ATHENS, Ohio -- Some people at high risk of developing hypertension may have a problem in a part of the brain that controls pain sensitivity, according to new research at Ohio University. Scientists say the research is a step toward finding better ways to detect high blood pressure before its onset.
Researchers have known for some time that people at high risk of developing hypertension have a decreased pain sensitivity. A study done last year at Ohio University found that the cause may lie in a problem with a pain control center of the brain, said Chris France, associate professor of psychology and lead author of the study.
"We can trace the decreased pain sensitivity back to something in the brain," he said. "That's a pretty big leap, because it could easily have been a problem in the tissues or in the nerves sending signals to the brain."
In the study, 63 people with and without a parental history of hypertension were given a brief electric shock to the jaw while they clenched their teeth. Researchers monitored their involuntary muscle reactions to the shock and found that participants with a higher risk of developing hypertension showed a greater relaxation of the jaw muscle.
"We have a protective reflex that causes the jaw muscles to relax under certain conditions and we know this response is influenced by certain areas of the brain that control pain perception," France said. "The longer relaxation periods in offspring of hypertensives suggest that they may have abnormally enhanced activity in central nervous system areas that can suppress pain."
The overactive brain center could be doing several things to inhibit pain, he said. The brain could be overproducing natural opiates that dull pain. Or there could be a malfunction in a brain system that sends signals to the spinal cord to prevent pain signals from getting to the brain. Because pain signals never reach the brain, the person may be less aware of a potential source of injury or harm.
"The research suggests that those things that are affecting pain may also affect blood pressure control," France said. "That's important because of the way hypertension develops. It doesn't happen quickly. If a patient knows he or she is at high risk, and there are other physiological symptoms to watch for, we might be able to prevent high blood pressure from developing."
The research was published in a recent issue of the journal Psychophysiology. Other authors were Kenneth Holroyd, professor of psychology; Gary Page, Valerie Bonk, Michelle Meade, and Kathryn Stewart, graduate students in psychology; and Douglas French, a former post-doctoral researcher in psychology, all at Ohio University
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