Hypertension redefined
Izzo urges using systolic reading rather than diastolic

By LOIS BAKER
News Services Editor

Systolic blood pressure, the first-or higher-number in a blood-pressure reading, is the important factor in determining whether a person has hypertension, experts state in a new National Institutes of Health-sponsored clinical advisory statement released today.

Traditionally, diastolic blood pressure, the second or lower number, was thought to be more important.

Joseph Izzo, UB professor of medicine and pharmacology, and vice chair of research for the Department of Medicine, is the primary author of the advisory, which appears in the May issue of Hypertension.

The document was developed by the coordinating committee of the National High Blood Pressure Education Program, which is part of the National Heart, Lung and Blood Institute.

Making systolic blood pressure the major criterion for diagnosis, staging and therapeutic management of hypertension, particularly in middle-aged and older Americans, represents "a major paradigm shift," the advisory states. It also calls for more vigorous control efforts and for abolishing the use of age-adjusted blood-pressure targets.

"This shift affects 25 million people in the United States whose lives can be improved by the change," Izzo said.

Specifically, the new recommendations are:

- Systolic blood pressure should become the principal clinical endpoint for detection, evaluation and treatment of hypertension, especially in middle-aged and older Americans.

- Blood pressure should be maintained below 140/90 mmHg throughout one's lifetime; above this level, early therapy is essential to protect against organ damage.

- More stringent blood-pressure control is necessary in persons with high-risk conditions: hypertensive patients with diabetes should keep their blood below 135/85 mmHg and persons with renal or heart failure should reduce their blood pressure to the lowest level possible.

- Age-adjusted blood-pressure targets are inappropriate, including the unsubstantiated but persistent clinical folklore that "100-+-your-age" is an acceptable systolic blood-pressure level.

Systolic blood pressure represents the maximum force exerted by the heart against the blood vessels during the heart's pumping phase. Diastolic pressure is the resting pressure during the heart's relaxation phase. The defining systolic number is 140: A higher measurement indicates a need for blood-pressure reduction through drugs or lifestyle change.

Izzo said much evidence points to systolic pressure as the critical factor in determining the risk of heart disease. "For example, systolic hypertension is the most prevalent risk factor in heart failure, stroke and kidney failure. It is clear that lowering systolic pressure is associated with better outcomes in cardiovascular and renal disease.

"Systolic hypertension interacts with other major risk factors, such as high cholesterol and diabetes, which also increase with age, to amplify the age-related risk of cardiovascular events."

Isolated systolic hypertension is the most common form of hypertension and is present in about two-thirds of people over the age of 60 with diagnosed high blood pressure, he said. Isolated systolic hypertension is defined as systolic pressure at or above 140 mm/Hg and diastolic under 90 mm/Hg.

Treating isolated systolic hypertension reduces the incidence of stroke, heart attack, heart failure and kidney failure, as well as reducing overall cardiovascular disease-related sickness and death.

Using diastolic blood pressure to define hypertension in persons middle-aged and older actually misrepresents the risk of potential heart problems, Izzo said. "Systolic blood pressure increases steadily with age in industrialized Western societies, whereas diastolic blood pressure increases until about age 55 and then declines. So in older persons, diastolic blood pressure is inversely related to cardiovascular risk."

Additional authors on the study are Daniel Levy, director of the Framingham Heart Study of the National Heart, Lung and Blood Institute, and Henry R. Black, Roberts Professor and chair of the Department of Preventive Medicine, and associate vice-president for research at Rush-Presbyterian-St. Luke's Medical Center in Chicago.