Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
2001-12-31
2004-06-01
Yu, Justine R. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S423700, C604S067000
Reexamination Certificate
active
06742999
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for delivering single-phase or multiphase fluids without altering the properties thereof.
Especially less stable multiphase fluids, for example emulsions and dispersions, which can experience irreversible changes by an energy insertion, can disadvantageously get during the delivery in corresponding devices, like pumps, into instable areas.
A very sensitive fluid system is blood. This opaque red body liquid of vertebrate animals circulates in a closed vascular system, wherein the rhythmical contraction of the heart presses the blood into the different areas of the organism. In this case the blood transports the respiratory gases, which are oxygen and carbon dioxide, as well as nutrients, metabolic products and body own substances. In this case, the blood vascular system including the heart is hermetically sealed from the environment, so that the blood experiences no changes in the healthy organism, when it is pumped via the heart through the body.
It is known, that the blood tends, when contacting with materials foreign to the body or through foreign energy affect, to a haemolysis and a thrombi formation. The formation of thrombi can be deadly for the organism, as they lead to a clogging up in the far branched vascular system. Haemolysis describes the condition, that the red blood cells are lysed destroyed further than the physiological degree. The causes for the haemolysis could be mechanical or metabolical. Increased haemolysis causes multiple organ damage and can lead to the death of the human being.
On the other hand it has been shown, that it is principally possible to support the pump capacity of the heart under specific constructive conditions or even to replace the natural heart by an artificial heart, but a constant operation of implanted heart support pumps or artificial hearts is at the moment only limitedly possible, as the interaction of these artificial products with the blood still lead to disadvantageous changes of the blood.
In the known State of the Art different development directions of blood pumps are distinguishable. Heart support pumps and artificial hearts can be designed starting from the required pressure difference and the volume flow, as well as the displacement principal as a so-called pulsating pump or according to the turbo principle as a radial or axial flow device. At the moment these three named designs are developed in parallel. The flow devices show because of the high capacity density of this type of devices smaller dimensions than piston devices. Within the group of pumps, which function according to the turbo principal, the axial pump variant is as a rule smaller than the radial variant. A turbo device can be designed generally for the given pressure difference and the given volume flow very differently, for example as an axial or a radial pump with greatly different rotational speeds.
The axial blood pumps known from the State of the Art, comprise generally an outer cylindrical pipe, in which a delivery element rotates, which is formed as a rotor of a motor stator arranged outside and which, therefore, transports the blood in an axial direction. The support of the delivery element is a problem. A purely mechanical support is disadvantageous because of the damage of the blood and even because of the relatively high friction values. Also the up-to-now described magnet bearing types have not lead to a satisfactory solution.
From Kawahito et al.: In Phase 1 Ex Vivo Studies of the Baylor/NASA Axial Flow Ventricular Assist Device, in: Heart Replacement Artificial Heart 5, pages 245-252, Springer Verlag Tokyo 1996, Publisher T. Akutso and H. Koyagani, an axial blood pump according to the state of the art for the support of an ill heart is known, which can be implanted into the chest area of a patient. The axial blood pump has a rotating impeller with a blading, which is supported within a blood carrying pipe and is driven by means of an electric motor.
For this the impeller is formed as a rotor of the electric motor and is coupled by means of magnets mounted on the blading with the stator of the electric motor fast with the housing. An axial and a radial support of the rotor takes place via a toe bearing , in which the rotor is supported point-by-point on bearing elements arranged in the flow. Such an arrangement is also known from U.S. Pat. No. 4,957,504.
The known blood pump has the disadvantage, that the to be delivered blood experiences in a considerable extent a traumatisation and damage. In this case the danger lies generally in the formation of thrombi. The reason for this lies essentially in the formation of wake areas of the bearings.
A further disadvantage is undoubtedly the limited endurance of the mechanical bearing because of wear.
U.S. Pat. No. 4,779,614 discloses an implantable axial blood pump, which consists of an outer cylindrical pipe and a rotor hub rotating in this pipe for the blood delivery. The rotor is magnetically supported and carries at the same time the rotor magnets of the drive and the impeller blades. The magnetically supported rotor forms with the stator blading mounted on the outer pipe long, narrow gaps. The arrangement of two motor-stator-combinations respectively on the ends of the pump shall stabilize the positioning of the rotor. The positioning in the direction of the axis is stabilized by another pair of magnets, which shall take up the axial forces of the rotor as well. Although a relatively wide annular gap for the fluid flow is provided and with the magnetic bearing of the rotor important development goals for the implantable blood pump concerning a compact design and free from sealing and support problems can be aimed at, the blood pump has great disadvantages concerning the function and the structural design of the pump. The exceptionally long narrow gaps between the rotor hub and the stator blades on the stator increase the danger of a blood damage by high velocity gradient of the gap flows. The arrangement of two motors required for the rotor stabilization is designwise cumbersome. Furthermore, the rotor is not form-fittingly secured in the axial direction and is therefore a residual risk.
The U.S. Pat. No. 5,385,581 also discloses an axial blood pump with magnet bearing. The bearing magnets arranged in the rotor and in the stator area are charged with an opposing polarity.
Disadvantageously this leads to the breakdown of the pump, when the bearing fails. Furthermore, it is disadvantageous that no so-called post guide lattice is provided, i.e. the total pressure is produced by the impeller, and the residual spin energy remains in the flow.
A further axial blood pump with magnetic bearing is known from WO97/49 440. The magnetic bearing is carried out at the conically formed rotor ends of the rotor, which forms the impeller. The fixedly arranged pole shoes are arranged opposite to the rotor ends, which pole shoes guide the flow of the permanent magnets. The bearing necessitates an active stabilization with at least four stabilization coils in axial as well as in radial direction. In a further variant the bearings with radially magnetized permanent magnet rings with changing magnetization direction are proposed, which are indeed difficult to control.
From WO 98/11 650 a further axial blood pump with a so-called bearingless motor is known. The “bearingless” motor is a combination of a motor and a magnetic bearing. The position of the rotor is stabilized passively by permanent magnets with reference to three degrees of freedom translation in the x-direction, tipping in the x- and y-direction. The passive stabilization is achieved by a permanent magnetic rotor ring, which is surrounded on the stator side by a soft iron ring. Control and driving coils, which are connected to the soft iron ring, allow a drive with reference to three degrees of freedom. The low bearing stiffness requires additional measures. Furthermore, a bearing stabilization is necessary in the x- and y-direction, which leads to a great extent of measuring technology to be ap
Müller Johannes
Nüsser Peter
Peters Hans-Erhard
Berlin Heart AG
Liu Han L
Norris McLaughlin & Marcus PA
Yu Justine R.
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