Knowing your blood pressure ranges matters a lot to your health care provider and to you as well because when the heart beats, blood pulses through the arteries to travel throughout the body. However, it is not a steady stream like your garden hose. The pulse of the blood flow and the pressure it exerts change from moment to moment. The blood pressure reading reports two numbers, often in the format of “120 over 80.”

What exactly do the blood pressure numbers mean?

The first number references your systolic blood pressure, and the second number references your diastolic blood pressure. Together, these numbers indicate your overall blood pressure, which can partially determine your risk for certain health conditions, such as heart disease, heart attack and stroke. It is highest during the heartbeat (systolic pressure) and lowest between heartbeats (diastolic pressure). 

Why systolic and diastolic blood pressure are important?

Your systolic and diastolic numbers in a blood pressure reading are essential for diagnosing and treating either high or low blood pressure because providers measure blood pressure using these numbers because it is a standard way of describing the force of the pulsing blood. For example, a blood pressure reading considered normal for most healthy adults is usually below 120/80. Children and teens may have slightly lower normal blood pressure. Older adults may also have slightly higher or lower blood pressures that are considered normal. Both numbers give important information about your health. However, your healthcare provider might give more importance to high systolic pressure to determine your risk of heart disease.

Why both high and low systolic blood pressures are important?

The systolic, top number of a blood pressure reading measures the pressure blood applied against the artery walls when the heart squeezes (systole) that is when the heart pumps blood out to the body.

Having a normal systolic blood pressure is important for maintaining good blood flow to the body’s organs. When systolic blood pressure is too high or too low, either there is too much or too little pressure against the artery walls, or blood is not flowing through the body properly. This imbalance can lead to a range of health complications. According to the Centers for Disease Control and Prevention (CDC), a systolic blood pressure reading under 120 mmHg is considered normal. However, readings under 90 mmHg are an indicator of low blood pressure and can be a cause for concern too.

There are three stages of high systolic blood pressure:

The systolic pressure goes up when a person is exercising, or under stress, which is considered normal. However, when the pressure is high while a person is resting, that is not normal and is considered high blood pressure. High systolic blood pressure is usually caused by the stiffening of the arteries, which makes the heart have to work harder to push blood through them.

Low systolic pressure, which is below 90 mmHg, is called hypotension. This can cause lightheadedness, dizziness, or fainting. If low blood pressure is not treated, it may cause organs like the kidneys to start shutting down. Systolic hypotension can occur if the amount of blood in your body becomes too low due to severe dehydration or major bleeding. In these cases, there just is not enough blood to push through the body. This can also happen if the heart muscle is too weak to push blood normally—if the heart muscle is damaged (cardiomyopathy) or if the arteries suddenly widen too much (as in vasovagal syncope, a reflex that causes fainting) or you may feel dizzy when you stand up because gravity is pulling blood down toward your feet (orthostatic hypotension).

Why low and high diastolic blood pressure are important?

Your diastolic blood pressure (the bottom number) is the pressure in your blood vessels when the heart is at rest. The heart rests between beats so it can refill with blood. The pause between beats is called "diastole." Normal diastolic blood pressure during quiet rest is below 80 mmHg and it is considered dangerously low when it is 60 mmHg or lower and dangerously high when it is 110 mmHg or over. 

Why doctors focus on systolic blood pressure?

In recent years, doctors shifted their focus to systolic readings when trying to determine the risk of heart problems independent of age, sex and other cardiovascular risk factors. However, recent studies recommend that both patients and physicians need to pay attention not only to the systolic blood pressure but also to the diastolic blood pressure especially in younger people. Although, hypertension remains an extremely common cause of cardiovascular complications such as stroke, heart attack and kidney failure. Hypertension as a "silent killer" damages blood vessels and can lead to serious health problems. While there are medications available to treat the condition, experts say people of all ages can help avoid high blood pressure by eating a well-balanced diet that's low in sodium, limiting alcohol, avoiding tobacco use, engaging in regular physical activity, managing stress and maintaining a healthy weight.

Primary hypertension can affect both systolic and diastolic pressure to a similar degree. Nevertheless, especially in older people, it affects the systolic pressure called ‘isolated systolic hypertension.’ As you age, your arteries tend to become less elastic to accommodate surges of blood. Blood flowing through your arteries at high pressure can damage the inner lining of these vessels, accelerating the buildup of cholesterol-laden plaque that stiffens and narrows the arteries, a condition known as atherosclerosis. When same volume of blood has to pass through a smaller area, the systolic pressure tends to rise, while the diastolic pressure remains the same or gradually falls over time into the 50s or even the 40s.

To ensure accurate readings when you're checking your blood pressure at home, be sure to sit comfortably with your back supported, your feet flat on the floor, and your arm resting on a table with your palm facing up. If needed, support your arm with a pillow so that your elbow is at the level of your heart.