Blood Pressure Readings

When your doctor says, “Your blood pressure is 135 over 85,” what do the numbers really mean?

The first number is the systolic blood pressure (SBP), the amount of pressure in your arteries as the heart pumps. Systole is the rhythmic contraction of your heart muscle when it’s expelling blood from your left ventricle — the large chamber on the left side of your heart. The aortic valve sits between that chamber and your aorta, the large artery that takes blood away from the heart to the rest of the body. During systole, the aortic valve is open and blood flows freely to the rest of your body.

The second number is the diastolic blood pressure (DBP), the lowest point of blood pressure. After your heart empties the blood from the ventricle, the aortic valve shuts to prevent blood from returning into the heart from the rest of your body. Your heart muscle relaxes and the ventricle expands as blood from the lungs fills it up. At that moment, the blood pressure rapidly falls within your arteries until it reaches its DBP, its lowest point. Before the pressure falls further, the ventricle contracts again and the blood pressure starts to rise back up to the systolic level. With this information and the guidance in the following sections, you can determine whether your numbers are normal or high.

After you’ve established your SBP and DBP, your doctor determines whether your blood pressure is high and whether it should be treated. But first, how high is too high?

At birth, your blood pressure is around 90/60 mm Hg or even lower. It gradually rises as you grow older, and normal adult blood pressure is between 120/80 mm Hg and 139/89 mm Hg. Numbers higher than these indicate high blood pressure.

No fixed number serves as a guide for high diastolic or systolic blood pressure. Doctors have established 140/90 mm Hg as the point at which action is taken, but a person with a reading of 120/80 mm Hg is still at lower risk of blood pressure complications than a person with a 130/85 mm Hg.

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