DIALYSIS SYSTEM HAVING PUMP REVERSING DISINFECTION

Abstract

A peritoneal dialysis (PD) system includes a housing, a PD fluid pump housed by the housing, an inline heater in fluid communication with the PD fluid pump, a temperature sensor, and a control unit. The PD fluid pump and the inline heater are under control of the control unit, which receives a temperature signal from the temperature sensor. The control unit, in one embodiment, is configured to perform a heat disinfection sequence in which the control unit causes the PD fluid pump to pump disinfection fluid in a forward direction, while the inline heater heats the disinfection fluid, and in a reverse direction after the temperature signal indicates that a temperature of the disinfection fluid has fallen to or has fallen below a minimum disinfection temperature.

Claims

1. A peritoneal dialysis (PD) system comprising: a housing; a PD fluid pump housed by the housing; an inline heater in fluid communication with the PD fluid pump; a temperature sensor; and a control unit, the PD fluid pump and the inline heater being under control of the control unit, the control unit configured to: receive a temperature signal from the temperature sensor, and perform a heat disinfection sequence in which the control unit causes the PD fluid pump to pump disinfection fluid in a forward direction, while the inline heater heats the disinfection fluid, and in a reverse direction after the temperature signal indicates that a temperature of the disinfection fluid has fallen to or has fallen below a minimum disinfection temperature.

2. The PD system of claim 1, wherein the control unit is configured to cause the PD fluid pump to pump the disinfection fluid in the reverse direction after the temperature signal indicates, over a designated amount of time, that the temperature of the disinfection fluid has fallen to or has fallen below the minimum disinfection temperature.

3. The PD system of claim 1, wherein the temperature sensor is located upstream of the inline heater when the PD fluid pump is pumping the disinfection fluid in the forward direction.

4. The PD system of claim 1, wherein the temperature signal is used as closed loop feedback to the control unit for controlling the inline heater when the PD fluid pump is pumping the disinfection fluid in the reverse direction.

5. The PD system of claim 1, wherein the temperature sensor is a first temperature sensor, and which includes a second temperature sensor located downstream of the inline heater when the PD fluid pump is pumping the disinfection fluid in the forward direction, and wherein a temperature signal from the second temperature sensor is used as closed loop feedback to the control unit for controlling the inline heater when the PD fluid pump is pumping the disinfection fluid in the forward direction.

6. The PD system of claim 5, wherein the inline heater is controlled such that a temperature of the disinfection fluid exiting the inline heater is about 85? C.

7. The PD system of claim 1, wherein the control unit is configured to cause the PD fluid pump to pump the disinfection fluid in the reverse direction for a number of pump strokes.

8. The PD system of claim 1, wherein the control unit is configured to cause the PD fluid pump to pump the disinfection fluid in the reverse direction until a certain temperature is reached, as indicated by the temperature sensor.

9. The PD system of claim 1, wherein the control unit is configured to cause the PD fluid pump to pump the disinfection fluid in the reverse direction until a certain temperature is reached, as indicated by the temperature sensor, followed by a number of pump strokes in the reverse direction.

10. The PD system of claim 1, wherein the heat disinfection sequence is performed using a disinfection loop including: a reusable patient line extending from the housing, the reusable patient line including a distal end configured to be connected to a patient line connector provided by the housing; and at least one reusable PD fluid line extending from the housing, the at least one reusable PD fluid line including a distal end configured to be connected to a PD fluid line connector provided by the housing.

11. The PD system of claim 1, wherein at least one of (i) the minimum disinfection temperature is from 65? C. (149? F.) to 95? C. (203? F.) or (ii) the disinfection fluid is PD fluid.

12. A peritoneal dialysis (PD) system comprising: a housing; a PD fluid pump housed by the housing; an inline heater in fluid communication with the PD fluid pump; a temperature sensor; and a control unit, the PD fluid pump and the inline heater being under control of the control unit, the control unit configured to: receive a temperature signal from the temperature sensor, and perform a heat disinfection sequence in which the control unit causes the PD fluid pump to pump disinfection fluid in a forward direction, while the inline heater heats the disinfection fluid, and in a reverse direction in which the control unit controls the inline heater using a feed forward algorithm that takes into account the temperature signal and a flowrate of the disinfection fluid.

13. The PD system of claim 12, wherein the temperature signal provides a heater inlet temperature, and wherein the feed forward algorithm subtracts the inlet temperature from a target temperature.

14. The PD system of claim 12, wherein the flowrate of the disinfection fluid is calculated by the control unit by accumulating known pump volumes pumped by the PD fluid pump.

15. The PD system of claim 12, which includes a flowmeter in fluid communication with the PD fluid pump, and wherein the flowrate of the disinfection fluid is measured by the flowmeter.

16. The PD system of claim 12, wherein the feed forward algorithm is structured to calculate an output power=(a target temperature?an inlet temperature obtained from the temperature signal)?(the disinfection fluid flowrate)?(the specific heater of water).

17. The PD system of claim 16, wherein the target temperature is 85? C.

18. The PD system of claim 12, wherein the temperature sensor is located downstream of the inline heater when the PD fluid pump is pumping the disinfection fluid in the forward direction, and wherein the temperature signal is used as closed loop feedback to the control unit for controlling the inline heater when the PD fluid pump is pumping the disinfection fluid in the forward direction.

19. The PD system of claim 12, wherein the control unit is configured to cause (i) the PD fluid pump to pump the disinfection fluid in the forward direction for a number of pump strokes, and (ii) the PD fluid pump to automatically reverse and pump the disinfection fluid in the reverse direction for a number of pump strokes.

20. The PD system of claim 19, wherein the control unit is further configured to repeat (i) and (ii) until a total disinfection time is reached.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] FIG. 1 is a fluid flow schematic of one embodiment for a medical fluid, e.g., PD fluid, system that is set for treatment.

[0052] FIG. 2 is a fluid flow schematic of one embodiment for a medical fluid, e.g., PD fluid, system of FIG. 1, which has been rearranged for disinfection.

[0053] FIG. 3 includes plots showing inline heater inlet temperature versus inline heater outlet temperature when the pump reversing disinfection of the present disclosure is not used or employed.

[0054] FIG. 4 is a process flow diagram illustrating one embodiment for reversing the flow of heated PD fluid during a disinfection sequence of the present disclosure.

[0055] FIG. 5 is a process flow diagram illustrating another embodiment for reversing the flow of heated PD fluid during a disinfection sequence of the present disclosure.

[0056] FIG. 6 illustrates a partial fluid path showing an inline heater and temperature sensors for closed loop control, which may be employed for both forward and reverse PD fluid disinfection flow.

[0057] FIG. 7 illustrates a partial fluid path showing an inline heater and an upstream temperature sensor for an open loop forward heating control algorithm used during reverse PD fluid disinfection flow.

[0058] FIG. 8 includes plots showing inline heater inlet temperature and inline heater outlet temperature over time, and illustrating the effects of the pump reversing disinfection of the present disclosure.

DETAILED DESCRIPTION

System Overview

[0059] Referring now to the drawings and in particular to FIG. 1, a medical system having the pump reversing heat disinfection of the present disclosure is illustrated via peritoneal dialysis (PD) system 10. System 10 includes a PD machine or cycler 20 and a control unit 100 having one or more processor 102, one or more memory 104, video controller 106 and user interface 108. User interface 108 may alternatively or additionally be a remote user interface, e.g., via a tablet or smartphone. Control unit 100 may also include a transceiver and a wired or wireless connection to a network (not illustrated), e.g., the internet, for sending treatment data to and receiving prescription instructions/changes from a doctor's or clinician's server interfacing with a doctor's or clinician's computer. Control unit 100 in an embodiment controls all electrical fluid flow and heating components of system 10 and receives outputs from all sensors of system 10. System 10 in the illustrated embodiment includes durable and reusable components that contact fresh and used PD fluid, which necessitates that PD machine or cycler 20 be disinfected between treatments, e.g., via heat disinfection.

[0060] System 10 in FIG. 1 includes an inline resistive heater 56, reusable supply lines or tubes 52a1 to 52a4 and 52b, air trap 60 operating with respective upper and lower level sensors 62a and 62b, air trap valve 54d, vent valve 54e located along vent line 52e, reusable line or tubing 52c, PD fluid pump 70, temperature sensors 58a and 58b and possibly a third temperature sensor 58c, pressure sensors 78a, 78b1, 78b2 and 78c, reusable patient tubing or lines 52f and 52g having respective valves 54f and 54g, dual lumen patient line 28, a hose reel 80 for retracting patient line 28, reusable drain tubing or line 52i extending to drain line connector 34 and having a drain line valve 54i, and reusable recirculation tubing or lines 52r1 and 52r2 operating with respective disinfection valves 54r1 and 54r2. A third recirculation or disinfection tubing or line 52r3 extends between disinfection or PD fluid line connectors 30a and 30b for use during disinfection. A fourth recirculation or disinfection tubing or line 52r4 extends between disinfection connectors 30c and 30d for use during disinfection.

[0061] System 10 further includes PD fluid containers or bags 38a to 38c (e.g., holding the same or different formulations of PD fluid), which connect to distal ends 24e of reusable PD fluid lines 24a to 24c, respectively. System 10d further includes a fourth PD fluid container or bag 38d that connects to a distal end 24e of reusable PD fluid line 24d. Fourth PD fluid container or bag 38d may hold the same or different type (e.g., icodextrin) of PD fluid than provided in PD fluid containers or bags 38a to 38c. Reusable PD fluid lines 24a to 24d extend in one embodiment through apertures (not illustrated) defined or provided by housing 22 of cycler 20.

[0062] System 10 in the illustrated embodiment includes four disinfection or PD fluid line connectors 30a to 30d for connecting to distal ends 24e of reusable PD fluid lines 24a to 24d, respectively, during disinfection. System 10 also provides a patient line connector 32 that includes an internal lumen, e.g., a U-shaped lumen, which for disinfection directs fresh or used dialysis fluid from one PD fluid lumen of a connected distal end 28e of dual lumen patient line 28 into the other PD fluid lumen. Reusable supply tubing or lines 52a1 to 52a4 communicate with reusable supply lines 24a to 24d, respectively. Reusable supply tubing or lines 52a1 to 52a3 operate with valves 54a to 54c, respectively, to allow PD fluid from a desired PD fluid container or bag 38a to 38c to be pulled into cycler 20. Three-way valve 94a in the illustrated example allows for control unit 100 to select between (i) 2.27% (or other) glucose dialysis fluid from container or bag 38b or 38c and (ii) icodextrin from container or bag 38d. In the illustrated embodiment, icodextrin from container or bag 38d is connected to the normally closed port of three-way valve 94a.

[0063] System 10 is constructed in one embodiment such that drain line 52i during a patient fill is fluidly connected downstream from PD fluid pump 70. In this manner, if drain valve 54i fails or somehow leaks during the patient fill of patient P, fresh PD fluid is pushed down disposable drain line 36 instead of used PD fluid potentially being pulled into pump 70. Disposable drain line 36 is in one embodiment removed for disinfection, wherein drain line connector 34 is capped via a cap 34c to form a closed disinfection loop. PD fluid pump 70 may be an inherently accurate pump, such as a piston pump, or less accurate pump, such as a gear pump that operates in cooperation with a flowmeter (not illustrated) to control fresh and used PD fluid flowrate and volume.

[0064] System 10 may further include a leak detection pan 82 located at the bottom of housing 22 of cycler 20 and a corresponding leak detection sensor 84 outputting to control unit 100. In the illustrated example, system 10 is provided with an additional pressure sensor 78c located upstream of PD fluid pump 70, which allows for the measurement of the suction pressure of pump 70 to help control unit 100 more accurately determine pump volume. Additional pressure sensor 78c in the illustrated embodiment is located along vent line 52e, which may be filled with air or a mixture of air and PD fluid, but which should nevertheless be at the same negative pressure as PD fluid located within PD fluid line 52c.

[0065] System 10 in the example of FIG. 1 includes redundant pressure sensors 78b1 and 78b2, the output of one of which is used for pump control, as discussed herein, while the output of the other pressure sensor is a safety or watchdog output to make sure the control pressure sensor is reading accurately. Pressure sensors 78b1 and 78b2 are located along a line including a third recirculation valve 54r3. System 10 may further employ one or more cross, marked via an X in FIG. 1, which may (i) reduce the overall amount and volume of the internal, reusable tubing, (ii) reduce the number of valves needed, and (iii) allow the portion of the fluid circuitry shared by both fresh and used PD fluid to be minimized.

[0066] System 10 in the example of FIG. 1 further includes a source of acid, such as a citric acid container or bag 66. Citric acid container or bag 66 is in selective fluid communication with second three-way valve 94b via a citric acid valve 54m located along a citric acid line 52m. Citric acid line 52m is connected in one embodiment to the normally closed port of second three-way valve 94b, so as to provide redundant valves between citric acid container or bag 66 and the PD fluid circuit during treatment. The redundant valves ensure that no citric (or other) acid reaches the treatment fluid lines during treatment. Citric (or other) acid is used instead during disinfection.

[0067] Control unit 100, in an embodiment, uses feedback from any one or more of pressure sensors 78a to 78c to enable PD machine 20 to deliver fresh, heated PD fluid to the patient at, for example, 14 kPa (2.0 psig) or higher. The pressure feedback is used to enable PD machine 20 to remove used PD fluid or effluent from the patient at, for example, between ?5 kPa (?0.73 psig) and ?15 kPa (?2.2 psig), such as ?9 kPa (?1.3 psig) or higher (more negative). The pressure feedback may be used in a proportional, integral, derivative (PID) pressure routine for pumping fresh and used PD fluid at a desired positive or negative pressure.

[0068] Inline resistive heater 56, under control of control unit 100, is capable of heating fresh PD fluid to body temperature, e.g., 37? C., for delivery to patient P at a desired flowrate. Control unit 100, in an embodiment, uses feedback from temperature sensor 58a in a PID temperature routine for pumping fresh PD fluid to patient P at a desired temperature. The control and operation of inline resistive heater 56 for heat disinfection is discussed in detail below.

[0069] FIG. 1 also illustrates that system 10 includes and uses a disposable filter set 40, which communicates fluidly with the fresh and used PD fluid lumens of dual lumen patient line 28. Disposable filter set 40 includes a disposable connector 42 that connects to a distal end 28e of reusable patient line 28. Disposable filter set 40 also includes a connector 44 that connects to the patient's transfer set. Disposable filter set 40 further includes a sterilizing grade filter membrane 46 that further filters fresh PD fluid. Disposable filter set 40 is provided in one embodiment as a last chance filter for PD machine 20, which has been heat disinfected between treatments. Any pathogens that may remain after disinfection, albeit unlikely, are filtered from the PD fluid via the sterilizing grade filter membrane 46 of disposable filter set 40.

[0070] FIG. 1 illustrates system 10 setup for treatment with PD fluid containers or bags 38a to 38d connected via reusable, flexible PD fluid lines 24a to 24d, respectively. Dual lumen patient line 28 is connected to patient P via disposable filter set 40. Disposable drain line 36 is connected to drain line connector 34. In FIG. 1, PD machine or cycler 20 of system 10 is configured to perform multiple patient drains, patient fills, patient dwells, and a priming procedure, as part of or in preparation for treatment.

[0071] FIG. 2 illustrates system 10 in a disinfection mode. PD fluid containers or bags 38a to 38d are removed and flexible PD fluid lines 24a to 24d are plugged instead in a sealed manner into disinfection or PD fluid line connectors 30a to 30d, respectively. Reusable dual lumen patient line 28 is disconnected from disposable filter set 40 (which is discarded), and distal end 28e of dual lumen patient line 28 is plugged sealingly into patient line connector 32. Disposable drain line 36 is removed from drain line connector 34 and discarded. Drain line connector 34 is capped via cap 34c to form a closed disinfection loop 90. PD machine or cycler 20 of system 10 in FIG. 2 is configured to perform a disinfection sequence, e.g., a heat disinfection sequence in which fresh PD fluid is heated via inline heater 56 to a disinfection temperature of, e.g., 75? C. or greater. PD fluid pump 70 circulates the heated PD fluid closed disinfection loop 90 for an amount of time needed to properly disinfect the fluid components and lines of the disinfection loop.

Pump Reversing Heat Disinfection

[0072] In one embodiment, control unit 100 causes PD fluid pump 70 and the valves of system 10 at the beginning of a heat disinfection sequence to move the heated PD fluid in a normal treatment direction, e.g., from left to right, across PD fluid pump 70 in FIG. 2. Heated PD fluid may split between fresh patient tubing or line 52f and drain tubing or line 52i. Heated PD fluid flow splitting through fresh patient tubing or line 52f proceeds to flow through: the fresh PD lumen of dual lumen patient line 28, the used PD lumen of dual lumen patient line 28, used patient tubing or line 52g, and tubing or line 52c, back to PD fluid pump 70. Heated PD fluid flow splitting through fresh patient tubing or line 52f also further splits into the line including pressure sensors 78b1 and 78b2 and third recirculation valve 54r3 after which it joins the heated PD fluid flow through recirculation line 52r1.

[0073] Heated PD fluid flow splitting through drain tubing or line 52i proceeds to flow through drain line connector 34, recirculation tubing or line 52r2, recirculation tubing or line 52r1, reusable flexible PD fluid lines 24a to 24d, tubing or lines 52a1 to 52a4, recirculation tubing or lines 52r3 and 52r4, back to the inlet of inline heater 56. The length of internal reusable tubing and reusable flexible PD fluid lines 24a to 24d between the outlet of inline heater 56 and the inlet of inline heater 56 may be ten meters or more. Heat loss will occur over the length of the lines. A potential problem may accordingly occur in which while the PD fluid leaving inline heater 56 is at a temperature sufficient to produce a desired amount of disinfection, the temperature of PD fluid returning to and entering inline heater 56 is below what is considered a threshold minimum disinfection temperature.

[0074] In one example, control unit 100 under feedback from temperature sensor 58a energizes inline heater 56 such that PD fluid exiting the heater is at or about 85? C. 85? C. (185? F.) is in one embodiment be a desired output disinfection temperature because it is above a recommended minimum disinfection temperature of, e.g., 75? C. (167? F.) and it is below a temperate in which the PD fluid may start to boil. If the temperature of PD fluid reaching heater inlet 56i of inline heater 56 falls below the recommended minimum disinfection temperature of, e.g., 65? C. (149? F.) to 95? C. (203? F.), such as 75? C. (167? F.), then corrective action needs to be taken. FIG. 3 includes plots illustrating the temperature at heater inlet 56i versus the temperature at heater outlet 56o without the pump reversing of the present disclosure. Here, the temperature of outlet 56o of heater 56 varies between 80? C. (176? F.) and 90? C. (194? F.) and remains above the recommended minimum disinfection temperature of, e.g., 75? C. (167? F.), however, the temperature of inlet 56i of heater 56 approaches but remains below 70? C. (158? F.). The temperature of inlet 56i of heater 56 accordingly likely falls below the recommended minimum disinfection temperature of, e.g., 75? C. (167? F.). Time varies in minutes in the illustrated embodiment.

[0075] Corrective measures to raise the temperature of inlet 56i of heater 56 illustrated in FIG. 3 may include raising the heater outlet temperature, increasing disinfection time or some combination of both. But raising the heater outlet temperature above 85? C. runs the risk of beginning to boil the PD fluid, while increasing disinfection time increases component wear. System 10 and associated methodology instead solve the potential low temperature problem by programing control unit 100 to automatically reverse the pumping direction of PD fluid pump 70 one or more time during the disinfection sequence so that freshly heated PD fluid, e.g., at 85? C., is outputted from what is typically the heater inlet 56i of inline heater 56. Inline heater 56 is in one embodiment bidirectional, such that PD fluid flowing in either direction from inlet 56i to outlet 56o, or from outlet 56o to inlet 56i may be heated to a desired temperature under the control of control unit 100. It may be possible to use an inline heater 56 that is not bidirectional. Here, control unit 100 may cause PD fluid to be heated in the normal direction for a desired number of pump strokes and to a desired and controlled temperature, after which PD fluid pump 70 is caused to pump in the reverse direction for the same desired number of pump strokes to push the freshly heated PD fluid out heater inlet 56i. While pumping in the reverse direction, inline heater 56 may or may not be powered.

[0076] Reversing the pumping direction of PD fluid pump 70 one or more time during the disinfection sequence causes the freshly heated PD fluid, e.g., to 85? C., to be distributed more evenly. Here, the hotter freshly heated PD fluid mixes with the cooler PD fluid returning to inline heater 56, bringing the mixed PD fluid temperature to above the recommended minimum disinfection temperature of, e.g., 75? C. The more even distribution of freshly heated PD fluid helps to eliminate pockets of closed disinfection loop 90 that may fall below the recommended minimum disinfection temperature. The more even distribution of freshly heated PD fluid also helps to reduce the amount of time needed for the disinfection sequence. For example, the time for the disinfection sequence may be cut roughly in half from two hours to one hour using the pump reversing heated PD fluid disinfection of the present disclosure.

[0077] FIG. 4 shows one method 110, which may be implemented in control unit 100 for controlling the pump reversing during heat disinfection of the present disclosure. At oval 112, method 110 begins. At block 114, control unit 100 opens all two-way valves associated with disinfection loop 90 and runs PD fluid pump 70 in a forward treatment direction (left to right through pump 70 in FIGS. 1 and 2), which is also considered to be the normal disinfection sequence direction. At block 114, control unit 100 also uses feedback from temperature sensor 58a and a heating algorithm, such as a proportional, integral, derivative (PID) heating algorithm, to control inline heater 56 to output heated PD fluid at heater outlet 56o at a desired disinfection temperature, such as 85? C.

[0078] At block 116, control unit 100 monitors the output of temperature sensor 58c, which is the temperature of heated PD fluid reentering inline heater 56 at heater inlet 56i. At diamond 118, control unit 100 determines whether the temperature of the PD fluid reentering inline heater 56 at heater inlet 56i, as indicated by temperature sensor 58c, has fallen below a recommended minimum disinfection temperature of, e.g. 75? C., for a threshold or designated amount of time, such as sixty seconds. Including a threshold amount of time in the query at diamond 118 allows for the PD fluid temperature at heater inlet 56i to fall below the recommended minimum disinfection temperature for short periods of time, or inadvertently, without overreacting to the temporary temperature drop. It is contemplated to optimize the threshold amount of time to allow for a looser version of method 110, e.g., longer than one minute, or for a tighter version of method 110, e.g., five to sixty seconds.

[0079] If the temperature of the PD fluid reentering inline heater 56 at heater inlet 56i has not fallen below the recommended minimum disinfection temperature for the threshold amount of time, as determined at diamond 118, then at diamond 120, control unit 100 determines whether a total disinfection sequence time has been reached. Proper disinfection of disinfection loop 90 involves the movement of PD fluid heated at or above the recommended minimum disinfection temperature through disinfection loop 90 for a specified period of time, e.g., two hours. Once the total or specified disinfection time is reached, as determined at diamond 120, the disinfection sequence is completed and method 110 ends at oval 122.

[0080] If at diamond 120, if the total or specified disinfection time has not been reached, method 110 returns to block 114 as illustrated in FIG. 4. The loop just described between block 114 and diamond 120 is repeated until either the total or specified disinfection time has been reached (at diamond 120) or the temperature of the PD fluid reentering inline heater 56 at heater inlet 56i has fallen below the recommended minimum disinfection temperature for the threshold amount of time (at block 118).

[0081] At block 118, when the temperature of the PD fluid reentering inline heater 56 at heater inlet 56i has fallen below the recommended minimum disinfection temperature for the threshold amount of time, control unit 100 at block 124 causes PD fluid pump 70 to reverse and pump in the opposite direction (right to left in FIGS. 1 and 2). Control unit 100 also sequences any of the valves of disinfection loop 90 as needed, e.g., sequences three-way valve 94a. It is contemplated for control unit 100 to control the amount or time that the pumping of PD fluid pump 70 is reversed in a plurality of different ways. In one way, control unit 100 causes PD fluid pump 70 to pump in the reverse direction for a number of pump strokes, e.g., one-hundred pump strokes. In a second way, control unit 100 causes PD fluid pump 70 to pump in the reverse direction until a certain temperature is reached at temperature sensor 58c, e.g., 85? C. (commanded output of heater 56), wherein temperature sensor 58c is the downstream temperature sensor during reverse pumping. In a third way, control unit 100 causes PD fluid pump 70 to pump in the reverse direction until a certain temperature is reached at temperature sensor 58c, e.g., 85? C., after which a preset number of additional pump strokes are performed in the reverse pumping direction.

[0082] When the reversed pumping of PD fluid pump 70 is completed via any of the ways discussed above, method 110 returns to block 114 as illustrated in FIG. 4. As discussed in connection with diamond 118 and block 124, temperature sensor 58c located just upstream of heater inlet 56i in the normal pumping direction is used as part of the trigger for beginning the pump reversing (diamond 118) and possibly in determining how long the pump reversing is performed (block 124). The output of temperature sensor 58c is also used as feedback to control unit 100 for controlling the powering of inline heater 56 while the pumping of PD fluid pump 70 is reversed, so that a maximum temperature, e.g., 85? C. is not exceeded.

[0083] FIG. 5 illustrates an alternative method 130 in which temperature sensor 58c located just upstream of heater inlet 56i may not be needed, which is advantageous for reducing cost, eliminating a sensor that may need calibration from time to time, and eliminating a part that may need to be replaced. At block 132, method 130 begins. At block 134, control unit 100 opens all two-way valves associated with disinfection loop 90. At block 134, control unit 100 also uses feedback from temperature sensor 58a and a heating algorithm, such as a proportional, integral, derivative (PID) heating algorithm, to control inline heater 56 to output heated PD fluid at heater outlet 56o at a desired disinfection temperature, such as 85? C. At block 134, control unit 100 causes PD fluid pump 70 to pump in the normal treatment (forward) direction (left to right through pump 70 in FIGS. 1 and 2) for a preset number of pump strokes, e.g., 100 pump strokes.

[0084] At block 136, after the preset number of pump strokes in the treatment direction have been completed, control unit 100 causes PD fluid pump 70 to automatically reverse and pump in the opposite direction (right to left in FIGS. 1 and 2). Control unit 100 also sequences any of the valves of disinfection loop 90 as needed, e.g., sequences three-way valve 94a. In one embodiment, control unit 100 causes PD fluid pump 70 to pump in the reverse direction for a preset number of pump strokes, e.g., one-hundred pump strokes. As discussed below, control unit 100 may in one embodiment use forward open loop heater control during the pump reversing of method 130, which does not require the use of temperature sensor 58c (but closed loop control using temperature sensor 58c could be performed alternatively).

[0085] At diamond 138, after the preset number of pump strokes in the reverse direction have been completed, control unit 100 determines whether a total disinfection sequence time has been reached. Proper disinfection of disinfection loop 90 for method 130 again involves the movement of PD fluid heated at or above the recommended minimum disinfection temperature through disinfection loop 90 for a specified period of time. If the total or specified disinfection time has not been is reached, as determined at diamond 138, method 130 returns to block 134. Once the total or specified disinfection time is reached, as determined at diamond 138, the disinfection sequence is completed and method 130 ends at oval 140.

[0086] FIG. 6 illustrates one embodiment for using a downstream pressure sensor for closed loop control, which may be employed in method 110 for both forward and reverse heated PD fluid disinfection flow and in method 130 for forward heated PD fluid disinfection flow. FIG. 6 illustrates a portion of disinfection loop 90 having inline heater 56, temperature sensor 58a outputting to control unit 100 and temperature sensor 58c outputting to control unit 100. In the forward direction, the output from temperature sensor 58a is used for feedback control. In reverse direction, the output from temperature sensor 58c is used for feedback control.

[0087] FIG. 5 illustrates that for closed loop control, control unit 100 reads the temperature from the pertinent temperature sensor 58a, 58c. Control unit 100 also stores a target temperature, e.g., 85? C. Control unit 100 calculates an error between the commanded or target temperature and the temperature read from the pertinent temperature sensor 58a, 58c. Control unit 100 then inputs the calculated error into the heating algorithm, e.g., PID heating algorithm. An output from the heating algorithm is used by control unit 100 to determine how much power to deliver to inline heater. The cycle just described is repeated at some processing frequency.

[0088] It should be appreciated that for both methods 110 and 130, closed loop control in the forward direction should very quickly produce a temperature reading at temperature sensor 58a in the range of the commanded temperature, e.g., 85? C. For method 100, which triggers the reverse flow when temperature sensor 58c senses a low temperature for a certain period of time as discussed above, that same temperature sensor 58c, which is then used for closed loop control, will initially read a lower temperature corresponding to a mixture of hot PD fluid exiting inline heater 56 in the reverse direction and cooler PD fluid residing just upstream from heater inlet 56i. Here, a period of time will occur before temperature sensor 58c begins to read temperatures in the range of the commanded temperature, e.g., 85? C.

[0089] FIG. 7 illustrates an alternative way to control inline heater 56 during reverse PD fluid flow, which involves a forward open loop control, and which does not require temperature sensor 58c (missing in FIG. 7). The forward open loop heater control is accordingly suitable for the reverse PD fluid flow of method 130. The forward open loop heater control of FIG. 7 used during the reverse PD fluid flow of method 130 uses an output from temperature sensor 58a to control unit 100. It should be appreciated that during reverse PD fluid flow, temperature sensor 58a is located upstream of heater outlet 56o of inline heater 56.

[0090] FIG. 6 illustrates that for open loop control, control unit 100 reads the temperature from temperature sensor 58a and also stores a target temperature, e.g., 85? C. Control unit 100 also determines (calculates or measures) a current PD fluid flowrate. If a piston pump is used as PD fluid pump 70 and no flowmeter is provided, control unit 100 calculates the current flowrate by accumulating known volume pump strokes pumped by PD fluid pump 70 and dividing the accumulated volume by an amount of time needed to make the pump strokes accumulated. If instead a separate flowmeter is provided (not illustrated in FIGS. 1 and 2), then control unit 100 measures the flowrate by reading an output from the flowmeter.

[0091] At FIG. 7, control unit 100 inputs the temperature from temperature sensor 58a and the determined flowrate into a feed forward heater algorithm. An output from the feed forward heater algorithm (or derivative or correlation thereof) is used by control unit 100 to determine how much power to deliver to inline heater. The cycle just described is repeated at some processing frequency. In one example, the feed forward heater algorithm may be:

required heater output power=(target temperature?inlet temperature)?PD fluid flowrate?specific heater of water

In an example in which the inlet temperature read by temperature sensor 58a is 70? C., the target temperature is 85? C., the determined flowrate is 300 ml/min (5 ml/second), and the specific heat of water is 4.184 (Jouls/grams?? K), then the needed output power is (85-70)?5?4.184, which equals 313.8 Watts of heating power. In an embodiment, memory 104 of control unit stores a lookup table for inline heater 56, which correlates how much current or heater inlet power is needed to achieve 313.8 Watts of heating power (or closest power stored).

[0092] FIG. 8 illustrates two temperature plots Ti and To over time, which are of the temperature at inlet 56i of inline heater 56 and the temperature at outlet 56o of inline heater 56, respectively. The reversing of PD fluid pump 70 during disinfection caused by control unit 100 occurs, e.g., at times t.sub.rev, where a sharp increase in temperature occurs at inlet 56i of heater 56. The stopping of the reversing of PD fluid pump 70 during disinfection caused by control unit 100 to instead pump again in the normal direction occurs, e.g., at times t.sub.norm, where a sharp increase in temperature occurs at outlet 56o of heater 56. It should be appreciated that while temperatures in both temperature plots Ti and To are shown falling to about 60? C. (140? F.), which is likely below the minimum disinfection temperature, the power (or duty cycle) to heater 56 may be increased such that the minimum temperatures for temperature plots Ti and To do not, or do not significantly, fall below minimum disinfection temperature, e.g., 75? C. (167? F.). Time varies in minutes in the illustrated embodiment. The importance of FIG. 8 is to show that the pump reversing does have a significant and immediate impact of the temperature at inlet 56i of inline heater 56.

[0093] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. It is therefore intended that such changes and modifications be covered by the appended claims.