Assessment of the accuracy of indirect blood pressure measurements.

This study assessed the accuracy of indirect blood pressure (BP) measurements by simultaneously performing three kinds of indirect BP measurement on the left arm (auscultatory, microphone and oscillometric methods) and a direct BP measurement on the left arm. The subjects were 34 hospitalized patients, ranging in age from 18 to 73 years (average 47.5 years). Highly significant correlations in systolic or diastolic BP between a given pair of the three indirect methods. The indirect methods underestimated systolic BP and overestimated diastolic BP compared with the direct method, with differences of -12.2 +/- 10.5/+4.6 +/- 7.6 (systolic/diastolic BP) with the oscillometric method, -8.1 +/- 9.7/+1.2 +/- 8.9 with the microphone method and -10.6 +/- 8.1/+3.7 +/- 6.5 mmHg with the auscultatory method. The difference in systolic BP between the auscultatory and direct methods was greater and the difference in diastolic BP was smaller in subjects older than 50 years than in those aged 50 years or less (p < 0.001 for systolic BP, p < 0.05 for diastolic BP). The auscultatory method revealed greater systolic BP in subjects with increased carotid arterial wall stiffness assessed by echoarteriography. Thus, it is concluded that there are inherent differences in BP between the indirect and direct methods which can be attributed to the changes in arterial wall physical properties partly due to aging.