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Measuring BP. Reliable devices?

todd121
Posts: 578
Joined: Dec 2012

Because I'm on this drug trial and one of the possible side effects can be increased blood pressure, I decided to buy a blood pressure machine and monitor it myself at home. The first machine I bought was an inexpensive automatic one at the local pharmacy. I think it was about $25. It was useless. The readings were all over the place and made no sense. I returned it.

My son pointed me to a company called Withings that makes a scale and also a BP monitoring device that interface with my iPhone. The device had some decent reviews (but also a few bad ones, which were related to it not working at all). I tried it. In the first few weeks I was using it, my readings seemed to be consistently what my BP was (in the low 130's/high 70's). But after a few weeks I started seeing consistent readings in the low-mid 140's/low-mid 80's. I started worrying that my BP was going up because of the drug I'm taking. Two nights ago (the night before I was going to my doctor for my 6-week checkup), I measured 154/87. I talked to my uncle, and he said I should probably be put on blood pressure medicine. However, he also suggested taking my machine with me and comparing the results of my machine with the machine at my doctor's office.

I went in to the doctor yesterday morning, and when they measure my BP it was 126/76. I felt relieved. I brought my device out and measure it, and once again it measured 144/86. We went back and forth a few times, and the doctor's machine (which is also automatic, but uses disposable, paper cuffs), measured high 120's or low 130's/high 70's or low 80's. One of the 3 measurements I did on the doctor's machine, did measure 86 for the bottom number, but the upper numbers were all much lower than on my machine. I decided my machine isn't reliable. My doctor completely set aside my worries (because all my blood tests were normal, he doubted I was having increased blood pressure from the drug).

Later that day, though, I was in the pharmacy and decided to try their public machine. It measured 144/87. But I had been walking quite a bit before that...

Has anyone had good luck with auomatic BP machines at home? How do you find one that is reliable? Do you have to spend a lot of money to get a good machine? (The one I bought that interfaces to my iPhone was over a $100, so not cheap). Any recommendations on a good, inexpensive, automatic machine would be appreciated. Is it possible to take your own blood pressure the old way? If that would be more reliable, I wouldn't mind doing that.

Because I have only 1 kidney, I want to be careful about my BP. High BP can damage kidneys over time, from what I've read.

Thanks,

Todd

Texas_wedge's picture
Texas_wedge
Posts: 2807
Joined: Nov 2011

Welcome to the real world Todd! 

The reality is that your first machine was probably perfectly OK.  Modern digital sphygmomanometers are pretty reliable, if they come from reputable manufacturers. 

We tend to assume that BP is a simple, familiar and well-understood phenomenon.  Nothing could be further from the truth.  Most nurses and doctors don't have the slightest clue about it.  The idea of going to your doctor and having your "blood pressure" checked, say annually, is totally ludicrous and can well have misleading (and even potentially fatal) consequences.  It's still an area, simple as it seems, of great mystery, in which new discoveries are constantly being made.  

Your blood pressure is affected by numerous factors and is varying grossly all the time.  It's significantly affected by thoughts and stress - you can probably verify this by checking it in relation to listening to Jerry's CD or engaging in other forms of meditation (e.g. Vissana,  Transcendental, Mindfulness). The digital devices use formulae and yours, I presume, also shows heart rate, which is taken into account.  I can change my heart-rate by a few points at will which must be factored into the accuracy tolerance which should be quoted with your sphyg. 

I've been making a bit of a study of the subject for a year or two and I check my BP daily, using 3 different machines, one radial and two brachial, rotating the order systematically and noting the time of day.  I record the outputs of all three, which also show pulse rate and I take the latter manually in advance of the measures.  My doctors regard my measurements at home as more reliable than those they can take with super-expensive state-of-the-art hospital machines costing thousands.  One reason is the 'white-coat effect'.  Also, they cannot guarantee proper conditions - your BP needs to be taken under scrupulous conditions - on an empty bladder, not within an hour or so of having a meal, or coffee, or alcohol, after a quiet period of relaxation and without you talking or being talked to.  The cuff needs to be the correct size for your arm, at the correct tightness and correctly located - many nurses and doctors don't appreciate any of the finer points, making the "measurement" almost meaningless.

BP is also subject to substantial diurnal variation and we each have our own pattern of circadian rhythms.  For most of us, there is the 'early morning surge' and BP changes through the day, being lower at night.  However, some of us are 'reverse dippers' who have higher BP at night than during the day and this is of diagnostic significance.  Also significant is wide difference between BP taken between left and right sides ( expert advice is that BP should be taken on both arms, but this is very seldom done).  Even low BP can be bad if there are wild systolic spikes and, of course, with measures taken only once in a blue moon this will usually be undetectable.

At best, we can only get a rough picture of our blood pressure profile.  I take mine, most often before breakfast and before I take my morning BP med, with the three devices at intervals of approx. 5 minutes, after taking my pulse manually.  Sometimes all three machines show much the same diastolic measure, but widely varying systolic - that can change by at least 20 points in five minutes, sitting quietly, relaxed, in exactly the same position. On other occasions, the systolic will be concordant but the diastolic will show dramatic variations between the three meters.  The sequence seems immaterial, so it's not contingent on which device is used first.  There tends to be a marked difference between measures at wrist and upper arm. This is usually regarded as indicative of the lesser reliability of wrist monitors.  However, there are some suggestions that both may be equally valid but reflect different takes on physiological functions - I have yet to form any theories about this and will (maybe sometime, maybe never)  research it further.

There's been a marked advance by the use of ambulatory BP monitors, worn continuously for, e.g. 24 hours but the appreciation of most docs/nurses of how to make sense of this is so far sadly lacking.

There's a great deal more I could say on the topic but maybe this will do for starters.

todd121
Posts: 578
Joined: Dec 2012

I'm glad to know I've been observing something that is really an issue.

That first machine I had was giving readouts that made no sense at all like 202/130 and widely varying results (much more widely varying than what you mentioned). It could be that particular machine had a problem.

The new one is more consistent and the numbers don't sound absolutely ridiculous, but do seem to be higher (particularly the systolic, which seems to be 20 mm higher). I measured using my doctor's machine and the systolic was 122, then went to mine and it was 144, then went back to my doctor's and it was 126. In between I stayed seated and was resting.

Last night I had my BP taken manually by a friend who is a nurse and does this 20-30 times a day, and it was measured at 122/76.

I think I'm going to do as you do and get another machine and measure it with both machines and when my friend is available, have it taken manually. Seems like more data is needed to figure out if I'm having higher BP.

Todd

Texas_wedge's picture
Texas_wedge
Posts: 2807
Joined: Nov 2011

I'll be interested to learn of your results if you pursue it in that way, Todd.  I had my Onc meeting yesterday and my cancer nurse took mine at 166/97.  My Onc was happy to accept that my home readings are much more reliable.  She says she has other patients whose BP skyrockets as soon as they walk into the Hospital!

By the way, it sounds to me that your BP isn't elevated at all.

I am alive
Posts: 221
Joined: Jul 2012

My God Tex! You are an amazing fountain of knowledge on this topic (as on so many others)! I've just started taking BP meds so  this is an area of particular interest. You are right - nobody tells you any of the back story. I'm lapping this up like a parched dog.  Here's one question: what does a reverse diurnal rhythm indicate? (yep. That's what I seem to gave.)

I am alive
Posts: 221
Joined: Jul 2012

  After posting above I jumped on Google and discovered that my low-ish a.m. BP and higher p.m. BP is normal. See how much I don't know about BP? 

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