Whenever we visit a doctor, one of the important health aspects which the doctor assesses is the 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.
Systolic vs Diastolic
The main difference between Systolic and Diastolic is that Systolic number indicates the highest or maximum level of the blood pressure as the heart exerts while breathing, while 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 certain parameters can shed light on subtle aspects:
Comparison Table Between Systolic and Diastolic (in Tabular Form)
| 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 important than Diastolic blood pressure | Less important with exceptions |
| Normal blood pressure measured in both numbers | 120 | 80 |
| From which age this number becomes 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 |
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 top-most pressure applied by the heart as it is moving the blood through the arteries. Systolic blood pressure is normally measured at quiet times when the heart beats come to normal rest.
Systolic blood pressure for a normal 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 as 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 the blood in a normal 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 a normal 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.
Main Differences Between Systolic and Diastolic
- Systolic blood pressure is the top number on the reading of a sphygmomanometer (i.e. instrument used for measuring blood pressure). Diastolic blood pressure is the lowest number in the reading.
- 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.
- Systolic pressure is more important than Diastolic blood pressure in general scenarios as it indicates the risk of stroke or heart disease.
- Systolic blood pressure for a normal reading should be between 90 and less than 120. Diastolic blood pressure for a normal reading should be between 60 and 80.
- Systolic pressure increases with age. Diastolic pressure decreases with age.
- Systolic pressure may show frequent fluctuations. Diastolic pressure will show fewer fluctuations.
Conclusion
Systolic and Diastolic blood pressures are both considered critical. A too high reading may indicate hypertension, while too low reading can indicate insufficient blood movement to critical parts of the body.
Again, the Systolic blood pressure and Diastolic blood pressure may fluctuate considerably from time to time depending on the state of heart, stress level, and other components.
Though Systolic and Diastolic pressure reading is important to determine the blood pressure, however, the said pressure should also be considered taking into account the pulse pressure values. The difference or gap between Systolic and Diastolic blood pressure reading is known as pulse pressure.
Old people can have a wider gap in pulse pressure as Systolic pressure goes up (because of stiff arteries) while Diastolic pressure stays the same or declines a little. In overall terms, both Systolic and Diastolic blood pressures are important to accurately measure the blood pressure and the state of heart and eventually any presence of heart diseases.
References
- https://jamanetwork.com/journals/jama/articlepdf/195749/JOC21616.pdf
- https://www.nature.com/articles/nm1394
- https://journals.lww.com/jgpt/00004872-200208000-00001.fulltext