Digital Blood Pressure Monitors Are Easy To Use But...
Don't buy a wrist or finger monitor. Digital blood pressure monitors may be accurate but have it positioned properly. Movement is more critical. Read these and other tips from this physician’s 30+ years experience.
Description of First Blood Pressure Monitors
All blood pressure measuring devices use an inflatable bladder encircling the limb. From there on there is a lot of divergence. The earliest devices, called sphygmomanometers, used a rubber bulb to provide the inflation and a glass-encased vertical column of mercury to indicate the amount of air pressure in the bladder.
They also required the operator to use a stethoscope to listen to the arm just below the bladder and over the artery being compressed. These initial devices are still the most accurate types of monitors but by virtue of having a column of mercury 300 millimeters high (or 11.8 inches) they are necessarily bulky and relatively heavy.
Widespread use of blood pressure measurement did not prevail until around 1910.
The main parts were:
- Inflatable bladder encircling the arm
- Bulb to inflate the bladder
- Column of mercury to indicate the bladder pressure
- Stethoscope to listen to the artery being compressed
The need for a lighter and smaller device led to the development of the aneroid instrument. This is basically a replacement for the bulky column of mercury using a 2-3 inch round dial with a spring loaded pointing needle. The dial is graduated in mm of mercury so as to be consistent with and compatible with the previous readings taken with the mercury devices. Thus they become delightfully lighter, smaller and portable. These are nearly as accurate but need to be calibrated more often (at least annually) and after any significant accidental drop.
Some of these have the stethoscope listening end attached to the cuff that is presumed to be placed properly when the cuff is applied to the arm. This is where I start to get uneasy.
Digital Blood Pressure Monitors
These relative latecomers to the blood pressure scene replace everything in the above list but the bladder and the inflation bulb. Some devices also replace the inflation bulb thus becoming fully automatic.
In place of the stethoscope they use pressure sensors to detect pressure variations. Software is require to interpret the data gathered and translate it into systolic and diastolic readings that are digitally displayed. This has the advantage of eliminating user judgment error.
In place of the pressure displaying gauge or column of mercury or aneroid gauge, is another mechanism inside the cuff providing bladder pressure data. This data is then transmitted to the digital blood pressure monitor itself for integration with the data described above to provide actual numbers for the systolic and diastolic blood pressure. The method of acquiring the data and the software for interpreting it vary from company to company and are industrial secrets.
This technique is called the oscillometric system which was developed by a Japanese company called A and D Medical/Lifesource. Most digital blood pressure monitors use this system although there are some others.
An automatic inflator/deflator may replace the inflation bulb providing more consistency.
Some considerations in digital blood pressure monitors:
Some devices perform the inflating and deflating, which has the advantage of reducing operator technique error.
Others variously print the readings, memorize them, average them and allow for multiple users. All this adds up to a lot of convenience and reduction of user error. But inherent problems are also present in the digital blood pressure monitors:
Limb movements, both voluntary and involuntary, cause artifactual "noise", which the older devices had difficulty in distinguishing from the proper signals. This appears to have been largely overcome by some of the modern devices. Just relaxing your arm and not moving it will go a long way to overcome this so just don't move it.
Cuff placement and arm positioning are more critical thus requiring the operator pay good attention to this part.
Parts that cost only a relatively few dollars substitute for two wonderful human senses, vision and hearing. Can they possibly be as good as yours? Or better? In their own way, perhaps so. This is partly because they don't measure sights or sounds but measure pressure variations.
Quality varies a lot from one instrument to another and from company to company.
Large arms require a DC adaptor rather than batteries because of the higher power demand.
These also require periodic calibration and maintenance as do the other types.
Doctor's Practical Guide
The digital blood pressure monitors are tops in convenience and ease of use.
They also reduce operator error and virtually eliminate the necessity for operator judgement.
In accuracy and reliability they are behind the mercury and the aneroid but not by much especially with the better ones.
Maintenance is more costly as it can often be done only in the factory. Not a huge consideration.
Some are made only for one arm, left or right. Little known tip: the left arm averages about 4 mm lower than the right arm due to the positioning of the heart, thus a 4 mm error is inherent in the devices for left arm only. On the other hand, the digital monitors tend to read a little high so this probably evens out.
My bottom line: With the automatic home blood pressure monitors you:
- Position the cuff on your arm.
- Sit back and relax your arm.
- Press the button.
In a short while your blood pressure displays. Nice and convenient, what could be easier? But this requires a certain amount of trust because you didn't see it or hear it.
With the mercury or the aneroid you see it and you hear it.
If you just don't want to learn how to take blood pressure with the stethoscope and gauge (auscultatory method) then the digital monitor is a very good alternative, a good second choice. Certainly a great deal better than not taking it at all.
I am currently evaluating one of the better ones from Lifesource made by A and D Medical. So far I am very pleased. Update: I am very pleased and now find myself using only the digital monitor because of the ease of use and the apparent equality in accuracy.
For another description of considerations for choosing a monitor for you to use at home go to:
Home Blood Pressure Monitors
For How and Why to take your own blood pressure see:
How To Take Blood Pressure
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