Systole and diastole are stages of the cardiac cycle, systole is the contraction phase of the heart where blood is pumped into the vessels, and diastole is the relaxation phase that allows blood to enter the heart.
In a normal adult person, the average systolic pressure is 120 millimeters of mercury (mmHg), and in the diastolic it is 80 mmHg.
Diastolic pressure occurs at the beginning of the cardiac cycle, it is the low pressure in the arteries when the pumping chambers of the heart fill with blood. Near the end of the cardiac cycle, systolic pressure occurs when the ventricles contract.
Blood pressure reading
The blood pressure reading is calculated in millimeters of mercury (mmHg) and is given in two numbers.
The highest number is the systolic blood pressure reading which symbolizes the maximum pressure exerted when the heart contracts.
The lower number is the diastolic blood pressure reading which means the minimum pressure in the arteries when the heart is calm.
If the doctor says that the pressure is 120 by 80, it means that in systole it is 120 mmHg and in diastole it is 80 mmHg.
Heartbeats are listened to with a stethoscope, the first beat marks the beginning of systole and the second is the beginning of diastole.
Normal and abnormal values of systolic and diastolic pressure
In children, the systolic measurement is unstable and ranges from 95 to 100 mmHg, and in adults it varies from 90 to 120 mmHg. The diastolic measurement is 65 mmHg in children, and in adults it is maintained at 60 to 80 mmHg.
In certain cases, the following numbers are equal in adults:
- Hypotension: if the systolic reading is less than 90 mmHg and/or the diastolic reading is less than 60 mmHg.
- Prehypertension: If the systolic reading is 121 to 139 mmHg and the diastolic reading is 81 to 89 mmHg.
- Stage 1 hypertension: if the systolic reading is 140 to 159 mmHg and the diastolic reading is 90 to 99 mmHg.
- Stage 2 hypertension: if the systolic reading is 160 mmHg and the diastolic reading is 100 mmHg.
Difference between Systole and Diastole in tabular form
| Systole | Diastole | |
| Definition | It is the contraction stage of the cardiac cycle of the heart. | It is the relaxation stage of the cardiac cycle. |
| Function | The heart contracts by pumping blood from the heart into the aorta and pulmonary artery. | The heart relaxes allowing the cardiac chambers to fill with blood, which comes from the pulmonary veins and venae cavae. |
| Blood pressure | High. | Short. |
| medium pressure | The recommended systolic pressure for an adult person is 120 mmHg. For a child it is 100 mmHg (5 to 10 years). | The recommended diastolic pressure for an adult is 80 mmHg. For children it is 65 mmHg. |
| Blood vessels | Contracted. | relaxed. |
| blood pressure reading | The higher number is the systolic pressure. | The lower number is the diastolic pressure. |
| phases | It has two phases called atrial systole and ventricular systole. | It consists of two events called atrial diastole and ventricular diastole. |
