Principles of Fluid Mechanics Applied to Some Situations in the Human Circulation and particularly to the Testing of Valves in a Pulse Duplicator

The use of a pulse duplicator to test prosthetic aortic valves or to investigate the mechanics of diseased valves after death is now well established (McMillan, Daley, and Matthews, 1952; McMillan, 1955). In testing an artificial valve, two main questions have to be answered. The first concerns the mechanical strength of the valve and therefore its ability to withstand for many years pressures and flow rates comparable to those it would experience in the human body. The second problem is to determine whether the flow characteristics of the prosthetic valve are suitable for clinical use. Until now the pulse duplicator has been used to answer only the first question and little attention has been paid to the second. In preliminary experiments with a new type of pulse duplicator, we experienced some difficulty in producing simultaneously with water a pressure wave form and quantity flow comparable to those produced by blood in life. So far as the authors are aware, almost all pulse duplicators hitherto reported use water as a working fluid (Davila, Trout, Sunner, and Glover, 1956; Kelley, Goodale, and Castleman, 1960; Callaghan, Willans, and Cardozo, 1961). The use of glycerinewater mixtures, as reported by Marx, Baldwin, and Kittle (1959) and Starkey, Sirak, Collins and Hagan (1963), is exceptional. There are sound practical reasons for this, but the significance of the results when using water instead of blood is open to criticism. Blood is more viscous than water, and it seems that it should be easier to perfuse water through a heart than blood. In practice, the reverse appeared to be true. This difficulty forced on us the more fundamental examination of the problem, which is the subject of this paper. TYPES OF FLUID FLOW