Sphygmomanometers: The Original Blood Pressure Device
The Original Blood Pressure Device
easuring blood pressure is a staple of any office visit, and a blood pressure monitor is a key diagnostic tool for nurses, doctors and other medical professionals. But its proper name isn’t a blood pressure cuff at all — rather, it’s a sphygmomanometer.
In terms of its ubiquity and importance, a blood pressure monitor ranks right up there with a stethoscope on the list of must-have medical devices.
Here, we’ll briefly explain what a sphygmomanometer is and how it works, as well as the meaning behind its long, complex name. Then we’ll break down the two main types of sphygmomanometers (manual and digital) and how to measure blood pressure using one. We’ll then delve into the history of measuring blood pressure and explain how, in less than 300 years, we advanced from shooting blood up a glass tube (yes, really) to using a device that automatically computes blood pressure for us.
What Is a Sphygmomanometer?
A sphygmomanometer is a device for measuring blood pressure, and it goes by several different names, including blood pressure meter, blood pressure monitor, and blood pressure gauge. A sphygmomanometer consists of an inflatable cuff, a measuring unit and a device to inflate the cuff, usually a manually operated rubber bulb or an electrically operated pump. The cuff is used to collapse and then release the artery beneath it as the practitioner measures at what pressure the blood begins to flow and at what pressure the blood flows unimpeded.
Blood pressure refers to the amount of force applied to the artery walls. High blood pressure, also known as hypertension, is an incredibly common health problem: More than 100 million Americans have high blood pressure, which is the most common cause of cardiovascular disease-related deaths, according to the American Heart Association. High blood pressure can contribute to damaged and narrow arteries, aneurysms, coronary artery disease, an enlarged heart, kidney failure and scarring, stroke, heart failure and more.
High blood pressure is sometimes called the “silent killer” because there are no warning signs or symptoms of the damage it causes, which is why it’s important to directly measure your blood pressure regularly. Needless to say, being able to properly measure blood pressure with a sphygmomanometer is an important clinical skill for any medical professional.
The name sphygmomanometer comes from the Greek prefix sphygmos, meaning “pulse,” attached to the scientific term manometer. A manometer is a device that measures pressure by looking at how much the pressure causes a column of fluid to rise against a scale. The pormanteau of a name came about because the device originally measured blood pressure by tracking how much the pressure caused mercury to rise in a column (more on mercury sphygmomanometers later).
Both manual and digital sphygmomanometers are available, with each type offering different benefits in terms of accuracy and convenience. Let’s break down the pros and cons of each type.
Manual sphygmomanometers (a.k.a. manual blood pressure monitors) are usually used in conjunction with a stethoscope, which allows for auscultation — or listening to the sounds of the body, the blood flow in this case — to help determine blood pressure. This requires a quiet environment to hear the stethoscope readings, which may not always be possible in a noisy clinic.
There are two types of manual sphygmomanometers:
Mercury sphygmomanometersThis type shows blood pressure by causing a rise in a column of mercury that looks a bit like a traditional glass thermometer. These are extremely accurate and do not require calibration, which is why mercury sphygmomanometers were widely considered the “gold standard” for measuring blood pressure. However, concerns about the use of mercury have emerged as more research has been conducted into the toxicity of this chemical, and over the past 15 years, more and more medical professionals have looked to alternatives to the mercury sphygmomanometer.
Aneroid sphygmomanometersThe word aneroid literally means “without water,” so it should not be surprising that aneroid sphygmomanometers show blood pressure on a dial rather than a column of mercury. Because of the lack of mercury, aneroid sphygmomanometers are considered safer, but they can also be less accurate and may have to be calibrated, especially if the model is inexpensive. Jarring an aneroid sphygmomanometer can cause the hands of the dial to move, resulting in inaccurate blood pressure readings; aneroid models mounted on walls or stands are moved less, and thus run less risk of jarring.
Digital sphygmomanometers (a.k.a. automatic blood pressure monitors) do not require the use of a stethoscope and instead employ oscillometric measurements and electronic calculations to determine blood pressure. As the blood pumps through an artery, it causes vibrations in the arterial wall that the instrument detects and then translates into electric signals. Because the measurements and calculations can be made without listening through a stethoscope, automatic blood pressure monitors can be used in noisy environments.
In decreasing order of accuracy, the cuff of a digital sphygmomanometer may be placed around the upper arm, wrist or finger — but don’t confuse it with a pulse oximeter.
Automatic blood pressure monitors can usually give a pretty accurate reading on mean blood pressure and pulse, but they are not as accurate at measuring systolic and diastolic blood pressure when compared with both mercury and aneroid sphygmomanometers. Systolic pressure is measured when the ventricles of the heart contract, while diastolic pressure is measured when the ventricles of the heart relax.
Because this type does not require a trained practitioner to operate, doctors may advise that certain patients (such as those with chronically high blood pressure) monitor their own blood pressure at home using a digital automatic blood pressure monitor. However, digital sphygmomanometers — especially at-home models — are prone to inaccurate measurements, especially when operated by a non-professional. Patients should not make any changes to their medication doses or other treatment regimens based on at-home blood pressure readings without discussing the changes with their doctor first.
How to Operate a Sphygmomanometer?
While getting your blood pressure measured is a staple of any office visit, doing it correctly takes practice and knowledge. Here are the steps needed to take someone’s blood pressure using a sphygmomanometer:
- 1. First, ensure the cuff is the correct size for the patient’s arm. At least 80 percent of the arm — but not more than 100 percent — should be covered by the air bladder inside the cuff. Using a cuff that is too small or too large will result in a reading that is too high or too low, so start with the right size.
- 2. Also ensure the valve and bulb are attached securely and that there are no leaks anywhere, as this will interfere with getting an accurate measurement.
- 3. Wrap the cuff around the upper arm with the lower edge of the cuff about one inch above the antecubital fossa (a.k.a. the inside of the elbow).
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