Transfer membrane apparatus

#The invention is concerned with apparatus for effecting transfer of heat or mass between two fluids of which at least one is usually a liquid, through a transfer membrane. Such apparatus is used in blood oxygenators, that is artificial lungs, and dialysers, such as artificial kidneys, in which case one fluid is blood, and the other is oxygen or dialysate. In practice the efficiency of the transfer across the membrane is limited by the extent to which the total volume of fluid can be brought into close proximity with the membrane. It is not sufficient to reduce the thickness of the fluid layers, by reducing the thickness of the conduits in which they flow, as this increases undesirably the pressure drop across the apparatus and leads to uneven perfusion and regions of stagnation, which, in the case of blood, provides a danger of thrombosis.

#We believe that the proper solution lies in so shaping the fluid flow conduits that significant mixing of the fluid occurs within the conduits. It has previously been proposed in British Patent Specification No. 1,442,754 to provide an apparatus comprising a conduit for flow of one of the fluids at least partially defined by the membrane, a transverse dimension of the conduit varying, either inherently or in response to pressure of fluid therein, in a regularly repeating manner, to provide a multiplicity of hollows in the membrane, the apparatus also comprising means communicating with the conduit for passing fluid through the conduit in pulsatile flow, the arrangement being such that pulsation of fluid past the hollows gives rise in the hollows to rotational fluid flow having components of motion parallel and perpendicular to the general direction of flow in the conduit of the fluid.

#The conduit may be defined between two predominantly planar surfaces, so that it has an elongate cross section transverse to the general direction of mean flow through the conduit, at least one of the surfaces then being provided by the membrane in which the requisite hollows are provided by parallel furrows. Alternatively, the conduit may be tubular, that is essentially axisymmetric with its wall provided by a membrane and having alternate annular or helical hollows and ridges. In either case, it has previously been proposed to cause the two fluids, between which transfer is to be effected through the membrane, to flow on opposite sides of the membrane in countercurrent or crosscurrent.

#An example of a dialyser in the form of an artificial kidney, and constructed in accordance with the present invention, is illustrated diagrammatically in the accompanying drawings, in which:

#FIG. 1 is a plan;

#FIGS. 2, 3 and 4 are sections taken on the lines II--II. III--III. and IV--IV respectively in FIG. 1; and,

#The illustrated dialyser comprises a rectangular housing formed of a cover and base parts 10 and 11 which are secured together by screws 12 and which are internally stepped to provide an internal generally rectangular shallow chamber 13. Located within the chamber 13 and supported by its close proximity to the walls of the chamber, is a membrane envelope assembly 14. As will become apparent from a subsequent description of FIGS. 5 and 6, the membrane envelope assembly includes four superimposed membrane layers of which the upper and lower membranes are impermeable and the inner two membranes semi-permeable. Adjacent membranes are sealed together around the outer edge of the assembly 14 and partway along a central line 15 to provide three superposed U-shaped conduits each defined between two predominantly planar surfaces so that each conduit has an elongate cross section transverse to its length. The upper and the lower conduit are intended for dialysate and the central conduit for blood.

#At each end of the U the conduits of the membrane assembly are coupled with a system for the circulation of blood and dialysate. Thus blood is fed into one end (the upper right hand end in FIG. 1) of the blood conduit by means of a roller pump 16 and a duct 17 which leads into a manifold 18. The manifold 18 is provided with a rolling diaphragm 19 operated by an actuator 20. The manifold 18 communicates through passages 21 in the cover 10 with a manifold portion 22 at the adjacent end of the blood conduit. The seal between the manifold portion and the housing may involve for example a distributor in the membrane assembly which is clamped between the cover and base of the housing in alignment with the openings 21.

#At its other end the blood circuit discharges in a similar manner into a manifold 18A also provided with a rolling diaphragm 19A and actuator 20A. A return blood duct 17A leads from the manifold 18A.