DALLAS, Texas, Aug. 7, 1998 -- Stress is inevitable, but a woman's response to it may affect her stroke risk.
Researchers report in this month's Stroke: Journal of the American Heart Association that women who exhibit large increases in blood pressure and heart rate during mental stress may develop accelerated atherosclerosis -- the disease process that obstructs blood vessels and triggers a heart attack or stroke -- in the carotid arteries, the vessels that carry blood to the brain.
"You're going to have stress, but altering one's response to stress can be beneficial," says the study's lead author, Karen Matthews, Ph.D., of the University of Pittsburgh. "If women have a large pulse pressure response to stress, then they should consider stress management and inform their physician." Researchers studied 254 healthy postmenopausal women and found that intima-media thickness (IMT) -- a measurement of the thickness of a blood vessel -- was greater in the carotid arteries of women with the highest change in pulse rate during mental stress. Of the women in the study, 93 percent were white and between 50 and 60 years old.
The amount of change in blood pressure and heart rate from two stressful tasks was measured. In one stressful task, mirror image tracing, the women traced the outline of a star via a mirror image as many times as possible in three minutes. After a rest period, the second stressful task involved study participants preparing and delivering a speech defending themselves from an accusation.
Measurement of blood pressure during the stressful tasks found significant increases in blood pressure. For example, during the mirror tracing task, the participants' systolic blood pressure rose an average of 21.2 millimeters of mercury (mm/Hg). There was an even larger increase (34.0 mm/Hg) in systolic blood pressure during the speech task.
The researchers found that women with the highest IMT also had the greatest increase in blood pressure during stressful tasks. Greater IMT was associated with a high resting systolic blood pressure and pulse pressure and a lower resting heart rate.
The association between pulse pressure and atherosclerosis in the blood vessels to the brain was stronger for the mirror image tracing task, created to determine how much the blood vessels in the brain constricted during stress. The speech task tended to elicit a release of chemicals into the bloodstream, which stimulate the heart muscle and increase blood pressure, says Matthews. "We were able to develop a situation that is typical of everyday living," says Matthews. "In women who respond and have their pulse pressure increase, we found that later on they have thicker IMT and plaque.
"There is some debate on the interpretation of IMT. Some people think it's a marker of atherosclerosis, others think it might be the result of structural damage or previous history of elevated pressure. Exactly how to interpret it is open to question. Nonetheless, we thought the link we found was quite intriguing."
As the walls of the blood vessels to the brain age, they can lose their flexibility and muscular tissue, which is sometimes replaced by less-flexible tissue or fatty plaques, neither of which can stretch.
As a consequence of this aging process, the ability of the arteries to distribute blood effectively is reduced. People who exhibit frequent increases in blood pressure during stress may accelerate the rate of aging and increase their risk of having a stroke.
Matthews adds that although the findings from this study point to the importance of stress-induced changes in pulse pressure for early atherosclerosis in women's carotid arteries, they do not ignore the importance of other stress-induced increases in blood pressure, heart beat, or release of heart-stimulating chemicals into the bloodstream.
"The sample is unique -- middle-aged women with low levels of risk factors and no clinical disease at the time of the stress testing," says Matthews. "Perhaps in individuals with high levels of risk factors or overt disease these other indicators may be more critical."
Co-authors are Jane F. Owens, Dr. PH; Lewis H. Kuller, M.D., Dr. PH; Kim Sutton-Tyrrell, Dr. PH; Holly C. Lassila, Ph.D.; and Sidney K. Wolfson, M.D.
NR 98-4933 (Stroke/Matthews)