Blood pump

Details Blood pump Blood pump

2003-01-17

2004-06-22

Freay, Charles G. (Department: 3746)

Pumps

Motor driven

Pump within rotary working member

C417S423100, C417S423120, C604S151000, C415S102000, C415S111000, C415S170100, C415S900000

Reexamination Certificate

active

06752602

ABSTRACT:

The present invention relates to a blood pump, in particular a ventricular cardiac support pump, according to the preamble of claim
1
.
For the treatment of cardiac insufficiency, as well as conservative medication-based approaches, various surgical treatments have been developed from the replacement or reconstruction of heart valves via electrical stimulation of the cardiac muscle through to heart transplant. Because of the limited availability of the required donor hearts and the growing waiting lists however, the latter treatment option—which in critical cases however offers the greatest possible potential treatment success—can only benefit a low number of patients. Annually 20 to 30% of patients on the waiting list for heart transplants die before a suitable donor organ can be found.
The (temporary) support of insufficient circulation by ventricular assistance devices (VAD), such as suitable cardiac support pumps, dates back to the beginning of the 70s and is today an established concept successfully applied in many transplant centres. As well as devices to assist the left ventricle (LVAD), in particular also devices are available to assist both diseased ventricles of the heart (BVAD). Such systems are sometimes implanted totally intracorporeal so that the patient can continue to be treated as an out-patient and in particular while awaiting a transplant is no longer tied to the hospital as an in-patient.
In concrete terms ventricular assistance devices constitute an extracardial bypass as they pump blood from the left ventricle into the rising aorta. As a result the load on the left ventricle is reduced. If correspondingly the right ventricle is also insufficient, a pump bypassing this must be fitted accordingly. VAD are in principle placed so that the native heart remains in situ, in contrast to artificial hearts.
Recent scientific publications show that a damaged cardiac muscle on which however the load is relieved by VAD has the ability to regenerate; in some cases no transplant is required and the VAD can be removed.
Ventricular support systems of the known type are in principle divided into pumps with pulsatile flow and those with continuous flow. Pulsatile cardiac support pumps simulate the native heart in function and rhythm and in an action cycle produce both a filling and an expulsion phase for blood by means of a blood chamber which typically consists of an elastic plastic bag, where valves ensure a directed blood flow. Such systems have proved clinically successful and allow the support of patients for periods of up to around two years. Nonetheless pulsatile cardiac support systems have some disadvantages. These VAD are usually bulky and are difficult to implant without problems in the patient's body. The efficiency of pulsatile VAD is also very low due to the complex drive mechanism, and the drive and control system is complex and hence particularly susceptible to fault in long-term implantation. Above all however the long contact time of the blood during the filling phase leads to more thromboses which then carry a risk of central embolism with neurological failure or similar; this risk of thrombosis is supported by the turbulence occurring at the valves with increased shear stress in the blood flow.
Non-pulsatile VAD in contrast to the technology described above generate a continuous blood flow and require a relatively small blood chamber without elastic lining and cardiac valves. Accordingly the size of the support pump can be reduced considerably which makes it accessible to a larger patient group. There is also a considerably reduced risk of thrombosis due to the absence of an elastic membrane in the blood chamber and cardiac valves. As also the drive system of non-pulsatile VAD is simple and efficient, conventional brush-free DC motors are used with an energy consumption of less than 8 Watt, which is low.
The non-pulsatile circulation support however brings other difficulties. Due to the absence of cardiac valves (which allow directed blood flow) in the case of pump failure there is a risk of recirculating blood, which risk must be eliminated by additional measures. The output of a non-pulsatile VAD is also difficult to determine as there is no blood chamber with defined volume, so more precise information on the output can only be given by precise flow measurements (with an implanted flow meter for example).
Non-pulsatile blood pumps can be divided into centrifugal and axial pumps, where technologically the latter currently play no great role in practical clinical use, so only the centrifugal pumps are discussed below as the relevant state of the art (and as the genus for the present invention).
Commercial centrifugal pumps for cardiac support accelerate the blood perpendicular to the direction of the incoming blood flow and usually have a conical blood chamber in which is rotatably suspended a rotor (usually magnetically coupled). Traditionally the blood is supplied to the tip of the blood chamber through an inlet cannula, distributed evenly over the rotor and accelerated centrifugally, and blood leaves the blood chamber in the area of the greatest pressure and greatest speed through an outlet channel with an axis usually perpendicular to the rotor axis. The blood is usually accelerated by rotor blades provided on the rotor. However in such known centrifugal pumps with conical blood chamber, there is a relatively complex flow pattern of the transported blood with an inverse pressure ratio on the back of the rotor, with the risk that precisely in the area of the rotor shaft (the term “shaft” in the context of the present application is synonymous with “axis” and used accordingly), there is a risk of thrombosis formation at its mounting or on the rotor top. Thus a thrombus growing on the pump shaft would be able to grow in the peripheral direction and lead to a continuous increase in friction with a clearly increased energy consumption and the risk of pump arrest; in addition there is a risk of emerging thrombus or embolism formation in the patients system.
U.S. Pat. No. 5,924,848 discloses a generic blood pump with the features in the preamble of claim
1
, where here the blood chamber, in contrast to the state of the art described above, is formed as a double cone with two opposing inlets at the relevant tips of the double cone. This technologically has a rotor which can rotate without bearings in the blood chamber of the pump housing and is held in position by hydrodynamic forces. As the inventor explains, such a solution as well as ensuring increased efficiency in particular avoids the problem of mounting and again the resultant thrombosis formation etc.
However this known solution too does not appear optimum and in particular in practical clinical use, under changing conditions of use, is potentially problematic. Namely it can be assumed that any position changes of a patient (with an implanted pump) lead to pressure changes and hence flow changes at the inlets of the pump and to not inconsiderable mechanical stresses on the rotor; due to the (efficiency-related) short distances between the tips of the rotor blades and the pump housing (approximately 1 to 3 mm) the rotor can easily collide with the internal pump housing with the risk of damage, increased wear and failure.
The object of the present invention is therefore to improve a known blood pump, in particular for ventricular cardiac support, in that the practical operating properties are improved in relation to known pump solutions, in particular the suitability for various operating and patient conditions is increased and the risk of harmful thrombosis formation can be reduced. At the same time a new pump to be created is characterised by low wear, high reliability and low energy consumption.
This task is solved by the blood pump with the features of claim
1
; advantageous refinements of the invention are described in the sub-claims.
According to the invention it is provided that the rotor axis (rotor shaft) is rotatably mounted at the ends in mechanically active bearings, where in each

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