What causes systolic blood pressure and what is happening when this is measured? What causes diastolic pressure?

Expert Answers
coleman-rn eNotes educator| Certified Educator

A blood pressure reading can help determine how healthy the heart is. 

When the heart beats(contracts), blood is pumped out to the body. The heart essentially tightens and then relaxes. The blood is forced out of the heart to the rest of the body during this tightening. The systolic pressure is measured as blood leaves the body. 

The diastolic pressure is measured when the heart is relaxed. During this time, blood flow in the heart is decreased. At this time, the heart is also refilling with blood. Once the blood has circulated throughout the body, it must return to the heart so more oxygen can enter the blood before it returns to the body again. 

Both of these measurements, measure blood flow in the arteries of the heart. 

The systolic reading will be higher than the diastolic reading. 

The BP reading is recorded using numbers that are documented with the systolic pressure being your top number and the diastolic pressure being your bottom number. 

The reading will look like this: 120/80 or 




Anything over 120/80 is not normal and should be assessed by a MD for possible treatment. 

gsenviro eNotes educator| Certified Educator

The blood pressure measurement yields two numbers, a high number corresponding to the systolic blood pressure and a lower number called diastolic blood pressure.

These pressures (systolic and diastolic) refer to the pressure created in the arteries when the blood flows through them. 

When the heart beats, it contracts and forces the blood through the arteries, from where it goes to the rest of the body. This creates a pressure on the arteries and this pressure is called systolic pressure.

When the heart is at rest between the beats, the arteries experience a lower pressure due to blood flow. This pressure is termed as diastolic pressure.

The normal values are 120 for systolic pressure and 80 for diastolic pressure. Values above 120 for systolic pressure means high blood pressure and may cause higher risk of heart diseases.

ssing45 | Student

Systolic blood pressure is measured the moment the left ventricle (last big heart chamber before body) of your heart squeezes the blood out to the arteries of your body.  So, systolic blood pressure is the highest measurement for blood pressure.  Diastolic blood pressure is measured when there is no heart squeezing blood out to the arteries so they are basically just sitting there with no extra pressure except the pressure that is part of the blood passively moving to fill up the chambers of the heart.  FYI the third number in parenthesis that you always see 120/80 (90) is called the mean arterial pressure or MAP.  That is that average pressure of both the systolic and diastolic measurements.