High blood pressure has long been linked with bad heart outcomes. But research just released from the University of Alabama at Birmingham indicates that older adults with a low diastolic (the bottom number) and a high upper number face greater odds of developing new-onset heart failure.

The findings are published in Hypertension, a journal of the American Heart Association.

The association describes heart failure as a weakened heart muscle that can no longer pump hard enough to provide adequate blood to the body's cells. It notes that symptoms include fatigue and shortness of breath and trouble with everyday activities.

With heart failure, the heart muscle can't pump adequate blood to meet the body's needs for blood and oxygen. It tries to compensate by enlarging so it can pump more blood, growing thicker muscle mass and pumping faster. The blood vessels try to be helpful, too, narrowing to keep blood pressure up. And the body diverts blood to the heart and brain, since they are the most vital organs, but that shorts the supply needed by other tissues and organs. Eventually, it can't mask what's happening, but sometimes people do not know for months or even years that their hearts are failing because of those masking "helps."

Blood pressure is a mathematical formula that looks at the pressure exerted on vessels when the heart is beating "over" the pressure in blood vessels between beats — 120/80 is considered optimal.

The researchers coined the term "isolated diastolic hypotension" to describe a condition where the diastolic or between-beat pressure is less than 60 mm Hg and the systolic blood pressure is not low, measured at above 100 mm Hg. The researchers said it's similar to a condition called isolated systolic hypertension, when the systolic blood pressure alone is elevated (above 140 mm Hg), but the diastolic is not elevated. That is common in older adults and it, too, increases the risk one will experience heart failure.

"Our findings showed that older adults who have low diastolic blood pressure but not low systolic blood pressure were more likely to develop new-onset heart failure than those with higher levels of diastolic blood pressure," said Dr. Ali Ahmed, study senior investigator, professor of medicine in the Division of Gerontology, Geriatrics and Palliative Care and also director of Alabama's geriatric heart-failure clinic. "Older adults with low diastolic blood pressure also had higher risk of death."

The researchers found that those who control their high systolic blood pressure with medications can also develop isolated diastolic hypotension.

The trick for some doctors will be figuring out how to prescribe medications to reduce the elevated systolic blood pressure without taking the diastolic blood pressure down too far as well, said study lead author Dr. Jason Guichard, a cardiology fellow.

"Unfortunately, when the diastolic blood pressure is low in the absence of any antihypertensive medications, there is little that can be done," Ahmed said in a release accompanying the study. "Whether addressing other risk factors for heart failure would reduce the risk of heart failure in these individuals remains unclear."

The study included 545 older adults with isolated diastolic hypotension and 2,348 "propensity-matched" older adults without the condition, balanced on 58 baseline characteristics that included traditional risk factors for heart failure. They were all part of the Cardiovascular Health Study, a large population-based study of Medicare-eligible older adults recruited between 1992-93, who were followed for more than a dozen years. This study was funded by the National Heart, Lung and Blood Institute.