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DURHAM, N.C. -- A Duke University Medical Center study of
dialysis patients indicates that a new way of looking at
traditional blood pressure numbers may be important in
determining which patients are at highest risk of dying.

Almost 20 percent of dialysis patients die each year,
usually from heart disease. By better understanding pulse
pressure, doctors may be able to identify high-risk patients
and take steps to keep those patients alive. The study is
featured in the March 27, 2002 issue of the Journal of the
American Medical Association.

The study looked at pulse pressure, which is the difference
between blood pressure's two key numbers: systolic blood
pressure (top number) and diastolic blood pressure (bottom
number). For example, a blood pressure 120/80 has a pulse
pressure of 40. Pulse pressure has previously been shown to be
a powerful predictors of heart attacks, heart failure and death
in patients who are not on dialysis.

The Duke University researchers examined pulse pressure in
dialysis patients because this population shows an unusual
relationship between traditional blood pressure measurements
and death.

"In the general population, people who have higher blood
pressure have a greater risk of dying," said Dr. Preston
Klassen, lead author of the study and nephrologist at Duke
University Medical Center. "In dialysis patients, that
relationship at first glance appears to be reversed. Dialysis
patients with higher blood pressures seem to live longer than
dialysis patients with lower blood pressures. We decided to
examine pulse pressures in dialysis patients to see what the
relationship was between pulse pressure and death."

The Duke researchers examined existing data from more than
37,000 patients undergoing hemodialysis across the United
States. They analyzed patients' pulse pressures and then
correlated that information with which patients died during the
course of one year. The analysis showed that dialysis patients,
like patients in the general population, had a greater risk of
dying if they had higher pulse pressures.

In particular, these results suggest that for any given
level of systolic blood pressure, greater pulse pressure
correlates with increased risk of death. Let's say you have one
person with a blood pressure of 140/60 and another person with
a blood pressure of 140/90," said Klassen. "Conventional wisdom
would say that the second person is at greater risk than the
first person because their bottom number is higher. But in
fact, it's the first person that is at greater risk. The first
person has a wider distance between the two numbers, a pulse
pressure of 80, compared to the second person with a pulse
pressure of 50."

While the study shows that a high pulse pressure is an
indicator for risk of death in dialysis patients, researchers
don't know how to lower pulse pressures specifically. "Even if
we did know how to lower pulse pressures, we wouldn't know if
this would reduce death," Klassen said. "We need more research
to understand if diet, exercise or drug therapy may be useful
in lowering pulse pressures." At that point, researchers would
need to see if lowering pulse pressure does, in fact, help
patients.

Klassen warns that the wrong message to take away from this
study is that dialysis patients should have high blood
pressure. He suggests that physicians need to be more
aggressive in identifying and treating high blood pressure in
all patients, particularly in those with kidney disease before
they start dialysis.

"The reason that dialysis patients with higher systolic
blood pressures appear to live longer than those with normal or
lower pressures is probably because of years of hypertension,"
he said. "Hearts subjected to longstanding hypertension may
ultimately fail and be unable to generate high blood pressure.
Their blood pressures are low because they have weaker hearts,
which also puts them at greater risk of dying from heart
attacks, heart failure and other causes."

Klassen said most dialysis patients have high pulse
pressures. A pulse pressure above 50 is considered elevated and
thought to represent increased risk for heart disease and death
in the general population.

"We found that over 90 percent of dialysis patients had a
pulse pressure greater than 50. This is probably related to
stiffening of blood vessels, which happens more frequently in
dialysis patients." During hemodialysis a patient's blood is
passed through a machine that filters water and toxic compounds
created by the body. Approximately 63 percent of patients with
kidney failure receive hemodialysis to replace kidney function,
while 30 percent have a kidney transplant and 7 percent receive
another form of dialysis called peritoneal dialysis. The most
common causes of kidney failure are diabetes and
hypertension.

Klassen said this research might also have implications for
the general population as well.

"This study will hopefully help us learn more about the best
way to look at blood pressure in patients," he said.
"Researchers are starting to get the idea that it is important
to look at both the top and bottom numbers and how they relate
to one another when studying blood pressure. It's not just the
top number by itself or the bottom number by itself that
matters. It may be the relationship between the numbers -- the
distance between them -- that gives important information."

The study was partly funded by an American Kidney Fund Clinical
Scientist in Nephrology grant.

Co-authors include Donal N. Reddan, Elizabeth R. DeLong,
Ph.D., Joseph Coladonato, M.D., and Lynda Szczech, M.D., all of
Duke; William Owen, M.D., previously of Duke, now with Baxter
Healthcare International, Waukegan, Ill.; and Edmund G. Lowrie,
M.D. and J. Michael Lazarus, both with Fresenius Medical Care North
America, Lexington, Mass. Lowrie is also affiliated with
Duke.