TO MEASURE BLOOD PRESSURE, WHAT DO YOU NEED TO KNOW?
First, if you are going to measure blood pressure (yours or a family member's) you should get a working understanding of what blood pressure is. Click here to view the blood pressure explanation page. Then return to this page to learn how to measure it.
Back already? The quick answer is that the way to measure blood pressure is to get the pressure cuff of a sphygmomanometer (from Greek words meaning 'pulse meter') on your upper-arm, inflate the cuff, and observe/record the measurements.
That measuring device might be electronic, or it might be a dial pressure-gauge, along with the good old-fashioned, Mark 1 human ear, which is how most doctors measure blood pressure and have been doing for more than a century. OK, your doctor has not been doing it that long, but doctors as a class have been measuring blood pressure with a stethoscope and a visual indicator since the beginning of the 20th century.
So, how does that work, anyway?
Funny you should ask. A pressure cuff is just that, a cuff that goes around your upper-arm, and that can be inflated with air to create a constricting pressure around your arm. It's purpose is to temporarily, and controllably overpower the blood pressure inside the brachial artery of your arm. The cuff is usually a rubber or plastic bladder, inside a fabric cover, and the fabric cover has hook-and-loop (Velcro (R) or other brand) strips at each end, so you can fasten it around your arm and adjust the fit.
It has a couple of tubes coming out of the bladder. One is the air inlet/outlet, which might be worked by a little squeeze-bulb hand-pump, or by a small electric compressor. The other tube coming out of the cuff's air-bladder goes to a gauge. On the manual (analog) version, the indicator is normally a dial aneroid gauge.
With that, you'll need a reasonably good stethoscope - that's the device that doctors use to listen to your heart, lungs, other body noises, and - oddly enough - the beat of your pulse in your arm while they measure blood pressure.
Actually, the original and gold standard of BP measurement doesn't rely on a mechanical gauge, which requires calibrating, but instead uses a vertical tube of mercury at the other end of the air-hose with a scale to indicate how high the mercury column is pushed (sorta like an old-fashioned glass thermometer with the mercury or alcohol inside). Those are really the best method because they read directly, with no need for calibration or interpretation, but they are cumbersome and unlikely for home use.
First things first (or view the video near the end of these instructions):
1. Sit down
Sit in a relaxed position, with one arm (some recommend the left, the side nearest the heart, while others recommend the right - we suggest that you try both and pick the one that consistently gives you the worst BP numbers; in this situation, it's best to go with the more pessimistic reading). Support the arm at roughly heart height. You don't want it hanging down by your side, and you don't want it up over your head.
Maybe you have a sofa with its armrest at just the right height to support the arm being tested. Maybe you can sit beside your kitchen table, place a small pillow on the table and rest your arm there. Or prop yourself in bed and rest your arm on a pile of pillows at the appropriate height.
You want your body and arm relaxed, so you are not performing work to keep yourself erect, and your arm is not tensed to keep it in position.
2. Place the Cuff
You want the cuff around your upper arm (the bicep/tricep area above your elbow), with the tubes exiting the cuff at the inside of your elbow. Many cuffs are marked with an arrow that should point at your brachial artery. Some have two arrows, one that points to the right location if you wear the cuff on your left arm, and another that points to the artery if you wear the cuff on your right arm.
You won't actually see the artery, but if you are not too fat (sorry...) you should be able to see a large vein, just under the skin at the crook of the elbow - that's the one the nurses/technicians aim for when you donate blood, or when blood is extracted for testing. It's also the one that inexperienced junkies use... but we won't go into that. The artery is buried deeper in the crook of the elbow (arteries need more protection than veins), but just to one side of the vein (the side closer to your body).
The cuff should just rest with its bottom edge (where the tubes come out) at the crook of the elbow, but not bunched up when you bend your arm. The indicator arrow - if there is one - should be pointing where the artery lives. The cuff should be snug enough that it stays in place without slipping down your arm (you should not need to keep your arm bent to prevent the cuff from sliding), but at the same time, it should not be tight.
3. Arrange the Stethoscope
The stethoscope should have one side with a thin "drum-head" tympanic diaphragm. Slip one edge of the head of the stethoscope under the bottom edge of the cuff, so that the cuff helps to hold the stethoscope head with the diaphragm flat against the skin over the brachial artery. Usually friction will do the trick. You want the stethoscope head to remain in place, firmly over the artery, without you needing to hold it there. For a manual reading, you are going to need your other hand for other purposes.
4. Position the Gauge for Easy Reading
This means what it says. You want the gauge to be facing you so that you can read the dial without using your hands. Many cuffs have a loop or strap and the gauge has a clip on the back, such that clipping the gauge to the strap/loop puts it at a usable viewing angle.
5. Place the Stethoscope Earpieces in Your Ears
Do it now because you might want both hands for the task, and you won't be able to do much with the cuffed arm when the cuff is inflated. Avoid bumping the stethoscope head
6. Close the Valve and Inflate the Cuff
The squeeze-bulb has an inlet one-way valve at one end, and an adjustable valve at the other end where it connects to the hose going to the cuff. The adjustable valve usually has a knurled screw that you can easily manipulate with a couple of fingers on the same hand as holds the bulb. Close the valve, and every squeeze of the bulb pushes air up the tube and into the bladder of the cuff. Open the valve, and air can escape from the tube, meaning that it can escape from the cuff, and any pumping of the bulb doesn't do much to inflate the cuff, because the air escapes out the valve before it goes up the tube.
So, you want the valve closed tightly for this part of the procedure.
Begin pumping by rhythmically squeezing the bulb. After a few seconds, you should feel the cuff begin to tighten, and see the gauge register some pressure.
Pump up the cuff until the blood isn't getting into your lower arm - not something to do for more than a couple of minutes at a time. The stethoscope head must remain in place over the artery at the inside of your elbow.
OK, you're not trying to make your arm turn purple. Just shut off that artery for a few seconds.
If you stop pumping and moving, you should be able to hear through the stethoscope - - silence. If you have stopped pumping and you hear your pulsebeat in your arm, then you have not inflated enough.
7. Slowly Ease the Valve Open
While listening carefully, gently release the valve just a tiny bit. If you start too quickly, you can overshoot the change that you are listening for.
Watch the gauge slowly unwind and listen at the same time.
At some point in the smooth descent of the gauge reading, the needle will begin to pulse, seeming to momentarily hesitate on the way down. Simultaneously, you should hear the first distant-sounding thumps, or loud-and-soft rushing sounds. The sounds will be synchronized with the twitching of the gauge needle.
Make a mental note of the reading when you first hear a good, solid sound. That point will be somewhere above 100 - probably above 140 if your pressure is higher-than-wonderful.
8. Keep Bleeding-off the Pressure and Listening
As the needle goes below 100, pay close attention again. Now you are listening (and watching) for the point where the sounds fade out.
When you hear the last faint "boom", note the reading. If your pressure is where your doctor wants it to be, that second number will be well below 80, somewhere near 70.
9. Record the Two Numbers
That's simple enough - if you don't write them down, you won't remember them.
Any old piece of paper will do for the moment. This isn't your final reading.
Click Here To Download This Video
10. Wait and Do It Again
Yup. Wait a few minutes, with the cuff completely empty, no pressure on the arm.
Then get the ear-pieces back in your ears, settle the stethescope head over the artery, close the valve, and pump it up again, a good twenty points or more above where you think your highest number is likely to be.
Once more, start releasing pressure slowly, and watching the gauge. Again, note when the first beats become audible and visible. You've already heard what the middle of range sounds like, so you know what you're listening for as the starting point. Again, make a mental note of that new number.
Let the air out of the cuff, slowing it a bit as you dip below 100, and carefully note the pressure as the sounds disappear.
Again, write the numbers down.
If you have time, wait several minutes then do it all a third time.
11. Record the Middle (or Worst) Reading
If you did three sets of readings, record "officially" the middle-value set. Don't mix them. That is, don't take a systolic (the high or starting number) from one set and a diastolic (the low or ending number) from another set.
If you did just two, record the worse one.
You should do this regularly. If not daily, at least weekly.
Keep the record in a spreadsheet or on a calendar. You want to be able to show the trend over time. Spreadsheets are more fun - they can show graphs. Calendars just sorta sit there.
Before we forget...
Here's the handy selection of our Blood Pressure / Hypertension related pages on this site:
PROBLEM: You don't hear a starting point - your arm is already making a noise when you first start to open the valve.
PROBABLE CAUSE: You didn't pump the pressure high enough before starting the descent. Try it higher... unless you need to go over 200, in which case, get to a doctor quickly. Either you need further coaching in how to do this, or you are in the middle of a medical emergency.
PROBLEM: The sounds are so faint that you can barely hear them, and can't be confident that you are getting legitimate starting and stopping readings.
PROBABLE CAUSE 1: You might not be placing the stethoscope head properly. It needs to rest flat against the skin, and it must be directly over the brachial artery for best results. If you try several times, adjusting your placement and still can't get a decent level of sound, see the other possible reasons below.
PROBABLE CAUSE 2: You have the stethoscope ear-pieces in backwards. Seriously. Cheap stethoscopes don't have a bias or slant, so there's no front or back, but better-quality stethoscopes have a tilt that makes the earpieces sit properly in most people's ear canals when they are oriented the right way. Check the instructions. Or just try them the other way, and listen to your own heartbeat, just below your ribs to see which way sounds better.
PROBABLE CAUSE 3: You've got a really cheap stethoscope. Spend a few bucks at a medical supply house. You'll have these for years, and this is a serious thing you are doing, so don't cheap out. As they say, you don't always get what you pay for, but you never get what you don't pay for.
PROBABLE CAUSE 4: You are morbidly obese and the thick layer of fat is muffling the sound. Chances are, if you are that fat, your pressure is also dangerously high - especially if you've been that fat for many years.
PROBABLE CAUSE 5: Have you had your hearing checked? Really, if you have a good stethoscope, properly inserted in your ears, the head properly placed with the flexible diaphragm against your skin just at the inside crook of the elbow, and you aren't hugely fat, then there aren't many other causes to consider.
PROBLEM: Your readings are drastically higher or drastically lower (say, by 15 or 20 mm) than what your doctor measures, or you can't seem to get consistent results.
PROBABLE CAUSE: You might have a size problem. Arms come in different sizes, and so do pressure cuffs. A cuff that starts off looser (because it's too big for your arm) will generally tend to give an exaggeratedly low reading... unless it's so excessively large that the bladder inside the cuff actually overlaps itself before you start inflating. That can sometimes give bizarrely high readings.
A cuff that's too small on your arm will tend to give exaggeratedly high readings.
If you are big and muscular, you need the same big cuff as a guy who is morbidly obese and just has fat arms.
If you are skinny and wiry (or starved or sick) you might need the same small cuff as a slim young woman or a teenage boy.
Either way, don't worry about it; just buy the cuff you really need. Or better, buy two or three sizes so that you have appropriate sizes for the members of your family.
Or, Go Digital
If the foregoing sounds a little complicated to do, just get an electronic pressure cuff to measure blood pressure - it will pump the cuff and take the readings at the push of a button. Or have your doctor do the measuring. Or donate blood. To keep a watchful eye on your pressure, that's a lot of visits to the doctor or the blood-donor clinic. So that's why we suggest you get yourself a good quality blood-pressure measuring kit, and self-administer most of the time.
If the "manual" method described above is too much trouble, an electronic cuff is better than nothing. If nothing else, it has the allure of a new toy, and that might get you to use it long enough to make a habit out of watching your blood pressure.
The electronic cuffs are convenient and quick, and don't require much thinking, but they do have drawbacks.
One drawback is shared - to a certain extent - with the dial aneroid gauge: they need to be calibrated, or you don't know for sure that they are telling you anything like the truth.
Now, "calibrating" can mean various things to various people. Some guys would not be happy unless you had done some serious number of measurements on several people, while taking the same measurements with a mercury-column sphygmomanometer (the gold standard).
Other folks would be a little more practical. You aren't really looking to measure blood pressure with micron (microbar?) precision. You want a good, reasonably accurate measurement, and you want to repeat over time to see a trend - is your condition worsening, or are your countermeasures being effective.
So, just bring your device/kit to your doctor's office, and when the doctor takes your pressure, ask 'em to do it again with your kit, or do it yourself, right there. Your doctor shouldn't mind, because it's part of your pro-active health management.
Of course, get practiced first. Your yearly (or less frequent) visit to the doctor is not the time to be learning the basic technique. On the other hand, there might be a technician in the same office, or a public-health nurse available to tell you the same things that we told you above, but with a nice, encouraging smile.
Once you know that your kit gives you a good match for what the doc measures, OR that it's off - but in a consistent, repeatable manner - then you have the information that you need to self-track your blood pressure. If your device always registered 5mm higher than the doctor's professional measurement, then just take your measurements each day, or week, and subtract 5 from the numbers when you record them. No big deal.
Now, we mentioned another drawback. This one affects only the electronic cuffs. They don't actually measure systolic and diastolic blood pressure. Rather, they measure an average, and then calculate some likely values for the high and low. We'd trust us and the mechanical/manual procedure before we'd trust something that "wings it" with a calculated guess. But that's just us.
Once Again, What Do Good and Bad Numbers Look Like?
A pressure of 120 systolic and 80 diastolic, or 120/80 used to be considered good and healthy. Now, apparently, they've lowered the diastolic optimum to a number closer to 70.
80 for diastolic is not bad, but it's now considered to be edging close to borderline territory, at least if it's measured consistently in a younger person. Diastolic pressure of 90 is definitely in "you really need to do something about this" territory. Over 100, and we're talking emergency. Similarly, systolic numbers up to about 130 are not worrisome - just keep an eye on it. At 140, you're supposed to be taking action to maybe lower it a bit. In the 150s, you should be worried, and up close to 200, you won't be standing much longer.
A FURTHER NOTE ABOUT EQUIPMENT
You should buy the best that you can afford. Going cheap on the electronic cuffs is asking for inaccuracy and imprecision.(Precision is how reliably you get the same numbers in the same condition, or if you were shooting at a target, how small the grouping of your shots - how reliably you can keep putting your shots (measurements) in the same place - independently of whether you were near the bull's-eye or not. Accuracy, of course, is how close you were to the actual number or bulls-eye. You want both.)
Electronic cuffs that go around your wrist or your finger are just not as good as the ones that go around the upper arm.
In good quality equipment, there are several sizes of cuff. Each cuff is meant to go around an arm of a certain diameter. It can be wrapped around an arm that's larger or smaller, but it gives the best, most reliable measure when the circumference of your arm is in the "sweet spot" for that size of cuff. Having a cuff too small for your arm tends to give pressure readings that are exaggerated on the high side. Conversely, a cuff that's too large for your arm will tend to read low. Well, we should be more precise - the cuff won't read low, the gauge will read low.
We've had electronic cuffs, both good and so-so. But we find that simpler is better. Manual doesn't need batteries, and there are fewer complicated parts to go wrong.
One thing that eventually effects any blood pressure cuff is aging of the air bladder. Cheaper materials dry out and crack and start leaking - making them useless - sooner than better-quality materials. But the more expensive cuffs (whether manual or electric) tend to have removable/replacable air bladders, so you can just swap out the old, dry, cracked one and the set is ready for another bunch of years.
If you are going the manual route to measure blood pressure, you want to buy the best-quality stethoscope you can manage (Littmann is a good brand). Get it from a medical-supply house, rather than your neighborhood DrugMart.
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