Pump preload index/indicator
A method of estimating an amount of work available to be performed by a blood pump implanted in a patient includes calculating a first coordinate value characterizing a volume of blood impelled in the pump and a second coordinate value characterizing a differential pressure across the pump for each of a plurality of flow rate data points of a given cardiac cycle of the patient, each flow rate data point indicative of a flow rate of blood through the pump. An area enclosed by the first and second coordinate values of the plurality of flow rate data points is determined, the determined area being indicative of an amount of work available to be performed by the blood pump.
1. A control circuit for estimating an amount of work available to be performed by a blood pump implanted in a patient, comprising:
a flow rate determination circuit configured to repeatedly determine flow rate data points, each flow rate data point indicative of a flow rate of blood through the pump;
a volume determination circuit configured to calculate, for each determined flow rate data point of a given cardiac cycle of the patient, a first coordinate value characterizing a volume of blood impelled by the pump;
a pressure head determination circuit configured to calculate, for each determined flow rate data point of the given cardiac cycle, a second coordinate value characterizing a pressure head exerted by the pump; and
a pump work determination circuit configured to calculate an area enclosed by the first and second coordinate values of the flow rate data points of the given cardiac cycle, the calculated area is indicative of an amount of work available to be performed by the blood pump.
2. The control circuit of claim 1 , further including:
a flow rate average tracking circuit configured to track a running average of the determined flow rate data points; and
a cardiac cycle determination circuit configured to determine a beginning flow rate data point and an end flow rate data point of the given cardiac cycle of the patient, each of the beginning and end flow rate data points corresponding to a crossing of the determined flow rate data points over the running average.
3. The control circuit of claim 2 , wherein the cardiac cycle determination circuit is configured to determine the beginning and end flow rate data points based on at least one from the group consisting of:
an identification of consecutive instances of the determined flow rate data points having a negative slope and crossing the running average;
an identification of consecutive instances of the determined flow rate data points having a positive slope and crossing the running average; and
an identification of three consecutive instances of the determined flow rate data points crossing of the running average, wherein a first of the three consecutive instances corresponds to the beginning flow rate data point and a third of the three consecutive instances corresponds to the end flow rate data point.
4. The control circuit of claim 1 , wherein, for each determined flow rate data point of a given cardiac cycle of the patient, the volume determination circuit is configured to calculate the first coordinate value using a derivative of the flow rate data point.
5. The control circuit of claim 1 , further comprising a speed determination circuit for determining a rotational speed of the blood pump, wherein, for each determined flow rate data point of the given cardiac cycle, the pressure head determination circuit is configured to calculate the second coordinate value using the flow rate data point and the determined rotational speed of the blood pump.
6. The control circuit of claim 5 , further comprising a memory configured to store a reference file containing a correlation between flow rate and pressure head of the pump for a given operational speed, wherein the pressure head determination circuit is operable to determine the second coordinate value using interpolation based on the reference file.
7. The control circuit of claim 1 , wherein the pump includes a housing having an axis, and a rotor disposed within the housing, the rotor being rotatable around the axis.