Noninvasive Blood Pressure Monitoring
Edition: July 2001 - Vol 9 Number 07
Blood pressure monitoring may not be new, but constant modifications to monitoring devices and technologies have kept the market up to date.
The first blood pressure device was developed in 1774 in Italy by Dr. R. Pagnini, according to ''U.S. Blood Pressure and Temperature Monitors Market (#7725-56)'' by Frost & Sullivan. The original instrument could measure pressure in the arteries resulting from cardiac impulsions, and was designed to perform invasive tests on animals.
In 1896, Italian scientist Scipione Riva-Rocci developed the first noninvasive monitor, complete with a pneumatic cuff. At the turn of the century, in 1905, Dr. Korotkoff of Russia learned the importance of using a stethoscope during cuff deflation to listen to arterial blood flow. Hence, physicians now could produce a value for systolic pressure, while diastolic pressure could be measured by the disappearance of sound.
Today, blood pressure monitoring devices range from manual systems that reflect the older equipment to sleek, electronic units. The oldest of these systems the mercury column sphygmomanometer continues to be used because of its accuracy.
The Importance of Monitoring Blood Pressure
Blood pressure is a combination of the force initiated by the heart as it pumps blood into the arteries and through the circulatory system, and that of the arteries as they resist blood flow, according to the American Heart Association. The AHA considers a measurement of 130 over 85 normal for adults. The higher number is the systolic reading, which refers to the pressure while the heart is beating. The lower or diastolic number signifies the pressure when the heart is resting between beats.
The AHA recommends that patients whose blood pressure ranges from 130 to 139 over 85 to 89 be closely monitored for high blood pressure or hypertension. The more difficult it is for blood to flow, the higher these numbers will be. To prevent hypertension from developing, the AHA recommends that physicians test their patients once every two years.
Noninvasive vs. Invasive Monitoring
Blood pressure can be taken via invasive or noninvasive means. Invasive techniques employ needles or catheters with intravascular transducers built into the tips, according to Frost and Sullivan. Traditionally, these methods are considered the most accurate, however technical advances have enhanced the precision of noninvasive techniques as well.
Noninvasive means for measuring blood pressure including aneroid, mercury and digital systems are more convenient and feasible for use in physician practices and clinics. These methods involve using a monitoring device, together with a cuff and stethoscope, to listen for Korotkoff or sharp tapping or knocking sounds. Korotkoff sounds occur when cuff pressure rises to a level where circulation is occluded in the lower arm. The sound of blood forced through the compressed artery can be heard by the physician or technician.
The Cuff of the Matter
Both mercury and aneroid manometers are attached to a cuff's bladder. Technically, the physician monitors the pressure in the cuff. The patient's blood pressure is tested indirectly. Korotkoff's sounds occur in five phases:
Faint, clear tapping (systolic pressure).
Murmurs or swishing sounds.
Crisper, louder sounds.
Distinct, abrupt muffle of sound.
Lack of sound (diastolic pressure in adults).
Korotkoffs have a low frequency that cannot be heard by the physician without an aid such as a stethoscope.
To obtain the most accurate blood pressure readings, the physician or technician must ensure that both the stethoscope and cuff are in working order. The stethoscope tubing must be free of holes and wax from the ear tips. The cuff must be sized appropriately for each patient, and the bladder must be airtight.
The patient, too, must be relaxed and prepped for the procedure. He or she should be seated or laying down for five minutes prior to testing. The patient's arm should be flexed and supported at heart level. The cuff should be placed over a bare arm, not clothing, and the arm should be free of I.V. lines, shunts, edema, injury or paralysis. Alcohol or tobacco intake within 15 minutes prior to testing can alter the measurement.
Aneroid blood pressure gauges or those that operate without liquid tend to be smaller than mercury gauges. A common type of aneroid device is a round, compass-like unit consisting of a dial and thin brass corrugated bellows inside. The dial normally rises to 300 mm Hg. A coiled spring or hair spring connects to a pinion within the device and returns the dial pointer to zero when the pressure is released.
When a working gauge is connected to a blood pressure cuff, the pin resting on the expanding bellows is lifted as the pressure in the cuff rises. This movement is transmitted by a second pin, which helps move the dial pointer.
Mercury devices work by inflating the rubber cuff around the patient's arm until the blood flow stops. After inflating the cuff and taking the patient's blood pressure, the cuff is deflated. The mercury, in turn, rises up a measurement tube. The cuff pressure is measured against the level of mercury in the tube. In addition to using an appropriately sized cuff that is leak-free, the mercury must be clear and at the zero mark before testing to ensure accurate results.
Digital units as with aneroid and mercury devices work in conjunction with a cuff and bladder set. These systems also include a monitor and a tube set. Most electronic models currently on the market offer automatic cuff inflation, eliminating a need to preset inflation levels. They may also have the ability to measure up to three readings and average the total for a more accurate end measurement. Two different options for measurement are usually available: oscillatory and auscultatory.
While blood pressure monitoring technique - as with any testing procedure - will vary somewhat from one patient to the next, there are some general guidelines for operating a digital unit:
1. Place patient in an appropriate position and support arm.
2. Wrap appropriately sized cuff around upper arm, just above the elbow joint. (Rule of thumb: There should be enough space for one finger to fit between the arm and the cuff.)
3. Select desired mode of measurement.
4. Press start button to begin. The cuff should automatically inflate to an appropriate or pre-set level.
5. Record the systolic and diastolic readings and pulse rate displayed.
When it comes to purchasing blood pressure monitors, potential customers might include diabetes centers, family and general practitioners, and physician assistants and registered nurses. Other potential customers are med-surg units in hospitals and cardiologists.
OMRON offers the following questions for reps to consider prior to meeting with new customers:
Is the clinic or office interested in a full or partial conversion of blood pressure monitors?
Who, and how many, will be included in the evaluation process?
Which evaluators' approval is necessary for a conversion?
How long will the evaluation last?
Will there be an opportunity for the rep to make a group presentation?
Will the rep be permitted in the exam room during the evaluation process to answer questions?
Although updating blood pressure monitors makes sense for physicians for a number of reasons (i.e. to purchase modern, accurate devices at a lower cost), change can be troublesome in any office. A better understanding of the customer's evaluation process may help alleviate some of the frustration associated with selling.