Electromagnetic flowmeter

Abstract

Abstract A noninvasive electromagnetic flowmeter particularly adapted to measure arterial blood flow in human beings is provided. A homogeneous magnetic field is produced in the region of the artery under measurement by means of at least one electromagnetic coil or a permanent magnet suitably positioned near the human being. Blood flow induced signals are sensed by electrodes placed on the skin adjacent the artery and fed to a measurement and control circuit. Electrocardiogram signals are sensed by a second pair of electrodes placed on the body near the heart and synchronize the operation of this system. One embodiment of the control and measurement system comprises a pair of auxiliary electrodes located where a strong and sharp cardiogram pulse can be repeatedly obtained to be used as a synchronizing signal and as a clock, at least one coil of large enough size having enough turns of wire to be adequate for the production of a strong and homogeneous magnetic field in the region of the artery under study, a source of D.C. current to feed that coil, means to reverse that D.C. current after a given number of heart cycles in accordance with a program controlled by the sychronizing signal, a pair of measuring electrodes placed on the skin adjacent the artery, an amplifier to amplify the signal appearing between said measuring elecrodes, with filtering means to eliminate the D.C. unbalance of the electrodes and the high frequency noise, means to paralyze the amplifier and to reverse its output during current reversal, and means synchronized by the synchronizing signal to average the pulsatile signal measured between the measuring electrodes during successive heart cycles so as to extract the repetitive wave shape of the blood flow pulses from the large random noise in which it is otherwise buried. In another embodiment of the control and measurement system, the coil in which a stable current is maintained during all the measuring intervals, as described in the paragraph above, is replaced by an electrically reversible permanent magnet. This permanent magnet is surrounded by a magnetizing coil in which DC current pulses of short duration are passed only at the times when the polarity of the magnetic field, and therefore the polarity of the permanent magnet, have to be reversed. There is no current in the magnetizing coil during the intervals when measurements of blood flow cycles are made and averaged. In still another embodiment of the control and measurement system, a permanent magnet is also used, but the reversal of the magnetic field, at the times when it is needed, is obtained by mechanically reversing or displacing the permanent magnet.

Inventors

• 👤 H Doll
• 👤 H Broner

Bibliographic Details