Korotkoff sounds at diastole—a phenomenon of dynamic instability of fluid-filled shells

Abstract

A theoretical analysis of the phenomenon of Korotkoff sounds at diastole is presented together with experimental results. The formulation of the mathematical analysis is based on facts derived from fundamental experiments with a laboratory model which simulates the brachial artery and the sphygmomanometer and which exhibits Korotkoff sounds under controlled conditions. The Korotkoff sounds at diastole are interpreted as a phenomenon of dynamic instability (oscillations with increasing amplitude), the instability being induced by the application of a pressure cuff. The results of the analysis verify experimental observations regarding the effects of the cuff length, wall thickness and elasticity of the vessel on the diastolic pressure. They also yield good approximations for the difference between the auscultatory diastolic pressure and the true minimum of the pressure in the simulated artery as well as in the human brachial. The results indicate that the auscultatory reading is always higher than the true minimum of the intraluminal pressure by an amount that depends on the physical and geometric properties of the vessel. Besides this, the theoretical analysis predicts that the Korotkoff sounds near the diastolic pressure have predominantly low frequency components and that withincreasing cuff pressure the sounds not only become more intense but also begin to include components with a higher pitch.