Jane Miller, age 13, of Idaho Falls, Ida., for her question:
WHAT IS NORMAL BLOOD PRESSURE?
Blood pressure is the pressure that blood exerts against the walls of the body's arteries. There are individual differences in pressure that is called normal. Exercise, stress and excitement can raise your blood pressure quickly.
Systolic pressure represents the blood pressure when the heart is contracting. Diastolic pressure represents the blood pressure while the heart is relaxing. In the average adult, normal systolic pressure is thought to be about 100 to 120 millimeters and normal diastolic pressure is about 65 to 80 millimeters.
To obtain a person's blood pressure, doctors use an instrument called a sphygmomanometer. The instrument is made up of a glass tube with mercury, a wide rubber cuff that can be filled with air and a hollow rubber ball which pumps air into the cuff.
First the doctor or nurse wraps the cuff around the patient's arm. A stethoscope is then placed over the arteries of the arm just below the cuff.
The doctor then pumps air into the cuff, causing it to press down on the arteries. This stops the flow of blood and the sound.
Slowly the air is let out of the cuff. When the pressure of the cuff becomes less than the blood pressure, the blood flow returns. The pressure at which the flow of blood resumes is the systolic pressure. This pressure can be read on the scale of the mercury tube.
The doctor continues to let air into the cuff until the sounds become muffled. The pressure at this point is the diastolic pressure.
Measurements of blood pressure are written like this as two numbers: 120/80. Systolic pressure is listed first and the second number refers to diastolic pressure.
Doctors consider a systolic blood pressure over 150 millimeters to be high. A high diastolic pressure is over 90 millimeters.
Blood pressure depends on the strength and rate of the heart's contraction, the volume of blood in the circulatory system and the elasticity of the arteries.
Blood pressure usually rises with age because the arteries become less elastic and slow down the flow of blood. This is a normal condition.
Exercise and excitement can temporarily increase the blood pressure, but it will return to normal with rest.
High blood pressure is called essential hypertension. Sometimes it can cause heart failure, kidney failure or strokes.
Pressure that is too low is called hypotension. This low blood pressure rarely indicates serious disease and generally doctors do not have to treat it.
Loss of blood in an accident results in a drop of blood pressure. Blood is then usually forced into the arteries from other parts of the body that hold substantial supplies of it. If too much blood is lost, doctors often have to give transfusions to normalize pressure.