Random-zero sphygmomanometer, Rose's tape, and the accuracy of the blood pressure measurements in children

In the Cardiovascular Risk in Young Finns project, blood pressure (BP) was measured in 3549 randomly selected children aged 6-18 y in 1980, and 2887 and 2500 of the same individuals in 1983 and 1986, respectively. An ordinary mercury sphygmomanometer (OMS) was used in the first two surveys and a random-zero sphygmomanometer (RZS) in the third survey. Systolic and diastolic BP were lower when measured with an RZS than with an OMS and the shape of the age-related BP curve obtained with an RZS was significantly different from that obtained with an OMS, because low BP values were apparently measured more accurately with the former. Use of the RZS did not affect the distribution of the BP values. Rose's tape readings were used to evaluate the effect of training and to control the accuracy of the BP measurements. According to Rose's tape readings, Korotkoff's 4th phase BP was more difficult to measure accurately than 5th phase (p = 0.002). The mean values for the differences between the correct and actual BP readings on the Rose's tape were -1.2 mm Hg (SD 2.1) for systolic BP, 8.3 mm Hg (SD 13.6) for diastolic Korotkoff's 4th phase BP, and 1.2 mm Hg (SD 7.0) for diastolic Korotkoff's 5th phase BP, with a negative value indicating that the BP phase was measured lower than the correct value. Terminal digit preference was present in each survey to such an extent that it could have hampered the reaching of reliable conclusions from the data obtained with an OMS. The bias caused by terminal digit preference was obviated by the RZS.(ABSTRACT TRUNCATED AT 250 WORDS)