Development of a system for quantitative diagnosis of myocardial infarction and atherosclerosis based on non-invasive measurement of small vibrations on the heart wall or arterial walls and their analysis

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In this research, we have developed a new method to measure local pulse wave velocity, which is an index of the hardness in the range of several millimeters on the aortic wall. In the standard method, the pulse wave velocity (PWV) is obtained from the difference in arrival time of pressure waves propagating from the carotid artery to the femoral artery. In this method, the measurable points are limited to those where the aorta exists near the skin surface and the distance between such points is considerable long, i.e., several hundred millimeters. It is important for early diagnosis, however, to measure the local hardness of the surface of the arterial wall. To increase the spatial resolution, it is necessary to measure vibrations due to pulse waves with frequency components up to about 50 Hz.Therefore, we have developed a new system to noninvasively measure small vibration signals on the heart wall or the aortic wall from the surface of the skin based on the ultrasonic Doppler effect. … More By this system, small vibrations with amplitudes of 10 - 100 mum on the motion due to heart beat with the large amplitude of 10 mm are successfully detected in the frequency range up to 1 kHz continuously for more than ten beat periods from the chest.This research also developed a new method for obtaining local PWV by simultaneously measuring small vibrations at two points on the surface of the tube wall and the aortic wall. By the developed method, high spatial resolution, which is necessary in the evaluation of local hardness, is attained. By comparing the static experiments and dynamic experiments using a silicon tube, it is confirmed that the local hardness (Young's modulus) of the vessel wall is also evaluated with high spatial resolution.By applying the developed system and the method to in vivo experiments, the PWV of the vibration wave transmitted between the two points on the aortic wall is obtained even for the aortic wall near the aortic valve. The distance between the two points is about several millimeters. The local elasticity (Young's modulus) is also evaluated for each measurement point. Thus, the developed system will be effective for local evaluation of the hardness on the aortic wall. Less