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Rotary Blood Pump

Introduction

Patients whose heart is failing may benefit from left ventricular assist (a mechanical device which takes over or augments the pumping function of the left ventricle of the heart) in one of three modes:

  • bridge to recovery – a left ventricular assist device (VAD) is used for a short duration (up to 90 days) whilst the heart is treated, e.g. for bacterial endocarditis, or whilst natural de-modelling returns the heart to near-original size and contractility
  • bridge to transplant – a VAD is used to keep the patient alive and to improve end-organ condition whilst a donor heart is found
  • destination therapy – where a patient cannot receive a heart transplant due to ineligibility or underlying medical complications (e.g. not able to tolerate immuno-suppressant therapy) a VAD is used long-term instead of a transplant.

The most versatile type of VAD is the implantable rotary blood pump – a small axial or centrifugal pump which is implanted into the chest or abdomen and which draws blood from the apex of the left ventricle, energises it and returns the blood to the ascending aorta.  Worldwide, implantable rotary blood pumps constitute the third generation of VAD and are available clinically; however these devices are prohibitively expensive.

This research is developing a low-cost implantable rotary blood pump with a unique hydrodynamic/magnetic bearing system which will be used in bridge to transplant or recovery.  Recipients of this device will be able to leave hospital and lead a relatively normal life – albeit in constant companionship with a bag containing a controller and batteries.


In More Detail...

The design is based on a low specific speed centrifugal pump which incorporates a semi-open impeller with magnets in the lower shroud.  These magnets are used as part of the magnetic bearing system as well as in the drive system – they cause the rotor to spin under the action of a rotating magnetic field set up by coils in the pump housing.  In addition, a hydrodynamic bearing is incorporated in to the lower surface of the shroud.  This configuration allows the rotor to ‘float’ in the blood and not need mechanical bearings or seals which generate heat and cause haemolysis (the destruction of red blood cells).

Rotary Blood Pump

Some advantages this design has over already commercial rotary blood pumps are:

  • the semi-open rotor configuration allows better fluid dynamics on the rotor and thus improved efficiency – this means the patient will carry lighter batteries as he goes about daily life
  • the design requires much reduced manufacturing tolerances thus enabling it to be injection moulded and to use off-the-shelf components which will drastically reduce its cost and make it available to all health care providers.

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