I encourage my patients to use the blood pressure machines found in most pharmacies, but I often find that the readings seem significantly lower than those I obtain in my office using a standard mercury sphygmomanometer.
I encourage my patients to use the blood pressure machines found in most pharmacies, but I often find that the readings seem significantly lower than those I obtain in my office using a standard mercury sphygmomanometer. What principle is used in these machines? Is it based on the usual Korotkoff sounds? Is it accurate? Also, has there ever been a good study comparing the results obtained with these machines against a simultaneous mercury manometer?
----- Joseph Chersky, MD
Beverly Hills, Calif
On average, home blood pressure readings obtained with the types of devices typically used at home tend to be lower than measurements taken in the office using a standard mercury sphygmomanometer. The upper limit of normal for blood pressure measured at home is 135/85 mm Hg, which is comparable to 140/90 mm Hg in the office. The values for a normal home blood pressure were derived from several large clinical outcome studies.
Most home devices use an oscillometric technique for deriving systolic and diastolic blood pressure values. Older devices did use Korotkoff sounds, but the more modern units do not use this technology. Many devices actually measure the blood pressure as the cuff is being automatically inflated and then record it once again during deflation. The accuracy of home blood pressure recorders has been a concern over the years. Most devices have failed to meet international standards, such as the International Protocol, the British Hypertension Society (BHS) protocol, or the Association for the Advancement of Medical Instrumentation (AAMI) protocol.
The dabl Educational Trust Web site (http://www.dableducational.org) is an excellent source of information on home blood pressure recorders. It provides numerous references to studies that have compared the different automated devices with a mercury device using the International Protocol1 (the current standard for comparing an automated blood pressure measurement device with a mercury sphygmomanometer), as well as the BHS and AAMI protocols. In addition, this site lists currently available devices that have been validated as well as devices that have been tested and found to be unsatisfactory.
The journal Blood Pressure Monitoring is another excellent source of information about automated blood pressure recording devices. At least once a year, this journal publishes a supplement that contains articles on current issues related to automated blood pressure measurement.
----- Martin Myers, MD
Professor of Medicine, Division of Cardiology
Sunnybrook Health Sciences Centre
O'Brien E, Pickering T, Asmar R, et al; Working Group on Blood Pressure Monitoring of the European Society of Hypertension. International Protocol for validation of blood pressure measuring devices in adults. Blood Press Monit. 2002;7:3-17.