David Malin, age 13, of Charlotte, N.C., for his question:
WHAT IS HIGH BLOOD PRESSURE?
Blood pressure that is normal for one person may well be higher or lower than another person's pressure. And the same person may vary in blood pressure from day to day or even from hour to hour. So you can't say that high blood pressure is any pressure above a so called norm.
Doctors call high blood pressure "essential hypertension" when its cause is unknown.
Many factors, however, can make a person's blood pressure go up. Blood pressure is affected by the health of the body's organs and tissue, particularly the heart, arteries, kidneys and the ductless glands such as the adrenal gland.
Pressure is also affected by the contractive pumping action of the heart's left ventricle, the volume of blood thrust into the aorta by the heart, the condition of the blood including thickness or viscosity and the resistance of the arteries to the volume of blood delivered to them.
Blood pressure readings include two numbers, such as 120/80. The first number refers to systolic pressure and the second number refers to diastolic pressure. Systolic pressure is the force with which blood is pumped by the heart during the period of the heart's contraction. Diastolic pressure is the force with which blood is pumped by the heart during dilation or relaxation.
Normal systolic blood pressure for adults is about 120 millimeters. Pressures over 150 are considered high by medical authorities.
Doctors also consider diastolic pressures over 90 millimeters to be high.
Blood pressure usually rises with age because the arteries become less elastic and slow down the flow of blood. High blood pressure, however, can cause heart failure, strokes or kidney failure.
Treatment for high blood pressure includes diet control, although sometimes medications are prescribed.
Low blood pressure is called hypotension. It rarely indicates serious disease and generally requires no special medical attention.
Sometimes, however, hypotension can be caused by some other disease that lowers the blood's pressure. It can be a symptom of tuberculosis, some types of cancer, rheumatism and conditions lowering the secretions of the adrenal glands.
Doctors use an instrument called a sphygmomanometer to measure blood pressure. The instrument includes a glass tube with mercury, a cuff or wide rubber band that can be filled with air and a hollow rubber ball which pumps air into the cuff.
Blood pr essure is the pressure that blood exerts against the walls of the arteries. The amount of pressure depends upon the strength and rate of the heart's contraction, the elasticity of the arteries and the volume of the blood in the circulatory system.