1The 4th Department of Internal Medicine, Jikei University School of Medicine, 2Medical Engineering Laboratory, Jikei University School of Medicine, 3Toshiba Co. Medical Engineering Laboratory, 4Toshiba Medical Engineering Co.
A new method was developed for measuring left coronary blood flow noninvasively on the basis of the phantom experiments. Origin of noises generated when the coronary blood flow was measured, was investigated using ultrasonic Doppler simulator. The noises were classified into three groups: (a) Wall echo signal, (b) Higher harmonic components of the wall echo signal, (c) Multiple Doppler beats. On the basis of these results, we have developed a vessel tracking ultrasonic pulsed Doppler flowmeter to eliminate these noises. The system consisted of the following two techniques: (1) Sample position tracking; Sample position can be always set in a moving vessel by a wall echo tracking method with a phase-locked-loop. (2) Doppler reference signal starts at the sample position in order to cancel the Doppler shifts caused by movement of the vessel. These techniques were combined with a commercially available pulsed Doppler apparatus SSH-40B (Toshiba). Validity of these techniques was proved by using a blood vessel phantom. The blood flow velocity of the left anterior descending artery was measured in three normal cases and seven patients with hypertension, valvular heart disease and cardiomyopathy through the third intercostal space along the left sternal border. The velocity pattern was characterized by crescendo-decrescendo shape in diastole, and the peak velocity appeared in diastole ranged from 19 to 69 cm/sec, with no significant difference between normal cases and patients. Pressure-flow relationship was obtained by measuring coronary artery blood flow with the vessel-tracking technique and the aortic pressure obtained from cardiac catheterization. A linear relationship was found to be exist between them.