Blood pressure measures the amount of pressure within blood vessel walls. It is represented by a pair of numbers, each measured in millimeters of mercury (mmHg). The first number is known as systolic and the second number as diastolic. To measure blood pressure one needs a sphygmomanometer, which displays the corresponding pressure, and a stethoscope, used to hear the heartbeat.
Systolic is a Greek word meaning “a drawing together or a contraction.” It is the first beat heard during blood pressure taking. It measures the maximum pressure within the blood vessels when the heart contracts.
Diastolic is a Greek word meaning “drawing apart.” It is the last beat heard during blood pressure taking. It measures the minimum pressure within blood vessels when the heart is relaxed.
|First beat heard||Last beat heard|
|Maximum pressure when heart is contracting||Minimum pressure when heart is relaxed|
|Ventricle contracting||Ventricle filled with blood|
|90 to 120 mmHg||60 to 80 mmHg|
Let us compare the two in terms of when it is heard, sound produced, contraction of the heart and the chambers, and normal values obtained.
- The cuff of the sphygmomanometer is put around the arm and filled with air and gently released. The practitioner will listen through a stethoscope to hear for heart beats. The first heart beat is known as the systolic pressure. The practitioner will listen until the last beat is heard. The last heart beat is known as the diastolic pressure.
- Practitioners associate the systolic pressure as a “lub” sound. Whereas diastolic pressure as “dub.” When combined the heart produces a “lub-dub sound.”
- Systolic pressure denotes the maximum pressure along the blood vessels when the heart is contracting, whereas diastolic pressure indicates the minimum pressure along the blood vessels when the heart is relaxed.
- There are four chambers of the heart: right and left atrium and right and left ventricles. There are two valves preventing blood from flowing in between the chambers. During the systolic phase the ventricle and valve are closed and blood flows to the atrium. Once the atrium is filled with blood, blood flows to the valve which will open, and the ventricle relaxes. Blood will then flow from the atrium to the ventricle. The flowing and filling of the ventricles is known as the diastolic phase.
- According to the American Heart Association, the normal systolic pressure has a usual value ranging from 90 to 120 mmHg. The normal diastolic pressure ranges from 60 to 80 mmHg. Anything below or above this would need consultation from a licensed physician.
The following video will help you better understand the difference between systolic and diastolic pressure.