Artificial heart system implementing suction recognition and avoidance methods
A system and method of controlling the operation of a pump system includes modulating the speed of the pump and calculating a system condition parameter having a value related to the area of a hysteresis loop generated by a system operating parameter that varies in response to pump speed. The condition of the system is determined in response to the value of the system condition parameter.
1. A method of controlling the operation of a pump system, the method comprising:
modulating the speed of a pump;
monitoring a system operating parameter that varies in response to modulating the speed of the pump;
calculating hysteresis in the system operating parameter resulting from modulating the speed of the pump;
determining an expected value for the hysteresis;
determining a pump inlet suction condition of the pump system in response to the calculated hysteresis deviating from the expected value; and
reducing the speed of the pump in response to determining the pump inlet suction condition.
2. The method recited in claim 1 , wherein the system operating parameter comprises pump rotor axial position.
3. The method recited in claim 1 , wherein the system operating parameter comprises motor power of the pump.
4. The method recited in claim 1 , wherein the pump comprises a blood pump.
5. The method recited in claim 1 , wherein:
calculating hysteresis comprises performing an integral calculation on the system operating parameter; and
determining the expected value for the hysteresis comprises summing a total of the integral calculation over a moving time window.
6. The method recited in claim 5 , wherein modulating the pump speed comprises performing an integer number of modulations within the time window.
7. A method of controlling the operation of a pump system, the method comprising:
modulating the speed of a pump;
calculating a system condition parameter having a value related to a hysteresis loop generated by a system operating parameter that varies in response to pump speed;
determining a pump inlet suction condition of the pump system in response to the value of the system condition parameter, wherein the system operating parameter comprises pump rotor axial position, and wherein the system condition parameter is calculated according to:
I
S
P
=
∫
t
=
0
t
=
n
sec
L
(
t
)
dN
N
max
-
N
min
wherein L(t) is the pump rotor axial position, N max -N min is a modulated speed range, dN is the change in pump speed, and n sec is the time interval of the integral in seconds; and
reducing the speed of the pump in response to determining the pump inlet suction condition.
8. A method of controlling the operation of a pump system, the method comprising:
modulating the speed of a pump;
calculating a system condition parameter having a value related to a hysteresis loop generated by a system operating parameter that varies in response to pump speed;
determining a pump inlet suction condition of the pump system in response to the value of the system condition parameter, wherein the system operating parameter comprises motor power of the pump, and wherein the system condition parameter is calculated according to:
I
S
P
=
∫
t
=
0
t
=
n
sec
P
(
t
)
N
(
t
)
2
dN
N
max
-
N
min
wherein P(t) is the pump motor power, N(t) is the pump speed, N max -N min is a modulated speed range, dN is the change in pump speed, and n sec is the time interval of the integral in seconds; and
reducing the speed of the pump in response to determining the pump inlet suction condition.
9. A pump system comprising: a pump; and a pump controller configured to: modulate the speed of the pump; monitor a system operating parameter that varies in response to modulating the speed of the pump; calculate hysteresis in the system operating parameter resulting from modulating the speed of the pump; determine an expected value for the hysteresis; determine an undesired a pump inlet suction condition of the pump system in response to the calculated hysteresis deviating from the expected value; and reduce the speed of the pump in response to determining the pump inlet suction condition.
10. The system recited in claim 9 , wherein the system operating parameter comprises pump rotor axial position.
11. The system recited in claim 9 , wherein the system operating parameter comprises motor power of the pump.
12. The system recited in claim 9 , wherein to determine the condition of the system, the pump controller is adapted to:
repeat the calculation of the system condition parameter over several iterations; and
determine when the value of a current iteration of the calculated system condition parameter deviates from a limit value by a predetermined amount.
13. The system recited in claim 9 , wherein the pump comprises a blood pump.
14. The system recited in claim 9 , wherein the pump comprises an electrical motor coupled to a rotor that carries first and second impellers at opposite ends thereof.
15. The system recited in claim 14 , wherein the pump comprises an artificial heart, wherein the first impeller communicates with a patient's systemic vasculature and the second impeller communicates with the patient's pulmonary vasculature, the pump being operable to circulate blood from the first impeller through the systemic vasculature to the second impeller, and from the second impeller through the pulmonary vasculature back to the first impeller.
16. The system recited in claim 9 , wherein the controller is further configured to:
calculate the hysteresis by performing an integral calculation on the system operating parameter; and
determine the expected value for the hysteresis by summing a total of the integral calculation over a moving time window.
17. The system recited in claim 16 , wherein the controller is further configured to modulate the pump speed by performing an integer number of modulations within the time window.
18. A pump system comprising:
a pump; and
a pump controller adapted to calculate a system condition parameter having a value related to a hysteresis loop generated by a system operating parameter that varies in response to pump speed, and determine the condition of the pump system in response to the value of the system condition parameter, wherein the system operating parameter comprises pump rotor axial position, and wherein the system condition parameter is calculated according to:
I
S
P
=
∫
t
=
0
t
=
n
sec
L
(
t
)
dN
N
max
-
N
min
wherein L(t) is the pump rotor axial position, N max -N min is a modulated speed range, dN is the change in pump speed, and n sec is the time interval of the integral in seconds; and
wherein the pump controller is adapted to determine a pump inlet suction condition in response to the system condition parameter and to reduce the speed of the pump in response to determining the pump inlet suction condition.
19. A pump system comprising:
a pump; and
a pump controller adapted to calculate a system condition parameter having a value related to a hysteresis loop generated by a system operating parameter that varies in response to pump speed, and determine the condition of the pump system in response to the value of the system condition parameter, wherein the system operating parameter comprises motor power of the pump, and wherein the system condition parameter is calculated according to:
I
S
P
=
∫
t
=
0
t
=
n
sec
P
(
t
)
N
(
t
)
2
dN
N
max
-
N
min
wherein P(t) is the pump motor power, N(t) is the pump speed, N max -N min is a modulated speed range, dN is the change in pump speed, and n sec is the time interval of the integral in seconds; and
wherein the pump controller is adapted to determine a pump inlet suction condition in response to the system condition parameter and to reduce the speed of the pump in response to determining the pump inlet suction condition.