Some observations on industrial pumps for extracorporeal circulation in man.

Following the introduction by Gibbon (1937) of a practical method of extracorporeal circulation, many other machines have been developed capable of pumping and oxygenating blood. The mode of oxygenation has varied from machine to machine, but the circulation of the blood, with a few exceptions, has been carried out by some form of "tube" pump, because they are easy to sterilize. In such pumps pressure is applied externally to flexible tubing by rollers, mechanical fingers, or plattens in a sequential manner, thus ensuring a unidirectional flow without the use of valves. The output can be varied by altering the rate or degree of compression of the tubing. When run in the non-occlusive position, i.e., the walls of the tubing not in apposition, these pumps cause little haemolysis; but under these circumstances, their efficiency decreases and the output becomes dependent upon peripheral resistance. This investigation was undertaken to compare the properties of other types of pumps, with special regard to the destruction of red blood corpuscles, ease of control of flow rate, simplicity of sterilization, and suitability for clinical practice. With this in mind, a preliminary survey was made of commercial industrial pumps having an output of up to 5 litres per minute. Seven were chosen for trial, the selection being made as representative as possible of the five basic pumping mechanisms. These mechanisms can be classified as follows (Fig. 1).