ELECTROMAGNETIC BLOOD FLOWMETER

Typical Number in Hospital: 1

Cost Bands: 5

References: 3,9

Faraday's principle of electromagnetic induction can be applied to any electrical conductor (including blood) which moves through a magnetic field. The electromagnetic blood flowmeter is sometimes used during vascular surgery to measure the quantity of blood passing through a vessel or graft, before during or after surgery. A circular probe with a gap to fit the vessel is fitted around the vessel. This probe applies an alternating magnetic field across the vessel and detects the voltage induced by the flow via small electrodes in contact with the vessel.

Alternating magnetic fields (typically at 400 Hz) are used since the induced voltages are in the microvolt region and d.c. electrode potentials may cause significant errors with unchanging magnetic fields. A number of probes are required to fit the various diameters of blood vessel.

An alternative design carries the sensing device on the tip of a special catheter which passes inside the vessel and generates a magnetic field in the space around it and has the electrodes on its surface.

Electromagnetic flowmeters have existed for measurement of blood flow rate outside the body during open heart surgery.