The
formula doctors use to evaluate treadmill stress tests, and thereby assess heart health,
doesn't account for important differences between men and women, a new study
contends.
A
revised formula would better determine peak exercise rate,
or the maximum number of heart beats per minute, for each sex, the researchers...
said.
"Exercise
physiology has been known to differ for men and women of different ages,"
said Dr. Gregg Fonarow, associate chief of cardiology at the University of
California, Los Angeles, and spokesman for the American Heart Association.
The
proposal for a sex-specific maximal heart rate warrants further
research, he said. "This may represent a valuable improvement for guiding
exercise stress testing," added Fonarow, who was not involved in the
study.
Doctors now use the formula "220 minus age" to determine
how hard patients should work out during exercise stress tests. Many people
also use this formula to set their target heart rate during workouts.
For the new study, a team led by Dr. Thomas Allison, director of
stress testing at the Mayo Clinic in Rochester, Minn., reviewed 25,000
stress-test results. They saw significant differences between men and women.
Allison's group found that although peak heart rate declines with
age for both sexes, the rate declines more gradually in women. This difference
results in an overestimated peak heart rate in younger women and underestimated
peak heart rate in older women, the researchers said.
The findings are scheduled for presentation Saturday at the annual
meeting of the American College of Cardiology, in Washington, D.C.
Based on their findings, the study authors developed a new
formula.
According to the revised formula, the maximum heart rate for women
aged 40 to 89 should be 200 minus 67 percent of their age. For men, the
preferred formula is 216 minus 93 percent of their age, the study authors said.
"We want to make sure that when people do the stress test,
they have an accurate expectation of what a normal peak heart rate is,"
Allison said in an American College of Cardiology news release.
Because of limited test results for women under 40, the
researchers were unable to recommend a new formula for this group.
Allison's team also found that younger men have a lower resting
heart rate and higher peak heart rate than women. In addition, men's heart
rates rise more dramatically during exercise and return to normal more quickly
after stopping, the researchers said.
Heart experts welcomed the preliminary results.
"This is timely and we've needed it for a while," said
Dr. Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York City.
"All of these differences are very important, not only for
diagnosis, but also for teaching people how best to exercise to get the most
cardiovascular fitness," she said.
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