4 of 4 models of automated blood pressure cuffs fail to read my BP

[.Scott]

TL;DR

When my blood pressure is measure by ear, a reasonable value is determined. But 4 different automated models produce the same readings that are more than 30 points too high. Why?

The topic is a mix of physics, fluid mechanics, and medicine.

At work, they have a couple of blood pressure kiosks - that look something like this:

Up till about a year ago, I was using something that I got at a local Walgreen's drug store - it looked something like this:

Finally, my wife has a wrist unit and the local Fire department brought their unit over and described it as "the most expensive automated blood pressure cuff you could find". I have tried all four of these and compared them side-by-side with either what a clinician at my doctors office or an experienced advanced life support paramedic determined by listening.
Consistently, BP values in the range of 150 (as determined by the clinician or ALS paramedic) are being read by these automated machines as over 180 to 190.

It turns out, these automated cuffs use a completely different measurement process than what is heard manually.

The National Library of Medicine has this to say:

Oscillatory Blood Pressure Monitoring Devices​ ... With an oscillatory device, a cuff is inflated over the upper arm or wrist. The new models use “fuzzy logic” to decide how much the cuff should be inflated to reach a pressure about 20 mm Hg above systolic pressure for any individual. When the cuff is fully inflated to this pressure, no blood flow occurs through the artery. As the cuff is deflated below the systolic pressure, the reducing pressure exerted on the artery allows blood to flow through it and sets up a detectable vibration in the arterial wall. When the cuff pressure falls below the patient's diastolic pressure, blood flows smoothly through the artery in the usual pulses, without any vibration being set up in the wall. Vibrations occur at any point where the cuff pressure is sufficiently high that the blood has to push the arterial wall open in order to flow through the artery. The vibrations are transferred from the arterial wall, through the air inside the cuff, into a transducer in the monitor that converts the measurements into electrical signals. ...

Obviously, my arm does not match the model arm that these devices have been designed for.
So, how would you make an arm that at 175 mm Hg will provide no audible beat but will still produce this arterial fluttering?

 

[Baluncore]

Have you checked that others read correctly?
Are you the only one?

 

[jack action]

Maybe it's you. If you feel calmer with humans and/or feel "trapped" while in the machine (or just hearing the pump buzzing), your blood pressure can be higher with the machines.

From my experience with one bought at a local drugstore similar to yours, taking it a second and even a third time shows a decreasing blood pressure.

 

[.Scott]

Have you checked that others read correctly?
Are you the only one?

Here's the sequence:
About a year ago, there were questions about the efficacy of my BP medication dose. I wanted to eliminate my home BP cuff as an issue, so I took it along to a doctors visit. While there, we tested the machine a few times and the clinician took my BP once - but carefully because she knew it would be compared to the machine. My cuff consistently showed a BP reading 30+ points higher than hers, so we concluded that my cuff was bad and I threw it out.
On Monday, while I was coming out of the fitness center, I noticed that my current work location has a BP kiosk. So, I checked my BP and it was alarmingly high. But I recalled that measurements take a year ago at a similar kiosk at my old work location was also giving me high readings - readings that I had taken as accurate.
Yesterday, on the way into the fitness center, I checked my BP at the kiosk again. It was about 185/105. I rechecked several times - one reading came it at 175/100 but all the other readings were about 185/100.
When I got home yesterday, I used my wife's automated wrist cuff and got 183/105.
So, I called the local fire department and they came over for a visit. I explained the situation, so their most able ALS paramedic took a very careful reading 150/90. They then offered to take it with their machine. Since I was talking about buying a new one myself, they described theirs as "the most expensive model you can find". They took two readings - about 190/100 and 200/100.
The paramedic then said that he had listened very carefully and there was no audible beat at all once the cuff pressure had reached 150.

 

[.Scott]

Maybe it's you. If you feel calmer with humans and/or feel "trapped" while in the machine (or just hearing the pump buzzing), your blood pressure can be higher with the machines.

Besides being very comfortable with machines, the kiosk was probably the most relaxing method. I could take my time. The sign suggested relaxing for 30 seconds before starting - I relaxed longer than that. And, as I said, I took many measurements.

Still, it is possible. I remember 30 years ago when trying to get a drivers license photo. I would instinctively react to the sounds of the camera by blinking - resulting in several bad shots before I was instructed to close my eyes, wait, the open them - and they would take the shot just as I was opening them.

From my experience with one bought at a local drugstore similar to yours, taking it a second and even a third time shows a decreasing blood pressure.

When I used the drugstore model, I commonly took two or three measurements. And when I visited the doctors office with it, we took at least two measurements.

I'm also a pretty good bleeder. When donating whole blood, I can fill the pint in less than 4 minutes.

 

[berkeman]

the cuff should be inflated to reach a pressure about 20 mm Hg above systolic pressure for any individual.

Consistently, BP values in the range of 150 (as determined by the clinician or ALS paramedic) are being read by these automated machines as over 180 to 190.

It is not uncommon for the discomfort of an inflated cuff to increase BP. I experience this myself and I've seen it in a number of my patients.

https://pubmed.ncbi.nlm.nih.gov/17890965/

When listening to the blood flow sounds (auscultating the Korotkoff sounds), I find it best to get the diastolic and systolic numbers on the way up (while inflating the cuff), and stop inflating just slightly above the systolic pressure where the sounds go away. I then crack open the pressure release valve and verify the two numbers on the way down. I never overinflate to 20mmHg above systolic pressure, since that aggravates my patients and often makes the Korotkoff sounds come back (which would result in me getting higher BP numbers than I should).

There is a model of automated BP cuff that takes your BP on the way up and stops as soon as it gets the systolic pressure reading. I got mine from CVS Health, model BP3MV1-3X CVS (800230). It's a rebrand of a private manufacturer that calls this model something like "gentle measurement" something something. It gives me the same numbers that I get when I auscultate my own BP, and when my doc or nurse takes my BP manually.

Funny story -- I used to be on the medical staff for an annual SWAT exercise in my county, where the SWAT officers stayed up for 48 hours straight participating in numerous scenarios (simulated terrorist events, live fire exercises, obstacle courses, etc.). It was a very stressful event for the SWAT teams, and there were 4 medical check stations spaced out in the 48 hour sequence. Our job was to check the officers' vital signs and give them a 30 minute rest period. If their vital signs were too elevated, they could be pulled from the competition, which you can imagine would be pretty unpopular with the officers (who were carrying guns). For the first couple years of the event there was a lot of friction between the SWAT teams and the medical staff, since the officers did not want to get pulled out of the competition. Our medical directors pretty quickly realized that it was a mistake to use automated BP machines on these officers, and everybody switched to manual BPs. Much nicer!

[Edited to fix a typo in the CVS model number]

 

[.Scott]

There is a model of automated BP cuff that takes your BP on the way up and stops as soon as it gets the systolic pressure reading. I got mine from CVS Health, model BP3MV-3X CVS (800230). It's a rebrand of a private manufacturer that calls this model something like "gentle measurement" something something. It gives me the same numbers that I get when I auscultate my own BP, and when my doc or nurse takes my BP manually.

With Google, I could only find mention of BP3MV1-3X CVS (note the "1"). And apparently, that model has been discontinued.
But the term "gentle measurement" is associates with "Inflation Mode Technology (IMT)"
There is a a Microlife product with that technology, the "BP B3 Comfort PC". So far, I have not found it available for sale.

Also, I noticed that there is a "Intelligent Inflation Technology" which often pops up in my "Inflation Mode Technology" searches. They are not at all the same.

I found one. It advertises it as "Advanced Inflation Technology".

 

[berkeman]

find mention of BP3MV1-3X CVS (note the "1")

Yes, sorry for the typo. I will edit the "1" into my post.

There is a a Microlife product with that technology

That company name does sound familiar.

 

[berkeman]

I found one. It advertises it as "Advanced Inflation Technology".

That model also has a very useful feature to report if your heartbeat is irregular (which can often indicate atrial fibrillation "a-fib"), which is important to let your doctor know about if you have it.

Irregular Heartbeat Detection alerts the user to an irregular heartbeat during measurement.