Fluid flow resistance monitoring system

• US 6,416,291 B1
• Filed: 06/23/2000
• Issued: 07/09/2002
• Est. Priority Date: 07/30/1996
• Status: Expired due to Term

• Current Assignee: Carefusion 303 Incorporated (Becton, Dickinson & Co)
• Original Assignee: ALARIS Medical Systems, Inc. (Becton, Dickinson & Co)
• Inventors: Butterfield, Robert D., Farquhar, Allen B.
• Primary Examiner(s): Freay, Charles G.
• Assistant Examiner(s): GRAY, MICHAEL KUHN
• Application Number:
  US09/602,831
• Time in Patent Office: 746 Days
• Field of Search: 417/9, 417/20, 417/22, 417/29, 417/31, 417/38, 417/43, 417/44.2, 417/477.1, 417/477.3, 417/477.6, 417/477.13, 604/9, 604/50
• US Class Current: 417/44.2
• CPC Class Codes: A61M 5/16859 Evaluation of pressure response, e.g. to an applied pulse

Abstract

Flow parameters in a fluid delivery assembly are determined by monitoring pressure responses and processing those responses along with information regarding the fluid flow. In one aspect, a processor controls the pump to pump flow quantities in accordance with a pseudorandom code. Portions of the resulting pressure signal sensed at the conduit is averaged, and the averaged values are then decoded in accordance with the pseudorandom code. An estimate of the equilibrium pressure is generated from the decoded average pressure values, while a summation of the pressure samples is generated from the undecoded pressure signals. The resistance to fluid flow of the system is determined from the estimated equilibrium pressure and pressure summation. For low flow rates, a processor controls the pump to pump fluid in a series of fluid boluses, with each fluid bolus delivered in the beginning of a separate timeslot. The equilibrium pressure is measured at the end of each timeslot, and a summation of the pressure samples is generated from the pressure signals. For high flow rates, the pump is controlled to vary the flow rate and the change in pressure is divided by the change in flow to directly determine the resistance. A resistance display continuously displays the resistance of the system. The pseudorandom coding and decoding can be used to filter out pressure-response crosstalk caused by multiple fluid infusion segments feeding into a common line.

Claims

1. A method for monitoring a flow parameter in a fluid delivery system in which a flow control device acts on a fluid conduit to control the flow of fluid through the conduit, the method comprising the steps of:

outputting a pseudorandom code;

controlling the flow control device to act on the fluid conduit to cause a pattern of flow variation in the conduit in accordance with the pseudorandom code;

monitoring pressure of the fluid in the conduit and generating pressure signals representing said monitored pressure;

determining average pressure values for at least some of the pressure signals;

decoding the average pressure values in accordance with the pseudorandom code; and

processing the decoded average pressure values to determine the flow parameter.

2. The method of claim 1, wherein the step of determining a flow parameter includes determining flow resistance.

3. The method of claim 1, comprising the further step of:

processing the decoded averaged pressure values to determine an estimated equilibrium pressure.

4. The method of claim 1, wherein the step of outputting a pseudorandom code comprises outputting a PRBS code.

5. The method of claim 4, wherein the flow control device comprises an infusion pump having a plurality of movement steps per cycle, each step causing a step volume of fluid to flow through the conduit, and the method comprises the further step of:

controlling the infusion pump to group the movement steps into a plurality of supersteps, each superstep causing a superstep volume of fluid to flow through the conduit, with each superstep volume being approximately equal to the other superstep volumes.

6. The method of claim 5, comprising the further step of:

assigning a timeslot having a timeslot length to each element of the PRBS code;

wherein the step of controlling the infusion pump includes controlling the infusion pump to induce at least one superstep volume of fluid to flow in the conduit during each timeslot that has a corresponding PRBS element of 1, and controlling the infusion pump to induce no volume of fluid to flow during each timeslot that has a corresponding PRBS element of 0.

7. The method of claim 6, wherein the step of controlling the infusion pump includes controlling the infusion pump to induce the superstep volume of fluid to flow as a single bolus of fluid delivered at the beginning of the timeslot using an acceleration/deceleration flow waveform.

8. The method of claim 6, wherein the step of controlling the infusion pump includes controlling the infusion pump to induce two or more superstep volumes of fluid to flow in each timeslot as a series of two or more adjacent fluid boluses delivered at the beginning of the timeslot, with each of said adjacent fluid boluses delivered in accordance with an acceleration/deceleration waveform.

9. The method of claim 6, comprising the further steps of:

selecting a flow rate; and

determining the timeslot length and associated superstep volume in accordance with the selected flow rate to produce the selected flow rate.

10. A system for infusing fluid to a patient through a conduit, the system comprising:

an infusion pump acting on the conduit and having a plurality of movement steps per cycle, each step causing a step volume of fluid to flow through the conduit; and

a pressure sensor coupled to the conduit for providing pressure signals in response to pressure sensed in the conduit;

a processor configured to output a PRBS code having a codelength and a plurality of elements, assign a timeslot to each element of the PRBS code, control the flow control device to act on the conduit to cause flow in the conduit in a pattern of flow variation in accordance with the PRBS code, receive the pressure signals, determine average pressure values for at least some of the pressure signals, decode the average pressure values in accordance with the PRBS code, and process the decoded average pressure values to determine a flow parameter.

11. The system of claim 10, wherein the processor is configured to control the infusion pump to group the pump movement steps into a plurality of supersteps, each superstep causing a superstep volume of fluid to flow through the conduit, with each superstep volume being approximately equal to the other superstep volumes.

12. The system of claim 11, wherein one or more of the timeslots are active timeslots, and the processor is configured to control the infusion pump to induce at least one superstep volume of fluid to flow in the conduit at the beginning of each active timeslot.

13. The system of claim 12, wherein the processor is configured to determine average pressure values for at least some of the pressure signals from the tail portion in each active timeslot.

14. A system for infusing fluid to a patient through a conduit, the system comprising:

a first infusion device acting on a first segment of the conduit;

a pressure sensor coupled to the conduit and providing pressure signals in response to fluid pressure sensed in the conduit;

a processor configured to output a first pseudorandom code having a codelength, control the first infusion device to act on the first segment of the conduit to cause fluid flow in accordance with the first pseudorandom code, receive the pressure signals, determine average pressure values for at least some of the pressure signals, decode the average pressure signals in accordance with the first pseudorandom code to create first decoded average pressure values, and process the first decoded average pressure values to determine a first flow parameter; and

a second infusion device acting on a second segment of the conduit.

15. The system of claim 14, wherein the first segment and second segment are separate branches of the conduit that are joined at a point downstream of both the first and second infusion devices.

16. The system of claim 14, wherein the processor is configured to output a second pseudorandom code having a codelength, and control the second infusion device to act on the conduit to cause flow in accordance with the second pseudorandom code.

17. The system of claim 16, wherein processor is configured to select a second pseudorandom code that is different from the first pseudorandom code.

18. The system of claim 17, wherein the processor is configured to select first and second pseudorandom codes that enhance the ability of the processor to filter out crosstalk from the second infusion device.

19. The system of claim 16, wherein the processor is configured to decode the average pressure signals in accordance with the second pseudorandom code to create second decoded average pressure values, and process the second decoded average pressure values to determine a second flow parameter.

20. A method for monitoring at least one flow parameter in a fluid conduit in which a first infusion device acts on a first fluid conduit segment, and a second infusion device acts on a second fluid conduit segment to control the flow of fluid through the conduit, the method comprising the steps of:

providing pressure signals in response to fluid pressure sensed in the conduit;

outputting a first pseudorandom code having a codelength;

controlling the first infusion device to infuse fluid in a pattern of flow variation in accordance with the first pseudorandom code;

monitoring pressure of the fluid in the conduit and generating pressure signals representing said monitored pressure;

determining average pressure values for at least some of the pressure signals;

decoding the average pressure values in accordance with the first pseudorandom code to create first decoded average pressure values; and

processing the first decoded average pressure values to determine a first flow parameter.

21. The method of claim 20, comprising the further steps of:

outputting a second pseudorandom code having a codelength;

controlling the second infusion device to infuse fluid in a pattern of flow variation in accordance with the second pseudorandom code.

22. The method of claim 21, wherein the step of outputting the second pseudorandom code includes the step of selecting the second pseudorandom code to enhance the ability of the processor to filter out crosstalk from the second infusion device.

23. The method of claim 21, comprising the further steps of:

decoding the average pressure values in accordance with the second pseudorandom code to create second decoded average pressure values; and

processing the second decoded average pressure values to determine a second flow parameter.