CANNULA PUMP VALVES

Abstract: A cannula valve unit is provided for the control of liquid flow that comprises an inlet valve and an outlet valve and has ends adapted for connecting to a cannula. The unit is cylindrical and has cross-sectional areas for liquid flow substantially equal to the cross-sectional area of the cannula with which it is used. The inlet and outlet valves are designed to reduce stress on blood cells in the instance where the liquid is blood.

Description: CANNULA PUMP VALVES FIELD OF THE INVENTION The present invention relates to valves used with cannula for the control of liquid flow and especially to valves used for medical purposes with cannula that are part of blood circulatory assist systems. BACKGROUND OF THE INVENTION Cardiovascular and pulmonary assist devices have been under development since Gibbon developed the first workable heart lung machine and used it to perform open heart surgery on a young woman in 1951. Since then, many different clinical needs have been identified for circulatory assist devices. The needs range from short term circulatory assist devices to permanent implant devices. In all cases a premiere challenge of a circulatory assist system is to handle blood flow with a minimum of stress to delicate blood cells. Damage to blood cells in circulatory assist systems using prior art valves is a problem. In the valves and pumps of circulatory assist systems the blood experiences abrupt changes in either the rate or direction of its flow. These changes are brought about by mechanical forces acting on the blood which can damage blood cells. Furthermore, the changes themselves, if they lead to turbulent blood flow can cause damage to the blood. Therefore, it is in the valves or the pump of a circulatory assist system that blood cells are most apt to be damaged. The proper design of valves for the control of blood flow is thus extremely important to minimizing damage to blood cells. Improvements in valve design that reduce stress on blood in the valves used to control blood flow are therefore needed and desirable. PCT application PCT/IL96/0045 for a Cardiac Assist Device, published on Jan 30,1997 as WO97/02850, which is assigned to the assignees of the present invention, and which is incorporated herein by reference, describes the use of blood flow control valves coupled to cannula in cardiac assist systems. The process of incorporating valves to cannulae is a cumbersome, labor intensive process that requires a high degree of care and attention. It would be desirable to have blood flow control valves that are more easily and efficiently incorporated into cannulae. A constraint on the design of valves that are used inside the body is that they minimize any displacement or trauma that their introduction into the body or presence in the body might cause. They should disrupt the shape of devices with which they are used that are already well designed for use inside the human body as little as possible. For valves used inside the body connected to cannulae or incorporated into cannulae, this requires that the valves do not distort or change the shape of the cannulae. It is therefore desirable that such valves harmonize with the shape of the cannulae with which they are used. SUMMARY OF THE INVENTION It is an object of one aspect of the present invention to provide a cannula valve unit for use in liquid flow control systems requiring a cannula with an inlet and outlet valve, and especially for use with a medical cannula in circulatory assist systems, that is easily incorporated into the cannula. A cannula valve unit in accordance with the present invention comprises a one way inlet valve and a one way outlet valve joined together to form a single unit having ends for coupling to a cannula. The cannula valve unit therefore includes in a single unit two valves that are incorporated into a cannula in circulatory assist systems. Both ends of the cannula valve unit are made so that the ends are easily coupled to a cannula. Preferably, the ends are provided with adapters for coupling to the cannula. Preferably, the adapters are tubular extensions. The outside diameters of the tubular extensions are preferably approximately equal to the inside diameter of the cannula. The cannula valve unit is incorporated into the cannula by cutting the cannula into two pieces at the point of the cannula where it is desired to incorporate the cannula valve unit or by otherwise providing a two piece cannula with the desired dimensions. The tubular extensions are then inserted into the cut ends of the two pieces of the cannula, rejoining the two pieces of the cannula with the cannula valve unit between them. The tubular extensions of the cannula valve unit are preferably fixed in the cut ends of the cannula into which they are inserted by gluing or clamping. Thus, a single installation into a cannula of a cannula valve unit, in accordance with a preferred embodiment of the present invention, equips a cannula with an inlet valve and an outlet valve, thereby adapting the cannula for use in circulatory assist systems. The single installation in accordance with the present invention replaces two separate installations, one installation to fit an inlet valve to the cannula and a second separate installation to fit an outlet valve to the cannula. It is an aspect of the present invention to provide a cannula valve unit comprising a one way inlet valve and a one way outlet valve that, when incorporated into a cannula preserves the external shape of the cannula. A cannula valve unit in accordance with the present invention is preferably cylindrical. Preferably, the outside diameter of the cannula valve unit is substantially equal to the outside diameter of the cannula with which it is used. Therefore, when the cannula valve unit is incorporated into the body of the cannula, the cannula valve unit and cannula, form a single relatively homogeneous cannula. It is another object of the present invention to provide a cannula valve unit with component valves that open and close in such a way so as to reduce forces resulting from the opening and closing that might damage blood cells. A cannula valve unit in accordance with the present invention preferably comprises: a one way leaflet valve for the inlet of blood into the cannula valve unit; an opening which communicates with the leaflet valve for connecting the cannula valve unit to a cannula, an end of which is placed in a ventricle of a heart; one way cylindrical outlet valve through which blood exits the cannula valve unit and enters a blood vessel, for example the aorta; and an opening for connecting the cannula valve unit via a cannula to a pump. Blood enters the cannula valve unit axially through the leaflet valve and leaves the cannula valve unit in a general radial direction through holes in the cylindrical surface of the outlet valve. As indicated above, the cannula valve unit is preferably connected to a pump in a circulatory assist system via a cannula. The pump cyclically produces pressure differentials in the cannulae connected to the cannula valve unit and thereby also in the cannula valve unit. The pressure differentials cause blood to be alternately drawn through an input cannula into the cannula valve unit through the leaflet valve and expelled from the cannula valve unit through the cylindrical outlet valve into the blood vessel in which the cannula valve unit is placed. PCT application PCT/IL96/0045, referenced above, shows a cardiac assist system comprising a pump which operates cannula valves in the general manner described. The cylindrical outlet valve preferably comprises a base tube formed with holes. The base tube is preferably rigid and preferably made of stainless steel or hardened plastic. Alternatively the base tube may be made from a material or materials such that the base tube bends flexibly but maintains its cross section against deformation. For example the base tube may be a length of flexible medical cannula. The base tube is preferably fitted with a baffle sleeve that fits snugly on the base tube and covers the holes. The baffle sleeve preferably comprises at least one thin walled baffle sleeve layer formed from a biocompatible elastic material. By covering the holes, the baffle sleeve prevents blood from flowing into the base tube through the holes. However, if the pressure inside the base tube is sufficiently larger than the pressure outside the base tube, the baffle sleeve expands elastically in a cone shape in such a way as to uncover the holes and let blood flow out of the base tube. The cone shape preferably orients the blood flow to prevent the blood from impacting with high force directly on the walls of the blood vessel in which the cannula valve unit is placed. Large forces resulting from the impact of flowing blood on the walls of a blood vessel can cause damage to both blood cells and the blood vessel. When the pressure that caused the baffle sleeve to expand subsides, the baffle sleeve contracts to its original shape to again cover the holes and seal them against blood flow. The contraction is gentle and does not stress blood cells because of the elasticity of the material from which the baffle sleeve is made and because the wall of the baffle sleeve is thin. The baffle sleeve closes on the base tube with a smooth peristaltic motion that moves along the base tube from the end where the baffle sleeve is not expanded to the end where it is. Hereafter, the term "sleeve valve" is used to denote the cylindrical one way outlet valve. Israel patent application 119,899, filed Dec 24,1996, which is assigned to the assignees of the present invention and is incorporated herein by reference, describes a sleeve valve used as a one way outlet valve for a cannula. The one way leaflet valve of the cannula valve unit is preferably formed from a biocompatible elastic material. It preferably comprises two or three leaflets attached to a cylindrical part. The leaflet valve is joined to the sleeve valve by inserting and securing the leaflet valve inside an end of the base tube of the sleeve valve. When the pressure inside the base tube is less than the pressure on the other side of the leaflet valve, the leaflets are stretched open, away from each other, to let blood flow freely into the base tube. When the pressure inside the base tube is greater than the pressure outside the base tube, the leaflets close on each other, thereby closing the leaflet valve and preventing blood from flowing out of the end of the base tube through the leaflet valve. The leaflets close on each other gently, preventing any sharp impact force on blood cells. PCT application PCT/IL96/00044 which is assigned to the assignees of the present invention, and is incorporated herein by reference, describes a tri- leaflet one way valve and methods for producing such a valve. It is the structure of the leaflet valve that causes the leaflets to close gently. Under conditions of substantially equal pressure inside and outside the base tube, the leaflet valve is in an unstressed state. In the unstressed state the leaflet valve is partially open with the leaflets slightly apart. Therefore, when a pressure differential between the inside and outside of the base tube forces the leaflets to close on each, the structure of the leaflet valve undergoes an elastic distortion. The elastic distortion of the leaflet valve reduces the contact force between the surfaces and edges of the leaflet valve that close and touch each other. It is a further object of the present invention to provide a cannula valve unit that provides minimum resistance to blood flow and reduces abrupt changes in the velocity profile of blood that moves through the cannula valve unit. Large rapid changes in the velocity profile can result in damaging shear stress on blood components. A cannula valve unit in accordance with the present invention preferably has a base tube with an internal radius substantially equal to the internal radius of the cannula with which it is used. When blood flows into the cannula valve unit through the inlet leaflet valve, the leaflet valve preferably opens to a cross section nearly equal in area to the internal cross sectional area of the cannula. This is possible because the leaflet valve is partially open and the leaflets are thin and elastic. As a result, when the pressure inside the base tube is sufficiently less than the pressure outside the base tube, the leaflets stretch apart to such a degree that they are in contact or almost in contact with the inside wall of the base tube. Preferably, the sum of the areas of the holes in the sleeve valve substantially equals or is greater than the cross sectional area of the cannula. By substantially equalizing the cross sectional area of the base tube and the open inlet and outlet valves of the cannula valve unit with the cross sectional area of the cannula used with the cannula valve unit, undesirable accelerations of the blood as it flows through the cannula into and through the cannula valve unit are reduced. As a result, shear stresses on the blood that might damage blood components are reduced. The risk of formation of local turbulence and stationary pockets or pools of blood in the cannula valve unit and in the cannula is also lowered. - There is therefore provided, in accordance with a preferred embodiment of the present invention, a cannula valve unit for the control of blood flow in a cannula comprising a one way inlet valve and a one way outlet valve wherein the one way inlet valve and the one way outlet valve are joined together as a single unit having ends adapted for joining with a cannula on each end of the unit. Preferably the inlet and outlet valves are responsive to the pressure differences in the blood between points inside and outside of the cannula valve unit such that when blood flows into the cannula valve unit through the inlet valve, blood does not flow out through the outlet valve, and when blood flows out from the cannula valve unit through the outlet valve, blood does not flow in to the cannula through the inlet valve. In preferred embodiments of the invention the outlet valve is preferably a sleeve valve formed on a tube having at least one flow hole in its wall through which blood flows out of the cannula valve unit and having a first end and a second end. Preferably, the tube is substantially rigid. Alternatively, the tube bends flexibly and also maintains its cross section against deformation. Preferably, the inlet valve is positioned at and inside the first end of the tube. The second end preferably comprises a tubular extension for connecting to the cannula. An end cap preferably secures the inlet valve in the first end of the tube. Preferably, the end cap comprises a tubular extension for coupling to the cannula. The tube preferably has an inside diameter substantially equal to the inside diameter of the cannula with which the cannula valve unit is joined. Preferably, the outside diameter of the tube substantially equals the outside diameter of the cannula. When the inlet valve is maximally open it preferably has a cross section for fluid flow substantially equal to the cross sectional area of the tube. Preferably, when the cannula valve unit is connected via a cannula to a pump which causes pressure changes in the blood in the cannula valve unit so as to alternately draw fluid into the cannula valve unit and expel fluid from the cannula valve unit, when the pump operates to draw fluid into the cannula valve unit the inlet valve is maximally open. In some preferred embodiments of the invention the inlet valve is a leaflet valve. Preferably, the leaflets of the leaflet valve open to a maximally open position so that they substantially conform to the inside surface of the tube. In some preferred embodiments of the invention, the sleeve valve comprises a baffle sleeve with varying wall thickness which covers the at least one hole in the wall of the base tube. Alternatively or additionally, the moving parts of the baffle sleeve have varying wall thickness. Preferably, the baffle sleeve comprises a plurality of baffle sleeve layers. Preferably, some of the plurality of baffle sleeve layers are of different lengths. Alternatively or additionally, the wall thickness of the baffle sleeve decreases along the length of the baffle sleeve. Preferably, the wall thickness of the baffle sleeve decreases in the direction of the component of blood flow parallel to the axis of the cannula valve unit of blood which exits the cannula valve unit through the at least one flow hole covered by the baffle sleeve. There is further provided in accordance with a preferred embodiment of the invention a one way sleeve valve comprising: a tube formed with flow holes in its wall for the exit of liquid from the lumen of the tube; and a baffle sleeve made of a flexible material which hugs the outside of the tube so as to cover flow holes in the wall of the tube and which distends away from the surface of the tube when pressure in the lumen exceeds a certain threshold so as to uncover the flow holes; and wherein the tube bends flexibly and also maintains its cross section against deformation. Preferably, the wall thickness of the baffle sleeve varies. There is further provided in accordance with a preferred embodiment of the present invention a one way sleeve valve comprising: a tube formed with flow holes in its wall for the exit of liquid from the lumen of the tube; and a baffle sleeve made of a flexible material which hugs the outside of the tube so as to cover flow holes in the wall of the tube and which distends away from the surface of the tube when pressure in the lumen exceeds a certain threshold so as to uncover the flow holes; and wherein the wall thickness of the baffle sleeve varies. In preferred embodiments of the present invention where the wall thickness of the baffle sleeve varies, alternatively or additionally, the wall thickness of the moving parts of the baffle sleeve varies. Preferably, the wall thickness of the baffle sleeve decreases along the length of the baffle sleeve. The wall thickness of the baffle sleeve decreases preferably in the direction of the component of blood flow that is parallel to the axis of the cannula valve unit, of blood which exits the cannula valve unit through the at least one flow hole covered by the baffle sleeve. Additionally or alternatively, the baffle sleeve comprises a plurality of baffle sleeve layers. Preferably, some of the plurality of baffle sleeve layers are of different length. There is also provided in accordance with the present invention a one way leaflet valve assembly comprising: a leaflet valve having an inlet orifice and a plurality of leaflets which define a variable outlet orifice; a cylindrical part comprising a first input end and a second output end, having an inner diameter, with the first end communicating with the inlet orifice of the leaflet valve and where the second end is situated downstream of the leaflet valve outlet orifice; and wherein the leaflets close together to substantially close the variable orifice and open apart to increase the area of the variable orifice such that the area of the variable orifice is substantially equal to the cross sectional area of the cylindrical part. Preferably, the plurality of leaflets comprises two leaflets. Alternatively, the plurality of leaflets preferably comprises three leaflets. The leaflets are preferably formed from an elastic material. There is further provided in accordance with a preferred embodiment of the present invention a method for incorporating a cannula valve unit having ends and comprising inlet and outlet valves into a cannula comprising: providing a cannula in two pieces; joining an end of each of the cannula pieces to an end of the cannula valve unit. There is also provided, in accordance with a preferred embodiment of the present invention, a cannula comprising a first portion and a second portion wherein an end of the first portion is joined to an inlet end of a cannula valve unit in accordance with a preferred embodiment of the present invention, and an end of the second portion is joined to the other end of the cannula valve unit. There is also provided, in accordance with a preferred embodiment of the present invention, a aortic cannula comprising a first portion and a second portion, wherein an end of the first portion is joined to an inlet end of a cannula valve unit in accordance with a preferred embodiment of the present invention, and an end of the second portion is joined to the other end of the cannula valve unit, and wherein the length of the first portion is such that if another end of the first portion is placed into the left ventricle of the heart of a patient, the cannula valve unit is in the aorta at a position so as to assist in injecting blood from the left ventricle into the aorta. There is further provided in accordance with a preferred embodiment of the present invention, a cannula having a flexible portion, formed with at least one opening in its surface, and comprising a baffle sleeve formed from a flexible material, wherein the baffle sleeve hugs the outer surface. of the cannula and covers the at least one opening in the surface of the cannula so that when the pressure of a liquid in the cannula exceeds a certain value, the baffle sleeve distends away from the cannula, allowing liquid to flow out of the cannula through the at least one opening. The invention will be more clearly understood by reference to the following description of preferred embodiments thereof in conjunction with the figures, wherein identical structures, elements or parts which appear in the figures are labeled with the same numeral, and in which: BRIEF DESCRIPTION OF FIGURES Figs. 1A-1C illustrate the insertion of a cannula valve unit, in accordance with a preferred embodiment of the present invention, into a standard aortic cannula; Fig. 2A -Fig. 2B show respectively , an exploded view, in cross section, of a preferred breakdown of the parts of a cannula valve unit, and a cross sectional view of an assembled cannula valve unit in accordance with a preferred embodiment of the present invention; Fig. 3 shows a sleeve valve in accordance with a preferred embodiment of the present invention that has opened under pressure to allow blood to flow out through flow slots in its surface; Fig. 4 is a schematic of a construction of a tapered sleeve for a sleeve valve in accordance with a preferred embodiment of the present invention; Fig. 5 shows in perspective view the construction of a leaflet valve in accordance with a preferred embodiment of the present invention. Figs. 6A-6C show the operation of a cannula valve unit incorporated into a cannula and connected to a pump in accordance with a preferred embodiment of the present invention; Fig. 7 shows an aortic cannula of a circulatory assist system positioned in a heart to assist the left ventricle to pump blood into the aorta in accordance with a preferred embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figs. 1A-1C illustrate the incorporation of a cylindrical cannula valve unit 28, in accordance with a preferred embodiment of the present invention, into a conventional cannula 20. Fig. 1 A shows aortic cannula 20. One end of cannula 20 has a suction port 22 through which blood is drawn into cannula 20. The other end, end 21 of cannula 20 is for connecting to a pump (not shown). Fig IB shows cannula 20 cut into two pieces, pump piece 24 and suction piece 26, which are to be joined to cannula valve unit 28, alternatively the cannula can be provided in two pieces. Pump pieces 24 and suction piece 26 have cut ends 34 and 35 respectively. Cannula valve unit 28 has an inlet end 31 and a pump end 33. The ends 31 and 33 of cannula valve unit 28 have tubular extensions 30 and 32 respectively. The outside diameters of tubular extensions 30 and 32 are small enough so that tubular extensions 30 and 32 can be tightly inserted into cut ends 34 and 35 of pump piece 24 and suction piece 26 respectively. The wall thickness of tubular extensions 30 and 32 is small so that the inside dimension of tubular extensions 30 and 32 is substantially equal to the inside dimension of cannula 20. Cannula valve unit 28 is incorporated into cannula 20 by inserting tubular extension 30 at the inlet end 31 of cannula valve unit 28 into cut end 35 of suction piece 26 and tubular extension 32 into cut end 34 of pump piece 24. Tubular extensions 30 and 32 are preferably fixed in place in cut ends 34 and 35 by gluing or clamping. Alternatively, or additionally, tubular extensions 30 and 32 are tapered so that tubular extensions 30 and 32 may forcibly be inserted into cut ends 34 and 35 and held securely in place by friction. Preferably, the outside diameter of cannula valve unit 28 is approximately equal to the outside diameter of cannula 20. Fig. 1C shows the homogeneous aortic cannula 29 formed by joining cannula valve unit 28 to suction piece 24 and pump 26 of cannula 20 in accordance with a preferred embodiment of the invention. Fig. 2A and Fig. 2B show, respectively, in cross section, an exploded view of a preferred cannula valve unit 28 and an assembled cross section of cannula valve unit 28. Referring to Fig. 2A, cannula valve unit 28 preferably comprises an end cap 36, a leaflet valve 38 and a sleeve valve 40. Sleeve valve 40 is a one way cylindrical outlet valve through which blood flows out of cannula valve unit 28. Sleeve valve 40 comprises a base tube 42 with ends 33 and 43. Base tube 42 is preferably made of stainless steel, hardened plastic, or other suitable biocompatible material known in the art and is preferably substantially rigid. Alternatively, base tube 42 can be made from a material or materials such that base tube 42 bends flexibly but maintains its cross section against distortion. For example base tube 42 may be a length of flexible cannula. It should be recognized that although in the embodiment shown in Figs. 1-2 base tube 42 is preferably short, on the order of a few centimeters, a sleeve valve can advantageously be built as an integral part of a long length of flexible cannula. Base tube 42 is preferably formed with a plurality of flow openings, in its cylindrical surface, preferably in the form of elongated flow slots 48 (only some of which are seen in the figure). Flow slots 48 are preferably positioned symmetrically on the surface of base tube 42 and are preferably located close to end 33 of base tube 42. The long dimension of flow slots 48 are preferably parallel to the axis of base tube 42. The axial positions of flow slots 48 along the length of base tube 42 are preferably identical. The sum of the areas of flow slots 48 is preferably substantially equal to or greater than the cross sectional area of base tube 42. Base tube 42 preferably has a tubular extension 32 for joining to a cannula. Preferably, tubular extension 32 is formed as an integral part of base tube 42. Base tube 42 is preferably covered by a baffle sleeve. In a preferred embodiment of the invention, the baffle sleeve comprises two baffle sleeve layers, 44 and 46. Baffle sleeve layers 44 and 46 are preferably thin walled tubes made of flexible latex or other elastic biocompatible material. Baffle sleeve layers 44 and 46 fit snugly over base tube 42 and cover flow slots 48. Baffle sleeve layer 46 is longer than baffle sleeve layer 44 and extends further in the direction towards end 33 than does baffle sleeve layer 44. Towards end 43 of base tube 42 baffle sleeve layers 44 and 46 are preferably coextensive. Baffle sleeve layers 44 and 46 are preferably glued, or fixed by other means, to each other and to base tube 42 at their coextensive ends. As long as the pressure inside base tube 42 is equal to or less than the pressure outside base tube 42, hereafter referred to, "neutral pressure" and "negative pressure", respectively, baffle sleeve layers 44 and 46 seal flow slots 48 against blood flow. However, when the pressure of blood inside base tube 42 is greater than the pressure outside of base tube 42, hereafter referred to "positive pressure", baffle sleeve layers 44 and 46 distend away from base tube 42 uncovering flow slots 48 and allowing blood to flow out of cannula valve unit 28. The threshold positive pressure at which flow slots 48 are uncovered and the speed at which baffle sleeve layers 44 and 46 distend open and away from base tube 42 depend upon, among other things: the thickness and elasticity of the material from which baffle sleeve layers 44 and 46 are made; the unstressed diameters of baffle sleeve layers 44 and 46 with respect to the outside diameter of base tube 42; how and where baffle sleeve layers 44 and 46 are glued or otherwise attached to base tube 42; and the size and number of flow slots 48. Leaflet valve 38 is preferably a one way inlet valve through which blood enters into cannula valve unit 28. Leaflet valve 38 is preferably made of latex, silicon or other biocompatible elastic material. Leaflet valve 38 preferably comprises a rim 50, a circular cylindrical part 52 and two leaflets 54 and 56. Leaflet valve 38 is mounted to sleeve valve 40 and is fixed in place by inserting leaflet valve 38 into end 43 of base tube 42 and gluing cylindrical part 52 to the inside surface of base tube 42. When there is sufficient positive pressure inside base tube 42, leaflets 54 and 56 close on each other, thereby closing leaflet valve 38. When there is a sufficient negative pressure inside base tube 42 leaflets 54 and 56 are stretched open almost to the walls of base tube 42 and blood flows unimpeded into cannula valve unit 28. When the difference in pressure between the inside and outside of base tube 42 is substantially zero, leaflet valve 38 is slightly open. The slightly open "starting" disposition of leaflet valve 38 when it is not stressed has two advantages: it is easier to stretch leaflet valve 38 open to its maximum cross sectional area; and closing the leaflet valve requires an elastic deformation of the leaflet valve shape which prevents a hard, sharp closure of leaflets 54 and 56 on each other when the leaflet valve closes. End cap 36 is preferably made of stainless steel or hardened plastic or other suitable biocompatible material. Tubular extension 30 (for coupling to a cannula) is preferably formed as an integral part of end cap 36. End cap 36 is mounted onto end 43 of base tube 42, and is preferably fixed in place by gluing it to the outside surface of the base tube. End cap 36 completes the sealing of leaflet valve 38 to base tube 42 and provides cannula valve unit 28 with tubular extension 30 for coupling to a cannula. Fig. 3 shows a perspective view of a cannula valve unit 28, in accordance with a preferred embodiment of the present invention, with baffle sleeve layers 44 and 46 distended by positive pressure inside base tube 42 so that blood flows out through flow slots 48. The use of two baffle sleeve layers, 44 and 46, having different extents at end 33 of base tube 42 results in easier stretching of baffle sleeve layers 44 and 46 at points nearer to end 33 than at points further away from end 33. As a result, baffle sleeve layers 44 and 46 distend away from base tube 42, starting first at end 33 of cannula valve unit 28, and open smoothly in a cone shape to uncover flow tubes 48. Blood flows out through flow slots 48 in a radial direction but is redirected by the cone shape of distended baffle sleeve layers 44 and 46 so that the blood flow has a strong axial component parallel to base tube 42. As the positive pressure decreases, baffle sleeve layers 44 and 46 begin contracting back to their original position around base tube 42 with a motion that is the reverse of the opening motion.. Baffle sleeve layers 44 and 46 close on base tube 42 in a soft peristaltic motion which moves towards end 33 from distended points of baffle sleeve layers 44 and 46 near end 31. The peristaltic motion pushes blood remaining between baffle sleeve layers 44 and 46 and base tube 42 forward and out from under baffle sleeve layers 44 and 46 and into the blood stream. When the pressure becomes neutral or negative, baffle sleeve layers 44 and 46 are returned to their original positions, hugging base tube 42, and sealing flow slots 48 against blood flow. This two layer structure also ensures that when there is a positive pressure build up in base tube 42, baffle sleeve layers 44 and 46 do not form "blisters" over flow slots 48 while remaining tightly clamped around base tube 42 everywhere else. Blood would then not be able to flow out of cannula valve unit 28. Blood would flow out of flow slots 48 but would be trapped and perhaps damaged in the blisters between baffle sleeve layers 44 and 46 and base tube 42. This potential problem is obviated by the fact that, under positive pressure, the ends of baffle sleeve layers 44 and 46 situated near end 33 distend first because of their greater elasticity in comparison to other parts of baffle sleeve layers 44 and 46. The use of two baffle sleeve layers also ensures that baffle sleeve layers 44 and 46 will not curl back over on themselves when they distend open. Once curled over on themselves baffle sleeve layers 44 and 46 might not return to their original positions to cover flow slots 48 when the positive pressure which caused them to distend subsided. This problem is prevented by the decrease in elasticity of baffle sleeve layers 44 and 46 at points of baffle sleeve layers 44 and 46 further away from end 33. The decrease in elasticity makes it very difficult to bend or stretch baffle sleeve layers 44 and 46 through the 90 degree bend required for baffle sleeve layers 44 and 46 to curl over on themselves. There are alternative ways to construct a baffle sleeve that distends open symmetrically in a cone shape, closes with a gentle peristaltic motion and prevents the occurrence of the problems noted above. Fig. 4 shows a cannula valve unit 28, in accordance with a preferred embodiment of the invention, comprising a sleeve valve 40 with a baffle sleeve 60 with only one layer instead of two. The outside diameter of baffle sleeve 60 decreases in the direction towards end 33 so that the wall thickness of baffle sleeve 60 decreases in the direction towards end 33. Thus baffle sleeve 60 distends more easily at points closer to end 33 than at points closer to end 31. Baffle sleeve 60 therefore behaves similarly to the pair of baffle sleeve layers 44 and 46 shown in previous figures. Under the influence of positive pressure in base tube 42 baffle sleeve 60 distends away from base tube 42 in a cone. As the pressure decreases baffle sleeve 60 contracts around base tube 42 with a gentle peristaltic motion in the direction towards Figs. 5 shows in perspective view, details of the construction of leaflet valve 38 in accordance with a preferred embodiment of the present invention. Leaflet valve 38 preferably comprises a rim 50, a circular cylindrical part 52 and two, preferably thin, leaflets 54 and 56. Leaflets 54 and 56 are preferably mirror image planar surfaces, symmetric with respect to the axis of cylindrical part 52. Edges 64 and 66 of leaflets 54 and 56 respectively, and edges 68 ' and 70 of cylindrical surface 52 define a variable orifice 72 of leaflet valve 38. Variable orifice 72 preferably has the slot shape shown in Fig 5 when there is no pressure difference between the inside and the outside of leaflet valve 38. If the pressure on the outside of leaflet valve 38 is greater than the pressure inside leaflet valve 38, leaflets 54 and 56 will be pressed to each other and thereby reduce the size of, or close, variable orifice 72. If the pressure inside leaflet valve 38 is greater than the pressure outside of leaflet valve 38, leaflets 54 and 56 will stretch away from each other thereby increasing the cross sectional size of variable orifice 72. The wall thickness of cylindrical part 52 is preferably small so that the inside diameter of cylindrical part 52 is substantially equal to the inside diameter of the cannula valve unit with which it is used. Structural strength is given to the leaflet valve by rim 50. When leaflet valve 38 is installed in a cannula valve unit, in accordance with a preferred embodiment of the present invention, cylindrical part 52 is preferably glued to the inside surface of the base tube of the cannula valve unit. This adds further support to the structural integrity of the leaflet valve. Because of the thin wall structure of leaflet valve 38 variable orifice 72 opens to a maximum such that the cross sectional area of variable orifice 72 is very nearly equal to the cross sectional area of the inside of the cannula valve unit. Therefore, when fully open, leaflet valve 38 presents very little resistance to the maximum blood flow sustained by the cross sectional area of the cannula into which the cannula valve unit is incorporated. As a result, when blood flows into the cannula valve unit with leaflet valve 38 opened maximally, the pressure drop in the blood flowing through leaflet valve 38 is minimized. There is therefore very little acceleration of the blood in leaflet valve 38 and shear stresses on the blood are minimized. The flow through capacity of the cannula valve unit is substantially matched to the flow through capacity of the cannula and smooth laminar flow of the blood is promoted and turbulence suppressed. Figs. 6A-6C show the operation of a cannula valve unit incorporated into a cannula and connected to a pump in accordance with a preferred embodiment of the present invention. A pump (not shown) is connected to the end of the part of cannula 20 which is joined to pump end 33 of cannula valve unit 28. The action of the pump cyclically causes the pressure inside cannula valve unit 28 to be greater than (positive pressure) and less than (negative pressure) the pressure outside of cannula valve unit 28. When the pressure in cannula valve unit 28 is negative, blood is sucked into cannula valve unit 28 through leaflet valve 38. When the pressure inside cannula valve unit 28 is positive, blood is forced out of cannula valve unit 28 through flow slots 48 of sleeve valve 40. When the pressure inside cannula valve unit 28 is neutral (inside and outside substantially equal) blood moves very slowly if at all in cannula 20. Fig. 6A shows cannula valve unit 28 at a point in the pump cycle when the pressure inside cannula valve unit 28 is neutral. Leaflets 54 and 56 are in their unstressed positions and variable orifice 72 is partially open . Baffle sleeve layers 44 and 46 cover flow slots 48 but are not stressed by a pressure differential between the blood inside and outside of cannula valve unit 28. There is very little motion of the blood in cannula 20. Fig. 6B shows cannula valve unit 28 at a point in the pump cycle when the pressure inside cannula valve unit 28 is maximum negative pressure. Leaflets 54 and 56 are stretched to their maximum open position and are almost hugging the wall of base tube 42. Blood flow into cannula valve unit 28 is at a maximum. Flow lines 80 show the streaming of blood into cannula valve unit 28. Baffle sleeve layers 44 and 46 are tightly pressed against flow slots 48, sealing flow slots 48 and preventing blood flow through them into cannula valve 28. Fig. 6C shows cannula valve unit 28 at a point in the pump cycle when the pressure inside cannula valve unit 28 is maximum positive pressure. Leaflets 54 and 56 of leaflet valve 38 are pressed together and leaflet valve 38 is closed. The positive pressure forces baffle sleeve layers 44 and 46 to distend open away from base tube 40 and uncover flow slots 48. Blood flows out of cannula valve unit 28 through flow slots 48. Blood does not flow out of cannula valve unit 28 through leaflet valve 38. Flow lines 82 show the streaming of blood out from cannula valve unit 28 through flow slots 48. Fig. 7 shows an aortic cannula 20 assembled with a cannula valve unit 28, in accordance with a preferred embodiment of the present invention, inserted into a heart 83, to assist left ventricle 84 to pump blood into aorta 86. The suction end 22 of cannula 20 is inside left ventricle 84.. Cannula valve unit 28 is positioned in aorta 86. The pump end of cannula valve unit 28 (not shown) is connected to a length of cannula 20 which extends from aorta 86 to a peripheral artery 88. Cannula 20 exits peripheral artery 88 though an incision and is connected to blood reservoir 90 which is connected to a pump (not shown). A similar cardiac assist system comprising a blood reservoir and pump is shown in PCT/IL96/00045 referenced above. The heart is shown in the systolic part of the heart cycle. During the previous diastolic part of the heart cycle the pump decreased the pressure in reservoir 90 and caused blood to be sucked into cannula valve unit 28 and fill reservoir 90. In the present systolic part of the heart cycle shown in Fig. 7, the pump has increased the pressure in reservoir 90, causing the pressure in cannula valve unit 28 to rise above the surrounding ambient pressure in aorta 86. Baffle sleeve layers 44 and 46 (not shown separately) are elastically distended in a cone shape. Blood flows out of reservoir 90 into cannula valve unit 28 and out the flow slots (not shown) of cannula valve unit 28 into aorta 86. Although the discussion and the figure refer to the pump acting in phase with the heart cycle, sometimes the pump is used in a "counter pulsation mode" where the pump is out of phase with the heart. Although only the medical applications of a cannula valve unit in accordance with a preferred embodiment of the present invention have been discussed and illustrated, it should be recognized that the cannula valve unit is not limited to medical applications. It can be applied quite generally to the pumping of liquids and the control of liquid flow, and uses of the cannula valve unit for other than medical applications will occur to persons skilled in the art. Variations of the above described preferred embodiment will occur to persons of the art. For example, the inlet leaflet valve discussed in the text which is illustrated showing two leaves and which is preferably designed so that the leaflets open completely and close gently might be replaced with an inlet valve comprising 3 leaflets as described in PCT/IL96/00044 referenced above. The above detailed description is provided by way of example and is not meant to limit the scope of the invention which is limited only by the following claims.

Claims: CLAIMS 1. A cannula valve unit for the control of blood flow in a cannula comprising: a one way inlet valve; and a one way outlet valve, wherein the one way inlet valve and the one way outlet valve are joined together as a single unit having ends adapted for joining with a cannula on each end of the unit. 2. A cannula valve unit according to claim 1 wherein the inlet and outlet valves are responsive to the pressure differences in the blood between points inside and outside of the cannula valve unit such that when blood flows into the cannula valve unit through the inlet valve, blood does not flow out through the outlet valve, and when blood flows out from the cannula valve unit through the outlet valve, blood does not flow in to the cannula through the inlet valve. 3. A cannula valve unit according to any of the preceding claims wherein the outlet valve is a sleeve valve formed on a tube having: at least one flow hole in its wall through which blood flows out of the cannula valve unit; and a first end and a second end. 4. A cannula valve unit according to claim 3 wherein the tube is substantially rigid. 5. A cannula valve according to claim 3 wherein the tube bends flexibly and also maintains its cross section against deformation. 6. A cannula valve unit according to any of claims 3-5 wherein the inlet valve is positioned at and inside the first end of the tube. 7. A cannula valve unit according to claim 6 comprising an end cap which secures the inlet valve in the first end of the tube. 8. A cannula valve unit according to claim 7 wherein the end cap comprises a tubular extension for coupling to the cannula. 9. A cannula valve unit according to any of claims 3-8 wherein the second end comprises a tubular extension for connecting to the cannula. 10. A cannula valve unit according to any of claims 3 - 9 wherein the tube has an inside diameter substantially equal to the inside diameter of the cannula with which the cannula valve unit is joined. 11. A cannula valve unit according to any of claims 3 - 10 wherein the tube has an outside diameter substantially equal to the outside diameter of the cannula with which the cannula valve unit is joined. 12. A cannula valve unit according to any of claims 7 - 11 wherein the inlet valve when maximally open has a cross section for fluid flow substantially equal to the cross sectional area of the tube. 13. A cannula valve unit according to claim 12, wherein, when the cannula valve unit is connected to a pump via a cannula, and the pump causes pressure changes in the blood in the cannula valve unit so as to alternately draw fluid into the cannula valve unit and expel fluid from the carmula valve unit, such that when the pump operates to draw fluid into the cannula valve unit the inlet valve is maximally open. 14. A cannula valve unit according to any of the preceding claims wherein the inlet valve is a leaflet valve. 15. A cannula valve unit according to claim 14 wherein the leaflets open to a maximally open position so that they substantially conform to the inside surface of the tube. 16. A cannula valve unit according to any of claims 3-15 wherein the sleeve valve comprises a baffle sleeve with varying wall thickness which covers flow holes in the wall of the sleeve valve. 17. A cannula valve unit according to claim 16 wherein the moving parts of the baffle sleeve have varying wall thickness. 18. A cannula valve unit according to any of claims 3-17 wherein the baffle sleeve comprises a plurality of baffle sleeve layers. 19. A cannula valve unit according to claim 18 wherein some of the plurality of baffle sleeve layers are of different lengths. 20. A cannula valve unit according to any of claims 16-19 wherein the wall thickness of the baffle sleeve decreases along the length of the baffle sleeve. 21. A cannula valve unit according to claim 20, wherein the wall thickness of the baffle sleeve decreases in the direction from a non opening part of the baffle sleeve to an opening end of the baffle sleeve. 22. A one way sleeve valve comprising: a tube formed with flow holes in its wall for the exit of liquid from a lumen of the tube; and a baffle sleeve made of a flexible material which hugs the outside of the tube so as to cover flow holes in the wall of the tube and which distends away from the surface of the tube under pressure in.the lumen so as to uncover the flow holes; and wherein the tube bends flexibly and also maintains its cross section against deformation. 23. A sleeve valve according to claim 22 wherein the wall thickness of the baffle sleeve varies along the length of the tube. 24. A one way sleeve valve comprising: a tube formed with flow holes in its wall for the exit of liquid from the lumen of the tube; and a baffle sleeve made of a flexible material which hugs the outside of the tube so as to cover flow holes in the wall of the tube and which distends away from the surface of the tube when pressure in the lumen exceeds a certain threshold so as to uncover the flow holes; and wherein the wall thickness of the baffle sleeve varies along the length of the tube. 25. A sleeve valve according to claim 23 or claim 24 wherein portions of the baffle sleeve move to uncover the flow holes and wherein the wall thickness of the moving parts of the baffle sleeve varies. 26. A sleeve valve according to claims 22-25 wherein the baffle sleeve comprises a plurality of baffle sleeve layers. 27. A sleeve valve according to claims 26 wherein some of the plurality of baffle sleeve layers are of different length. 28. A sleeve valve according to claims 22-27 wherein the wall thickness of the baffle sleeve decreases along the length of the baffle sleeve. 29. A sleeve valve according to claim 28, wherein the wall thickness of the baffle sleeve decreases in the direction from a non opening part of the baffle sleeve to an opening end of the baffle sleeve. 30. A one way leaflet valve assembly comprising: a leaflet valve having an inlet orifice and a plurality of leaflets which define a variable outlet orifice; a cylindrical part comprising a first input end and a second output end, and having an inner diameter, and wherein the first end communicates with the inlet orifice of the leaflet valve and the second end is situated downstream of the leaflet valve outlet orifice; and wherein the leaflets close together to substantially close the variable orifice and " open apart to increase the area of the variable orifice such that the area of the variable orifice is substantially equal to the cross sectional area of the cylindrical part. 31. A one way leaflet valve according to claim 30 where the plurality of leaflets comprises two leaflets. 32. A one way leaflet valve according to claim 30 where the plurality of leaflets comprises three leaflets. 33. A one way leaflet valve according to any of claims 30 - 32 wherein the leaflets are formed from an elastic material. 34. A method for incorporating a cannula valve unit having ends and comprising inlet and outlet valves into a cannula comprising: providing a cannula in first and second separate portions; joining an end of each of the cannula portions to an end of the cannula valve unit. 35. A method for incorporating a cannula valve unit having ends and comprising inlet and outlet valves into a cannula comprising: cutting a cannula into, a first portion and a separate second portion; joining an end of each of the cannula portions to an end of the cannula valve unit. 36. A cannula produced according to the methods of claim 34 or claim 35. 37. A cannula according to claim 36 comprising a cannula valve unit according to any of claims 1-21. 38. An aortic cannula according to claim 36 or claim 37 wherein the length of the first portion is such that if another end of the first portion is placed into the left ventricle of the heart of a patient, the cannula valve unit is situated in the aorta at a position so as to assist injecting blood from the left ventricle into the aorta. 39. A cannula comprising: a flexible portion formed with at least one opening in its surface; a baffle sleeve formed from a flexible material which hugs the outer surface of the flexible portion and covers the at least one opening; wherein, in response to the pressure of a liquid inside the flexible portion, the baffle sleeve distends away from the flexible portion, allowing liquid to flow out of the cannula through the at least one opening.

Inventors: HAIMOVICH DUDU, ROTTENBERG DAN, HAIMOVICH, DUDU, ROTTENBERG, DAN
Applicants: HAIMOVICH DUDU, MEDICARD LTD, ROTTENBERG DAN, HAIMOVICH, DUDU, MEDICARD LTD., ROTTENBERG, DAN
Application year: 1997
Main classification: A61M39
IPC codes: A61F2, A61M1, A61M25