An A.C. Induction Flow Meter for Measurement of Blood Flow in Intact Blood Vessels

Abstract

The principle of the electro-magnetic flow meter2 is based on the fact that an electromotive force is induced in the blood as it flows through a magnetic field (the direction of flow forming preferably a right angle with the magnetic lines of force).∗ The induced e.m.f. is linearly proportional to the velocity of flow. It is tapped by two electrodes placed at right angles to the magnetic lines of force and to the direction of flow. Owing to the electrical conductivity of the blood vessel wall the pick-up electrodes merely have to touch the outside of the vessel to establish a sufficient electrical contact with moving blood. Fig. 1 shows the perspective view of the arrangement and the dimensions of the magnet.The modification presented here employs an electro-magnet fed by an alternating current. The use of an alternating magnetic field eliminates the disturbances due to polarization and variable galvanic potentials and makes it possible to use an a.c. amplifier. It introduces, however, the new difficulty ...