A Blood Flowmeter for Use in Coronary Heart Disease Research

In connection with research on coronary heart diseases, the need arose to measure extremely low blood flows in uncannulated vessels in the immediate vicinity of the heart in a living animal. Measurement of flood flow in this instance is complicated by the typically small flow rates, the requirement to transmit faithfully the pulsating components of the flow, and the large interfering cardiac voltages in the vicinity of the implanted vessel. Nearly all of the development effort described in this paper was devoted to extending the range of the electromagnetic type of flowmeter. Critical system parameters in this particular application were found to be the input impedance level and coupling methods of the preamplifier, phase accuracy of the timing voltages, and common-mode rejection of the carrier amplifier. Significant but relatively less important factors are the coil-drive method, the waveshape of the coil-drive current, and the noise level of the gating system. The blood flowmeter described in this paper has been in daily use at the Buffalo Veterans´ Administration Hospital since mid-June 1959. During most of this period, medical personnel have been operating the instrument and have performed the electrical adjustments which occasionally are needed to maintain the instrument at a suitable performance level.