Published in I Spy Physiology - a blog by the American Physiological Society
High blood pressure has been coined the “silent killer” because it has no symptoms, which causes many people to go undiagnosed. A blood pressure reading that stays high for long periods of time is called hypertension. It’s one of the leading risk factors for heart disease.
In addition to being silent, hypertension is also unequal—rates in black people are much higher than in any other racial group in the U.S. An estimated 46 percent of black adults in the U.S. have hypertension. But because guidelines for diagnosis changed recently, this number is likely to be underestimated.
The physiological reasons behind this racial discrepancy are unclear. Some studies suggest differences in the response to stress. One study showed that young black men had greater nervous system responses than white men when faced with a physically stressful situation—in this case, plunging their hand into an ice water bath.
The researchers looked at activity (called sympathetic activity) in a part of the nervous system that regulates heart rate, force of heart contractions and can decrease the size (constriction) of the blood vessels. Constriction of blood vessels during exercise is good, as it redirects blood and oxygen to the muscles. However, too much sympathetic activity can result in unneeded blood vessel constriction and an increase in heart rate that significantly raises blood pressure. The black participants’ surge in sympathetic activity in the ice water test was accompanied by large spikes in blood pressure, which has been linked to future development of hypertension.
A more recent study suggests that the racial disparity may also lie in the blood vessels’ response to nervous system activity during periods of rest. The researchers inserted a tiny probe into a nerve of the leg to measure sympathetic activity in the muscles. They also looked at blood flow in the artery of the leg and blood pressure throughout the resting period. They found that black men had greater vessel constriction and higher blood pressure than white men, even when accounting for other variables that may affect blood pressure such as weight.
Seeing how blood vessels react—or overreact— to nervous system activity helps scientists understand more about the factors that potentially increase the risk of hypertension in black adults. The next step is to find ways to reduce these responses and lower the risks of hypertension and heart disease in this population.
April is National Minority Health Month. Visit the U.S. Department of Health and Human Services’ Office of Minority Health to learn how people from diverse cultures can stay healthy.