Flow estimation using hall-effect sensors
Methods and apparatus for estimating flow rate in a blood circulation assist system employing impeller eccentricity. A method includes magnetically rotating an impeller within a blood flow channel of a blood pump. The impeller is levitated within the blood flow channel transverse to the impeller axis of rotation. A rotational speed for the impeller is determined. At least one impeller transverse position parameter is determined. The at least one impeller transverse position parameter is based on at least one of (1) an amount of a bearing current that is used to levitate the impeller transverse to the impeller axis of rotation, and (2) a position of the impeller within the blood flow channel transverse to the impeller axis of rotation. A flow rate of blood pumped by the blood pump is estimated based on the impeller rotational speed and the at least one impeller transverse position parameter.
1. A blood circulation assist system, comprising:
a blood pump including an impeller disposed within a blood flow channel of the blood pump and a motor stator operable to magnetically rotate the impeller, the impeller having an impeller axis of rotation around which the impeller is rotated, the motor stator being further operable to magnetically levitate the impeller within the blood flow channel transverse to the impeller axis of rotation; and
a controller operatively coupled with the blood pump, the controller being configured to:
determine at least one impeller transverse position parameter that is based on at least one of (1) an amount of a bearing current that is used to levitate the impeller transverse to the impeller axis of rotation, and (2) a position of the impeller within the blood flow channel transverse to the impeller axis of rotation; and
estimate a pressure differential across the impeller based on the at least one impeller transverse position parameter.
2. The blood circulation assist system of claim 1 , wherein the controller is configured to:
determine a rotational speed of the impeller;
determine an amount of a drive current used to rotate the impeller;
estimate the pressure differential across the impeller based on the rotational speed of the impeller and the drive current when the amount of the drive current is below a first drive current threshold; and
estimate the pressure differential across the impeller based on the rotational speed of the impeller and the at least one impeller transverse position parameter when the amount of the drive current is above the first drive current threshold.
3. The blood circulation assist system of claim 2 , wherein the controller is configured to estimate the pressure differential across the impeller based on the rotational speed of the impeller, the drive current, and the at least one impeller transverse position parameter when the amount of the drive current is between a second drive current threshold and a third drive current threshold.
4. The blood circulation assist system of claim 2 , wherein the first drive current threshold varies based on the rotational speed of the impeller.
5. The blood circulation assist system of claim 2 , wherein the first drive current threshold is based on characteristics of variation in the amount of bearing current used to levitate the impeller transverse to the impeller axis of rotation in response to variation in the impeller rotational speed.
6. The blood circulation assist system of claim 5 , wherein the first drive current threshold is selected such that the amount of bearing current used to levitate the impeller transverse to the impeller axis increases in response to a decrease in the impeller rotational speed for drive currents above the first drive current threshold.
7. The blood circulation assist system of claim 1 , wherein the at least one impeller transverse position parameter is indicative of the position of the impeller within the blood flow channel transverse to the impeller axis of rotation.
8. The blood circulation assist system of claim 7 , further comprising at least one hall sensor generating output indicative of the position of the impeller within the blood flow channel transverse to the impeller axis of rotation.
9. The blood circulation system of claim 8 , wherein the controller is further configured to at least one of:
control operation of the blood pump to produce a desired pressure differential across the impeller; and
detect the occurrence of an abnormal condition of the blood pump based on the estimated pressure differential across the impeller.
10. The blood circulation assist system of claim 7 , wherein the controller is configured to control the position of the impeller within the blood flow channel transverse to the impeller axis of rotation so as to substantially minimize power consumption of the blood pump.
11. A method of estimating a pressure differential across an impeller of a blood pump, the method comprising:
magnetically rotating the impeller around an impeller axis of rotation within a blood flow channel of the blood pump;
magnetically levitating the impeller within the blood flow channel transverse to the impeller axis of rotation;
determining at least one impeller transverse position parameter that is based on at least one of (1) an amount of a bearing current that is used to levitate the impeller transverse to the impeller axis of rotation, and (2) a position of the impeller within the blood flow channel transverse to the impeller axis of rotation; and
estimating the pressure differential across the impeller based on the at least one impeller transverse position parameter.
12. The method of claim 11 , further comprising determining a rotational speed of the impeller, and wherein the pressure differential across the impeller is estimated further based on the rotational speed of the impeller.
13. The method of claim 11 , further comprising:
determining a rotational speed of the impeller;
determining an amount of a drive current used to rotate the impeller;
estimating the pressure differential across the impeller based on the rotational speed of the impeller and the amount of the drive current when the amount of the drive current is below a first drive current threshold; and
estimating the pressure differential across the impeller based on the rotational speed of the impeller and the at least one impeller transverse position parameter when the amount of the drive current is above the first drive current threshold.
14. The method of claim 13 , further comprising estimating the pressure differential across the impeller based on the rotational speed of the impeller, the drive current, and the at least one impeller transverse position parameter when the amount of the drive current is between a second drive current threshold and a third drive current threshold.
15. The method of claim 13 , wherein the first drive current threshold is based on characteristics of variation in the amount of bearing current used to levitate the impeller transverse to the impeller axis of rotation in response to variation in the rotational speed of the impeller.
16. The method of claim 13 , wherein the first drive current threshold is selected such that the amount of the bearing current used to levitate the impeller transverse to the impeller axis increases in response to a decrease in the impeller rotational speed when the amount of the drive current is above the first drive current threshold.
17. The method of claim 11 , further comprising controlling the position of the impeller within the blood flow channel transverse to the impeller axis of rotation so as to substantially minimize power consumption of the blood pump.
18. The method of claim 11 , further comprising controlling operation of the blood pump to produce a desired pressure differential across the impeller.
19. The method of claim 18 , further comprising detecting an adverse condition of the blood pump based on the estimated pressure differential across the impeller.