Externally Valved Shunt for Cardiopulmonary Bypass Pump

The present invention seeks to improve on the type of cardiopulmonary bypass pumping apparatus shown in prior U.S. Pat. Nos. 4,134,425 and 4,293,961, both issued to Runge. In both of these patents, a compressible tubing shunt is utilized in the compression chamber of a pulsatile flow pump. The compressible shunt in both patents is equipped with interior proximal and distal valves near opposite ends of the pump compression chamber. The manufacturing of shunt tubing from polyurethane or the like with internal valving is quite expensive, particularly where such tubing is used for one operation only and then discarded. Also, the internal shunt valving causes some hemolysis.

Because of the above, it is highly desirable to provide a cardiopulmonary bypass pumping system in which valveless tubing for the shunt may be employed, and it is the objective of the present invention to satisfy this requirement in an efficient, economical and operationally safe and reliable manner.

More particularly, in accordance with the present invention a pair of gravity biased freely pivotally suspended valve roller elements are provided within the compression chamber or housing of the pump near opposite ends of the chamber to act on the exterior of the shunt tubing so as to close off and open the shunt tubing to control blood flow therethrough in a prescribed repetitive cycle of operation. The gravity biased valve elements respond directly to fluid pressure in the shunt at two points near opposite ends of the pump compression plate beneath which a compressible sack of the shunt is located.

Other objects and advantages of the invention will become apparent during the course of the following description.

FIG. 1 is a perspective view of a valveless shunt and cardiopulmonary bypass pump according to the present invention.

FIG. 2 is an enlarged vertical section through the shunt and pump taken on line 2--2 of FIG. 1.

FIG. 3 is a transverse vertical section taken on line 3--3 of FIG. 2.

FIGS. 4, 5 and 6 are partly schematic views depicting the operation of external shunt valves during an operating cycle.

Referring to the drawings in detail wherein like numerals designate like parts, a cardiopulmonary bypass pump 10 substantially in accordance with the aforementioned patents includes a drive mechanism housing 11 fixed to an open ended compression chamber or housing 12 which may be rectangular in cross section. Within this housing, a flat pump compression plate 13 carried by drive members 14 and 15 of the pump mechanism is moved in reciprocation on a generally vertical path to cyclically compress and release a sack portion 16 of a tubing shunt 17 which extends through the open ended housing 12. The tubing shunt 17 can be formed of polyurethane or similar synthetic material. The tubing shunt contains no internal valves. It is used with the pump mechanism for one surgical operation and is then discarded, as previously explained.

Fixed to the bottom wall of the housing 12 is a flat valve plate 18 having a beveled edge 19 at its downstream or systemic end. The valve plate 18 is cut off vertically at 20' near its upstream or reserve end, and a small plate segment 18' having a beveled edge 20 is fixed to the bottom wall of housing 12 in spaced relationship to the cut off edge 20'. The two beveled edges 19 and 20 are steeply inclined as shown.

Within the compression housing 12 near its ends and on opposite sides of the compression plate 13 is a pair of transverse axis preferably cylindrical gravity biased valve elements 21 and 22. These roller-like valve elements are located adjacent to the beveled edges 19 and 20 ' of valve plate 18. They are located between the two side walls of the open ended housing 12.

The valve elements 21 and 22 are suspended on arms 23 from overhead lugs 24 fixed to the top wall of housing 12 through suitable pivot elements 25. In this manner, the gravity biased valve elements are free-hanging within the housing 12. In addition to being influenced by gravity, the valve elements 21 and 22 are acted upon by fluid (blood) pressure within the tubing shunt 17, as will be fully explained in the description of the operating cycle. The valve elements 21 and 22 in cooperation with the valve plate 18 form two independently operating external pinch valves for the flexible tubular shunt 17 on opposite sides of its compressible sack portion 16.

Beginning with FIG. 4, the pump compression plate 13 is just beginning to exert downward pressure on the filled compressible sack 16. Both external valves are closed due to the engagement of the valve elements 21 and 22 with beveled edges 19 and 20. The tubing shunt 17 is therefore pinched closed at two points by the valves. The upstream valve 21-20 on the reserve side of the shunt is closed due to the angle of the adjacent lever or arm 23 and the increasing pressure in the sack 16, which is greater than the upstream reserve side pressure in the shunt 17. Thus the element 21 is engaged with the beveled edge 20 to act as a pinch valve in its closed position at this time. The downstream or systemic valve 22-19 is closed in FIG. 4 because systemic pressure in the shunt is greater than the pressure in the sack 16, and this greater pressure acting with gravity holds the element 22 against the beveled edge 19. It is to be noted that gravity assists in closing the pinched valve consisting of element 22 and beveled edge 19, whereas gravity assists in opening the upstream pinched valve comprised of element 21 and beveled edge 20. There is no blood flow into or out of the sack 16 under the conditions shown in FIG. 4. The upstream or reserve and sack pressures are equal until the plate 13 begins to exert downward pressure on the sack 16. With this arrangement, pinch valve 21-20 is certain to close when the compression plate 13 starts its downward travel, FIG. 4.

Progressing to FIG. 5, the compression plate 13 has compressed the sack 16 and the sack is emptying. Upstream valve 20-21 remains closed due to the angle of arm 23 and the effect of increased pressure created in a bulge 16' as a result of the compression plate 13 moving down. The pressure in the bulge 16' at this time is greater than the upstream reserve pressure in the shunt 17. The downstream valve 22-19, FIG. 5, is open because the pressure in bulge 16a caused by compression of sack 16 is greater than downstream systemic pressure in the shunt, the pivoted gravity biased valve element 22 responding to fluid pressure and rising to permit an outflow of blood from the compressed sack.

Referring to FIG. 6, the sack 16 fills passively as pump compression plate 13 rises. The upstream external valve 21-20 opens due to gravity and also due to upstream reserve pressure being greater than sack pressure at this time. Downstream valve 22-19 closes because systemic pressure is now greater than pressure within the sack 16. Gravity also assists in closing downstream valve 22-19.

The operating cycle is completed by progressing from the arrangement in FIG. 6 back to the condition shown in FIG. 4.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of the invention or scope of the subjoined claims.