CA2047534A1 - Pump for the delivery of blood - Google Patents

Abstract

Abstract of the Disclosure The pump for delivering blood has a torus-shaped deformable bag disposed coaxially about a central section within the pump housing. An annular thruster is also provided coaxially of the central section and engages the bag. An electric motor within the housing drives a threaded spindle which in turn drives a nut connected with the thruster via radial spokes in order to move the thruster against the bag to deform the bag in order to exhaust blood therefrom. In another embodiment, a pair of torus-shaped deformable bags are provided within the pump housing on opposite sides of the thruster. Both bags may be used for pumping blood or one bag may be used to form a work store of gas.

Description

~ P6389 A PUMP FOR DELIVERING BLOOD

This invention relates to a pump for delivering blood.
More particularly, this invention relates to a pump which can be implanted in a patient to assist in the pumping of blood in the patient.

Pump systems for asslsting the activity of the heart of a patient who is awaiting a heart transplant have been proposed by various institutions and manufacturers.

A first group arranges the drive at the periphery of a deformable chamber and not in the direction of deformation of the chamber. This group includes a development by Stanford University with the firm of NOVACOR MEDICAL (Portner, P.M., P.E.Oyer, J.S.Jassawalla H.Chen, P.J.Miller, D.H.LaForge, G.F.Green, N.E.Shumway:
A Totally Implantable Ventricular Assist Device for End Stage Heart Disease, from: Unger, Felex: Assisted Circulation 2, Publishers Springer, Berlin, Heidelberg, New York, Tokyo 1984, pages 115-140~ which shows a type NOVACOR MK 22 C with two electromagnets which are respectively pivotable by hinges from a bearer-body and lie opposite one another at a short distance apart. Upon actuation of one magnet, spiral springs are released which project into the chamber as far as the axis of deformation and, in each case, act upon a pressure plate so that the cham~er is compressed by two thrust motions.

Another development is that by the Massachusetts General Hospital with the firm of ABIOMED (Nose, Y.: Totally Implantable Artificial Organ; Cardiac Prosthesis, Artificial Organs, Vol. 10, No. 2, 1986, pages 102-113) which shows two chambers in series which are connected together through check-valves. By pumping a hydraulic liquid to and fro by a pump, the volume of one or the other chamber at a time is reduced.

A second group of pumps arranges the drive in the direction of deformation of the chamber and deforms the chamber by displacing a membrane towards one wall of a housing, for example, as described in U.S. Patents 4,822,357 and 4,004,299; EPA 0 231 687 and German 0.S.
38 10 660. This group also includes a development by the Texas Heart Institute with the firm of GOULD INC.
(Altieri, Frank D.: Status of Implantable Energy Systems to Actuate and Control Ventricular Assist Devices, Artificial Organs, Vol. 7, No. 1, 1983, pages 5-20) which shows a chamber closed off by a membrane.
In this case, a continuously rotating electric motor via a reduction gear turns a cam disc having three high points which act upon three levers in order to displace the membrane via a thrustplate.

Another development is that by the Childrens Hospital Medical Center ~Boston) with the firm of Thermetics Inc.
(Gernes, D.~., W.F.Bernard, W.C.Clay, C.W.Sherman, D.Burke: Development of an Implantable, Integrated, Electrically Powered Ventricular Assist System, Vol.
XXIX Transactions - American Society for Artificial Ir.ternal Organs, 1983, pages 546-550) which shows a type MX IV with a slowly rotating electric motor which per revolution moves two guide rollers upwards along a helix and downwards again along a curve into a starting position in order to move a thrustplate against a membrane.

Still another development is that by the Pennsylvania State University (Weiss, W.J.: in Moller, D.P.F., Bucherl, E.S.: Proceedings Second World Symposium Artificial Heart, Volume 1, Publishers: Friedrich Vieweg ~ Sohn, 1986, page 120) which shows a d.c. motor which turns a helical cam in a cylindrical jacket in order to transmit the motion via rollers to a thrustplate which is displaceable along the axis of the cylinder and acts upon a membrane.

Still another development is that by the Cleveland Clinic Foundation with the firm of NIMBUS INC. (Nose, Y.: Totally Implantable Artificial Or~an; Cardiac Prosthesis, Artificial Organs, Vol. 10, No. 2, 1986, pages 102-113) which shows a micropump which pumps to and fro a carrier liquid which deforms a chamber by pressure so that the blood contained in the chamber is ejected.

Pumps of this kind may be connected to the heart of a ~5 mammal or human being, e.g., in parallel or in series with the left chamber of the heart in order to assist the activity of the heart. In the event such a pump is provided as an implant, the pump should fulfil very severe requirements as regards the admissible weight, admissible volume demanded, reliability and life. The pumps cited here are, from this aspect, only suited to a limited degree as implants.

Other pumps which use a rollerscrew to effect a linear motion are also known from Weiss, W.J.: Permanent Circulatory Support Systems at The Pennsylvania State 4_ University; IEEE Transactions on Biomedical Engineering, Vol. 37, No. 2, February 20, 1990.

From ethical considerations, one problem of these pumps which arises is that of inserting an intermittently-operating pump at the side of a weakened natural heart in order to bridge over part of its weakness, i.e., in the case of breakdown of the mechanical pump, the patient would be in the same situation as before its insertion, that is, left to his natural heart. There exists medical experience that blood-pumping units which assist the activity of the heart from outside the body cause infections in a fairly short time via the passages into the skin of the body. Furthermore, the radius of action of a patient who is attached via supply lines, such as to a heart-lung machine, is restricted to a few meters.

Accordingly, it ls an object of the invention to provide a compact and light pumping system which may be implanted near a natural heart.

It is another object of the invention to provide a pump for assisting a natural heart which is constructed in an efficient, reliable manner.

It is another object of the invention to assure an efficient pumping action for blood in a pump for a ventricular assist device.
Briefly, the invention provides a pump for delivering blood which includes a housing having a plurality of sections secured to each other to define a sealed space with a central section extended axially within the space and with a plurality of longitudinal slots therein. In addition, the pump has a torus-shaped deformable bag which defines a chamber for receiving a supply of blood and is disposed coaxially about the cen~ral section within the housing as well as an annular thruster which is disposed in the housing coaxial of the central section for engaging the bag. A drive means is also provided for moving the annular thruster at least in a direction to compress the deformable bag and thus cause a flow of blood out of the bag.

The drive means for the thruster includes an electric motor which is also disposed in the housing. This motor includes a stator mounted on one of the housing sections and a rotor which is rotatably mounted on one of the housing sections. In addition, the rotor is shaped so as to define a hollow shaft for rotating on an axis coaxial of the central housing section. In addition, the drive includes a threaded spindle which is secured at one end to the rotor and rotatably mounted at an opposite end in the central section for rotation on the axis of the hollow shaft. Still further, a nut is threaded onto the spindle and is disposed within the central housing section while a plurality of radial spokes are secured to the thruster and which pass through the slots of the central housing section to engage the nut whereby, upon rotation of the spindle in one direction, the nut and thruster are moved in this direction in order to compress the bag for exhausting blood from the chamber.

The pump is constructed with a suitable valve for emitting a flow of blood under pressure into the chamber defined by the deformable bag as well as with a second valve for exhausting a flow of blood under pressure from the chamber defined by the deformable bag.

The construction of the pump is such that the deformable bag is made of a pressure-resistant material while the spindle and nut which act upon the thruster form a linear drive.

In another embodiment~ the pump may be provided with a second torus-shaped bag concentric to the central housing section which is disposed between the thruster and one of the housing sections on a side opposite the first bag. In this embodiment, the second bag may be filled with gas or may be connected via suitable inlet valves and outlet valves to convey blood therethrough.

In still another embodiment, a membrane may be disposed in the housing to define a torus-shaped chamber for receiving this blood supply.
The advantages of the pump are to be seen in that a system which is in itself encapsulated is implantable, that the weight and volume of the implant is relatively low, that the moving masses in the implant are small, that the rotating motion is transferred by few parts into a linear motion and that all of the elements transmitting motion are constructed for low specific loadings and for long life.

These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanied drawings wherein:

Fig. 1 diagrammatically illustrates a pump for transporting blood therethrough;

Fig 2. illustrates a cross-sectional v.iew of a pump having a simple bag for the pumping of blood;

Fig. 3 illustrates a cross-sectional view of a pump constructed in accordance with the invention with a torus-shaped deformable bag;

Fig. 4 illustrates a view similar to Fig. 3 with the deformable bag in a compressed state in accordance with the invention;

Fig. 5 illustrates a modified pump having a membrane for forming a torus-shaped chamber for receiving a supply of blood in accordance with the invention;

Fig. 6 illustrates a detail view in accordance with Fig.
5 with only one housing section sealed to the housing by the membrane; and Fig. 7 illustrates a modified pump constructed in accordance with the invention having two alternately deformable bags.
In Fig. 1, the principle of the pump is represented.
Blood flows via a check-valve 2 or non-return valve to a chamber 4 which, through deformation, is variable in volume. A thruster 5 driven by a drive 6 deforms the chamber 4 and ejects blood via a check-valve or non-return valve 3. With the return motion of the thruster 5, blood flows in via the check-valve 2 whilst the check-valve 3 is closed. The return motion of the thruster S is effected positively, whereby the thruster 5 can release itself from the wall of the chamber 4, so that no reduced pressure arises in the chamber 4 and the pressure of the blood flowing in is employed mainly for rounding out the deformed chamber 4.

Referring to Fig. 2, the pump 1 is of disc shape with a longitudinal axis 15 which up to the connections ~not shown) between the chamber 4 and the check valves 2, 3 is also the axis of symmetry for the arrangement. The pump 1 has a housing 16 which consists of two halves 16a, 16c closed hermetically via a static seal 25, and a partition 16e. The chamber 4 which is formed by a pressure-resistant deformable bag 9, bears against one housing section 16c to which are also fitted the connection openings to the check-valves 2, 3. Through a connection opening 31, part of the gas present in the housing 16 may, in filling the chamber 4, be led into a compensating chamber (not shown) in order to generate a gentle buffer.

The drive 6 and thruster 5 are arranged to be supported from two sections 16a, 16e of the housing. The drive 6 includes an electric motor 10 having a stator part 17 fixed in the one of the sections 16a of the housing and a rotor 12 which is supported via ball bearings 19 in the two sections 16a, 16e of the housing. The rotor 12 is in the form of a hollow shaft 11 which received a nut 13 in fixed relation and in which a spindle 14 is threaded. The spindle 14 is connected rigidly to the thruster 5 which is guided by a collar 22 along the housing section 16e. Through guide grooves 23a in the housing section 16e and guide studs 24 in the collar 22, security against twisting arises. This permits only linear motions of the spindle 14 with the thruster 5.
In order to correspond with the admissible stroke for the compression of the bag 9 and to ~orrespond with the pitch of the thread between the nu' 13 and the spindle 14, the direction of rotation of the hollow-shafted motor 10 is reversed after a certain number of revolutions.

Referring to Figs. 3 and 4, wherein like reference characters indicate like parts as above, the pump has a plurality of sections secured to each other to define a sealed enclosed space while a torus-shaped deformable bag 9a is provided to form a chamber 4 for receiving a supply of blood. The connections between the chamber 4 and the check-valves 2, 3 are not shown. Inside the torus-shaped bag 9a of internal diameter Di, a spindle 14 is supported, upon which a nut 13 travels in and out periodically. An electric motor 10 is fixed by a stator part 17 into one housing section 16a while a rotor 12 made as a hollow shaft 11 is rigidly connected via a plate 27 to the spindle 14 coaxially through a screw 28.
The rotor 12 is supported in the housing section 16a via a ball bearing 19 and inside the torus-shaped bag 9a via a supporting bearing 18. The supporting bearing 18 is let into a central section or supporting body 16b which is connected rigidly to the outer section 16a of the housing. The mounting and checking of the functional capability of the drive 6 are thereby not dependent upon the closing of the housing 16 by the housing section 16c although the space between the bearings for the rotor 12 corresponds with almost the whole axial length~
The nut 13 is threaded to ride on the spindle 14 and is connected via radial spokes 20 to claws 21 on the thruster 5. By a key 29 which is let in and runs in a longitudinal groove 23b in the supporting body 16b, the nut 13 is secured against twisting and, upon turning of the spindle 14, moves into the rotor 12 or into the torus-shaped bag 9a. In this way, a short axial construction is achieved in the direction of the longitudinal axis 15, which because of the gain in space makes implantation possible for the assistance of the natural heart. In order to reduce friction between the nut 13 and spindle 14, a roller screw drive may be used in which the motion between the nut 13 and spindle 14 is transmitted by roller bodies. Roller screw drives are carried, e.g., in the delivery programme of ROLLVIS S.A.
chemin du Pont-du-Centenaire, CH-1228 Geneva.

The suppor~ing body 16b has longitudinal slots 30 through which the spokes 20 from the nut 13 protect to the annular thruster 5. For reduction of the axial size overall, the spokes 20 and claws 21 also, at times, dip axially between the radial connections to the supporting body 16b.

The thruster 5 is prolonged axially by a collar 22 and bears by a guide ring 26 against a cylindrical part of the supporting ~ody 16b. Independently of its position, therefore, the thruster 5 is guided without bending moment on the nut 13, on a cylindrical outer face and an inner face offset axially with respect to the latter on the supporting body 16b. This reduces the wear between the nut 13 and the spindle 14. Alternating loadings and wear are factors of considerable risk to the functional capability if, e.g., a use of 2 years at 120 ejection movements per minute is assumed. For this reason, in Figs. 2 and 3, the length of thread on the nut 13 is more than twice the diameter of the thread on the spindle 14.

In Fig. 4 the torus-shaped bag 9a is shown in the compressed state. Accordingly, it would by all means be conceivable to let the supporting body act upon the bag 9a from the opposite side and to pull the bag 9a by a nut 13 on the drive 6. But this calls for a continuous partition between the bag 9a and the hollow-shafted electric motor 10 against which the bag can bear and along which the connections for the chamber 4 must be led out.

Fig. 5 corresponds with Fig. 3 with the torus-shaped bag 9a replaced by a rolling membrane 9b which is squeezed to make a seal between one housing section 16c and a housing ring 16d. The connections to the check-valves 2, 3 lie in the housing ring 16d.

~11--In Fig. 6 the housing 16 is composed of two outer housing sections 16a, 16c, the clamping of the membrane 9b forming at the same time the housing seal.

In Fig. 7, a pump having two torus-shaped bags 9a, 34 is shown, which are compressed alternately by the thruster 5 lying between them. The thrusters and the sections 16a, 16c of the housing are so constructed that a rolling motion of the toruslike bags 9a, 34 takes place during compression and during filling under internal pressure. The securing of thP thruster 5 and the nut 13 connected thereto against twisting takes place between the spo~es 20 and the slots 30 in the supporting body 16b. The actual longitudinal guidance of the thruster 5 which is fixed onto the nut 13 is done by guide rings 31 which are likewise fixed onto the nut 13 and run in the supporting body 16b. Planet rollers 35 which are guided in bearing-rings 36 supported to be able to turn in the nut 13, roll by their threads and under slight prestress along the thread on the spindle 14 and the internal thread on the nut 13. End-position damping 33 is formed by a soft seal. The second torus-shaped bag 34 which may be built in without any essential increase in the outside dimensions of the housing opens up a number of possibilities.

First, both torus-shaped bags 9a, 34 may be used as blood bags for the same bypass if each bag exhibits individual inlet and outlet leads with non-return valves. Both directions of stroke are utilized for transporting blood and uniform work of delivery is generated. The necessary equalizing volume for the gas enclosed in the housing is smaller. 8ecause of the use of the s~roke in both directions, the structural size may be reduced.

Second, one bag may be made as a blood bag and the other as a closed store of gas. Xn this way, the necessary equalizing volume for the gas enclosed in the housing remains smaller still, whilst the bag employed as the S store of gas forms a work-store which delivers work during the compression of the blood bag. As long as the compression chosen for the stored gas is not too high, lower peak power is demanded of the driving motor.

A further application of the two torus-shaped bags 9a, 34 consists in one bag forming a bypass for the lefthand chamber of the heart and the other bag forming a bypass for the righthand chamber, with individual non-return valves 2, 3.

Claims (7)

1. A pump for delivering blood comprising a housing having a plurality of sections secured to each other to define a sealed space, and a central section extending axially within said space with a plurality of longitudinal slots therein;

a torus-shaped deformable bag defining a chamber for receiving a supply of blood, said bag being disposed coaxially about said central section within said housing;

a first valve for emitting a flow of blood under pressure into said chamber;

a second valve for exhuasting a flow of blood under pressure from said chamber;

an annular thruster in said housing coaxial of said central section for engaging said bag;

an electric motor in said housing, said motor including a stator mounted on one of said housing sections and a rotor rotatably mounted on said one of said housing sections and defining a hollow shaft for rotating on an axis coaxial of said central housing section;

a threaded spindle secured at one end to said rotor and rotatably mounted at an opposite end in said central section for rotation on said axis;

a nut threaded onto said spindle and disposed within said central housing section; and a plurality of radial spokes secured to said thruster and passing through said slots of said central housing section to engage said nut whereby upon rotation of said spindle in one direction, said nut and said thruster are moved in said direction to compress said bag for exhausting blood from said chamber through said second valve.

2. A pump as set forth in claim 1 which further comprises a second torus-shaped bag concentric to said central housing section and disposed between said thruster and one of said housing sections on a side of said thruster opposite said first bag.

3. A pump as set forth in claim 2 wherein said second bag is filled with gas.

4. A pump as set forth in claim 2 which further comprises an inlet valve connected to said second bag to deliver blood thereto and an outlet valve connected to said second bag to exhaust blood therefrom.

5. A pump as set forth in claim 1 wherein said housing is disc-shape.

6. A pump for delivering blood comprising a housing having a plurality of sections secured to each other to define an enclosed space and a central section extending axially in said space with a plurality of longitudinal slots therein;

a deformable membrane secured between two of said housing sections to define a torus-shaped chamber for receiving a supply of blood, said chamber being disposed coaxially about said central section;

a first valve for emitting a flow of blood under pressure into said chamber;

a second valve for exhuasing a flow of blood under pressure from said chamber;

an annular thruster in said housing coaxial of said central section for engaging said bag;

an electric motor in said housing, said motor including a stator mounted on one of said pair of housing sections and a rotor rotatably mounted on said one of said housing sections and defining a hollow shaft for rotating on an axis coaxial of said central housing section;

a threaded spindle secured at one end to said rotor and rotatably mounted at an opposite end in said central section for rotation on said axis;

a nut threaded onto said spindle and disposed within said central housing section; and a plurality of radial spokes secured to said thruster and passing through said slots of said central housing section to engage said nut whereby upon rotation of said spindle in one direction, said nut and said thruster are moved in said direction to compress said chamber for exhausting blood therefrom through said second valve.

7. A pump as set forth in claim 6 wherein said housing is disc-shaped.