart contracts and pushes blood out to the rest of your body. Diastole is when the heart relaxes and refills with blood. The pressures on your arterial walls during these periods are your systolic and diastolic blood pressures.
High or low blood pressure can result when either systolic or diastolic pressure is high or low. Monitoring your blood pressure can help you manage your risk of complications. Systolic blood pressure may be a stronger indicator of the risk of cardiovascular events like heart attack and stroke in people over 50.