A new approach to electromagnetic blood flow determination by means of catheter in an external magnetic field.

Maximal reduction in transverse catheter dimension has been achieved for the purpose of creating an intravascular electromagnetic flow sensor capable of percutaneous introduction into the vascular system. The electrodes are mounted on a flexible frame which collapses as it passes through a small branch blood vessel and expands to span the diameter of the main vascular trunk when entering it. Unlike the catheter flow sensors developed previously, which are velometers, i.e., sensors of fluid velocity, the present one is capable of measuring the volume rate of flow in branch blood vessels as well as in the major sections of the vascular tree. The magnetic field is provided by a large air core electromagnet placed externally to the animal or patient. A special circuit utilizing two electrodes and three leads permits reduction of the unwanted quadrature signal to zero. A standard sine wave electromagnetic flow meter channel designed for use with conventional electromagnetic flow transducers is adequate for flow measurements as well as for power supply to the large magnet. Illustrations of the performance of the apparatus in vitro and in vivo are presented.