The gentlebirth.org website is provided courtesy of
Ronnie Falcao, LM MS, a homebirth midwife in Mountain View, CA

Selecting a Sphygmomanometer or Blood Pressure Monitor

Time for a Better Sphygmomanometer

There's Lots of Information on the Web

In any case, the "column of mercury" reading became the definition of blood pressure (as in "so many millimeters of mercury", also written mm Hg, since Hg is the symbol for the element mercury).  And it is still the "gold standard" in that it is the most accurate measurement and is standard across many different instruments, so it's typically used by health care providers who don't need their equipment to be portable, and who need "accurate" readings that will be meaningful when compared with readings taken on other machines.

However, most homebirth midwives prefer more portable equipment, so I wasn't even considering getting any kind of sphygmomanometer with mercury.  I was looking primarily at the aneroid sphygmomanometer and the electronic blood pressure monitors.  I learned some interesting things:

• Sphygmomanometer means "(sphygmo = the pulse; mano = rare, thin, roomy; meter = to measure; manometer = an

instrument to measure pressure exerted by a liquid)
• Aneroid means "no liquid", derived from the French anéroïde, from Greek a- + Late Greek nEron water.  The term was first applied to barometers which operated by the effect of outside air pressure on a diaphragm forming one wall of an evacuated container, rather than a column of mercury.  I guess the term carried over into non-mercury sphygmomanometers.  Now, in the context of a sphygmomanometer, aneroid implies that there is a spring mechanism measuring the pressure in the cuff.
• A pocket aneroid sphygmomanometer isn't a tiny one that fits in your pocket - it's one where the gauge can be attached to a "pocket" on the cuff.  A hand aneroid sphygmomanometer has the gauge near the inflation bulb.
• Some of the newer sphygmomanometers have a "trigger deflation valve" allowing for smooth control of deflation; this was the feature that most drew me to the "Silver Ring" line described below.

 

Comparing aneroid sphygmomanometers and electronic blood pressure monitors:

[NOTE - June, 2005 - this web page is one of the oldest here . . . if you want more up-to-date information, you might want to read

The text suggests that the information was updated May 2005 when in fact the current list of Hypertension Society Machines is reviewed each month.

You might also be interested in a site that is dedicated to providing information to help people correctly measure their blood pressure and within the site is a page about blood pressure during pregnancy:

Blood pressure monitors which type is recommended to use at home?

Home blood pressure monitors recommended by the British Hypertension Society

and the companion page - Automatic Digital Blood Pressure Monitors from Omron available in the USA]

HM International offers a good selection of Omron blood pressure monitors as well as Littmann stethoscopes.  The claims are that Omron blood pressure monitors fall within acceptable accuracy ranges, comparable to mercury devices.

So, I poked around on the Web to see what I could find from medical source about the relative accuracy of electronic or oscillometric blood pressure monitors:

The accurate measurement of blood pressure -  Report of the Canadian Hypertension Society Consensus Conference "Diagnosis of hypertension in adults"

Are Home Blood Pressure Monitoring Devices Accurate? - The investigators concluded that there is a significant  number of inaccurate readings obtained using home blood  pressure monitoring devices.  However, this was an uncontrolled comparison using random devices and is more a heads-up to physicians to get details about a patient's home monitoring device before trusting reported results.

DISCUSSION OF HOME AMBULATORY BLOOD PRESSURE MONITORING - "The device that was the most accurate of the three tested was the Omron HEM-705CP"

American Society of Hypertension Releases Guidelines on Home and Ambulatory Blood Pressure Monitoring - Concludes that aneroid devices are more accurate than electronic devices but may not be suitable for all users.

And here are some abstracts from Medline:

Accuracy of oscillometric blood pressure monitoring in pregnancy and pre-eclampsia.
Gupta M, Shennan AH, Halligan A, Taylor DJ, de Swiet M
Br J Obstet Gynaecol 1997 Mar;104(3):350-5

CONCLUSION: The Omron HEM 705 CP does not reach acceptable accuracy criteria for blood pressure measurement when compared with trained observers in women with pre-eclampsia, as judged by the British Hypertension Society Protocol. It also failed to meet the AAMI criteria, although the methodology stipulated by the AAMI may not be  applicable to a pregnancy population.

The Blood pressure watch and Omron R1 were found to be inaccurate for children and adolescents.

Home self-monitoring of blood pressure: is fully automated oscillometric technique as good as conventional stethoscopic technique?
Stergiou GS, Voutsa AV, Achimastos AD, Mountokalakis TD
Am J Hypertens 1997 Apr;10(4 Pt 1):428-33

For hypertensive patients, oscillometric devices validated in the provider's office provided readings comparable to those taken by very carefully trained patients.

In clinical practice, HBP monitoring by using reliable automated devices is probably more feasible than to achieve a high standard of stethoscopic HBP measuring technique.

Blood pressure self-measurement in upper arm and in wrist for treatment control of arterial hypertension compared to ABPM.
Eckert S, Gleichmann S, Gleichmann U
Z Kardiol 1996;85 Suppl 3:109-11

The boso Oscillomat (upper arm) and Omron HEM-601 (wrist) were found to be comparable to automatic 24-h, ambulatory blood pressure measurement.

[The evaluation of a self-measurement arterial pressure monitor: the OMRON-HM 722C].
Cordoba R, Fuertes MI, Alvarez A, Molina I, Solans R, Melero I
Aten Primaria 1997 Sep 30;20(5):247-50

The OMRON-HM 722C self-measuring monitor could be useful for self-measurement of BP at home by primary care patients.

The Omron HEM-713C compares well with the standard mercury manometer, we therefore recommend its use in both research and clinical applications which require blood pressure measurements.

However, I was nervous about the specific study showing inaccurate readings for pregnant women, especially those with high blood pressure readings.  As a homebirth midwife, I wouldn't expect to be managing care for someone with serious high blood pressure, but there are times when a mom can have a sudden change in blood pressure during labor or postpartum, and I'd hate to be doubting my equipment during a time of crisis.

So, I made the decision to purchase an aneroid sphygmomanometer for my baseline blood pressure equipment.  Perhaps sometime in the next few years, I'll be able to purchase an electronic monitor for normal postpartum, knowing that I always have my aneroid as a backup instrument in case I don't trust the electronic readings.

Purchasing

Miscellaneous

More Blood Pressure Papers

And some related review material:
The Circulatory System - A basic review
Shock - including a discussion of hemorrhage, dehydration, heat stroke and anaphylactic shock.

And I also came across some information that's really fun, but not of much clinical value:
Hemodynamics
Hemodynamics II - Hemodynamics can be loosely defined as the physics of blood flow in the circulation
Fluid and Hemodynamic Derangements - an odd collection of interesting information.