Korotkoff Sounds

Abstract

The Korotkoff sounds which serve as criteria for sphygmomanometry are composed of at least two components, (1) an initial transient (K i ), and (2) a more prolonged "compression murmur" (K c ). In this experimental survey, the Doppler flow detection device was used to acquire evidence indicating that K i occurs at the very onset of flow under the cuff and probably represents an acceleration transient producing abrupt displacement of the arterial wall and surrounding tissues distal to the point of compression. It is nonspecific in nature and can be simulated by tapping the skin of the hand. K c follows the initial transient and appears to represent audible sounds from turbulence or eddies in the blood flowing from the constricted artery under the cuff. Muffling seems attributable to the attenuation of frequencies between 60 and 180 cycle/sec, as the initial transient sound disappears, leaving the "compression murmur" as the muffled sound. Studies of cineangiograms and casts of arteries demonstrated that the arterial lumen under the cuff is primarily tapered and that the circumference of the artery shrinks considerably as the wall is unloaded by decreased transmural pressure. In contrast, rubber tubes become unstable and flatten into a binodal configuration when externally compressed. It seems doubtful that rubber tubes constitute adequate models for arteries in situ in the study of the genesis of Korotkoff sounds.