The Electromagnetic Flowmeter and Its Use in the Operating Room

History of Blood Flow Measurement The first attempt to measure blood flow was by Chauveau, et al. in 1869. This was a mechanical device in which the moving blood was made to strike a mechanical linkage which moved in relation to the velocity of the blood. A variety of other mechanical devices were designed to measure blood flow in the late 1800's including the Stromuhr of Carl Ludwig and the differential pressure flowmeter designed by Otto Frank.' As late as 1942 an electromechanical rotameter was described by Gregg for measuring blood flow. 4 All of the above methods had one common problem. It was necessary to cut the blood vessel in half, and insert cannulating tubing to bring the blood into the mechanical flowmeter and then back into the body. In addition, mechanical flowmeters interfered with the free movement of the blood. Consequently records were obtained which gave only an approximation of blood flow in rnl/min, and did not show sudden flow changes with time. Because these mechanical flowmeter techniques required extensive surgical exposure and transverse section of the vessel to be studied, and produced moderate to severe obstruction of the flow, it was not possible to measure blood flow in human vessels. The rapidly growing electronics industry paved the way for deBurgh-Daly in 1926 and Kolin in 1936," who were the first to develop an extravascular, non traumatic electromagnetic flowmeter. This device was placed around the outside of an exposed vessel and did not require cutting or otherwise damaging the vessel. Kolin is generally credited with developing the first electromagnetic blood flowmeter, and this device is often used for blood flow measurement in animals and man at the time of surgery.