Both the higher and lower readings from blood pressure measurements are strongly and independently linked to cardiovascular health, according to Kaiser-Permanente researchers, who published a major study on the subject.

The higher number, called systolic pressure, measures pressure when the heart pumps blood into the arteries. The lower number, called diastolic, indicates artery pressure when the heart is resting between beats.

Blood pressure is one of the key indicators of human cardiovascular health, reflecting higher or lower risk of heart attack and stroke. High blood pressure can also be implicated in kidney disease, dementia and other conditions.

Patients should be up to date on current blood pressure readings and engage with their medical provider as needed, according to the study’s lead author, Alexander C. Flint, M.D.

“There is a very important role for broader public recognition that both of these (blood pressure) numbers are important,” he said.

Flint is a Kaiser stroke specialist and adjunct researcher with the Kaiser division of research.

Recommended guidelines for blood pressure intervention come from several authoritative sources including the American College of Cardiology and the American Heart Association.

For the general population, high blood pressure or hypertension is typically diagnosed and intervention is considered when blood pressure reaches 140/90 -- that is, the systolic pressure is above 140, the diastolic is above 90, or both.

For people with added risk factors such as diabetes or a history of stroke, the recommended threshold for intervention is 130/80.

(The numbers are often followed by the chemical symbol for mercury, Hg, reflecting pressure shown in millimeters of rise in a column of mercury.)

The U.S. Centers for Disease Control estimates that 75 million Americans – nearly one-third of the U.S. population – have high blood pressure.

It is a condition that can normally be dealt with simply and inexpensively, Flint said.

“The technology for measuring blood pressure is straightforward, simple and cost-effective. The technology and medications to be able to control blood pressure are straightforward, and the vast majority of anti-hypertensive medications are generic, quite affordable and generally well tolerated.”

In 2017, a high quality study published by the National Institutes of Health established two different hypertension thresholds, 130/80 for high risk patients and 140/90 for the general population.

Kaiser itself has a major program to diagnose and treat high blood pressure, achieving a control rate of better than 80 percent in patients with hypertension. This is some 20 percentage points higher than the national average for hypertension control.

The study published last week appeared in the New England Journal of Medicine. Authors were from both Northern California Kaiser-Permanente and Brigham and Women's Hospital in Boston.

It was the largest of its kind, involving a review of 36 million blood pressure readings taken of 1.3 million Northern California Kaiser-Permanente from 2007 through 2016.

Until recently, it was widely accepted that the higher (systolic) blood pressure reading was by far the more important indicator of cardiovascular risk, so that some authorities saw little need to pay attention to the lower (diastolic) number.

“The reason we did the study,” Flint said, was “to determine what the reality is and try to improve upon dogma with a large amount of data, to bring data to this discussion.

“Is it true that systolic is the only thing that matters, or is it really both (systolic and diastolic)?”

The study found very clearly that “both numbers independently and strongly predict the risk of heart attack and stroke.”

Flint considers it “critically important” that patients have continuous, integrated medical care to stay on top of blood pressure and treat it as needed.

Keeping blood pressure under control “helps prevent these very serious, life-changing, potentially fatal events like heart attack and stroke that are not only devastating for individuals and families but are extremely expensive for the healthcare system to deal with… If you can prevent them, that is an incredibly important aspect of healthcare.”

The study published last week appeared in the New England Journal of Medicine. Authors were from both Northern California Kaiser-Permanente and Brigham and Women's Hospital in Boston.