The number of "low" blood pressure also counts

THURSDAY, July 18, 2019 (HealthDay News) – When it comes to reading blood pressure, the "up" figure seems to be getting all the attention.

But a new and large study confirms that both numbers are actually essential for determining the risk of heart attack and stroke.

The blood pressure measurements are indicated by the numbers "high" and "low". The first reflects the systolic blood pressure, the amount of pressure in the arteries during the contraction of the heart. The second reflects the diastolic blood pressure, the pressure in the arteries between contractions of the heart muscle.

For years, systolic blood pressure has been considered the main one. This is based on studies – including the famous Framingham heart study – showing that high systolic blood pressure is a stronger predictor of heart disease and stroke.

At the same time, doctors are measuring both systolic and diastolic blood pressure, and the treatment guidelines are based on both. So how important is this diastolic number?

"The idea behind this new study was to remedy the confusion," said lead researcher Alexander Flint, a researcher at Kaiser Permanente Northern California's research division.

Using the medical records of 1.3 million patients, his team confirmed that high systolic blood pressure was indeed a higher risk factor for heart attack and stroke. But these risks have also increased along with diastolic pressure; and people with normal systolic readings were still at risk if their diastolic pressure was high.

"It's generally thought that systolic blood pressure is the only one that matters," said Flint. "But the diastolic really matters."

He and his colleagues reported on the findings of the July 18 issue of New England Journal of Medicine.

The definition of high blood pressure has been revamped in recent years. The guidelines issued in 2017 by the American College of Cardiology (ACC) and other cardiac groups lowered the diagnostic threshold of the disease, which went from 140/90 mm Hg to 130/80.

The fact that treatment guidelines include a diastolic pressure threshold implies its importance. Indeed, said Dr. Karol Watson, a member of the Prevention Section and the Board of Directors of ACC.

In fact, doctors once thought that diastolic blood pressure was the most important – based on research done at the time. Next are studies showing that systolic pressure was generally a better predictor of the risk of heart disease and stroke.

In addition, Watson said, high systolic blood pressure is more common because of natural changes in blood pressure with age.

"As we get older, systolic blood pressure continues to progress," she said. Diastolic blood pressure, on the other hand, usually peaks when people are between 40 and 60 years old and then decreases.

But it's clear, Watson said, that if the systolic and diastolic blood pressure are different, they both deserve attention.

In the latest study, cardiovascular risks increased with each "unit increase" in systolic pressure above 140, by about 18% on average. Meanwhile, each increase in diastolic blood pressure above 90% was related to a 6% increase in the risk of heart disease and stroke.

The researchers found a similar trend when they examined the increase in blood pressure above the 130/80 threshold. This, says Flint, supports the 2017 directive change.

The findings are based on more than 1.3 million patients in the Kaiser Permanente health system, whose blood pressure readings were recorded between 2007 and 2016. More than 44,000 patients were victims of a heart attack or stroke. A stroke over eight years.

According to Flint, it is the largest study of its kind to date.

According to Watson, patients need to be concerned about two-digit blood pressure. In her experience, she noted, patients often indicate the number that falls within the normal range and say, "But look, how good is it."

Flint nodded, saying that no one should "ignore" the diastolic number. "It's important not only for the treatment of blood pressure, but also for diagnosis," he said.

More information

The American Heart Association offers a guide to high blood pressure.