Individual pump calibration for ultrafiltration control in a dialysis apparatus

• US 9,962,476 B2
• Filed: 07/09/2014
• Issued: 05/08/2018
• Est. Priority Date: 07/15/2013
• Status: Active Grant

• Current Assignee: Gambro Lundia AB (Baxter International Inc.)
• Original Assignee: Gambro Lundia AB (Baxter International Inc.)
• Inventors: Jansson, Olof
• Primary Examiner(s): Barry, Chester T
• Application Number:
  US14/901,881
• Publication Number:
  US 20160367743A1
• Time in Patent Office: 1,399 Days
• Field of Search: None
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1615 using measurements made at different flow rates
• CPC Class Codes: A61M 1/165 with a dialyser bypass on the dialysis fluid line
• CPC Class Codes: A61M 1/34 Filtering material out of the blood by passing it through a membrane, i.e. hemofiltration or diafiltration
• CPC Class Codes: A61M 1/3403 Regulation parameters
• CPC Class Codes: A61M 1/3413 Diafiltration
• CPC Class Codes: A61M 2205/12 with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3351 Controlling upstream pump pressure
• CPC Class Codes: A61M 2205/3355 Controlling downstream pump pressure
• CPC Class Codes: A61M 2205/3389 Continuous level detection A61M2205/3393 takes precedence
• CPC Class Codes: A61M 2205/3396 Reservoirs being alternately filled and emptied for measuring flow rate or delivered volume
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2205/70 with testing or calibration facilities
• CPC Class Codes: A61M 2205/702 automatically during use
• CPC Class Codes: F04B 49/065 and making use of computers
• CPC Class Codes: F04B 51/00 Testing machines, pumps, or pumping installations

Abstract

A control unit (30) is arranged to control a dialysis fluid distribution system (12) comprising first and second volumetric pumps (PI, P2) arranged upstream and downstream of a dialyzer (13). The control unit (30) is operable in a calibration mode, to establish a bypass flow path that bypasses the dialyzer (13) and extends from the first pump (P1) to the second pump (P2) in fluid communication with a calibration chamber (26) and to operate the pumps (P1, P2) at different combinations of speeds that cause first and second changes in fluid level in the chamber (26). The first and second changes correspond to first and second known volumes in the chamber (26). The control unit (30) measures, by a level detector (28) in the chamber (26), first and second time periods for the first and second changes, and computes the stroke volumes of the pumps (P1, P2) as a function of the speeds of the pumps (PI, P2), the first and second time periods, and the first and second known volumes. By computing the stroke volumes, the control unit (30) is operable to achieve an accurate ultrafiltration (UF) rate in the dialyzer (13) by controlling the relative speeds of the pumps (P1, P2).

Claims

1. A dialysis apparatus, comprising:

a dialyzer;

a dialysis fluid distribution system connected for fluid communication with the dialyzer and comprising a first pump, a second pump, a calibration chamber, and a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, the dialysis fluid distribution system being operable to selectively establish a main flow path that extends from the first pump to the second pump via the dialyzer, and a bypass flow path that bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with the calibration chamber;

a control unit electrically connected to the dialysis fluid distribution system and being operable to control a respective frequency of the first and second pumps, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at the respective frequency, a respective stroke volume of dialysis fluid;

wherein the control unit is configured to, in a calibration mode, perform a first and second measurement procedure while operating the dialysis fluid distribution system to establish the bypass flow path;

wherein the first measurement procedure comprises;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

wherein the second measurement procedure comprises;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber;

wherein the control unit is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes; and

wherein the function is obtained by solving a system of equations that equates the first known volume to an accumulated difference between the flow rates generated by the first and second pumps during the first time period, and that equates the second known volume to an accumulated difference between the flow rates generated by the first and second pumps during the second time period.

2. The dialysis apparatus of claim 1, wherein the control unit is further configured to, in the calibration mode, store the stroke volume(s) computed in the calibration mode in an electronic memory for subsequent retrieval by the control unit in a treatment mode.

3. The dialysis apparatus of claim 1, wherein the first and second pumps are positive displacement pumps, and wherein the flow rates of dialysis fluid generated by the first and second pumps are given by the respective frequency multiplied by the respective stroke volume.

4. The dialysis apparatus of claim 1, wherein the control unit is configured to set the first and second combinations of frequencies such that the first change is an increase in dialysis fluid level in the calibration chamber, and the second change is a decrease in dialysis fluid level in the calibration chamber.

5. The dialysis apparatus of claim 1, wherein the first change is from a first level to a second level in the calibration chamber, and the second change is from the second level to the first level in the calibration chamber.

6. The dialysis apparatus of claim 1, wherein the control unit is configured to, in the first measurement procedure, set the first and second pumps to fixed first and second frequencies, and, in the second measurement procedure, set the first and second pumps to fixed third and fourth frequencies.

7. The dialysis apparatus of claim 6, wherein the function is given by:

8. The dialysis apparatus of claim 1, wherein each of the first and second pumps is one of a diaphragm pump and a piston pump.

9. The dialysis apparatus of claim 1, wherein the control unit is further operable in a treatment mode to operate the dialysis fluid distribution system to establish the main flow path and control the frequencies of the first and second pumps, based on the stroke volume(s) computed in the calibration mode, so as to achieve a predefined ultrafiltration rate in the dialyzer.

10. The dialysis apparatus of claim 9, wherein the predefined ultrafiltration rate is achieved by setting the frequencies of the first and second pumps to achieve a predefined difference between the flow rates generated by the first and second pumps.

11. The dialysis apparatus of claim 9, wherein the control unit is configured to, in the treatment mode, receive a set value for the flow rate of one of the first and second pumps, and compute, by applying the corresponding stroke volume computed in the calibration mode, the frequency of said one of the first and second pumps to achieve the set value.

12. The dialysis apparatus of claim 11, wherein said one of the first and second pumps is the first pump.

13. The dialysis apparatus of claim 11, wherein the control unit is configured to, in the treatment mode, receive a set value for the ultrafiltration rate in the dialyzer, compute an ultrafiltration control flow rate for the other of the first and second pumps based on the set values for the flow rate and the ultrafiltration rate, and compute, by applying the corresponding stroke volume computed in the calibration mode, the frequency of said other of the first and second pumps to achieve the ultrafiltration control flow rate.

14. A method of calibrating a dialysis fluid distribution system that comprises first and second pumps which are connected upstream and downstream of a dialyzer to pump a dialysis fluid through the dialyzer, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at a respective frequency, a respective stroke volume of the dialysis fluid, said method comprising:

operating the dialysis fluid distribution system to establish a bypass flow path, which bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with a calibration chamber;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps;

measuring a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps;

measuring a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber; and

computing at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes, wherein the function is obtained by solving a system of equations that equates the first known volume to an accumulated difference between the flow rates generated by the first and second pumps during the first time period, and that equates the second known volume to an accumulated difference between the flow rates generated by the first and second pumps during the second time period.

15. A computer-readable medium comprising program instructions which, when executed by a processing unit, are adapted to carry out the method of claim 14.

16. A control unit for a dialysis fluid distribution system arranged in a dialysis apparatus to pump a dialysis fluid through a dialyzer, wherein the dialysis fluid distribution system comprises first and second pumps which are connected upstream and downstream of the dialyzer to pump a dialysis fluid through the dialyzer, and are configured to generate a respective flow rate by repeatedly discharging, at a respective frequency, a respective stroke volume of the dialysis fluid, said control unit comprising:

a signal communication interface for connection to the dialysis fluid distribution system; and

a signal processor which is configured to, via the signal communication interface;

operate the dialysis fluid distribution system to establish a bypass flow path, which bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with a calibration chamber;

control the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps;

measure, by a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

control the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps; and

measure, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber; and

wherein the signal processor is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes.

17. A control unit for a dialysis fluid distribution system arranged in a dialysis apparatus to pump a dialysis fluid through a dialyzer, wherein the dialysis fluid distribution system comprises first and second pumps which are connected upstream and downstream of the dialyzer to pump a dialysis fluid through the dialyzer, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at a respective frequency, a respective stroke volume of the dialysis fluid, said control unit comprising:

means for operating the dialysis fluid distribution system to establish a bypass flow path, which bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with a calibration chamber;

means for controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps;

means for measuring a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

means for controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps;

means for measuring a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber; and

means for computing at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes.

18. A dialysis apparatus, comprising:

a dialyzer;

a dialysis fluid distribution system connected for fluid communication with the dialyzer and comprising a first pump, a second pump, a calibration chamber, and a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, the dialysis fluid distribution system being operable to selectively establish a main flow path that extends from the first pump to the second pump via the dialyzer, and a bypass flow path that bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with the calibration chamber;

a control unit electrically connected to the dialysis fluid distribution system and being operable to control a respective frequency of the first and second pumps, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at the respective frequency, a respective stroke volume of dialysis fluid;

wherein the control unit is configured to, in a calibration mode, perform a first and second measurement procedure while operating the dialysis fluid distribution system to establish the bypass flow path;

wherein the first measurement procedure comprises;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

wherein the second measurement procedure comprises;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber,

wherein the control unit is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes, and

wherein the control unit is configured to set the first and second combinations of frequencies such that the first change is an increase in dialysis fluid level in the calibration chamber, and the second change is a decrease in dialysis fluid level in the calibration chamber.

19. A dialysis apparatus, comprising:

a dialyzer;

a dialysis fluid distribution system connected for fluid communication with the dialyzer and comprising a first pump, a second pump, a calibration chamber, and a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, the dialysis fluid distribution system being operable to selectively establish a main flow path that extends from the first pump to the second pump via the dialyzer, and a bypass flow path that bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with the calibration chamber;

a control unit electrically connected to the dialysis fluid distribution system and being operable to control a respective frequency of the first and second pumps, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at the respective frequency, a respective stroke volume of dialysis fluid;

wherein the control unit is configured to, in a calibration mode, perform a first and second measurement procedure while operating the dialysis fluid distribution system to establish the bypass flow path;

wherein the first measurement procedure comprises;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

wherein the second measurement procedure comprises;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber,

wherein the control unit is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes, and

wherein the first change is from a first level to a second level in the calibration chamber, and the second change is from the second level to the first level in the calibration chamber.

20. A dialysis apparatus, comprising:

a dialyzer;

a dialysis fluid distribution system connected for fluid communication with the dialyzer and comprising a first pump, a second pump, a calibration chamber, and a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, the dialysis fluid distribution system being operable to selectively establish a main flow path that extends from the first pump to the second pump via the dialyzer, and a bypass flow path that bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with the calibration chamber;

a control unit electrically connected to the dialysis fluid distribution system and being operable to control a respective frequency of the first and second pumps, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at the respective frequency, a respective stroke volume of dialysis fluid;

wherein the control unit is configured to, in a calibration mode, perform a first and second measurement procedure while operating the dialysis fluid distribution system to establish the bypass flow path;

wherein the first measurement procedure comprises;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

wherein the second measurement procedure comprises;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber,

wherein the control unit is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes, and

wherein the control unit is configured to, in the first measurement procedure, set the first and second pumps to fixed first and second frequencies, and, in the second measurement procedure, set the first and second pumps to fixed third and fourth frequencies.

21. A dialysis apparatus, comprising:

a dialyzer;

a dialysis fluid distribution system connected for fluid communication with the dialyzer and comprising a first pump, a second pump, a calibration chamber, and a fluid level detector for sensing a level of dialysis fluid in the calibration chamber, the dialysis fluid distribution system being operable to selectively establish a main flow path that extends from the first pump to the second pump via the dialyzer, and a bypass flow path that bypasses the dialyzer and extends from the first pump to the second pump in fluid communication with the calibration chamber;

a control unit electrically connected to the dialysis fluid distribution system and being operable to control a respective frequency of the first and second pumps, wherein the first and second pumps are configured to generate a respective flow rate by repeatedly discharging, at the respective frequency, a respective stroke volume of dialysis fluid;

wherein the control unit is configured to, in a calibration mode, perform a first and second measurement procedure while operating the dialysis fluid distribution system to establish the bypass flow path;

wherein the first measurement procedure comprises;

controlling the first and second pumps to operate at a first combination of frequencies that results in a first flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a first time period corresponding to a first change in dialysis fluid level in the calibration chamber as a result of the first flow rate difference, the first change in dialysis fluid level corresponding to a first known volume in the calibration chamber;

wherein the second measurement procedure comprises;

controlling the first and second pumps to operate at a second combination of frequencies that differs from the first combination of frequencies and results in a second flow rate difference between the flow rates generated by the first and second pumps, and

measuring, by the fluid level detector, a second time period corresponding to a second change in dialysis fluid level in the calibration chamber as a result of the second flow rate difference, the second change in dialysis fluid level corresponding to a second known volume in the calibration chamber,

wherein the control unit is further configured to compute at least one of the stroke volumes of the first and second pumps as a function of the first and second combinations of frequencies, the first and second time periods, and the first and second known volumes,

wherein the control unit is further operable in a treatment mode to operate the dialysis fluid distribution system to establish the main flow path and control the frequencies of the first and second pumps, based on the stroke volume(s) computed in the calibration mode, so as to achieve a predefined ultrafiltration rate in the dialyzer, and

wherein the control unit is configured to, in the treatment mode, receive a set value for the flow rate of one of the first and second pumps, and compute, by applying the corresponding stroke volume computed in the calibration mode, the frequency of said one of the first and second pumps to achieve the set value.