Alternating pump gaps
A mechanical circulatory support system includes a ventricular assist device, a percutaneous cable, an external control unit, and an external power source. The ventricular assist device includes a housing, an impeller, levitation magnets, a stator assembly, and control electronics. The impeller includes a first annular disk, a second annular disk, centrifugal impeller blades, first magnet segments, and second magnet segments. The stator assembly includes stator coils operable to rotate the impeller and apply a first positioning force to the impeller. The levitation magnets apply a second positioning force to the impeller. The control electronics are configured to control currents supplied to the stator coils to control rotation of the impeller and to control the first positioning force applied to the impeller to control an axial position of the impeller within the housing.
1 . A mechanical circulatory support system comprising:
a ventricular assist device comprising a housing, an impeller, levitation magnets, a stator assembly, and control electronics, wherein the housing defines an inlet, a pump chamber, and an outlet, wherein the impeller is disposed and configured for magnetic suspension within the pump chamber, wherein the impeller comprises a first annular disk, a second annular disk, centrifugal impeller blades, first magnet segments, and second magnet segments, wherein the centrifugal impeller blades are disposed between the first annular disk and the second annular disk, wherein the first magnet segments are embedded in the first annular disk, wherein the second magnet segments are embedded in the second annular disk, wherein the stator assembly is disposed adjacent to the pump chamber so that the first annular disk is disposed between the stator assembly and the centrifugal impeller blades, wherein the stator assembly comprises stator coils operable to generate a stator magnetic field that interacts with the first magnet segments to rotate the impeller within the pump chamber and apply a first positioning force to the impeller, wherein the levitation magnets are disposed adjacent to the pump chamber so that the second annular disk is disposed between the levitation magnets and the centrifugal impeller blades so that the levitation magnets apply a second positioning force to the impeller, and wherein the control electronics are disposed within the housing and configured to control currents supplied to the stator coils to generate the stator magnetic field to control rotation of the impeller within the pump chamber and to control a magnitude of the first positioning force applied to the impeller to control an axial position of the impeller in the pump chamber;
a percutaneous cable connected to the ventricular assist device;
an external control unit connected to the ventricular assist device via the percutaneous cable; and
an external power source connected to the external control unit.
2 . The mechanical circulatory support system of claim 1 , wherein:
the ventricular assist device comprises impeller positions sensors configured to generate impeller position sensor output indicative of axial positions of the impeller in the pump chamber; and
the control electronics are configured to control phase voltages applied to the stator coils further based on the impeller position sensor output to control the axial position of the impeller in the pump chamber.
3 . The mechanical circulatory support system of claim 2 , wherein impeller position sensors are disposed adjacent to the pump chamber so that the first magnet segments are disposed between the impeller position sensors and the centrifugal impeller blades.
4 . The mechanical circulatory support system of claim 1 , wherein the second annular disk is parallel to the first annular disk.
5 . The mechanical circulatory support system of claim 1 , wherein:
the impeller has an impeller axis of rotation; and
the inlet is axially aligned with the impeller axis of rotation when the impeller is centered within the pump chamber.
6 . The mechanical circulatory support system of claim 1 , wherein:
the first annular disk defines a first annular disk central aperture; and
the housing comprises a protruding hub that extends into the first annular disk central aperture.
7 . The mechanical circulatory support system of claim 1 , wherein the external control unit comprises an internal battery.
8 . The mechanical circulatory support system of claim 1 , wherein the external power source comprises an external battery.
9 . The mechanical circulatory support system of claim 1 , wherein:
the housing defines a volute region through which blood flow output from the impeller is conveyed to the outlet;
a first member of the housing defines the inlet and partially defines each of the pump chamber, the volute region, and the outlet; and
a second member of the housing partially defines each of the pump chamber, the volute region, and the outlet.
10 . The mechanical circulatory support system of claim 9 , wherein the housing includes a flow-dividing guide wall disposed within the volute region.
11 . The mechanical circulatory support system of claim 1 , wherein the stator assembly is a three-phase stator assembly.
12 . The mechanical circulatory support system of claim 1 , wherein the stator assembly is disposed between the control electronics and the pump chamber.
13 . The mechanical circulatory support system of claim 1 , wherein:
the levitation magnets produce a stationary magnetic field that attracts the second magnet segments towards the levitation magnets; and
the stator assembly is configured for generating a rotating magnetic field that attracts the first magnetic segments towards the stator assembly.
14 . A mechanical circulatory support system comprising:
a ventricular assist device comprising a housing, an impeller, levitation magnets, a stator assembly, and control electronics, wherein the housing defines an inlet, a pump chamber, and an outlet, wherein the impeller is disposed and configured for magnetic suspension within the pump chamber, wherein the impeller comprises a first annular disk, a second annular disk, centrifugal impeller blades, first magnet segments, and second magnet segments, wherein the centrifugal impeller blades are disposed between the first annular disk and the second annular disk, wherein the first magnet segments are embedded in the first annular disk, wherein the second magnet segments are embedded in the second annular disk, wherein the stator assembly is disposed adjacent to the pump chamber so that the first annular disk is disposed between the stator assembly and the centrifugal impeller blades, wherein the stator assembly comprises stator coils operable to generate a stator magnetic field that interacts with the first magnet segments to rotate the impeller within the pump chamber and apply a first positioning force to the impeller, wherein the levitation magnets are disposed adjacent to the pump chamber so that the second annular disk is disposed between the levitation magnets and the centrifugal impeller blades so that the levitation magnets apply a second positioning force to the impeller, and wherein the control electronics comprise motor drive power electronics operable to control phase voltages applied to the stator coils to generate the stator magnetic field to control rotation of the impeller within the pump chamber and to control a magnitude of the first positioning force applied to the impeller;
a percutaneous cable connected to the ventricular assist device;
an external control unit connected to the ventricular assist device via the percutaneous cable; and
an external power source connected to the external control unit.
15 . The mechanical circulatory support system of claim 14 , wherein the control electronics employ a motor control algorithm to control the phase voltages applied to the stator coils.
16 . The mechanical circulatory support system of claim 14 , wherein the control electronics are configured to:
determine a target quadrature current based on a target rotational rate for the impeller;
determine a target direct current based on a target axial position for the impeller; and
control the motor drive power electronics based on the target quadrature current and the target direct current.
17 . The mechanical circulatory support system of claim 16 , wherein:
the ventricular assist device comprises impeller positions sensors configured to generate impeller position sensor output indicative of axial positions of the impeller in the pump chamber; and
the control electronics are configured to determine the target direct current further based on the impeller position sensor output.
18 . The mechanical circulatory support system of claim 17 , wherein the control electronics comprise a current sensing circuit configured to determine measured phase currents in the stator coils, and wherein the control electronics are further configured to:
estimate current rotational speed and current angle of the impeller based on the measured phase currents;
transform the measured phase currents into a two-axis rotating coordinate system to determine a measured quadrature phase current and a measured direct phase current;
determine the target quadrature current based on the measured quadrature phase current and the target rotational rate for the impeller;
determine an axial position deviation of the impeller based on the impeller position sensor output;
determine the target direct current based on the measured direct phase current and the axial position deviation of the impeller;
transform the target quadrature current and the target direct current back to determine target phase currents for the stator coils in a reference stationary reference frame; and
control the motor drive power electronics based on the target phase currents to apply phase voltages to the stator coils.
19 . The mechanical circulatory support system of claim 16 , wherein the target rotational rate for the impeller is based on one or more monitored patient physiological parameters.
20 . The mechanical circulatory support system of claim 14 , wherein the control electronics are configured to control the motor drive power electronics to implement a start-up sequence in which the stator coils are controlled to magnetically levitate the impeller prior to rotating the impeller.