Cuff sphygmomanometry: theoretical analyses for determining differences between diastolic and systolic arterial pressures and the corresponding cuff pressures in terms of quantities that can be measured on line.

Abstract

In conventional cuff sphygmomanometry the operator monitors the cuff pressure at the onset of the appearance and muffling of Korotkoff sounds, and associates them with the desired brachial arterial systolic and diastolic pressures. Based on stability analyses of the brachial arterial-cuff system, the differences between these monitored cuff pressures or the auscultatory pressures and the actual brachial arterial pressures have been shown to be functions of the geometrical, material and vibratory parameters of the brachial artery. This information delineates the importance of knowing these differences, for obtaining accurate measures of the brachial arterial pressures. Hence, in order to facilitate and provide the basis for the calculation of these differences in an online arrangement which can be used clinically, in this paper we express the modulus of elasticity of the tube material in terms of the velocities of pulse propagation in circular-cylindrical and biconcave-cylindrical tubes, at systole and diastole; the pulse velocity is in turn expressed in terms of quantities which can be measured online, namely the cuff width and the dominant frequency f of the disturbance, and hence of the Korotkoff sounds. We have further invoked experimental observations obtained by others during the laboratory simulation of Korotkoff sounds to delineate the values of the geometrical parameters of the brachial artery-cuff system and finally to obtain expressions for the differences between the auscultatory and direct brachial arterial pressures in terms of the measurable cuff width and the dominant frequency of the Korotkoff sounds; the paper hence concerns theoretical analyses for obtaining the actual systolic and diastolic brachial arterial pressures in terms of quantities that can be measured online.