Blood pressure readings done in the doctor’s office may have little value at predicting which patients who continue to have high blood pressure despite treatment will have a stroke, heart attack or heart failure, Brazilian researchers said on Monday.

About 10 to 30 percent of people with high blood pressure do not respond to treatment. For these patients, measuring blood pressure at regular intervals over a 24-hour period may prove a better way to manage their disease, they said.

Dr. Gil Salles of the Federal University of Rio de Janeiro in Brazil and colleagues studied 556 patients with resistant high blood pressure who attended an outpatient clinic between 1999 and 2004.

Patients in the study had their blood pressure monitored with a small device that took readings at regular intervals during a 24-hour period. These patients were followed up at least three to four times a year until December 2007.

After about five years of follow-up, 19.6 percent had some kind of heart problem or had died from heart disease.

The researchers found that blood pressure readings taken in the clinic did not predict these events, while readings done throughout the day using the ambulatory blood pressure monitor did. Especially telling were blood pressure readings taken during the night.

“This study has important clinical implications,” Salles, whose study appears in the Archives of Internal Medicine, said in a statement.

He said it reinforces the value of blood pressure monitoring that gives readings over a full 24-hour period, and it underscores the predictive value of nighttime blood pressure readings in patients with uncontrolled blood pressure.

High blood pressure that is left uncontrolled raises one’s risk of heart attack, stroke and other serious health problems. Based on worsening trends in the 24-hour monitoring, doctors could opt for more aggressive treatment strategies.

Blood pressure readings done in the doctor’s office often are skewed by the “white coat effect” in which the stress of being in the doctor’s office affects the reading. Some medical groups have called for home monitoring of blood pressure for this reason.

CHICAGO (Reuters)