Employing various blood pressure measurements yields valuable data: measures of aortic blood pressure and pulse wave velocity provide additional information on arterial stiffness and vascular health.
"Measurement of blood pressure has not changed in the past 100 years. We need more information about what's going on in the blood vessels; a regular measure with a sphygmomanometer does not provide information on how the small arteries are working. Additional measurement of central or aortic blood pressure may be more sensitive markers of vascular disease, and hopefully, we can use these measures to better stratify a patient's risk of cardiovascular disease," says Mohammed Rafey, MD, Department of Nephrology and Hypertension at Cleveland Clinic.
Additional BP measures
Among hypertension experts, there is a growing focus on central BP.
"We believe that central blood pressure--the pressure within the aorta--gives us more accurate information about vascular health, because it is a barometer for the level of arterial stiffness that's present," explains Martin Schreiber, Jr., MD, Chairman of the Department of Nephrology and Hypertension at Cleveland Clinic. The central augmentation index and pulse wave velocity are two additional measures that can provide further information about the patient's vascular system.
According to Dr. Rafey, measuring the central aortic BP takes about five to 10 minutes; a cuff is placed on the arm, and the pulse-wave velocity is measured with a tonometer, a small, wand-like instrument, that is placed on the radial pulse at the wrist. Dr. Rafey explains, "The pulse wave generated by contraction of the heart moves faster if your arteries are hard or stiff. Thus, a higher pulse-wave velocity indicates that there is arterial stiffness." The augmentation index, which also provides information on arterial stiffness, is also calculated from the data obtained with the tonometer.
"The parallel is with cholesterol: Knowing your total cholesterol is important, but having a breakdown of LDL, HDL and triglycerides is even more useful. The same depth of understanding we have of lipids is needed with blood pressure," says Dr. Schreiber.
Dr. Rafey likens it to another chronic health condition: "It's similar to diabetes; when glucose levels may vary when checked several times a day. But measuring glycated hemoglobin (A1C) gives a better picture of glucose control over a 3-month period. Similarly, traditional BP measures can vary widely, but these additional BP measures provide more stable information on arterial health. They don't usually change from day to day when performed under standard conditions."
Where hypertension is headed
At this time, central BP, the augmentation index, and the pulse wave velocity are not used as standard measurements when determining cardiovascular disease risk or what treatment is most appropriate.
"To make this part of evidence-based practice, we need results from large studies that show that better outcomes can be achieved with these measures," explains Dr. Rafey. "But things are moving forward; major clinical trials are under way gathering data on these measures of arterial stiffness."
The guidelines currently being followed in the U.S. for diagnosis and treatment of hypertension were released in 2003 by the Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. "Updated guidelines are scheduled to be released next year and may include some new measures, such as pulse wave velocity, to use to stratify heart disease risk," Dr. Rafey says.
Get accurate measurements
Even if your BP is being measured only with a sphygmomanometer (the cuff that is wrapped around your arm), getting accurate measurements is crucial.
"Three things can occur when BP is measured in a doctor's office that can interfere with accuracy: the white coat effect, white coat hypertension, and masked hypertension," says Dr. Rafey. The "white coat effect" is a transient spike in BP when it is measured by a doctor or a nurse; the BP usually returns to normal after 5 to 10 minutes. If you have "white coat hypertension," your BP will be elevated any time it is measured in a doctor's office; you will only get an accurate BP measure outside of your doctor's office. "Masked hypertension" is when your BP reading is normal in the doctor's office but high when taken at other locations. "In-home measures can also be inaccurate, so it must be done correctly," adds Dr. Rafey.
"When we measure BP, we look at an average of six readings; one reading is not an accurate reflection of BP," confirms Dr. Schreiber.
RELATED ARTICLE: WHAT YOU CAN DO
* If you have an in-home blood pressure monitor, make sure it is calibrated correctly and you follow the operating instructions exactly.
* Take BP readings in the morning and at night before taking medications and bring this information to your next appointment.
* Tell your doctor if BP readings in the office differ significantly from your in-home readings.