Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Donate Today!

Do you enjoy these
technical forums?
Donate Today! Click Here

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

rosetta (Electrical)
14 Mar 08 12:29
I am looking for a portable instrument that can be used to determine the "cuff pressure" of automatic blood pressure sphygmomanometers.  I noted a large disparity between the results (systolic/diastolic) of an automatic sphygmomanometer and that of a requested manually operated sphygmomanometer.  I questioned the physician about the exceptionally high values of the automatic device and he stated "the pressure is too high!"

The physicians have no way to adjust the cuff pressure of the automatic machines and I want to find out just how high some of them are going. During my follow-up inquiries, users have stated they have had tests where the cuff pressure was quite painful.
rosetta (Electrical)
18 Mar 08 12:13
I would like to clarify what I need.  I want to be able to insert "something" into the cuff, cycle the machine, and show the cuff pressure.  I will not be able to disconnect the hoses to the actual sphygmomanometer.
MikeHalloran (Mechanical)
18 Mar 08 20:43
I've had physicians exert a lot of pain with the manual machines they so trust.

But, I thought the 'cuff pressure' you seek to measure, and what's reported, was just that; the pressure in the pneumatically inflated torus... which at low flows should be equal throughout.  So all you need is to insert a tee and a transducer in the hose supplying air to the cuff.

If you want to measure the pressure at the skin interface, that's a different kettle of fish.

Mike Halloran
Pembroke Pines, FL, USA

rosetta (Electrical)
19 Mar 08 1:09
Mike Halloran, your comments about "measure the pressure at the skin interface" might just be the solution.  Manual sphygmomanometers are pretty cheap, and I don't see any reason why I cannot use a manual sphygmomanometer cuff around a piece of 3" pvc that simulates an arm.  I could inflate the manual sphygmomanometer to a specific pressure, wrap that with the cuff from the auto sphygmomanometer, activate it, and note the differential on the manometer of the manual sphygmomanometer.

This process would work on the auto sphygmomanometers that inflate to a point well above systolic.  There are some auto sphygmomanometers that incrementally inflate to just above systolic, but I don't think very many of those are in use.
rosetta (Electrical)
11 May 08 20:41
I purchased a manual sphygmomanometer with an analog aneroid pressure gauge. I found that a good rigid "arm" was an empty 10 Oz (305 gm) soup can.  I installed the sphygmomanometer on the can and inflated it to 80 mmHg, fit that into the sleeve of my auto sphygmomanometer and hit the ON button. The auto sphygmomanometer applied 210 mmHg to the "arm" on its initial inflation.

My auto machine instructions states to wait 15 minutes before retesting to allow the blood vessels to return to normal (what is normal by age?), but one doctors auto sphygmomanometer, he uses on my wife, automatically recycles immediately after a test, and will continue to recycle until the doctor turns it off. He records the average of several consecutive tests.

A cursory search of the literature indicates that as people age their arteries and blood vessels loose some of their flexibility, thus it takes longer for them to "fully open" if they are subjected to a compression. An excessive compression to begin with will result in the same issue, the blood vessels haven't reestablished ambient flow by the time the "machine" has read the systolic and diastolic pressure.  

The pressure applied to my artificial "arm" can be read directly by the analog pressure gauge. One only needs to inflate the "arm" under test to sufficient pressure to give it enough "body" that it can be compressed.

I am sure many other people have both manual and auto sphygmomanometers and can do the same test I have done.

I think the issue of excessive sphygmomanometer pressure should be examined thoroughly.

Some of the better auto sphygmomanometers inflate to only just above where blood flow stops, thus the pressure is limited. Still, there has to be a better way to measure blood pressure, as the current sphygmomanometer process can introduce errors.
MikeHalloran (Mechanical)
12 May 08 19:22
I've got an Omron auto wrist cuff.  It seems to inflate to ~30mm above the systolic pressure.  It's much less painful that the average physician, who seems to pump until the mercury is about to overflow before even listening.

It's also smart enough to recognize a heartbeat to some degree; it won't start a cycle until it's elevated to within a few cm of the heart's elevation.

I'm a little fuzzy on how the process could induce errors, or how you would detect them, since what's measured and reported is the pressure in a hopefully standardized cuff, not the pressure in the blood lumen.

 

Mike Halloran
Pembroke Pines, FL, USA

rosetta (Electrical)
12 May 08 19:57
How does your device "know" it is elevated to within a few cm of the heart's elevation?

They have an invasive method of measuring blood pressure directly but it is used only in special cases.

It would be nice if they could find a method somewhat like they use to measure intraocular pressure. Unfortunately, the flexibility of an artery can introduce errors, just as thick or thin corneas can cause tonometer errors.  I am sure some time in the future there will be a better device, and the medical history books will mention the sphygmomanometer in the same section as "bleeding a patient" to make him better.

If I did not question why my blood pressure was way high from an auto sphygmomanometer test I would be popping pills and making some drug company happy all the way to the bank.
MikeHalloran (Mechanical)
12 May 08 21:47
I haven't figured out how the Omron knows its elevation relative to the heart, but it works in real time, and is dead accurate.  When you start a cycle, the display shows a heart, with a flashing arrow to one side pointing at it.  If the arrow is on the left, you raise your wrist, and if it's on the right, you lower your wrist.. and the arrow moves closer to the heart proportionally.  When you're at an acceptable elevation and have superposed the arrow on the heart, the air pump starts.

 

Mike Halloran
Pembroke Pines, FL, USA

rosetta (Electrical)
13 May 08 11:57
The Omron A.P.S. (Advanced Positioning System) is an interesting feature. With a wrist monitor, you can move it quite a distance above or below the heart level, whereas the typical upper arm pressure band is always going to be close to the heart level by default.

After the Omron starts, can you then move it above your head or below your waist?  I wonder how many mmHg change this results in blood pressure? Any muscular action is bound to alter your blood pressure, so I doubt any one reading you get will be meaningful, but if you take enough readings it might indicate a trend.

A search on the A.P.S. term always brings up Omron, so it might be a proprietary term for that company.

 
MikeHalloran (Mechanical)
13 May 08 19:52
You have to be within ~+/- 2cm of where it wants to be to start the cycle.  Once the cycle starts, if you move it up or down more than ~8cm, it stops the cycle, vents the cuff, beeps, and reports an E instead of a pressure.

 

Mike Halloran
Pembroke Pines, FL, USA

rosetta (Electrical)
13 May 08 20:24
Hmmm, wonder how that works?  Apply the device to a cylindrical object, a small can, and see if it recognizes the "heart level" by movement.  Since the cuff is not pressurized, it must be detecting a heart beat with its audio sensor, but I don't know how that would identify where it is relative to your wrists position to the heart unless it recognizes some differential pressure.

How firm is the device applied to the wrist before pressurization?

My searches on the internet haven't found anything on the A.P.S.



 
MikeHalloran (Mechanical)
14 May 08 18:58
It straps on with a piece of velcro, pretty much like a regular cuff, except that half of the circumference is relatively rigid, and contacts the inner edge of your wrist.  There's a blood vessel near the surface, roughly at the intersection of the palmar face of the wrist and the inner/ upper/ forward edge.  I assume there's a pressure transducer buried in there somewhere.

 

Mike Halloran
Pembroke Pines, FL, USA

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close