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What Do Blood Pressure Readings Mean?

July 21, 2015 Posted in: Heart Health , Article

When you see your doctor, it seems like one of the first things they do is check your blood pressure readings. Even pharmacies and grocery stores have blood pressure machines for you to check your pressure on your own. So checking your blood pressure must be important, right? But what are those numbers actually telling you?

What Is Blood Pressure?

Blood pressure is the force that moves blood through your body. It is driven by the heart, and it changes as the heart muscle contracts and relaxes. There are two numbers involved in a blood pressure reading. The first is known as "systolic," and it measures the pressure when the heart muscle contracts. The second number is known as "diastolic," and it's the measurement of the pressure when the heart muscle is at rest. Blood pressure is read with the systolic number (the beat) over the diastolic (the rest), and it's measured in millimeters of mercury, or mm Hg. According to Continuing Education in Anaesthesia, Critical Care & Pain, Mercury is used because it is 13.6 times denser than water and therefore allows the instruments used in blood pressure readings to be smaller and more manageable for your doctor. A normal blood pressure reading, according to the American Heart Association, is a systolic number below 120 and a diastolic number under 80. This reading is typically read as 120/80, or 120 over 80 millimeters of mercury.


High blood pressure, or hypertension, is often a preventable disease, although some risk factors are out of the patient's control. African-Americans, older people, those who suffer from sleep apnea or kidney disease, and those with a family history of hypertension are more at risk for developing high blood pressure. Other risk factors can be controlled by the patient to some degree, such as not smoking, maintaining a health weight and active lifestyle, reducing stress, moderating alcohol consumption, and eating healthfully.

Both your lifestyle choices and genetics can contribute to the risk of high blood pressure. Hypertension is indicated with consistent readings exceeding 140 for systolic or 90 for diastolic.

Beginning with prehypertension, in which readings range 120–139/80–89, blood pressure tends to slowly increase over a period of years. Stage 1 hypertension exists when the systolic reading ranges 140–159 or the diastolic 90–99. Stage 2 occurs if the systolic reading is above 160 or the diastolic is above 100.

A systolic pressure exceeding 180 or a diastolic pressure above 110 is called a hypertensive crisis, and it's a life-threatening condition that requires emergency medical attention.


Blood pressure can also be hypotensive, or too low. Low pressure can occur when you stand up suddenly, when you spend too long standing, or after a meal. It may also occur for other reasons, such as anemia, infection, or certain chronic conditions. Symptoms include blurred vision, dizziness, fatigue, cold and clammy skin, or nausea. While low blood pressure is normal for some people, dehydration or improper dosage of blood pressure medications all cause blood pressure to drop.

For many people, the episode ends quickly with no ill effects. Resting for a moment or sitting with your feet higher than your heart can help people during mild episodes. However, hypotensive episodes can be dangerous because they are a leading cause of falls among older adults. Severe hypotensive episodes can lead to shock, which requires emergency care.

Measuring Blood Pressure

Blood pressure readings can be measured manually using a stethoscope and a device called a sphygmomanometer, or digitally. Unless you are trained on how to manually measure blood pressure, it's best to rely on a digital device. If you need to monitor your blood pressure at home, ask your doctor for a recommendation.

Pressures change from moment to moment, so any single measurement is not absolute. Instead, readings should be taken two or three times per sitting and at the same time each day. You should not exercise, smoke, or consume caffeine for a half hour before you begin any measurement. Be sure that you are sitting and that your arm is relaxed and supported by a chair arm or desk. Whatever numbers are consistent over a period of several days or weeks is called your "baseline" blood pressure.

Bear in mind, however, that many things can cause a sudden increase in blood pressure. Physical exertion, stress, and medications are just a few examples. For some people, simply going to get their blood pressure measured causes enough anxiety to spike the numbers.

High blood pressure is a serious, but treatable, health condition. Depending on your situation and your doctor's recommendation, you may need to make certain lifestyle changes, take medication, or both. Maintaining good blood pressure is important to healthy living, and you and your doctor can decide whether at-home readings are needed. Taking periodic blood pressure readings is the surest way to know how well you're keeping it under control.

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