High blood pressure is a strong predictor of stroke, but fluctuations in annual readings may also signal a higher risk in postmenopausal women, according to a new study by Daichi Shimbo, MD, the Florence Irving Assistant Professor of Medicine at Columbia University College of Physicians & Surgeons, and his colleagues.
Fluctuations in blood pressure measurements between doctors’ visits are common, and multiple factors including arm position or environmental factors are known to alter the reading.
“One visit the systolic pressure is 120, another day it’s 140, and the next it’s 130,” Shimbo says. “Most clinicians think of the variability as a nuisance of measuring blood pressure in the clinic setting, but that the variability itself doesn’t mean anything clinically. The way we deal with it is to average the numbers from multiple visits.”
But an analysis published two years suggested that systolic blood pressure variability is actually associated with an increase in the risk of stroke in patients who were already at high risk for stroke, including those with previous transient ischemic attack or minor stroke.
In the largest study of visit-to-visit variability to date, Shimbo’s study looked at approximately 60,000 postmenopausal women in the Women’s Health Initiative, with a wide range of cardiovascular disease risk, and who represent the broad ethnic, geographic, and socioeconomic background of women in the United States. Each woman in the study had her blood pressure measured annually for an average of almost 8 years.
After adjusting for age, estrogen use and other factors, Shimbo and his colleagues found that there was a 12 percent increase in the number of strokes for every 5 mmHg increase in systolic blood pressure variability, after taking into consideration a tendency for blood pressure to increase over time.
Surprisingly, the women with the most risk from variable blood pressures were women with average systolic blood pressure in the normal range (<120 mm Hg).
“This is the finding that strikes me,” Shimbo says. “If your average blood pressure over several visits was 110 mm Hg, your doctor would tell you your blood pressure is really good. But our results suggest that the up-and-down readings are actually increasing your risk of stroke.”
Still, Shimbo says postmenopausal women with variable blood pressure shouldn’t be too concerned. “We don’t know at this moment whether this finding applies to the typical physician’s office, where variability is probably higher than we see in rigorous research studies,” he says. “And we don’t know if treating people with blood pressure variability in the clinic setting would lower the risk of stroke.”
The research was published online July 2, 2012 in the journal Hypertension.