THURSDAY, April 12 (HealthDay News) -- Millions of middle-aged women experience it: that sudden onset of intense heat, sweating and flushing known as a hot flash.
Though it's long been believed that the drop in hormone levels that accompanies menopause contributes to hot flashes, experts say relatively little is known about what actually causes them, or what's occurring when women have one.
"About 70 percent of women experience hot flashes, but their underlying physiology isn't well understood," said Rebecca Thurston, an assistant professor of psychiatry, psychology and epidemiology at University of Pittsburgh.
A new study by Thurston and her colleagues attempts to get at the underlying physiology. Researchers had 21 perimenopausal and postmenopausal women aged 40 to 60 who reported having daily hot flashes wear a heart monitor over a 24-hour period. Perimenopause is the time leading up to menopause when the ovaries produce less estrogen but a woman still gets her period.
The heart monitor showed that during a hot flash, heart-rate variability -- a measure of beat-to-beat changes in heart rate -- decreased significantly, a sign that the parasympathetic nervous system isn't working as well as it normally does.
The parasympathetic nervous system is one aspect of the autonomic nervous system, which regulates unconscious bodily functions such as heart and respiration rates. While the sympathetic nervous system governs the fight-or-flight response, the parasympathetic nervous system is involved with "rest and restore," or regulating the body at rest, Thurston explained.
Other research has found an association between cardiovascular disease and decreased parasympathetic nervous system control of the heart. While researchers say it's too soon to conclude that hot flashes have a connection to heart disease, it's worth continuing to study them, Thurston said.
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