Quite often I have received letters with statements like “My doctor says that all digital machines are inaccurate and that only a doctor or an experienced nurse can take blood pressure accurately”. It is difficult to give an answer to such a statement without offending someone. There are still some people who believe that the earth is flat and that the moon is made out of blue cheese. The fact is that the first digital blood pressure monitors (from 30 years ago) were very difficult to use accurately and because it was a new technology, it was not well accepted by the medical sector. However, in the last 30 years, tremendous progress has been made and most monitors that are sold today (from reputable brands) are as accurate as a traditional mercury or aneroid device.
There are in fact international validation standards that compare digital monitors to “gold standard” mercury devices and then grade the devices according to the results. So when you need to buy a device for home use, you should look for a validation standard that has been applied to the device that you are planning on buying, such as the BHS (British Hypertension Society), the GüteZiegel (German validation standard), or the AAMI (American Association of Medical Instruments). If you find such a logo on the packaging or the advertising, it is probably a very accurate device.
Today, most digital monitors measure pressure by applying the so called ‘oscillometric method’. In an oscillometric measurement, the blood pressure is accurately detected by analyzing the pressure oscillations that happen during the deflation or inflation of the cuff. This method has been well accepted worldwide for more than thirty years and incidentally, it is applied in hospitals every day, whenever the patient’s pressure needs intensive and highly accurate control. Many doctors do not realize that home use digital monitors use exactly the same technology as the 20 000 dollar machines that they use in intensive care. If they did, they would probably change their opinion of home devices.
One of the main factors for different readings at the doctor’s office and at home using a home monitor is that the conditions for measuring blood pressure at the doctor’s office are not ideal. To accurately measure your blood pressure, you should consciously relax for at least 5 minutes before taking it. You should also take it at the same time of day as your last reading if you want to compare them. At the doctor’s office, you might also suffer from what is called “white coat hypertension”, where you are nervous and this causes the blood pressure to rise temporarily. It is now a given fact that measurement of blood pressure at home, also called HBPM (Home Blood Pressure Measurement) IS MORE REPRESENTATIVE OF THE PATIENTS REAL BLOOD PRESSURE than the casual one taken at the doctor’s office. This is provided of course that the patient uses the device correctly.
Many doctors and nurses prefer the stethoscope method because they can listen to the signals and get a deeper impression of the patient’s condition. A digital monitor only measures blood pressure and pulse, whereas an experienced doctor using a stethoscope can listen to many other sounds to get a better overall view of the patient’s health.
The technique of mercury or aneroid devices (also called auscultatory) requires careful training and application of specific methods. A slow deflation rate of 2 to 3 mmHg per second is essential to obtain accurate results with the doctor’s measurement. However, more often than not, doctors or nurses use a much higher deflation rate and obtain wrong results. This is because quite often, the doctor does not have the necessary time to really measure blood pressure. In fact, for a blood pressure measurement to be representative at the doctor’s office, he should measure the blood pressure at least three times in a row. It is important to realize that your blood pressure is fluctuating constantly and that the results are never exactly the same. When you use an electronic blood pressure monitor at home, you tend to do several measurements because it is so easy to do and you have more time than at the doctor’s office. It is quite normal for the measurement results not to be identical to each other. If your doctor were to measure the pressure three or four times (which he never does!) he would also get different values.
The most convincing fact is that the world’s leading experts on blood pressure monitoring prefer frequent home measurements by electronic devices against the casual measurements taken in their office! So if your doctor continues telling you that all digital devices are crap, it might be time for you to change your doctor.
Uwe Diegel
http://www.medactiv.comAbout HealthWorks
HealthWorks is a group of companies that work together to develop medical solutions based on the concept of HCD (Human Centered Development), where a product is developed with the end-user in mind so that he can intuitively use the product. HealthWorks products are developed as much by members of the public as by engineers and doctors.HealthWorks France
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