A Better Way to Gauge High Blood Pressure

24-hour monitoring more accurate than office readings

(HealthDay is the new name for HealthScoutNews.)

WEDNESDAY, June 11, 2003 (HealthDayNews) -- Are one or two doctor visits enough to diagnose high blood pressure and accurately assess your risk for cardiovascular disease?

Maybe not, a new study says.

A better measure of blood pressure levels may come from 24-hour monitoring of your blood pressure as you go about your daily life, concludes the study in the June 12 issue of the New England Journal of Medicine.

The researchers conclude that people already being treated for high blood pressure may better benefit from 24-hour monitoring, which could more accurately predict their risk for cardiovascular complications, such as heart attack or stroke.

"Patients whose mean 24-hour systolic blood pressure was 135 mmHg or higher when they were receiving treatment [for high blood pressure] were nearly twice as likely to have a cardiovascular event as patients with a mean 24-hour systolic blood pressure of less than 135 mmHg, regardless of their office blood pressure values," says one of the study's authors, Dr. Denis Clement, a professor of cardiology at Ghent University Hospital, Ghent, Belgium.

Blood pressure is a measure of the force your blood exerts on your blood vessel walls as it travels through them. The top number, systolic pressure, is a measure of the force of blood pumping as the heart contracts. The bottom number, or diastolic, is a measure of blood pressure when the heart is at rest.

Blood pressure readings can be affected by a number of things, including what you've eaten or how you're feeling. For example, many people have higher-than-normal blood pressure readings at the doctor's office because they're anxious about being there.

If you have blood pressure readings higher than 140/90 on two separate occasions, you have high blood pressure, also called hypertension. In new guidelines issued recently by the National Heart, Lung, and Blood Institute (NHLBI), people with blood pressure readings between 120/80 and 139/89 are now considered pre-hypertensive. Anything below that is considered normal.

Having high blood pressure puts you at risk for heart disease, stroke and kidney disease. Fifty million people in the United States have high blood pressure, according to the NHLBI.

For the current study, the researchers enrolled nearly 2,000 people who were being treated for high blood pressure. Their average age was about 56 years.

All of the study volunteers completed a 24-hour ambulatory blood pressure monitoring. That meant over a 24-hour period, their blood pressure was recorded at least every half hour while they participated in normal daily activities, and at least once an hour while they were sleeping.

After five years, the researchers reviewed the medical files of all of the volunteers to assess how accurate 24-hour monitoring had been in predicting future cardiovascular problems. During that time, 157 people had a "cardiovascular event," such as a heart attack or stroke.

People whose 24-hour systolic pressure had been above 135 mmHg were almost twice as likely to have had a heart attack or stroke as those with a normal systolic reading. This was true even if they had had a normal blood pressure reading at the doctor's office.

In an accompanying editorial in the journal, Dr. William White of the University of Connecticut School of Medicine points out that ambulatory blood pressure monitoring could also reduce the number of people who are unnecessarily treated for hypertension because they have "white coat hypertension," meaning they only have high blood pressure readings at the doctor's office.

The authors of the study aren't sure if their findings would apply to people who don't already have hypertension. But they suggest that when making future guidelines, policymakers should consider adding 24-hour ambulatory blood pressure readings as standard care for people with hypertension.

Dr. Dan Fisher, a cardiologist at New York University Medical Center, says that while 24-hour monitoring isn't something he routinely uses, there probably is a role for it. And, he says, the study's findings are "common sense."

"You definitely glean a lot more information if you do 24-hour monitoring, because your blood pressure is not a fixed number. It varies throughout the day," he says.

Fisher does, however, point out that the researchers weren't able to control for some important factors, such as family history of cardiovascular disease, diet, exercise and cholesterol levels.

More information

To learn more about preventing high blood pressure, visit the National Heart, Lung, and Blood Institute or the Journal of the American Medical Association.

SOURCES: Denis Clement, M.D., Ph.D., professor of cardiology, Ghent University Hospital, Ghent, Belgium; Daniel Fisher, M.D., cardiologist, New York University Medical Center, New York City; June 12, 2003, New England Journal of Medicine
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