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What Is Hypertension (High Blood Pressure)?
What is blood pressure and how is it measured?
Blood pressure is measured as millimeters of mercury (mmHg), although few people directly refer to these units. More often, you'll hear blood pressure described as two numbers, called the systolic (top) and diastolic (bottom) readings. These readings are often recorded as a fraction, with systolic over diastolic. For example: 120/70.
The systolic reading measures the force created when the heart contracts and pushes blood through the aorta and into the circulatory system.
The diastolic reading measures the force exerted by the walls of the arteries when the heart relaxes between contractions.
Blood pressure measurements vary during the course of the day, depending on your activity level and even your emotional state. Blood pressure is lower during periods of sleep and usually rises in response to exercise.
How do I know if I have high blood pressure?
In most instances, high blood pressure (hypertension) has no warning signs; so the best way to detect it is to have your blood pressure checked regularly.
A qualified physician will diagnose hypertension after several high blood pressure readings are recorded. Hypertension is generally defined as a blood pressure of 140/90 mmHg or greater. Hypertension can be further classified as follows:
|
Category |
Systolic reading (mmHg) |
Diastolic reading (mmHg |
Follow-up recommendation |
| Optimal |
120 |
80 |
Recheck in two years |
| Normal |
130 |
85 |
Recheck in 2 years |
| High Normal |
130-139 |
85-89 |
Recheck in one year |
Hypertension
Stage 1 (Mild) |
140-159 |
90-99 |
Confirm within two months |
Hypertension
Stage 2 (Moderate) |
160-179 |
100-109 |
Evaluate within one month |
Hypertension
Stage 3 (Severe) |
179 |
109 |
Evaluate immediately or within one week depending on situation |
From the Sixth Report of the Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure, National Institutes of Health (NIH) publication, 1997.
What causes hypertension and how prevalent is it?
In 90 percent to 95 percent of cases, hypertension has no known cause. This type of high blood pressure is known as essential hypertension. Less often, high blood pressure can result from other illnesses like kidney or adrenal gland problems. That type of high blood pressure is called secondary hypertension.
Based on reporting by the Centers for Disease Control and Prevention, National Center for Health Statistics, as many as 50 million Americans have hypertension. The prevalence of hypertension is 17 percent among white women, 26 percent among white men, 37 percent among black women, and 44 percent among black men 35-45 years of age.
In people over age 65, the incidence of high blood pressure is almost the same in men and women. In this age group, about 63 percent of whites and 76 percent of blacks have high blood pressure, most often only an elevated systolic pressure.
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External Resources:
National Institutes of Health, National Heart, Lung and Blood Institute National High Blood Pressure Education Program. The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. NIH Publication 98-4080, November 1997.
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Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure, National Institutes of Health (NIH) publication, 1997
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This article was reviewed by Simeon Margolis, M.D., Ph.D.
Professor of Medicine, Endocrinology and Biological Chemistry
The Johns Hopkins University School of Medicine
01/2003
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This article was published on
1999-06-24
This article was reviewed on
2003-02-03
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