What Do Systolic and Diastolic Mean?

Blood pressure measurement gauges the force of blood pushing against the walls of arteries. The systolic blood pressure (the number on top) is the pressure produced when the heart contracts and pushes out blood. The diastolic blood pressure (the number on the bottom) is the pressure when the heart relaxes and fills with blood between heartbeats.

Systolic and diastolic are terms related to blood pressure measurement, which gauges the force of blood pushing against the walls of arteries. 

• The systolic blood pressure (the number on top) is the pressure produced when the heart contracts and pushes out blood
• The diastolic blood pressure (the number on the bottom) is the pressure when the heart relaxes and fills with blood between heartbeats

Blood pressure readings are expressed as the systolic blood pressure number over the diastolic blood pressure number, such as 120/80 mmHg (“120 over 80”). 

Blood pressure ranges for adults are:

• High: Systolic (top number) of 130 or above and/or diastolic (bottom number) of 80 or above
• Elevated: Systolic between 120 and 129 and diastolic of 79 or below
• Normal: Systolic of 119 or below and diastolic of 79 or below
• Low: Systolic of less than 100 and/or diastolic of less than 60
  • Some people may have normal or asymptomatic blood pressures lower than 100/60
  • In people who have chronically high blood pressure (hypertension), symptoms of low blood pressure may occur at readings above 100/60

The normal blood pressure for adolescents 13 years or older is less than 120/80 mmHg. 

In younger children, the normal range for blood pressure is determined by the child's sex, age, and height. The normal range is expressed as a percentile, similar to charts used to track children's growth.

• Blood pressure is divided into three categories based upon the child's blood pressure percentile:
  • High: Either systolic and/or diastolic blood pressure is in the 95th percentile or greater, as measured on three or more separate occasions, or blood pressure exceeds 130/80 mmHg
  • Elevated: Systolic and/or diastolic blood pressure is in the 90th percentile or greater, but less than the 95th percentile, or blood pressure exceeds 120/80 mmHg 
  • Normal: Both systolic and diastolic blood pressure are less than 120/80 mmHg in adolescents 13 years or older, and for younger children blood pressure that is less than the 90th percentile based on the child’s sex, age and height
  • Low: There is no explicit range for low blood pressure in because of children’s variability in sizes and ages