APPARATUS AND METHOD FOR OCCLUSION DETECTION USING PUMP OPERATION MEASUREMENT AND PUMP MOTOR CURRENT
A technical solution for monitoring operation of a medical delivery device such as a wearable patch pump for occlusion is provided that employs sensing pump motor current during at least one of a dispense stroke and an aspirate in a pump cycle. The solution can be implemented alone or in combination with other occlusion sensing methods that use one or more of pump measurement data such as pump stroke duration (e.g., duration of aspirate stroke or dispense stroke in a rotational metering-type pump or a reciprocating-type pump), end-stop or limit switch activation, and duration difference between aspirate and dispense strokes to detect occlusion. Accuracy of occlusion detection based on measured data in a fluid delivery device is improved by using dead band normalization of loaded measured data to unloaded measured data.
1 . A wearable infusion patch pump comprising:
a pump comprising a chamber configured with at least one port to receive fluid into the chamber from a reservoir and to pass the fluid out of the chamber, and a pumping mechanism comprising a gearbox assembly operated by a motor to extend a piston in the chamber to control dispensing of a volume of the fluid from the chamber during a dispense stroke;
a current sensing device configured to detect motor current corresponding to current drawn by the motor during each said dispense stroke performed by the pumping mechanism among a plurality of dispense strokes; and
a processor, and for each of the plurality of dispense strokes n=1, . . . , x performed by the pumping mechanism, the processor is operated in accordance with programmed instructions to:
a) determine values from the motor current corresponding to said dispense stroke n chosen from a dead band value (iDeadband n ) and a maximum piston current value (iPistonMax n ), the dead band value (iDeadband n ) corresponding to a current drawn by the motor when the pumping mechanism is moving but without causing fluid to flow with respect to the chamber such that an increase in the motor current over the dead band value (iDeadband n ) corresponds to a torque acting on the motor when the piston in the pumping mechanism moves against the fluid in the chamber during said dispense stroke, and the maximum piston current value (iPistonMax n ) corresponding to a maximum amount of current drawn by the motor during a portion of said dispense stroke wherein the piston moves against the fluid in the chamber to dispense the fluid from the at least one port;
b) determine a stroke current value (iStroke n ) for said dispense stroke by subtracting the dead band value (iDeadband n ) from the maximum piston current value (iPistonMax n ) corresponding to the said dispense stroke n ;
c) determine a difference (Delta_iStroke) between the stroke current value (iStroke n ) and a previous stroke current value (iStroke n-1 ) determined for a previous one of the plurality of dispense stokes,
d) increment a counter when at least one occlusion condition is detected, the at least one occlusion condition comprising the difference (Delta_iStroke) exceeding a rapid rise threshold (iRapidRise) having a designated value corresponding to an increase in the motor current that indicates an unwanted occlusion occurring in the pump; and
e) terminating dispensing of the fluid from the chamber when the counter reaches a value T≥2.
2 . The wearable infusion patch pump of claim 1 , wherein the current sensing device comprises a resistor connected in series with the motor, and the processor being configured to calculate the motor current using a voltage measured across the resistor.
3 . The wearable infusion patch pump of claim 1 , wherein said dispense stroke is characterized by a stroke duration comprising a first time period corresponding to a dead band period during which the pumping mechanism is moving but without causing fluid to flow with respect to the chamber, and a second time period that follows the first time period and during which the pumping mechanism can cause the fluid to flow from the chamber.
4 . The wearable infusion patch pump of claim 3 , wherein the processor determines the dead band value (iDeadband n ) from calculating the motor current using a voltage measured across the resistor during the first time period.
5 . The wearable infusion patch pump of claim 3 , wherein the processor determines the maximum piston current value (iPistonMax n ) from calculating the motor current using a voltage measured across the resistor during the second time period.
6 . The wearable infusion patch pump of claim 5 , wherein the processor determines the maximum piston current value (iPistonMax n ) from calculating a maximum value of the motor current during a beginning portion of the second time period.
7 . The wearable infusion patch pump of claim 1 , wherein the pumping mechanism is configured to operate for at least a designated total number (X) of dispense strokes n=1, . . . , x to deliver the fluid from the chamber, and the stroke current value (iStroke n ) is determined using a first calculation during a designated initial number (n=1, . . . , Y) of the dispense strokes, and is determined using a second calculation different from the first calculation during a remaining number (n=Y+1, . . . , X) of the dispense strokes.
8 . The wearable infusion patch pump of claim 7 , wherein the first calculation corresponds to the processor subtracting the dead band value (iDeadband n ) from the maximum piston current value (iPistonMax n ) corresponding to said dispense stroke n=1, . . . , Y .
9 . The wearable infusion patch pump of claim 7 , wherein the second calculation comprises the processor determining a mean value of the dead band value (iDeadband n ) for each of the designated initial number (n=1, . . . , Y) of the dispense strokes, and using the first calculation when the dead band value for the dispense stroke is greater than or equal to the mean value and using the second calculation when the dead band value for the dispense stroke is less than the mean value, the second calculation corresponding to subtracting the mean value from the maximum piston current value corresponding to the said dispense stroke n=Y+1, . . . , X .
10 . The wearable infusion patch pump of claim 1 , wherein the processor is further configured to operate in accordance with programmed instructions to determine a current baseline value (iBaseline), and to use the current baseline value (iBaseline) instead of the stroke current value (iStroke n ) for the said dispense stroke to determine the difference (Delta_iStroke) when the stroke current value (iStroke n ) is less than the baseline value (iBaseline).
11 . The wearable infusion patch pump of claim 10 , wherein the processor is further configured to operate in accordance with programmed instructions to determine the baseline value (iBaseline) during an initial operation related to the pump chosen from manufacturing of the patch pump, assembling the patch pump, initializing the patch pump, and a priming operation by the pump.
12 . The wearable infusion patch pump of claim 11 , wherein the processor is further configured to operate in accordance with programmed instructions to calculate the baseline value (iBaseline) using a mean value of motor current corresponding to a predetermined number of said dispense stroke previously occurring during the initial operation and precluding the motor current from the mean value when the motor current differs from the mean value by a designated amount.
13 . The wearable infusion patch pump of claim 10 , wherein the processor is further configured to operate in accordance with programmed instructions to:
determine an acceptable backpressure threshold value (iDelta_Threshold) that corresponds to the motor current occurring while the piston is operating against patient-related backpressure that occurs when the pump is delivering the fluid into a patient and is less than an unwanted occlusion being detected by the processor, wherein the at least one occlusion condition further comprises the stroke current value (iStroke n ) exceeding an occlusion threshold value (iThreshold) corresponding to a sum of the current baseline value (iBaseline) and the acceptable backpressure threshold value (iDelta_Threshold).
14 . The wearable infusion patch pump of claim 1 , wherein the rapid rise threshold (iRapidRise) is determined experimentally during operation of the pump to be a value of the motor current at which an unwanted occlusion is not occurring in the pump.