TUESDAY, March 26, 2002 (HealthDayNews) -- Doctors can predict whether a dialysis patient will live longer simply by looking at his blood pressure figures.
The gap between the top and bottom numbers of a blood pressure reading is a significant predictor of a person's one-year risk of death, a new study has found. The figure, called "pulse pressure," has been linked to mortality with heart disease, advanced age, and even premature death in healthy people. But the new work is the largest study yet showing pulse pressure also plays a role in death from kidney failure.
Unfortunately, experts said, while calculating a kidney patient's pulse pressure might give a sense of how long he has to live, improving those odds is another matter entirely.
"We don't know what things affect that difference and what we can do to alter that difference, if anything," said Dr. Preston Klassen, a Duke University kidney expert and lead author of the study, which appears in tomorrow's Journal of the American Medical Association.
What is clear, Klassen and his colleagues said, is that raising the bottom (or diastolic) pressure to narrow the gulf is out of the question.
"The worst thing that could happen from this is that people think their blood pressure needs to be higher," Klassen said. "At this point, that's just absolutely incorrect."
"We may learn that, in fact, it is important to have higher diastolic pressures up to a certain point," Klassen added. "We just don't know. That's why the main message of this work really is: We need more research."
One in four American adults has high blood pressure, but the condition strikes 80 percent of patients with kidney failure.
High blood pressure, or hypertension, causes heart attacks, strokes, renal disease, and many other complications.
Blood pressure consists of two numbers: the top, or systolic reading, which reflects the heart's contracting pressure and pressure in the arteries; and the diastolic figure, which measures the pump's resting pressure. Pulse pressure is the difference between the two numbers. If your blood pressure is 130 over 90, your pulse pressure is 40, for example.
Doctors typically focus on maximum marks for either the systolic or diastolic number. But studies have shown that the difference between the two may be as important, or more important.
In the latest work, Klassen's group analyzed pulse pressures from the medical records of more than 37,000 people who were undergoing long-term hemodialysis -- the most common form of the toxin-clearing therapy -- for end-stage kidney disease. The research group was looking to see whether high pulse pressure affected the one-year risk of death.
The answer was yes.
Each 10-point increase in pulse pressure raised the odds of dying during the study period by 12 percent. Older patients, women, diabetics and those who'd been on dialysis longer were more likely to have elevated pulse pressure.
Higher systolic pressure, on the other hand, was associated with a lower risk of death, a finding that appears to reflect the fact that kidney patients with lower systolic pressures have weaker hearts, Klassen said.
"These patients have trouble with heart function and can't generate higher blood pressure," he said.
That leaves low diastolic pressure to account for the increased mortality, although it's not clear how.
Weak resting pressure indicates that the heart may be malnourished, Klassen said. And higher systolic pressure may result from narrow, rigid arteries. So the combination of the two spells trouble.
Dr. Gary Curhan, a kidney specialist at Harvard Medical School in Boston, said pulse pressure is "something we subconsciously pay attention to," but it's not at the forefront of dialysis care.
While Curhan believes that high pulse pressure reflects underlying heart and vessel disease, he said that if it truly were important in itself, doctors might be able to tweak it by keeping systolic pressure fixed and adjusting the diastolic number.
What To Do
To find out more about dialysis and other kidney facts, visit the National Kidney Foundation or the American Kidney Fund.
For more on high blood pressure, check out the National Library of Medicine.
