Hypertension Controlling Systolic Diastolic Blood Pressure

It’s important to be aware of your blood pressure reading, especially if you suffer from hypertension (high blood pressure). Many people know their blood pressure reading numbers, and that a reading of 140/90 (mmHg) or higher indicates hypertension. But what do those numbers really mean?

Systolic/Diastolic Blood Pressure

When a heart beats, it pumps oxygen-rich blood from the lungs into the aorta, through the circulatory system and back to the lungs to exchange carbon dioxide for oxygen. In between heartbeats, the heart muscle is at rest.

Every heartbeat increases pressure on the blood vessel walls as blood is forced into the arteries. This increase in pressure is called “systolic pressure,” and is the first number in a blood pressure reading. When the heart relaxes, pressure within the blood vessels drops. This drop in pressure is represented by the second number in a blood pressure reading, and is called “diastolic” blood pressure.

Systolic blood pressure readings represent the maximum blood pressure during the heart beat. Diastolic blood pressure, however, represents the lowest recordable pressure, just before the beginning of the next heartbeat. Systolic and diastolic blood pressure are measured in mmHG (millimeters of mercury).

Taking a Systolic/Diastolic Blood Pressure Reading

The most common way to take a systolic/diastolic blood pressure reading is with a device called a “sphygmomanometer,” otherwise known as a blood pressure cuff.

A blood pressure cuff is wrapped around your upper arm, and then inflated until the cuff reads 30 mmHG higher than the patient’s maximum systolic pressure (if this number is unknown, the cuff may be inflated to 210 mmHG). The brachial artery is monitored during this test.

Air is then slowly released from the cuff while the doctor listens for the pulse with a stethoscope (or the automatic blood cuff detects the pulse). The reading on the cuff’s measuring dial or mercury column at the moment pulse sounds are detected is the systolic blood pressure (the use of mercury columns in blood pressure cuff’s is why blood pressure readings are expressed in millimeters of mercury).

As the cuff’s pressure continues to drop, sounds of bloodflow will slowly fade. The point at which no sound is heard is the diastolic blood pressure.

What Systolic and Diastolic Blood Pressure Readings Mean

Ideally, a blood pressure reading for a healthy adult is less than 120/80. Abnormal readings indicate the following:

  • Hypotension (Low Blood Pressure): A systolic blood pressure lower than 90 or a diastolic reading lower than 25.
  • Mild Hypertension: A systolic pressure of 140 to 159 and a diastolic blood pressure between 90 and 99.
  • Moderate to Severe Hypertension: Any blood pressure reading 160/100 or higher.
  • Prehypertension: Any consistent blood pressure higher than 120/80 but lower than 139/89.

A single blood pressure reading is not enough to determine if a person has hypertension. Blood pressure changes depending on stress levels, alcohol consumption, smoking, and even their posture. To truly determine a person’s average blood pressure, readings must be taken consistently over time.


Schoenstadt, A. (n.d.). Systolic and diastolic blood pressure. Retrieved January 26, 2010, from the eMedTV Web site: http://blood-pressure.emedtv.com/systolic-blood-pressure/systolic-and-diastolic-blood-pressure.html.

U.S. Library of Medicine Staff. (2009). Blood pressure. Retrieved January 26, 2010, from the MedlinePlus Web site: http://www.nlm.nih.gov/medlineplus/ency/article/003398.htm.