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Home Blood Pressure Monitors Are Wrong 70 Percent of the Time, Says Study (arstechnica.com)
An anonymous reader quotes a report from Ars Technica: In a study out this week, about 70 percent of home blood-pressure devices tested were off by 5 mmHg or more. That's enough to throw off clinical decisions, such as stopping or starting medication. Nearly 30 percent were off by 10 mmHg or more, including many devices that had been validated by regulatory agencies. The findings, published in The American Journal of Hypertension, suggest that consumers should be cautious about picking out and using such devices -- and device manufacturers need to step up their game. Lead author Raj Padwal and his colleagues set out to test the accuracy of the devices themselves. Funded by the University of Alberta Hospital Foundation, they compared the home blood-pressure monitors of 85 patients with a gold-standard blood-pressure measurement technique. The patients' monitors varied by type, age, and validation-status. But they all used an automated oscillometric method, which measures oscillations in the brachial artery and uses an algorithm to calculate blood pressure. The gold-standard method was the old-school auscultatory method, which involves the arm-squeezing sphygmomanometer and a clinician listening for thumps with a stethoscope. Of the 85 home devices, 59 were inaccurate by 5 mmHg or more in either their systolic (the top number that's the maximum pressure of a heart beat) or diastolic (the bottom number that's the minimum between-beat pressure). That's 69 percent inaccurate. Of those, 25 (or 29 percent) were off by 10 mmHg or more. And six devices (seven percent) were off by 15 mmHg or more.
Why don't they give us the most accurate devices?
They don't even put the data anywhere, so we can't even figure it out for ourselves.
It's 2017 people.
Human blood pressure should be measured in centimeters of mercury, not millimeters. Saying a patient's blood pressure is say 135/78 is misleading, since blood pressure is DYNAMIC and continuously changes MOMENT TO MOMENT. Whoever decided it should be measured this way had either very limited knowledge of basic human physiology or a grave misunderstanding of how significant figures work.
When you have an event like a concert, people say "28,000 people attended" or whatever. They don't generally claim 28,351 people attended because the one implies that you know down to a single person how many were in attendance. The five, in the absence of the one, implies that the attendance is known to within +/-5 people, and the three means it is known to +/-50, if all trailing digits after that are zero, (and by convention, there's no decimal point used as a marker, such as 300. mg. That decimal implies that all the zeros to the left of that decimal point are known to be zeros).
So... the number of decimal places implies to what degree the number is known.
28351 means exactly that many were there, 28351 to a man.
28350 means 28345 X = 28355 ppl
28300 means 28250 X = 28350 ppl
28000 means 27500 X = 28500 ppl
& 30000 means 25000 X=35000 ppl. Note that each of these ranges includes the value 28351, the actual number who were there.
Similarly, if you asked how many people are at a festival, someone MIGHT be able to say at any given moment what the exact population there is, but as people are constantly leaving while others (and not generally in a one-to-one ratio or basis, any exact number given for any given time might be true, precise AND accurate, AT THAT MOMENT but could EASILY not be a good representation of attendance at any other time or during any arbitrarily chosen long period of time.
The same is true with blood pressure. (And I speak as a former Army medic who has taken a LOT of blood pressure readings in my day, and yeah, I knew what I was doing and I know what I'm talking about.
Even if you measure a patient's blood pressure perfectly, down to a nanometer of mercury (equivalent weight,) in a few seconds it'll change enough for your reading to be not just no longer true, but laughably inaccurate and worthless. Measureing like that would only be effective in watching for trends and detecting blood pressure at either extreme and you don't generally need to know (because the information is fundamentally worthless,) causing alarm where none's warranted.
We should measure BP in cmHg, rather than mmHg. This, a patient's blood pressure would be listed as 14/8 cmHg, and it would be true and accurate and useful in a way mmHg readings aren't.
If I may be permitted one more illustrative analogy... imagine if your car'sor motorcycle's speedometer doesn't tell you feet per hour, or even inches per hour which would be even more hilariously egregious.
"Do you know how fast you were going, sir?"
"Um... 343,200 feet per hour, officer?"
"Well, sir, I clocked you at 343,315 fph, and the speed limit is 316,800 fph. I'm going to have to issue you a citation."
"Ah man... how much is the fine?"
"Pretty steep, considering this is a construction area... it's going to cost you 22,000 cents, unless you wish to contest it in court, in which case follow the instructions on the back, to indicate your intentions within the next 259,200 seconds."
See how absurd that is?
Using cmHg would mean less time wasted trying to get it EXACT, when doing so is, as I've illustrated, POINTLESS!
It's less than 5% in a system that easily varies 20% in the course of an hour, and than vary nearly 50% in moments under stress. It's also easily affected by flexing the arm sitting in a different chair.