Real-time evaluation of transient response of arterial wall elasticity to administration of nitroglycerine

The authors previously (1996, 1997) developed a new method, the phased tracking method, for accurately tracking the movement of the heart wall and arterial wall based on both the phase and magnitude of the demodulated signals to determine the instantaneous position of an object. With this method, the local change in wall thickness during one heartbeat can be determined. They have now developed a real-time system for continuously measuring the change in thickness of the myocardium and arterial wall. In this system, four high-speed digital signal processing chips are employed for realizing the initially developed method in real time. The tracking results for both sides of the wall are superimposed on the M (motion)-mode image. The change in thickness of the arterial wall as small as several micrometers can be successfully detected in real time with good reproducibility. The elasticity of the arterial wall is derived from the blood pressure. In in vivo experiments, the rapid response of the change in wall thickness of the carotid artery to the administration of nitroglycerine (NTG) is evaluated for a young healthy subject and a young smoker. When the change in thickness is plotted against the simultaneously measured pressure, such curves also change due to the administration of NTG. This is shown every 35 seconds after the administration. This new real-time system offers potential for quantitative diagnosis of early-stage atherosclerosis by evaluation of the rapid response of the cardiovascular system to NTG.