Quality control aspects of blood pressure measurements in the multiple risk factor intervention trial

As hypertension was one of the three major risk factors singled out for determining risk factor eligibility and for intervention in the MRFIT, measurement of blood pressure (BP) was a crucial part of the trial. Therefore, quality control of this measurement was important in the screening of men eligible to participate in MRFIT, as well as in following the progress of those randomized. Of the 12,866 men randomized into the study, some were considered to be hypertensive at baseline and others whose BP increased during the trial were also defined as hypertensive. All those confirmed as hypertensive were given a goal BP and started on an antihypertensive regimen. In order to assess the impact of this intervention, it was important that the BP measurements be standardized to minimize error in measurement. Such quality control standards allowed for valid comparisons to be made between Special Intervention (SI) and Usual Care (UC) groups, between men receiving medication and those not, and between men in one clinic and those in all others. Blood pressure measurements were made in two ways: using a standard mercury sphygmomanometer and a random zero (RZ) sphygmomanometer. The standard sphygmomanometer is the instrument used in clinical practice and in earlier BP studies [1,2]. Because of its use over time as the standard device for taking BP readings, the standard mercury sphygmomanometer (Baumanometer No. 300 or 260) was used in the MRFIT to allow for comparison of results with other clinical trials. The design and operation of this instrument are based upon the combined principles of compression of the brachial artery under an elastic, inflatable cuff, direct auscultation of the Korotkoff sounds through a standard stethoscope, and direct registration of pressure levels by a mercury manometer.