Diastolic blood pressure

Alternative names
Blood pressure; Systolic blood pressure

Definition

Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped, and the size and flexibility of the arteries.

Blood pressure is continually changing depending on activity, temperature, diet, emotional state, posture, physical state, and medication use.

How the test is performed

Blood pressure is usually measured while you are seated with your arm resting on a table. Your arm should be slightly bent so that it is at the same level as your heart. The upper arm should be bare, with your sleeve comfortably rolled up.

Blood pressure readings are usually given as 2 numbers: for example, 110 over 70 (written as 110/70). The first number is the systolic blood pressure reading, and it represents the maximum pressure exerted when the heart contracts. The second number is the diastolic blood pressure reading, and it represents the pressure in the arteries when the heart is at rest.

To obtain your blood pressure measurement, your health care provider will wrap the blood pressure cuff snugly around your upper arm, positioning it so that the lower edge of the cuff is 1 inch above the bend of the elbow.

The provider will locate the large artery on the inside of the elbow by feeling for the pulse and will place the head of the stethoscope over this artery, below the cuff. It should not rub the cuff or any clothing because these noises may block out the pulse sounds. Correct positioning of the stethoscope is important to get an accurate recording.

Your provider will close the valve on the rubber inflating bulb and then will squeeze it rapidly to inflate the cuff until the dial or column of mercury reads 30 mmHg (millimeters of mercury) higher than the usual systolic pressure. If the usual systolic pressure is unknown, the cuff is inflated to 210 mmHg.

Now the valve is opened slightly, allowing the pressure to fall gradually (2 to 3 mmHg per second). As the pressure falls, the level on the dial or mercury tube at which the pulsing is first heard is recorded. This is the systolic pressure.

As the air continues to be let out, the sounds will disappear. The point at which the sound disappears is recorded. This is the diastolic pressure (the lowest amount of pressure in the arteries as the heart rests).

The procedure may be performed 2 or more times.

How to prepare for the test

The test may be done at any time. When it is performed for comparison purposes, it is usually done after resting for at least 5 minutes. All you need to perform a blood pressure measurement is a cuff and a device for detecting the pulse in the artery (stethoscope or microphone).

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

     
  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

How the test will feel
You will feel the pressure of the cuff on your arm. If the test is repeated a few times, you may feel temporary numbness or tingling in your hand.

Why the test is performed

Most people cannot sense if their blood pressure is high (hypertension) because there are usually no symptoms. High blood pressure increases the risk of heart failure, heart attack, stroke, and kidney failure. For people who have high blood pressure, this test is a way of monitoring the effectiveness of medications and dietary modifications.

Low blood pressure may be a sign of a variety of illnesses, including heart failure, infection, gland disorders, and dehydration.

Normal Values
In adults, the systolic pressure should be less than 120 mmHg, and the diastolic pressure should be less than 80 mmHg.

What abnormal results mean

     
  • Pre-high blood pressure: systolic pressure consistently 120 to 139, or diastolic 80 to 89  
  • Stage 1 high blood pressure: systolic pressure consistently 140 to 159, or diastolic 90 to 99  
  • Stage 2 high blood pressure: systolic pressure consistently 160 or over, or diastolic 100 or over  
  • Hypotension (blood pressure below normal): may be indicated by a systolic pressure lower than 90, or a pressure 25 mmHg lower than usual

Blood pressure readings may be affected by many different conditions, including:

     
  • Cardiovascular disorders  
  • Neurological conditions  
  • Kidney and urological disorders  
  • Pre-eclampsia in pregnant women  
  • Psychological factors such as stress, anger, or fear  
  • Various medications  
  • “White coat hypertension” may occur if the medical visit itself produces extreme anxiety

What the risks are
There are no significant risks associated with checking blood pressure.

Special considerations

Consult your provider if your blood pressure measurements are consistently high or low or if you have symptoms at the same time as the high or low reading.

Repeated measurements are important for screening or monitoring. A single high measurement does not necessarily mean hypertension. A single normal measurement does not necessarily mean that high blood pressure is not present.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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