The role of ambulatory monitoring in reducing the errors associated with blood pressure measurement.

The measurement of blood pressure for the clinical evaluation of hypertensive subjects is subject to three types of error. First is the error due to the measurement procedure itself. Although noninvasive methods are less accurate than invasive ones, they are preferred for clinical use both because of their convenience and safety, and because they form the basis of our knowledge of the risks associated with hypertension. Most automatic recorders use either the Korotkoff sound or oscillometric techniques, which generally provide an acceptable accuracy (to within 5 mmHg), although a new method (the K2 technique) may be the most accurate. The second error arises from the spontaneous variability of blood pressure, such that single clinic readings may vary by as much as 20 mmHg. This error can be reduced by multiple readings, e.g. obtained with ambulatory monitoring. The third type of error arises from a spurious elevation of blood pressure in the clinic (the white coat effect), which also may be as much as 20 mmHg. This can be reduced by including readings taken outside the clinic, e.g., by self- or ambulatory monitoring.