Surprising discovery about the most accurate way to measure blood pressure

This large, long-term study found that high blood pressure (BP) readings measured while lying down may better predict stroke, serious heart problems and death, according to the American Heart Association's website.

The findings were surprising and suggest that measuring blood pressure while lying down can help identify people who need treatment when their sitting readings appear normal, said study leader Dr. Stephen Juraschek, a general internist at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School.

BP readings typically fluctuate throughout the day. The “gold standard” for accuracy is to measure BP throughout the day, says Associate Professor Juraschek. But that requires wearing a monitor for 24 hours.

Over the years, research has shown over and over again that measuring blood pressure at night is the best predictor of cardiovascular disease, Juraschek says. But it's hard to do.

So Juraschek and colleagues wanted to determine whether measuring BP while lying down during the day — similar to measuring it while sleeping — could identify people at higher risk of cardiovascular disease.

They conducted the study by comparing the sitting and lying BP of 11,369 participants.

The average age of these people was 54 and they were followed for 25 to 28 years. People with a history of heart disease, heart failure or stroke were excluded.

Participants were divided into four groups:

• Group 1: No high blood pressure in either position
• Group 2: High blood pressure when sitting.
• Group 3: No high blood pressure when sitting but high blood pressure when lying down.
• Group 4: High blood pressure in both positions.

Results found, over time:

The group without high BP in either position had the lowest risk.

The group with high BP in both positions was at high risk.

But surprisingly, the group that did not have high blood pressure when sitting but only had high blood pressure when lying down had the same high risk as the group that had high blood pressure in both positions.

Specifically: People who do not have high blood pressure when sitting but only have high blood pressure when lying down - have a 53% higher risk of coronary heart disease, a 51% higher risk of heart failure, a 62% higher risk of stroke, a 78% higher risk of fatal coronary heart disease, and a 34% higher risk of death from all causes than people who do not have high blood pressure in either position, according to the American Heart Association.

In all cases, the risk of cardiovascular events predicted by BP measured lying down was more important than that measured sitting up and in many cases was almost higher, said Associate Professor Juraschek.

These findings imply that supine BP measurements may detect hypertension that would otherwise be missed by physicians, he said.

But he said more research is needed. And for now, measuring BP while sitting will remain key.