Home blood pressure monitors may be useful to some older adults who’ve suffered a stroke, but little help to others, a new study suggests.

Researchers found that overall, home monitors did not help stroke sufferers get a better handle on their blood pressure over one year.

The exception, though, was patients whose blood pressure was poorly controlled at the study’s start - meaning it was above the standard high blood pressure cutoff of 140/90 mm Hg.

In that case, patients given a home monitor cut an average of 11 points from their systolic blood pressure (the top number in a blood-pressure reading). That compared with just under five points among patients who were not given the devices.

That’s a meaningful difference, said Hayden B. Bosworth, a professor of medicine at Duke University in Durham, North Carolina, who was not involved in the study.

The lack of overall benefit in the study doesn’t mean stroke patients shouldn’t use blood pressure monitors, according to Bosworth, who studies ways to improve people’s management of high blood pressure and other chronic conditions.

“It may be a matter of finding the right people to give them to,” he said.

Sally M. Kerry, the lead researcher on the study, said that many people who’ve had a stroke are “very motivated” to prevent another. So they may already be doing their best to keep their numbers under control.

“The main issue seems to be with those who already have relatively well-controlled blood pressure. Home monitoring is unlikely to improve this, although people do find it reassuring,” Kerry, a researcher at Queen Mary, University of London in the UK, said in an email.

She and her colleagues report their findings in the Canadian Medical Association Journal.

Past studies have found that home monitoring may aid blood pressure control. A 2010 review of 37 clinical trials found that overall, people who used monitors shaved a few extra points from their blood pressure. They were also more likely to cut down on medication compared with patients who stuck with traditional doctor’s office measurements.

The new study focused on patients who’d recently had a stroke - a group, Bosworth noted, that hasn’t really been studied when it comes to home blood pressure monitoring. He said that’s probably in part because there is no real consensus on what stroke survivors’ blood pressure levels should be.

Kerry’s team randomly assigned the patients to either stick with standard care only or get a home monitor - along with instructions on how to use it and periodic phone calls from a nurse to check on how they were doing.

Over the next year, the results were mixed. Among the patients who didn’t seem to benefit were those who’d been left disabled by their stroke. Home monitors showed no effects on their blood pressure, while non-disabled patients cut about four points using a monitor.

“Some patients had difficulty in carrying out monitoring because they did not have a carer who lived with them to help,” Kerry said.

Bosworth pointed out that many people with high blood pressure already have home monitors, and these findings do not mean that stroke survivors can’t benefit.

It may just be that an elderly person left disabled by a stroke is “not the best” candidate, he said.

And for a monitor to benefit anyone, the numbers have to be put to good use, Bosworth said. That means a person’s healthcare provider has to know what the numbers are and make any needed adjustments in the patient’s medication.

Traditionally, people have had to bring their home readings to their doctor at each visit; some monitors automatically record each reading and allow you to print them out. But there is also “telemonitoring,” wherein wired or wireless technology is used to automatically send blood pressure readings to the doctor’s office.

That’s not widely used in the real world yet, but studies have suggested that telemonitoring boosts the effectiveness of home blood pressure measurements.

Home monitors range in cost from about $25 to more than $100, depending on the features. Experts generally suggest that you choose a monitor that has been validated for accuracy according to international criteria.

Some groups, like the British Hypertension Society and the Association for the Advancement of Medical Instrumentation, test blood pressure monitors’ reliability and keep lists of validated monitors on their websites.

The current study was funded by The Stroke Association, a UK charity.

If you do use a monitor, Kerry cautioned against interpreting the readings on your own and changing your medication dose.

In this study, she noted, some patients using home monitors did take it upon themselves to cut down on medication when they saw that their numbers looked good. And that, Kerry added, might be one reason why patients with fairly good control at the outset did not see a further improvement when they used a monitor.

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SOURCE: CMAJ, online November 5, 2012.