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Newer Blood Pressure Devices Less Accurate

June 21, 2010

A new comparison of two automated blood pressure machines suggests that newer devices are not necessarily better and could be msleading to some people that have high blood pressure.

Dr. Robert A. Kloner, Dr. Stanley H. Wishner, and Dr. Johanna Landgraf of Good Samaritan Hospital in Los Angeles discovered that readings were about two points lower, with the automated device compared to the mercury based devices.

The older “auscultatory” method uses a stethoscope and a mercury manometer.  The stethoscope placed over an artery in the patient’s arm lets doctors and nurses listen for pulse sounds return, and then disappear again, as a blood pressure cuff deflates and blood flows back into the artery.  The mercury manometer indicates the pressure at each of these time points in millimeters of mercury.

The newer devices calculate systolic and diastolic blood pressure based on the average pressure in the artery.  Oscillometric measurement requires less skill than the older techniques, and may be suitable for use by untrained staff and for automated patient home monitoring.

Kloner said in an interview with the Associated Press (AP) that researchers testing blood pressure medications used the older auscultatory technique. 

He said that there has been controversy over whether oscillometric devices are as accurate as the older technique. 

Kloner and his team compared auscultatory and oscillometric measurement by linking both devices to a single blood pressure cuff, allowing the doctors to compare measurements for the same patient.  They look at 337 consecutive patients visiting a heart doctor.

Average systolic blood pressure was 131, compared to 133 with the mercury manometer.  Diastolic pressures average 70, compared to 72.

Kloner said that while 2 points may not seem like much, there is strong evidence that even a 2-point reduction in blood pressure can reduce the risk of heart attack and stroke.

He added that the differences were larger for a significant number of patients.  For example, 7 percent of patients showed a discrepancy of 10 to 15 mm Hg and 4 percent had a 15 to 20 mm Hg difference; 2 percent had discrepancies of 20 mm Hg or higher.

About 10 percent of patients younger than 65 showed a discrepancy in blood pressure readings between the two techniques, nearly 30 percent of those 65 and older did.

Kloner said that this may have been because older people have stiffer, less resilient arteries, making the newer oscillatory technique less accurate. 

He recommends physicians that use automatic oscillometric devices in their offices to test them against a mercury manometer.  Patients should also discuss different approaches to blood pressure measurement with their doctor, he added.

Kloner said the most important thing is for people to get their blood pressures checked and to see if they do have high blood pressure, and to get treatment if they need it.

The study was recently released in the American Journal of Cardiology.

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