Comparison of Indirect and Direct Methods of Measuring Arterial Blood Pressure

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Abstract
Direct and indirect determinations of blood pressure are compared in 70 patients in immediate postoperative state, and results of statistical analysis of these data are presented. These studies demonstrate a frequent discrepancy between the direct and indirect readings. The greatest discrepancy is found in the young hypertensive group. The possible clinical value of this finding is considered. The decreasing order of accuracy for indirect methods of measurement is shown to be: oscillometric, auscultatory and palpatory. The drift of indirect readings is to fall increasingly below the direct measurement as blood pressure rises. The usual practice of employing one indirect technique only is not subject to criticism if the observer regards such a pressure estimation as an index to the true intra-arterial pressure. Changes in blood pressure can be detected by such a method but no conclusion should be drawn concerning absolute values. An attempt is made to explain some of the factors contributing to the variable error by which auscultatory readings underestimate the true intra-arterial pressure.