By the numbers
Blood pressure refers to the pressure, or force, that flowing blood exerts on the walls of blood vessels. It consists of two numbers, which are called systolic and diastolic blood pressure.
- Systolic pressure is a measure of the force exerted during the contraction, or active, part of a heartbeat, when the heart is pushing blood through the body. Systolic is the top, and higher, of the two numbers that make up a complete blood pressure measurement.
- Diastolic pressure is a measure of the force exerted during the relaxation part of a heartbeat. This is the pressure in your vessels between heartbeats, when the heart is at rest. Diastolic is the bottom, and lower, of the two blood pressure numbers.
Blood pressure is measured in millimeters (mm) of mercury (Hg), so an example reading would be 115/70 mmHg, with 115 being the systolic number and 70 the diastolic number. The most common method of taking a measurement is using an arm cuff, which has a pressure gauge attached. There are also wrist and finger blood pressure monitors available, which are designed to measure blood pressure.
When using the cuff method, the cuff is placed around the upper arm, inflated, and then allowed to deflate. The point at which your pulse begins to be heard indicates your systolic pressure. The point at which your pulse stops being heard indicates your diastolic pressure. These points are documented by a doctor or nurse listening through a stethoscope, or by the blood pressure monitor if it is fully automated.
According to health experts, normal systolic pressures range between 90 and 120 mmHg. Normal diastolic pressures range between 60 and 80 mmHg. Consistent blood pressure readings above 120/80 mmHg is considered high blood pressure and this raises your risk for serious diseases, including:
- Heart disease, which is hardening of the arteries that can lead to heart attacks
- Heart failure, which occurs when the heart cannot pump strongly enough to effectively move blood around the body
- Stroke, which occurs when blood vessels leading to or within the brain become blocked (causing a loss of blood flow to the brain) or burst (causing bleeding into the brain)
- Kidney failure, which occurs when the kidneys stop working and are unable to remove waste from the blood or to keep body chemicals in balance.
Fortunately, one high reading does not mean you have high blood pressure (known medically as hypertension), because normal everyday occurrences can make the numbers go up. Being excited, nervous, or active can raise blood pressure. Some people experience “white coat hypertension,” which results in falsely high blood pressure readings due to the stress of being in the doctor’s office.
If you have a few high readings, your doctor may loan you a home monitor or fit you with a continuous blood pressure monitor. You can use the monitors at the pharmacy as well, to track your own numbers. This allows you and your doctor to gather many pressure readings, so you can figure out if you’ve had a few “false highs” or if you truly have high blood pressure.
You will be diagnosed with high blood pressure only if your readings are consistently above 120/80 mmHg.
If you have high blood pressure, your doctor likely will recommend diet and lifestyle changes, such as exercising more regularly, eating less salt (sodium), eating more vegetables and fruit, or losing weight. Your doctor also may prescribe medication to keep your blood pressure in a healthy range.
The low down
Low blood pressure is much less common than high blood pressure, though it can be an issue for some people. Low blood pressure can cause dizziness, fainting, and in rare cases, it can be life threatening. Systolic pressures below 90 mmHg and diastolic pressures below 60 are considered low blood pressure.
Low blood pressure can be caused by dehydration or a serious medical condition. If you’re affected by low blood pressure, talk to your doctor to get to the bottom of the problem. If it’s a medical issue, this can be treated.
Some people experience a large drop in blood pressure when they stand up from sitting or lying down, which is a condition called orthostatic hypotension, or postural hypotension. People with this condition, and this fall in blood pressure upon standing, can have dizziness, light-headedness, or fainting. Some people with orthostatic hypotension complain of “seeing spots” when they stand up rapidly.
Mild cases orthostatic hypotension may not require treatment at all and feeling slightly light-headed upon rising quickly is common for many people. More serious cases require treatment, so talk to your doctor if you think this health issue is affecting you.