Surprising Findings About Taking Your Blood Pressure Lying Down

The simple act of having someone lie down and have their blood pressure taken might reveal more than expected about heart health according to preliminary research.

Using data gleaned from a substantial, long-running study, researchers discovered that when comparing readings taken while someone was sitting, readings that indicated high blood pressure in individuals lying down better predicted serious heart problems, stroke, and death.

Results will be presented Saturday in Boston at the American Heart Association’s Hypertension Scientific Sessions. The research is considered preliminary until full findings are published in a peer-reviewed journal. 

Senior researcher on the work, Dr. Stephen Juraschek, said the findings were surprising and suggest that having people lie down to measure their blood pressure could help identify people who need treatment despite having what appears to be normal readings while seated.

Managing hypertension, or high blood pressure, has long been understood to be essential to managing heart health. However, getting an accurate reading from a seated position can be complicated, according to Juraschek, an associate professor at Harvard Medical School and general internist at Beth Israel Deaconess Medical Center in Boston. 

The American College of Cardiology and AHA defines normal blood pressure for adults measured seated as a diastolic reading under 80 mmHg and a systolic reading of less than 120 mmHg. But, readings can fluctuate throughout the day.

Juraschek said the “gold standard” for accuracy is an ambulatory, or blood pressure taken various times throughout the day. However, that would require an individual to wear a monitor for 24 hours.

He said that over the years, research has shown “time and time again” that blood pressure measurements taken at nighttime are one of the best predictors of cardiovascular disease. But it is hard to get those readings. “It’s not comfortable to have your arm compressed repeatedly overnight,” said Juraschek. “It can affect your sleep.”

Juraschek and his colleagues wanted to lay the groundwork for determining whether having people lie down to have their blood pressure measured during the day might identify those at higher risk of cardiovascular disease, similar to taking blood pressure during sleep.

Researchers compared readings taken while seated and lying down

The researchers started by comparing readings taken while sitting with those taken when lying down.

Researchers turned to data collected from 11,369 people in the Atherosclerosis Risk in Communities Study. Participants’ blood pressure was measured while they were lying down and seated. 

The average age of participants was 54, and they had been followed for a median of 25 to 28 years. Individuals with a stroke, heart disease, and heart failure history were excluded. One-fourth of the participants were Black, and over half were women.

Participants were divided into four groups: One had high blood pressure only while sitting. One group had normal blood pressure readings both when lying down and seated. Another group, comprised of 16% of participants, had high blood pressure only when lying down. The last group had high blood pressure in both positions.

Over time, the group that didn’t have high blood pressure in either position had the lowest risk. The group with high blood pressure in both positions had a consistently higher risk. 

However, Jaruschek said that unexpectedly, the group that had high blood pressure only while lying down had similar risks to those with high readings in both positions, even after considering other cardiovascular risk factors. 

Individuals with high blood pressure only while lying down had a 53% chance of coronary heart disease, 62% higher risk of stroke, 51% higher risk of heart failure, 78% higher risk of fatal coronary heart disease, and a 34% higher risk of death from all causes when compared to people with normal blood pressure in both positions. 

Juraschek said the risk of problems predicted by supine blood pressure “in every single case, was more important than the seated, and in many cases was very close to having an elevation in both.”

Professor of medicine at UT Southwestern Medical Center in Dallas, Dr. Wanpen Vongpatanasin, called the study important but emphasized more research is necessary.

Work done previously has shown nighttime blood pressure can independently predict cardiovascular outcomes. Still, it remains unclear if that was related to the measurement’s timing or the participant’s position when being measured, said Vongpatanasin.

“This study suggests that supine blood pressure may be one explanation, as it has as much impact on long-term cardiovascular outcome as seated blood pressure,” she said.

Study wasn’t designed to examine possible explanations for the different readings. 

Jurascheck surmised that numerous factors could be responsible for these findings, ranging from the possibility that achieving an accurate reading is easier when a patient is lying down and relaxed, to the physics of how fluids travel around the body when it is flat instead of seated.

With more information and studies, supine blood pressure could help detect hypertension in people whose treatment is delayed because they’ve been “flying under the radar,” said Juraschek. It could also help identify people who may need treatment.

For now, Juraschek said that monitoring blood pressure while seated will remain the key. “There’s such a large body of evidence about treatment of seated blood pressure that we just can’t ignore.”