The main difference between high and low blood pressure is the fact that having high blood pressure significantly increases a person's health risks, while low blood pressure does not. The American Heart Association estimates that about 74.5 million adults in the United States have high blood pressure. Three factors determine blood pressure: the amount of blood pumped from the heart, the volume of blood in the blood vessels and the capacity of blood vessels.
Low blood pressure may cause dizziness, faintness, lightheadedness, confusion or blurred vision. High blood pressure is known as "the silent killer" because it often causes no symptoms until a vital organ has been damaged. Symptoms that may be caused by high blood pressure include headache, nosebleed, dizziness, flushed face and tiredness. If high blood pressure is left untreated, over time, damage to the brain, eyes, heart and kidneys can occur, resulting in fatigue, nausea, vomiting, shortness of breath, restlessness and blurred vision.
If blood pressure is too high, it can rupture a blood vessel and cause bleeding in the brain, known as hemorrhagic stroke, or other complications. If blood pressure is too low, the blood may be unable to supply enough oxygen and nutrients to the cells and efficiently remove waste from the cells.
Blood pressure varies naturally with age. Infants and children usually have lower blood pressure than adults. Activity also affects blood pressure, which is higher when a person is active and lower at rest. Time of day also affects blood pressure, which is highest in the morning and lowest at night, during sleep.
Measurement of blood pressure is usually given as two numbers. It's presented in the form of a fraction, with systolic pressure /(over) diastolic pressure, such as 125/85 (or 125 over 85). A reading below 120/80 is considered normal, below 95/60 is considered low blood pressure and higher than 140/90 is considered high blood pressure, or hypertension.
Risk factors for developing high blood pressure include stress, smoking, high cholesterol, lack of exercise and being overweight. Low blood pressure can be caused by decreased cardiac output, decreased volume of blood or increased capacity of blood vessels. Each of these conditions has several possible causes, including abnormal heart rhythm, heart muscle damage, heart valve disorders, pulmonary embolism, excessive bleeding or sweating, septic shock, excessive urination, exposure to heat, diarrhea or certain drug side effects.
Untreated high blood pressure increases a person's risk of developing heart disease, kidney failure and stroke at an early age. High blood pressure is the most important controllable risk factor for stroke and one of the three major ones for heart attack. On the contrary, healthy people with low normal blood pressure at rest tend to live longer, according to Dr. Robert Berkow, author of "Merck Manual of Medical Information."
- "Merck Manual of Medical Information: Home Edition"; Robert Berkow, M.D.; 1997
- American Heart Association: Blood Pressure
- Photo Credit blood pressure monitor image by Shirley Hirst from Fotolia.com
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