What Do Systolic and Diastolic Blood Pressure Numbers Mean?
When you check your blood pressure, you get two numbers. The first, or top, number, is called systolic blood pressure. The second, or bottom, number is called diastolic blood pressure.
These two numbers show how hard your heart works to pump blood throughout your body and how much pressure it puts on your blood vessels. If one or both numbers consistently stay too high, it's called hypertension. It can damage your organs over time and lead to serious health problems.
The difference between systolic pressure and diastolic pressure is that they reflect two different forces during one heartbeat:
Systolic pressure. This is the force against your arteries as your heart squeezes to pump out blood. It's a snapshot of how hard your heart is pumping at that moment
Diastolic pressure. This is the pressure in your arteries as your heart rests and fills with blood to get ready for the next heartbeat.
A healthy balance between your systolic and diastolic pressure helps ease the strain on your heart.
Why Do Systolic and Diastolic Blood Pressure Readings Matter?
If either number is too high or too low, it can signal a health problem.
Doctors always check your blood pressure because it offers important information about your overall condition, especially your heart health. High blood pressure, or hypertension, can damage your kidneys and eyes and raise your risk for stroke and heart attacks.
You're more likely to get high blood pressure as you get older. Your arteries may grow stiff or get clogged with fatty plaque. Among Americans aged 60 or older, more than 70% have hypertension. That's three times the rate for adults younger than 40.
While low blood pressure is less common, it can still be dangerous. Also called hypotension, low blood pressure may be caused by:
- Dehydration
- Pregnancy
- Certain medications, including antidepressants and drugs for high blood pressure
- Medical conditions, such as severe infections
- Injury or blood loss
The good news is that both high and low blood pressure are treatable. Lifestyle changes can help manage hypertension. Regular blood pressure checks are key to catching problems early.
Understanding Systolic and Diastolic Blood Pressure Readings
Your blood pressure numbers can go up and down throughout the day, depending on what you are doing. Caffeine, alcohol, smoking, certain medications, and stress are some of the factors that can affect your blood pressure.
Your arteries are like a garden hose. When blood pressure gets too high, it's like pushing water through the hose while pinching it with your fingers. That extra force can cause wear and tear on your blood vessels and require your heart to work harder.
One blood pressure reading isn’t always enough to tell if you have high blood pressure. Your doctor may check it multiple times to see if it stays high.
Blood pressure falls into different categories, from healthy to dangerous:
- Normal blood pressure:Your systolic blood pressure is less than 120, and diastolic blood pressure is less than 80.
- Elevated blood pressure: This is when your systolic pressure is 120-129, and your diastolic pressure is less than 80. Lifestyle changes and monitoring your blood pressure may be all you need at this point. Your doctor will let you know.
- Stage I hypertension: Systolic 130-139 or diastolic 80-89. Your doctor will recommend lifestyle changes and will consider whether you also need medication.
- Stage II hypertension: Systolic at least 140 or diastolic at least 90. Your doctor will recommend lifestyle changes and consider medication to lower your blood pressure.
- Hypertensive crisis: Your blood pressure is 180/120 or higher. You may or may not also have symptoms such as chest pain, shortness of breath, numbness/weakness, and vision or speech problems. This is an emergency. Call 911.
Blood pressure ranges in pregnancy
Systolic and diastolic blood pressure numbers change during pregnancy because hormones relax the blood vessels, which helps more blood reach the baby for healthy growth.
In a healthy pregnancy, blood pressure may follow a pattern:
- First and second trimesters: Blood pressure usually drops and reaches its lowest point around the middle of pregnancy. Some women may have low blood pressure and feel dizzy or lightheaded. This happens because pregnancy hormones relax blood vessels, allowing blood to flow more easily to the baby.
- Third trimester: Blood pressure slowly goes up to its normal level before birth.
But if your blood pressure becomes too high, it can cause conditions such as gestational hypertension or preeclampsia. These are serious conditions that require medical care right away.
Blood pressure chart
Use this chart to check your blood pressure levels. If your numbers are high, see your doctor.
How to Measure Systolic and Diastolic Blood Pressure Numbers
A doctor or nurse will take your blood pressure with a small gauge attached to an inflatable cuff. It's simple and painless.
The person taking your blood pressure wraps the cuff around your upper arm (or sometimes around your wrist or forearm, though those are less accurate).
Your doctor or nurse will use a stethoscope to listen to the blood flowing through your arteries.
They’ll inflate the cuff to a pressure higher than your systolic blood pressure, and it will tighten around your arm. Then, they’ll release it. As the cuff deflates, the systolic blood pressure is the first sound they hear through the stethoscope while looking at the gauge. It sounds like a whooshingnoise. The point where this noise goes away marks the diastolic blood pressure.
In a blood pressure reading, the systolic number always comes first and then the diastolic number. For example, your numbers may be "120 over 80" or written as 120/80.
Factors That Increase Systolic Blood Pressure Numbers
Your systolic blood pressure can increase for different reasons, and not all spikes mean you have high blood pressure.
Short-term changes in blood pressure can happen because of stress, caffeine, exercise, or other factors, but they usually return to normal. However, long-term high blood pressure can develop from lifestyle habits or health conditions and increase the risk of heart disease, stroke, and other serious health problems.
Knowing why this happens can help you manage your blood pressure and keep your heart healthy.
Other short-term causes include:
- Smoking
- Alcohol
- Exposure to cold weather
- Pain
- Dehydration
- Medications such as decongestants, antidepressants, nonsteroidal anti-inflammatory drugs (NSAIDs)
- Birth control with hormones
- Lack of sleep
- Loneliness
- Herbal supplements such as Arnica, Ephedra, Ginseng, Guarana, and Licorice
Long-term factors that can lead to high blood pressure include:
- Smoking
- Hardened arteries (arteriosclerosis)
- Overweight or obesity
- Too much salt in your diet
- Certain medications
- Chronic stress
Factors That Increase Diastolic Blood Pressure Numbers
When the bottom blood pressure number is too high, it signals a different type of hypertension. Genetics, lifestyle habits, and medical conditions can all play a role in high diastolic blood pressure.
You should identify the factors and take action to lower your risk and prevent serious health problems.
Many factors can cause high diastolic blood pressure, such as:
- A family history of hypertension
- Drinking alcohol
- High blood sugar levels
- Higher body mass index (BMI)
- Type 2 diabetes
- Smoking
- High triglyceride levels (a type of fat in the blood)
- Previous heart problems
- Lack of physical activity
What Is Isolated Systolic Hypertension?
If your top blood pressure number is high, but your bottom number is in a healthy range, you may have a type of high blood pressure called isolated systolic hypertension (ISH).
For example, this happens when your systolic (top) number is 130 or higher, while your diastolic (bottom) number stays below 80.
Older adults are more likely to have this condition. But it can also appear in younger people with some health conditions.
Some common causes include:
- Stiff arteries
- Hyperthyroidism
- Diabetes
- Obesity
- Heart valve disease
- Eating too much salt
- Chronic stress
Blood pressure medicine can treat isolated systolic hypertension, but lowering the top number too much may also cause the bottom number to drop too low, posing serious health risks.
What Is Isolated Diastolic Hypertension?
Isolated diastolic hypertension (IDH) takes place when the bottom blood pressure number (diastolic pressure) is high, while the top number (systolic pressure) remains within a normal range.
For example, a person with a blood pressure reading of 120/90 has IDH because their diastolic number is 90 or higher, even though their systolic number is normal.
This condition is more common in younger adults and people with health risks such as obesity and metabolic issues.
Several factors may contribute to IDH:
- Stiff arteries
- Hormonal imbalances
- Obesity
- Unhealthy diet
- Lack of exercise
IDH may also be linked to conditions such as chronic kidney disease or thyroid disorders.
A small increase in diastolic blood pressure may not be an immediate health risk, but you should take steps to bring it back to a normal level. Over time, high diastolic pressure can lead to systolic hypertension and increase the risk of heart disease, especially with age.
Low Systolic and Diastolic Blood Pressure Causes
Hypotension is the medical term for low blood pressure, meaning the force of blood against the artery walls is too weak.
A reading below 90/60 is considered low, but what's low for one person may be ok for another.
Several factors can cause low blood pressure, including:
- Dehydration
- Heart and valve conditions
- Hormonal or endocrine disorders
- Pregnancy
- Severe infections
- Severe allergic reactions (anaphylaxis)
- Low levels of B12, folate, and iron
Low blood pressure can cause various symptoms, including:
- Blurred or fading vision
- Dizziness or lightheadedness
- Fainting
- Fatigue
- Difficulty concentrating
- Nausea or an upset stomach
If you experience these symptoms frequently, talk to your doctor to find out the cause and the best way to manage them.
Systole vs. Diastole: Which Reading Is More Important?
Both blood pressure numbers are essential for checking your heart health. But researchers continue to debate how much weight to give each humber.
Research shows that high systolic numbers may predict stroke and heart disease, particularly in people aged 50 or older. However, some studies highlight the importance of diastolic blood pressure in predicting heart disease risk, especially in younger individuals.
Michael Hecht Olsen, MD, a hypertension and cardiovascular prevention professor at the University of Southern Denmark and lead author of a study on mean arterial pressure (MAP) found that MAP, which takes both systolic and diastolic readings into account, is a strong indicator of cardiovascular risk at any age.
MAP represents the average pressure in your arteries during a heartbeat and is calculated using both blood pressure numbers.
Takeaways
Blood pressure has two numbers: systolic (when the heart contracts and pumps blood) and diastolic (when the heart relaxes). High blood pressure raises the risk of heart disease and stroke, while low blood pressure may cause dizziness or fainting. In pregnancy, blood pressure drops in the first two trimesters and returns to normal in the third. Regular blood pressure checks help maintain a safe range, and a healthy lifestyle is crucial for managing your numbers.
Systole vs. Diastole Blood Pressure Numbers FAQs
Does systolic or diastolic determine blood pressure?
Blood pressure readings have two numbers: systolic and diastolic. The systolic number is the pressure in your arteries when your heart beats, while the diastolic indicates the pressure between beats when your heart relaxes. Both numbers are essential for understanding your heart health.
Is blood pressure higher during systole or diastole?
Blood pressure is higher during systole when the heart squeezes and pushes blood into the arteries.
How do you know if it's systole or diastole?
As the cuff deflates, the first sound you hear through the stethoscope is the systolic blood pressure, the top number in the reading. The sound continues until it stops. This marks the diastolic blood pressure, the bottom number in the reading.
What are ideal blood pressure systole and diastole numbers?
According to the American Heart Association, an ideal and healthy blood pressure means a systolic pressure of less than 120 and diastolic pressure of less than 80.
