Systolic and diastolic blood pressure indicates the force of blood on the walls of blood vessels as it travels through the body. Both types of blood pressure are measured in millimeters of mercury (mmHg), but when they are written together as a fraction, it is done without listing the mmHg unit of measurement, such as 120/80. Systolic blood pressure is the top number of the fraction, and diastolic blood pressure is the bottom number. Systolic and diastolic blood pressure measurements occur at opposite times as the heart beats.
The maximum pressure or force that is exerted on the blood vessels is recorded as the systolic blood pressure. It happens as the heart is beating and the contraction of the left ventricle of the heart pushes blood into the aorta. The systolic pressure allows the blood to carry oxygen and nutrients throughout the body.
By contrast, the diastolic blood pressure is the minimum force on the blood vessels in between heart beats when the heart is relaxed. The diastolic pressure is recorded just before the ventricle of the heart thrusts blood into the aorta. This measurement is the lowest when the ventricle is refilling with blood.
What is considered to be a normal reading for systolic and diastolic blood pressure varies slightly in different countries. For example, in the United States, normal readings for an adult are 90-120 mmHg for systolic and 60-80 mmHg for diastolic blood pressure. In the United Kingdom, up to 140 mmHg is normal for systolic, and up to 90 mmHg is normal for diastolic measurements.
Systolic and diastolic blood pressure readings for a person will naturally fluctuate throughout the day due to the body’s circadian rhythm. Blood pressure will also respond to changes in the body due to exercise, diseases, and drugs, among other things. It is best for a person to check the blood pressure readings several times during a day to get an average number rather than relying on just one measurement.
In general, the systolic reading is regarded as more important than the diastolic number for diagnosing various types of cardiovascular diseases for people over 50 years old. The systolic blood pressure will increase steadily with age for most people due to factors such as hardening of the arteries and the buildup of plaque in blood vessels over the long term. Consistently high blood pressure, or hypertension, can lead to organ damage or heart attacks.
