Difference Between Systolic and Diastolic

Whenever we visit a doctor, one of the essential health aspects which the doctor assesses is blood pressure. Measurement of blood pressure is critical as it indicates the pressure that the heart uses to drive blood around the body, which eventually determines if there is high or low pressure or a normal situation.

Blood pressure measurement will consist of two numbers, Systolic and Diastolic or the first/top and the second/lowest number.

Key Takeaways

1. Systolic blood pressure represents the highest pressure in the arteries when the heart contracts, pumping blood into the arteries.
2. Diastolic blood pressure is the lowest pressure in the arteries when the heart relaxes between beats, allowing the heart to refill with blood.
3. The main difference between systolic and diastolic blood pressure is their measurement points in the cardiac cycle, with systolic pressure occurring during heart contraction and diastolic pressure during heart relaxation.

Systolic vs Diastolic

The difference between Systolic and Diastolic is that the Systolic number indicates the highest or maximum level of blood pressure as the heart exerts while breathing. In contrast, the Diastolic number is the lowest level the pressure reaches as the heart eases during the heartbeats.

However, the above is not the only difference. A comparison between both the terms on specific parameters can shed light on subtle aspects:

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Comparison Table

Parameter of Comparison	Systolic	Diastolic
Meaning	Measures the force of blood against the arteries when the heart pushes the blood to the rest of the body parts	Measures the force of blood as the heart relaxes between beats
In simple terms, what does it mean?	Pressure when the heart muscles contract	Pressure when the heart muscles relax
At what stage is the number?	The top number on the reading	Lowest number
What does this number 120/80 in the blood pressure reading indicate?	120 is the Systolic pressure	80 is the Diastolic number
Level of importance	Systolic blood pressure is more critical than Diastolic blood pressure	Less important with exceptions
Normal blood pressure measured in both numbers	120	80
From which age did this number become very important in reading?	60 years and above or old people	No such age; however, for younger people, it is important
What is the ideal range of both these numbers so that an adult person can be considered healthy?	90 and less than 120	60 and less than 80
Does it indicate frequent changes?	Yes, especially when the heart is working more	Few
Does an increase in pulse pressure indicate an increase in Systolic pressure?	Yes	No
How does age matter?	Systolic pressure increases with age	Diastolic pressure decreases with age

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What is Systolic?

Systolic blood pressure is derived from the word “systole”, meaning the stage of the heartbeat when the heart muscle contracts and forces blood from the chambers into the arteries. Contraction indicates “drawing together”.

Systolic means the period of contraction. To put it more simply, Systolic pressure indicates the topmost pressure applied by the heart as it moves the blood through the arteries.

Systolic blood pressure is usually measured at quiet times when the heartbeats come to regular rest.

Systolic blood pressure for an average person will be 120 mmHg or below. Systolic blood pressure tends to rise when a person is jogging, running, exercising, or stressed out, as, during this time, the heart has to work more.

It can also be very high when the heart is beating very fast.

Systolic blood pressure can be lower than standard, which can be considered Systolic hypotension. This can cause a situation of dizziness and body parts failure if it is too low, which is a clear indication that the heart has become weak so as not to even be able to pump blood in a typical fashion.

 

What is Diastolic?

Diastolic blood pressure is derived from the word “diastole”, meaning the period of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood. Relaxation indicates “drawing apart”.

Diastolic means a period of relaxation. In simple terms, once the heart has contracted, the cardiac parts will relax for some time/moments to enable the refilling of blood for the next pumping or cycle.

Diastolic blood pressure indicates the pressure when the heart is relaxing (that is not actively pumping blood into the arteries).

Diastolic blood pressure for an average person will be 80 mmHg or below. A Diastolic blood reading of 90 or more indicates a case of high blood pressure.

Low Diastolic blood pressure of less than 60 mm Hg indicates a situation of isolated Diastolic hypotension which is nothing but a case of low blood pressure.

This means that the heart is not getting enough blood supply which can eventually lead to a scenario of weakening or heart failure.

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Main Differences Between Systolic and Diastolic

1. Systolic blood pressure is the top number on the sphygmomanometer reading (i.e. instrument used for measuring blood pressure). Diastolic blood pressure is the lowest number in the reading.
2. Systolic blood pressure measures the power of the heart as it contracts and forces blood from the chambers into the arteries. Diastolic blood pressure measures the force of blood against the artery walls as the heart relaxes.
3. Systolic pressure is more critical than Diastolic blood pressure in general scenarios as it indicates the risk of stroke or heart disease.
4. Systolic blood pressure for an average reading should be between 90 and less than 120. Diastolic blood pressure for a regular reading should be between 60 and 80.
5. Systolic pressure increases with age. Diastolic pressure decreases with age.
6. Systolic pressure may show frequent fluctuations. Diastolic pressure will show fewer fluctuations.

References

1. https://jamanetwork.com/journals/jama/articlepdf/195749/JOC21616.pdf
2. https://www.nature.com/articles/nm1394
3. https://journals.lww.com/jgpt/00004872-200208000-00001.fulltext