# Blood pressure machine **URL:** \ **Category:** Factual Questions\ **Created:** [April 15, 2007, 3:42pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212 "2007-04-15T15:42:22Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![ed241](https://avatars.discourse-cdn.com/v4/letter/e/9de053/32.png) [@ed241](https://boards.straightdope.com/u/ed241)\ **Post date:** [April 15, 2007, 3:42pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/1 "2007-04-15T15:42:22Z")
Hi There are blood pressure machines where I work and if I check my pressure 5 times I’ll get 5 differant readings are they always so unreliable? seems dangerous ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [April 15, 2007, 3:48pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/2 "2007-04-15T15:48:42Z")
Your blood pressure varies all the time. Many things can cause a temporary rise or drop in blood pressure. Perhaps the machines are accurate, and it is your blood pressure that in unreliable. ---
**Author:** ![633squadron](https://avatars.discourse-cdn.com/v4/letter/6/ee59a6/32.png) [@633squadron](https://boards.straightdope.com/u/633squadron)\ **Post date:** [April 15, 2007, 4:26pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/3 "2007-04-15T16:26:15Z")
[QUOTE=ed241] Hi There are blood pressure machines where I work and if I check my pressure 5 times I’ll get 5 differant readings are they always so unreliable? seems dangerous [/QUOTE] Blood pressure varies. The best way to double-check the machines is to compare them to a manual measurement. Now it seems to me that if your workplace has machines, it just may have the tools for a manual test as well, to wit: a stethoscope and a sphygmomanometer (I _love_ that word) aka blood pressure cuff. The instructions (in short): [ol] [li]Find a cuff that fits you. If you’re an adult of reasonable size, no problem.[/li][li]Wrap cuff around lower part of your upper arm, just above the inside of the elbow. Ensure it fits tight.[/li][li]Pump _way_ up, probably past 220. It should hurt a bit.[/li][li]Apply stethoscope over inside of elbow, over the artery (what’s it’s name? ask a g.d. anatomist!). You should hear _nothing_. That’s good.[/li][li]Now release the pressure until you start hearing the blood pumping in your artery. Note the pressure, that’s the top (systolic) number.[/li][li]Continue to release pressure until the pumping sound goes away. Note pressure. That’s the lower (diastolic) number.[/li][/ol] You have just approximated two pressures: the upper one shows what your blood pressure is when the heart’s “out” pulse is traveling through your artery. The lower one is the pressure in between pressure waves. Normal (is anyone?) is roughly 120/70 for a healthy adult male. I am not a doctor, so I won’t comment any further, except to say that numbers significantly away from normal should prompt you to get professional advice. ---
**Author:** ![Madd\_Maxx](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Madd\_Maxx](https://boards.straightdope.com/u/Madd_Maxx)\ **Post date:** [April 15, 2007, 6:06pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/4 "2007-04-15T18:06:54Z")
Also you aren’t supposed to take your blood pressure repeatedly in a short period of time, I believe you are supposed to wait 10 minutes. ---
**Author:** ![ticker](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@ticker](https://boards.straightdope.com/u/ticker)\ **Post date:** [April 15, 2007, 7:49pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/5 "2007-04-15T19:49:20Z")
[QUOTE=633squadron] [li]Apply stethoscope over inside of elbow, over the artery (what’s it’s name? ask a g.d. anatomist!). You should hear _nothing_. That’s good.[/li] [/QUOTE] With just a little practice you can take your own _without_ a stethoscope. As the pressure is released you should suddenly feel your pulse throbbing under the cuff - this is your systolic reading. Release the pressure further and the throbbing goes away - the diastolic. My doctor was always impressed that I could ‘guess’ the reading. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [April 15, 2007, 9:52pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/6 "2007-04-15T21:52:05Z")
Many doctors consider drug store, home and work blood pressures slightly unreliable. The machines are not always calibrated well, some people take their blood pressure over bulky clothing, etc. Normal blood pressure changes throughout the day, and this is increased by activity, anxiety and pain. I don’t think these machines are dangerous – they are often reasonably accurate and can help diagnose high blood pressure. The danger comes from reading to much into a small number of readings. An elevated blood pressure over a longer period of time is usually more concerning than one brief high blood pressure without other symptoms. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [April 15, 2007, 9:55pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/7 "2007-04-15T21:55:46Z")
On the old wall-mounted mercury blood pressure cuffs, you could approximate the BP from seeing when there is a small movement in the mercury meniscus. Pedants think there are really five blood pressure measurements, or Korotokoff sounds. More on that here: [http://www.medphys.ucl.ac.uk/teaching/undergrad/projects/2003/group\_03/how.html](http://www.medphys.ucl.ac.uk/teaching/undergrad/projects/2003/group_03/how.html) ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [April 16, 2007, 2:49pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/8 "2007-04-16T14:49:24Z")
What research there is shows that automated blood pressure cuffs are not particularly accurate: [http://www.nature.com/jhh/journal/v16/n9/full/1001463a.html](http://www.nature.com/jhh/journal/v16/n9/full/1001463a.html) > [@](#): > > In conclusion the Dinamap yields inaccurate estimates of both systolic and diastolic BP even under standardised, and thus optimal conditions. This inaccuracy is exaggerated at higher BP (\>160/90 mm Hg), although the number of measurements at higher pressures was small. We recommend that this device not be used when accurate BP measurement is needed for therapeutic decision-making. [http://archinte.ama-assn.org/cgi/content/abstract/158/7/714](http://archinte.ama-assn.org/cgi/content/abstract/158/7/714) > [@](#): > > The IVAC 4200 yields substandard estimates of systolic and diastolic BP even under standardized, thus optimum conditions. Also, if you’re doing repeated blood pressure measurements on the same arm, that can decrease the accuracy as well. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [April 16, 2007, 3:48pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/9 "2007-04-16T15:48:10Z")
On the electronic home-use cuffs, how accurate are the manually-pumped cuffs? My doctor considers the automatic wrist cuffs to be about as bad as the drugstore machines and suggested the purchase of a stethoscope and aneroid gauge arm cuff, but those things are becoming nearly as hard to find as the mercury-filled units. The ones I have found are alarmingly cheap, and I’m suspicious of any sort of medical equipment with moving parts that costs less than an office visit copay. So, for home use, what’s the best option? Buy the $15 aneroid cuff and hope it’s accurate and repeatable? Buy the $40 manual electronic arm cuff? Buy the $100 automatic arm cuff? ---
**Author:** ![ethelbert](https://avatars.discourse-cdn.com/v4/letter/e/958977/32.png) [@ethelbert](https://boards.straightdope.com/u/ethelbert)\ **Post date:** [April 16, 2007, 6:21pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/10 "2007-04-16T18:21:14Z")
I bought an automatic one (an Omron wrist model) and brought it to the doctor with me. After the the doctor (or the nurse) took the reading, I would wait five minutes and take my own measurement. The readings were always close (within 1 or 2 for the lower reading, within 2 or 3 for the upper). You want to be consistent in how you take the reading. You should rest in a straight backed chair with your feet on the ground for five minutes. Also, your blood pressure will vary according to the time of day, so take it at the same time each day. ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [April 16, 2007, 6:48pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/11 "2007-04-16T18:48:33Z")
[QUOTE=gotpasswords] So, for home use, what’s the best option? Buy the $15 aneroid cuff and hope it’s accurate and repeatable? Buy the $40 manual electronic arm cuff? Buy the $100 automatic arm cuff? [/QUOTE] [This](http://online.boundtree.com/store/product_index.asp?Cat=BLOOD+PRESSURE+%26+STETHOSCOPES&SubCat=BLOOD+PRESSURE+UNITS%2C+MANUAL&Prod=540762) is what we carry on the ambulance. They hold up well, they’re cheap, and they’re accurate (Guaranteed for 20 years!). The key to getting accurate results with a manual cuff is to put the stethoscope in the right place. It sounds silly but lots of people (especially those who should know better) don’t get it right. To be sure, you can palpate the brachial pulse on the medial side of the AC fossa (the other side of your elbow). Put the scope right there and you’re in the right spot. St. Urho Paramedic ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [April 16, 2007, 7:50pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/12 "2007-04-16T19:50:05Z")
[QUOTE=633squadron] a sphygmomanometer (I _love_ that word). [/QUOTE] In the interest of fighting ignorance and for anyone who may be searching for one online, it’s spelt _sphyngomanometer_ ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [April 16, 2007, 8:16pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/13 "2007-04-16T20:16:15Z")
Are you sure about that? All the dictionary sites have the sphygmomanometer spelling. I also get 662,000 google hits for that and 956 for your spelling. ---
**Author:** ![UncleRojelio](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unclerojelio/32/3160_2.png) [@UncleRojelio](https://boards.straightdope.com/u/UncleRojelio)\ **Post date:** [April 16, 2007, 8:24pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/14 "2007-04-16T20:24:25Z")
[QUOTE=Fear Itself] Your blood pressure varies all the time. Many things can cause a temporary rise or drop in blood pressure. Perhaps the machines are accurate, and it is your blood pressure that in unreliable. [/QUOTE] Anecdotal evidence: My blood pressure is always higher if the cute female nurse takes it than it is if the crusty old male doctor does it. ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [April 16, 2007, 9:51pm UTC](https://boards.straightdope.com/t/blood-pressure-machine/400212/15 "2007-04-16T21:51:01Z")
[QUOTE=St. Urho] Are you sure about that? All the dictionary sites have the sphygmomanometer spelling. I also get 662,000 google hits for that and 956 for your spelling. [/QUOTE] :smack: Stupid medical school pushing out the important knowledge, like spelling.