Systolic vs. Diastolic Blood Pressure
2022-08-08
By Richard N. Fogoros
Your blood pressure reading is composed of two numbers (e.g., 120/80). Systolic blood pressure, or the top number, is the amount of force put on the arteries as the heart beats. Diastolic blood pressure (the bottom number) is the amount of force on the arteries when the heart is resting.
This article delves into the differences between systolic and diastolic blood pressure, why both numbers are important, and what your blood pressure readings mean.
Why Your Blood Pressure Matters
When the heart beats, blood pulses through the arteries to travel throughout the body. However, it is not a steady stream like you might see from a garden hose.
The pulse of the blood flow and the pressure it exerts change from moment to moment. It's highest during the heartbeat (systolic pressure) and lowest between heartbeats (diastolic pressure).
Providers measure blood pressure using these numbers because it is a standard way of describing the force of the pulsing blood.
Your systolic and diastolic blood pressures are both important. If the readings are too high, you could have high blood pressure.1 If the readings are too low, there may not be enough blood flowing to your brain and other organs.
Furthermore, if there are changes in the difference between the two numbers, it's a clue that there could be a heart condition or other health problem.
Systolic Blood Pressure
During a heartbeat, the heart pushes blood out into the arteries. Systolic pressure is the measure of this force. This phase, known as systole, is the point at which blood pressure is the highest.
Systolic blood pressure is considered normal when the reading is below 120 mmHg (millimeters of mercury) while a person is sitting quietly at rest.
High Systolic Blood Pressure
The heart muscle pushes out blood with higher pressure when a person is exercising, under stress, or at any time when the heart rate is increased. The systolic pressure goes up with it.
In these cases, the increased pressure is normal. However, when the pressure is high while a person is resting, that is not normal and is considered high blood pressure.
Since your blood pressure can go up when you're active, it's important to take your blood pressure during periods of quiet rest to accurately diagnose high blood pressure (hypertension).
High systolic blood pressure is usually caused by the narrowing of the arteries, which makes the heart have to work harder to push blood through them.
Low Systolic Blood Pressure
There is such a thing as too-low systolic pressure, however. When the reading is significantly below normal, it's called hypotension. This can cause lightheadedness, dizziness, or fainting. If low blood pressure is not treated, it may cause organs like the kidneys to start shutting down.
Systolic hypotension can happen if the amount of blood in your body becomes too low. For example, low blood pressure can happen when you are severely dehydrated or when you have major bleeding. In these cases, there just isn't enough blood to push through the body.
Low blood pressure can also happen if the heart muscle is too weak to push blood normally—for example if the heart muscle is damaged (cardiomyopathy) or if the arteries suddenly widen too much (as in vasovagal syncope, a reflex that causes fainting).
Sometimes, low blood pressure happens when you change positions suddenly. You may feel dizzy when you stand up because gravity is pulling blood down toward your feet. This is a common condition called orthostatic hypotension.
Diastolic Blood Pressure
The heart rests between beats so it can refill with blood. The pause between beats is called s diastole. Your diastolic blood pressure is the measurement during this pause before the next heartbeat.
Normal diastolic blood pressure during quiet rest is below 80 mmHg.If you have high blood pressure, the diastolic number is often higher even during quiet rest.
Low diastolic pressure may be seen with dehydration or with severe bleeding.It also may happen if the arteries relax and widen.
Improving Blood Pressure Reading Accuracy
Your systolic and diastolic pressures—the highest and lowest points of your heartbeat—change depending on your activity level, stress, fluid intake, and other factors.
You need to do your best to limit how these other factors might change your pressure when you're taking a blood pressure reading.
For the most accurate reading, check your blood pressure when you are in a calm, warm space after you have been able to rest quietly for at least five minutes.
You should be relaxed, with your arms at your sides, and the cuff should be placed on your arm at about the level of your heart. Your legs should be uncrossed, and your bladder should be empty, as both of these factors can affect your reading.
Measuring blood pressure this way is a challenge in a busy provider's office. Your provider might suggest you take your blood pressure at home.
Your blood pressure reading is composed of two numbers (e.g., 120/80). Systolic blood pressure, or the top number, is the amount of force put on the arteries as the heart beats. Diastolic blood pressure (the bottom number) is the amount of force on the arteries when the heart is resting.
This article delves into the differences between systolic and diastolic blood pressure, why both numbers are important, and what your blood pressure readings mean.
Why Your Blood Pressure Matters
When the heart beats, blood pulses through the arteries to travel throughout the body. However, it is not a steady stream like you might see from a garden hose.
The pulse of the blood flow and the pressure it exerts change from moment to moment. It's highest during the heartbeat (systolic pressure) and lowest between heartbeats (diastolic pressure).
Providers measure blood pressure using these numbers because it is a standard way of describing the force of the pulsing blood.
Your systolic and diastolic blood pressures are both important. If the readings are too high, you could have high blood pressure.1 If the readings are too low, there may not be enough blood flowing to your brain and other organs.
Furthermore, if there are changes in the difference between the two numbers, it's a clue that there could be a heart condition or other health problem.
Systolic Blood Pressure
During a heartbeat, the heart pushes blood out into the arteries. Systolic pressure is the measure of this force. This phase, known as systole, is the point at which blood pressure is the highest.
Systolic blood pressure is considered normal when the reading is below 120 mmHg (millimeters of mercury) while a person is sitting quietly at rest.
High Systolic Blood Pressure
The heart muscle pushes out blood with higher pressure when a person is exercising, under stress, or at any time when the heart rate is increased. The systolic pressure goes up with it.
In these cases, the increased pressure is normal. However, when the pressure is high while a person is resting, that is not normal and is considered high blood pressure.
Since your blood pressure can go up when you're active, it's important to take your blood pressure during periods of quiet rest to accurately diagnose high blood pressure (hypertension).
High systolic blood pressure is usually caused by the narrowing of the arteries, which makes the heart have to work harder to push blood through them.
Low Systolic Blood Pressure
There is such a thing as too-low systolic pressure, however. When the reading is significantly below normal, it's called hypotension. This can cause lightheadedness, dizziness, or fainting. If low blood pressure is not treated, it may cause organs like the kidneys to start shutting down.
Systolic hypotension can happen if the amount of blood in your body becomes too low. For example, low blood pressure can happen when you are severely dehydrated or when you have major bleeding. In these cases, there just isn't enough blood to push through the body.
Low blood pressure can also happen if the heart muscle is too weak to push blood normally—for example if the heart muscle is damaged (cardiomyopathy) or if the arteries suddenly widen too much (as in vasovagal syncope, a reflex that causes fainting).
Sometimes, low blood pressure happens when you change positions suddenly. You may feel dizzy when you stand up because gravity is pulling blood down toward your feet. This is a common condition called orthostatic hypotension.
Diastolic Blood Pressure
The heart rests between beats so it can refill with blood. The pause between beats is called s diastole. Your diastolic blood pressure is the measurement during this pause before the next heartbeat.
Normal diastolic blood pressure during quiet rest is below 80 mmHg.If you have high blood pressure, the diastolic number is often higher even during quiet rest.
Low diastolic pressure may be seen with dehydration or with severe bleeding.It also may happen if the arteries relax and widen.
Improving Blood Pressure Reading Accuracy
Your systolic and diastolic pressures—the highest and lowest points of your heartbeat—change depending on your activity level, stress, fluid intake, and other factors.
You need to do your best to limit how these other factors might change your pressure when you're taking a blood pressure reading.
For the most accurate reading, check your blood pressure when you are in a calm, warm space after you have been able to rest quietly for at least five minutes.
You should be relaxed, with your arms at your sides, and the cuff should be placed on your arm at about the level of your heart. Your legs should be uncrossed, and your bladder should be empty, as both of these factors can affect your reading.
Measuring blood pressure this way is a challenge in a busy provider's office. Your provider might suggest you take your blood pressure at home.
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