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Home Blood Pressure monitoring: How accurate are home BP monitors?

Heart, Stroke | May 15, 2015 | Author: The Super Pharmacist

heart, Stroke

Home Blood Pressure monitoring: How accurate are home BP monitors?

Blood pressure monitors are virtually everywhere. In fact, having your blood pressure taken is often a free service. No modern pharmacy is without one. Likewise, dozens of home blood pressure monitors are commercially available, some of which are quite inexpensive. Sadly, just because you receive a number from your pharmacy blood pressure machine or your home device, does not mean you are getting accurate blood pressure measurement. This is particularly unfortunate because accurate blood pressure measurement is needed to diagnose hypertension and to track the effects of antihypertensive medications and treatment.

Can you trust the blood pressure readings you have been getting?

The Basics of Blood Pressure

The definition of “blood pressure” and the way it is measured is deceptively simple.

Traditionally, a physician will use a blood pressure cuff with the sphygmomanometer (blood pressure gauge) to compress a patient's artery, usually the brachial artery in the arm. Once the artery has been compressed, the physician slowly releases the pressure in the cuff while listening for blood flow through the artery.

A fully compressed artery makes no sound, since there is no blood flowing through it; however, a partially compressed artery allows some blood flow. That partial blood flow is turbulent and makes a sound that can be heard through the stethoscope. The pressure continues to be released until the artery is completely open. The fully open artery again makes no sound.

Systolic blood pressure (the top number) is the pressure at which the partially compressed artery first starts making sound.

Diastolic blood pressure (the bottom number) is the pressure at which the artery stops making sound.

Systolic blood pressure is the maximum squeezing pressure of the heart, while diastolic blood pressure is the pressure in the arteries when the heart is relaxed.

How to Measure Blood Pressure Accurately

Blood pressure changes all the time. Your blood pressure will change if you stand up from a seated position. Your blood pressure will change if you then take a walk, or start to jog. If someone startles you, your blood pressure will increase temporarily. Simply going to the doctor's office causes many people to experience “white coat hypertension,” which is a falsely elevated blood pressure caused by anxiety at the doctor’s office.

Under ideal conditions, everyone would have a blood pressure monitor that took constant blood pressure all the time for a period of several days. In fact, these machines actually exist but they can be quite expensive and are probably not necessary for most people.

Given how frequently blood pressure levels change from moment to moment, how can anyone get an accurate assessment of their blood pressure? Fortunately, physicians have already established what is required to take an accurate blood pressure. The correct measurement of blood pressure requires the following conditions:

Taking blood pressure at the proper time of day

Blood pressure should be measured at the same time each day and compared to other numbers taken at the same time. Patients should not eat, exercise, smoke, or drink caffeinated beverages for at least 30 min. prior to taking blood pressure. The patient should not have an overly full urinary bladder during blood pressure measurement and the room should not be cold. As with blood pressure measurement, blood pressure medication should be taken at the same time every day because this will affect readings.

UThe Basics of Blood Pressuresing an accurate measurement device

Devices is should be periodically calibrated to ensure that they accurately measure blood pressure. The accuracy of home blood pressure monitoring devices are discussed below.

Using the proper blood pressure cuff size

The correct cuff size is based on the patient's arm circumference. A too small cuff will substantially overestimate blood pressure.

Properly placing the blood pressure cuff

Most blood pressure cuffs will indicate where the cuff should be positioned relative to the artery. If using an at-home blood pressure monitor, follow the instructions carefully. Leg and wrist blood pressure measurements are accurate if the proper size cuff is used. Blood pressure will normally be 10 to 20% higher than in the upper arm (brachial artery). Wrist blood pressure may be accurate if the wrist is held at heart level during measurement.

Using the proper patient position and technique

The patient should be seated with back supported and legs uncrossed. The patient's arm should be bare, which means the shirt should be removed and not rolled up above the level of the cuff. The arm should be kept at the level of the heart, supported by the physician or a table, and not hanging loosely. Ideally, the patient should be quiet for at least 5 minutes before measuring blood pressure and measurement should be taken in a quiet room.

Obtaining an adequate number of measurements

Two or three blood pressure measurements should be taken separated by at least 2 minutes. The results should be averaged. If the numbers vary by more than 5 mmHg, additional measurements are needed to obtain a stable value.

The Accuracy of Home Blood Pressure Monitors

The accuracy of measuring blood pressure at home depends more on the person's technique then the device. In other words, most home blood pressure monitors do a good job of measuring blood pressure if they are used properly. 

  • The user should follow the recommendations listed above and all of the instructions included with the home blood pressure monitor.
  • The ideal home blood pressure monitor is an automated or semi-automated electronic upper arm cuff that has been validated.
  • It is also useful to take your home blood pressure monitor to your physician's office and compare blood pressure measurements between your device and your physician’s device.
  • If you are trying to confirm the diagnosis of hypertension, you should obtain the average of three measurements in the morning and three measurements at night separated by 5 minutes each over the course of at least one week. 
  • If you are tracking the effectiveness of blood pressure treatment, the average result of three measurements separated by at least 2 minutes each and taken at the same time each day should give accurate, reliable results.  Australia’s best online discount chemist


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