Choose Your Blood Pressure Monitor Wisely
Read this physician’s review and comparison of the many kinds of blood pressure monitor. Learn which ones are accurate and reliable and don’t cost a lot. We’ll go over the different kinds, how they work, their features and their advantages and disadvantages.
How They Work:
Any blood pressure monitor with which we might be concerned uses an inflatable bladder (cuff) encircling a body part (almost always the upper arm) and must include at least 80% of it.
A flexible bulb is connected by a hose to the cuff and provides the air inflation. The digital devices often have an automatic pump for air inflation thus adding a higher degree of consistency.
The air pressure within the bladder is displayed by a gauge except for the digital blood pressure monitors that display it with numerals. The operator listens with a stethoscope over the artery near the bladder or cuff to the sounds the pumping blood makes as the pressure in the bladder is gradually lowered by a valve.
The digital ones do not listen to sounds but rather measure the oscillations of pressure variations and convert the data to blood pressure. This method is called oscillometry or the oscillometric method.
As the pressure is allowed to fall at a measured rate the pressure at which the sounds (or oscillations) begin is called the systolic and the pressure at which they disappear is called the diastolic. Needless to say, the systolic is
always higher than the diastolic.
Those sounds are called the Korotkoff Sounds. These two pressures constitute the blood pressure and are displayed for example as 120 over 80.
Kinds of Blood Pressure Monitors
The First Ones, the Mercury Filled: This blood pressure monitor and all subsequent monitors use an inflatable cuff. The first ones used a column of mercury (Hg) to indicate the pressure in the cuff. The column could be as high as 300 millimeters (11.81 inches). This explains why pressures are read in millimeters (mm) of Hg. A stethoscope is used to listen to the Korotkoff sounds.
Characteristics: Must be a foot tall and upright and either sit on a table or desk, or be mounted on a wall or rolling stand. Not very portable, you wouldn’t want to carry it around in your pocket.
Accuracy: Excellent. The most accurate of all.
Reliability: The best. Needs only infrequent calibration.
Cost: Tends to be more expensive than others.
Aneroid: This means “without liquid” and thus means "not mercury". It consists of a round standard-looking air-pressure gauge with a rotating needle pointer and graduated in... yes, mm of Hg. This was so that continuity and comparison to all the previous readings could be preserved. Uses a stethoscope to listen to the Korotkoff sounds.
Characteristics: Light, small and portable. You wouldn’t mind carrying it in your pocket.
Accuracy: Very good to excellent.
Reliability: Good but should be calibrated once a year and any time it is dropped to the floor.
Cost: Less expensive than the mercury.
A sub-category: Some of these come as kits for self-monitoring with the business end of the stethoscope sewed into the cuff so that is automatically applied to the arm along with applying the cuff. Yes, this makes it a little easier, but to what purpose? Here is where you start to lose some control of measurement. Not a good idea. How do we know how good that end of the stethoscope really is? Is it really applied to the right place with the proper amount of pressure?
Digital: In general, these have an inflatable bladder as described above and as do all blood pressure monitors. Here is where there is considerable divergence. First, there is no stethoscope and nothing in the ears. In place of the stethoscope is a pressure-measuring device the purpose of which is to translate the pressure oscillations into visible digits.
Each device has proprietary software which is a company secret. This software, which varies from company to company, interprets the oscillations and translates them into systolic and diastolic pressure numbers. Some inflate the cuff for you, some lower the pressure and some do both. Others store multiple readings, average the readings, allow multiple users, give you a printout and even a few allow connection to a computer.
Characteristics: Usually sit on the table or desk. Easy to read. Reading more influenced by muscle movements, cuff placement, etc.
Accuracy: Some of the modern ones pass the accuracy standards of the rating agencies such as the Assoc. for the Advancement of Medical Instrumentation.
Reliability: Not quite as good as the mercury and aneroid but close.
Cost: Range from not very expensive to quite expensive but now comparable to the others.
The wrist blood pressure monitors are an offshoot of the digital types. See Wrist Blood Pressure Monitors.
For a more detailed discussion of digital devices see Digital Blood Pressure Monitors.
Doctors Practical Guide:
First of all, accuracy and reliability are the most important considerations. Remember, you are dealing here with your health and life.
Convenience and ease of use are also important factors because these might make the difference between taking your own pressure and not.
Cost certainly is important to most of us and rightly so. Why pay more than necessary?
We want to be confident in our measurement. I insist and so should you. My experience with the digital machines years ago was not good. Their readings were frequently erratic; I just didn't trust them. Now they are a lot better and I have one that I like a lot. I routinely read with both devices and I am pleased with them both.
The best way you can be sure you are getting the right reading is to hear it and see it yourself but the digital method is a good second choice.
My recommendation: At first I thought to choose a mercury device, mainly for accuracy, but the aneroids are nearly as accurate and smaller, lighter, more portable and less expensive. Having them calibrated once a year should take care of the reliability issue.
The digital monitors have improved a lot and are tops for convenience and ease of use. In fact, after you place the cuff on your arm it does the rest.
I now recommend both the aneroid and selected digitals. I am beginning to think that the good digitals are the best all-around choice for the non-professional.
Be sure and read my page on how to take your own blood pressure
and why. How To Take Blood Pressure
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