Systolic and diastolic refer to blood pressure readings at two different points during a full heartbeat, according to the American Heart Association. The systolic reading indicates the blood pressure in the arteries during a contraction. The diastolic reading indicates the blood pressure in the arteries between heart contractions.
The systolic reading typically receives the most attention from a blood pressure reading, informs the American Heart Association. As the heart contracts, the force must push the blood through the arteries to the rest of the body. The force imposes a pressure on the arteries that is measured as the systolic blood pressure. Normal systolic pressures are below 120 and are written as the top number in blood pressure measurement.
The diastolic reading is given as the bottom number in a blood pressure measurement, explains WebMD. The heart relaxes between beats to refill with blood. The pressure inside the arteries during the rest period is recorded as the diastolic pressure. Normal diastolic pressures are less than 80.
Systolic and diastolic blood pressures are indicated by sound, notes WebMD. Systolic blood pressures make a swooshing noise as blood moves through the arteries. The diastolic reading is taken when this noise stops, indicating the resting period.