抄録
We have developed a cardiovascular system to analyze the origin of Korotkoff sounds. Using the cardiovascular system, the sound field of an artificial blood vessel (silicone tube) was measured under normal vascular conditions of blood pressure and flow. We determined that the sounds emanating from the vessel wall were due to turbulent flow and shock wave. Furthermore, considering the tube law of an artery occluded by a cuff, it is clear that a shock wave could not occur at or in the vicinity of the measuring point of systolic pressure. Consequently, this shows that in the area of the measuring point, the eddy caused by turbulence induces the sounds. On the other hand, the sounds near the diastolic pressure measuring point are concluded to be caused by a shock wave. These two points were investigated experimentally through the measurement of arterial pressure using the cadiovascular system. Our experimental studies produced results which were in agreement with theoretical assumptions and clinical experiments. It was found that (1) the times required for Korotkoff sounds to occur changed in accordance with gradual decrease in cuff pressure, (2) the Korotkoff sounds during Swan I to II had a lower frequency than that detected during Swan II to III; the two sounds were different. After that point, the sounds exhibited a single spectral peak whose frequency was higher than that before, (3) the point of appearance of the shock wave was largely influenced by the silicone tube and the blood flow in the artery. Therefore it should be possible to estimate the change in these parameters from detection of Korotkoff sounds.
