Vent Interlock

Abstract

A control system for a perfusion system (1), the control system being configured to control a plurality of blood flow rates in the perfusion system during a weaning phase. The perfusion system comprises: a first blood line (26) in which blood is permitted to flow at a first flow rate; a second blood line (34) in which blood is permitted to flow at a second flow rate; an arterial blood line (22) in which blood is permitted to flow at an arterial flow rate; and an arterial pump (20) configured to circulate blood at the arterial flow rate in the arterial blood line. The control system comprises a controller configured to determine the first flow rate and the second flow rate and to process the first and second flow rates to determine a desired arterial flow rate. The controller is configured to operate in a first mode in which the controller modulates operation of the arterial pump (20) to adjust the arterial flow rate so that the arterial flow rate matches the desired arterial flow rate.

Claims

1. A control system for a perfusion system, the control system being configured to control a plurality of blood flow rates in the perfusion system during a weaning phase, the perfusion system including: a first blood line in which blood is permitted to flow at a first flow rate; a second blood line in which blood is permitted to flow at a second flow rate; an arterial blood line in which blood is permitted to flow at an arterial flow rate; and an arterial pump configured to circulate blood at the arterial flow rate in the arterial blood line, wherein the control system comprises: a controller configured to determine the first flow rate and the second flow rate and to process the first and second flow rates to determine a desired arterial flow rate, wherein the controller is configured to operate in a first mode in which the controller modulates operation of the arterial pump to adjust the arterial flow rate so that the arterial flow rate matches the desired arterial flow rate.

2. The control system according to claim 1, wherein the desired arterial flow rate is determined relative to the sum of the first flow rate and the second flow rate.

3. The control system according to claim 1, wherein the desired arterial flow rate is equal to, greater than, or less than the sum of the first flow rate and the second flow rate.

4. The control system according to claim 1, wherein the first flow rate is a venous flow rate, and the first blood line is a venous blood line for draining blood into a reservoir.

5. The control system according to claim 1, wherein the second flow rate is a vent flow rate, and the second blood line is a vent blood line for draining blood into a reservoir

6. The control system according to claim 1, wherein the perfusion system comprises a second pump configured to circulate blood at the second flow rate in the second blood line.

7. The control system according to claim 6, wherein the controller is configured to determine the second flow rate based on calculations using known system parameters.

8. The control system according to claim 7, wherein the known system parameters relate to: tube sizing parameters of the second blood line; pump sizing parameters of the second pump; and/or operational pump parameters of the second pump.

9. The control system according to claim 1, further comprising a first flow sensor configured to provide a first flow value indicative of the first flow rate in the first blood line.

10. The control system according to claim 1, further comprising a second flow sensor configured to provide a second flow value indicative of the second flow rate in the second blood line.

11. The control system according to claim 1, further comprising an arterial flow sensor configured to provide an arterial flow value indicative of the arterial flow rate in the arterial blood line, wherein the controller is configured to modulate operation of the arterial pump to adjust the arterial flow rate so that the arterial flow value indicated by the arterial flow sensor matches an arterial flow value indicative of the desired arterial flow rate.

12. The control system according to claim 1, further comprising an adjustable restriction responsive to the controller, wherein the adjustable restriction is configured to reduce the first flow rate in the first blood line to maintain a flow rate that does not exceed a restriction threshold.

13. The control system according to claim 12, wherein the adjustable restriction comprises a gradually actuatable occlusive device.

14. The control system according to claim 12, wherein the control system is configured to allow the restriction threshold and the desired arterial flow rate to be set independently.

15. The control system according to claim 1, wherein the controller is configured to operate in a second mode in which the controller modulates operation of the arterial pump to maintain the arterial flow rate independently of the first flow rate and/or the second flow rate.

16. A perfusion system comprising: a first blood line in which blood is permitted to flow at a first flow rate; a second blood line in which blood is permitted to flow at a second flow rate; an arterial blood line in which blood is permitted to flow at an arterial flow rate; an arterial pump configured to circulate blood at the arterial flow rate in the arterial line; and a control system according to claim 1.

17. A method of controlling, during a weaning phase, a plurality of blood flow rates in a perfusion system comprising: a first blood line in which blood is permitted to flow at a first flow rate; a second blood line in which blood is permitted to flow at a second flow rate; an arterial blood line in which blood is permitted to flow at an arterial flow rate; and an arterial pump configured to circulate blood at the arterial flow rate in the arterial line, the method comprising the steps of: determining, by a controller, the first flow rate and the second flow rate; processing, by the controller, the first and second flow rates to determine a desired arterial flow rate; and operating the controller in a first mode, thereby modulating operation of the arterial pump to adjust the arterial flow rate so that the arterial flow rate matches the desired arterial flow rate.

18. (canceled)

19. (canceled)

20. The method according to claim 17, wherein the first flow rate is a venous flow rate, and the first blood line is a venous line for draining blood into a reservoir.

21. The method according to claim 17, wherein the second flow rate is a vent flow rate, and the second blood line is a vent line for draining blood into a reservoir.

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. A non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause a controller comprising the processor to perform the method according to claim 17.

Description

DESCRIPTION OF THE FIGURES

[0071] Exemplary embodiments of the invention will now be described with reference to the Figures, in which:

[0072] FIG. 1 shows a schematic arrangement of components of a perfusion system comprising a control system being configured to control a plurality of blood flow rates in the perfusion system during a weaning phase in accordance with embodiments of the present invention;

[0073] FIG. 2 shows a schematic arrangement of components of a perfusion system comprising a control system being configured to control a plurality of blood flow rates in the perfusion system during a weaning phase in accordance with alternative embodiments of the present invention;

[0074] FIG. 3 shows a schematic arrangement of components of a perfusion system comprising a control system being configured to control a plurality of blood flow rates in the perfusion system during a weaning phase in accordance with yet further alternative embodiments of the present invention;

[0075] FIG. 4 shows steps of an exemplary sequence of method steps of a method for restricting the flow rate in a blood line.

[0076] FIG. 5 shows steps of an exemplary sequence of method steps of a method for controlling a plurality of blood flow rates in a perfusion system in accordance with embodiments of the present invention.

DESCRIPTION

[0077] FIG. 1 shows, schematically, components of a perfusion system 1. The perfusion system comprises a venous line 12 provided to receive venous blood V from a patient. Via the venous line 12, venous blood is permitted to flow into a reservoir 10 via a reservoir inlet 14. In the venous line 12, the control system comprises a venous flow sensor 26. The venous flow sensor 26 is configured to provide a flow value indicative of the flow rate in the venous line 12, and may be constituted by an ultrasonic flow meter.

[0078] The perfusion system 1 further comprises a vent line 34 provided to receive a mixture M of left ventricular blood and residual air from the left ventricle of the patient's heart. Via the vent line 34, the air-blood mixture is permitted to flow into the reservoir 10 via a reservoir inlet 36. The perfusion system 1 may further comprise a vent pump (not shown in FIG. 1) for drawing blood via the vent line 34 from the patient.

[0079] De-foaming agents may be added to the blood in the reservoir to remove the residual air from the blood. Alternatively, the air-blood mixture may flow into a de-foaming system (not shown in the figure), either prior to entry to the reservoir or after exit from the reservoir. The resulting venous blood is held in the reservoir 10 at atmospheric pressure.

[0080] The venous blood may be drawn from the reservoir 10 via a reservoir outlet 16 through the main line 22 of the perfusion system. The blood is pumped by a pump 20, which may be any suitable type of pump, such as a peristaltic pump (e.g., a roller pump) or a centrifugal pump. The pump causes blood to flow through the main line 22 in a direction indicated by arrows 18, via an oxygenator 30 and towards an outlet 24 of the perfusion system 1.

[0081] At the outlet 24, the blood is in a condition for administration to a patient. For instance, the blood may have been oxygenated in the oxygenator 30, and the blood will have a flow rate and line pressure sufficient to permit safe administration to a patient. The main line 22 can therefore be considered to be an arterial line 22. The terms main line and arterial line may be used interchangeably herein. In the absence of losses, it can be assumed that the flow rate and the line pressure are determined by the pump 20. If the pump 20 generates higher throughput, the arterial flow rate is faster. Conversely, if the pump 20 generates lower throughput, the arterial flow rate is slower.

[0082] The venous line 12 and the main line 22 may be constituted by flexible tubing. The tubes may have a different length and/or diameter. The tubes may have different strength or flexibility characteristics.

[0083] In an embodiment, the venous line 12 constitutes a first blood line, the venous flow sensor 26 constitutes a first flow sensor, and the vent line 34 constitutes a second blood line.

[0084] Downstream of the reservoir 10, (in FIG. 1 also downstream of the oxygenator 30), the perfusion system is provided with a main flow sensor 32. The main flow sensor 32 allows the flow rate of the blood provided towards the patient to be measured. The main flow sensor 32 may also be considered to be an arterial flow sensor. These terms may be used interchangeably herein. The flow rate towards the patient may be regarded as output, or arterial, flow rate. The flow sensor 32 is configured to provide an arterial flow value indicative of the arterial flow rate in the main blood line, i.e., of the flow rate through the outlet 24.

[0085] A controller (not shown in FIG. 1) is configured to determine the venous flow rate and the vent flow rate. The controller may determine the vent flow rate based on pump parameters and known data connected with the tubing that constitutes vent line 34.

[0086] The controller is configured to receive a venous flow value indicative of the venous flow rate, as determined by the flow sensor 26. The controller may determine a venous flow rate from the venous flow value. The controller is configured to process the vent flow rate and the venous flow value to determine a desired arterial flow rate. For example, the controller may sum the venous flow rate and the vent flow rate (of which the flow values are indicative) to determine a desired arterial flow rate.

[0087] In a first mode, the controller is configured to operate the pump 20 to maintain the desired arterial flow rate. The arterial flow value may be derived from operational parameters of the pump 20. The arterial flow value may be determined by the flow sensor 32. The controller comprises decision logic to determine whether or not the arterial flow rate (as indicated by the arterial flow value) matches the desired arterial flow rate. If the arterial flow rate does not match the desired arterial flow rate, the controller will modulate the operation of pump 20 in order to match the arterial flow rate to the desired arterial flow rate. For example, if the arterial flow rate is greater than the desired arterial flow rate the controller will reduce the throughput of the pump 20 in order to reduce the arterial flow rate.

[0088] In an embodiment, the controller may be configured to receive as an input a desired offset. The desired offset indicates that the desired arterial flow rate should be greater than or less than the sum of the venous flow rate and the vent flow rate, as dictated by the value of the offset. The offset may be a specified amount (e.g. 1 lpm) or it may be a percentage offset (e.g. 10% greater than the sum). In such an embodiment, the controller is configured to modulate the operation of the pump 20 in order to match the arterial flow rate to the desired arterial flow rate as modified by the offset.

[0089] The first mode allows, for example, the arterial flow rate to be matched to the sum of the venous flow rate with the vent flow rate. This keeps the level of blood in the reservoir 10 at a constant level, safely and automatically maintaining the balance between the venous reservoir blood volume and the patient blood volume. This relationship continues even if the venous flow rate becomes zero (e.g. if a restriction arrangement restricted venous line 12 to prevent any blood flow). At a zero venous flow rate, the pump 20 will run at precisely the same flow rate as the vent flow rate (i.e. the arterial flow rate=the vent flow rate).

[0090] In a second mode, the controller modulates operation of the arterial pump 20 to maintain the arterial flow rate independently of the first flow rate and/or the second flow rate. This allows the patient's vascular system to be filled or drained by maintaining the arterial flow rate at a set rate, while adjusting the venous flow rate and/or the vent flow rate.

[0091] Turning to FIG. 2, a schematic representation of components of a perfusion system 2 is shown. The perfusion system 2 is equivalent to perfusion system 1 except, in the vent line 34, the control system further comprises a vent flow sensor 38. Perfusion system 2 has the same operating principles as perfusion system 1, except that the controller may receive a vent flow value indicative of the vent flow rate in the vent blood line directly from the vent flow sensor 38. This means that the controller is not required to determine the vent flow rate using calculations related to known system parameters, though it may still determine in this way if so required.

[0092] Turning to FIG. 3, a schematic representation of components of a perfusion system 3 is shown. The perfusion system 3 is equivalent to perfusion system 2 except in the venous line 12, the control system further comprises a flow-restricting arrangement 28. The above description of configuration and functionality of perfusion system 2 equivalently applies to perfusion system 3. Perfusion system 3 has the additional functionality as described below. While perfusion system 3 is shown to utilise a vent flow sensor 38, it will be appreciated that perfusion system 3 need not comprise such a sensor, and could instead operate on the principles of perfusion system 1.

[0093] The flow-restricting arrangement 28 may be configured to allow the flow to be restricted gradually. For instance, the flow-restricting arrangement 28 may be constituted by a motorised clamp suitable to squeeze a flexible tube.

[0094] In an embodiment, the venous line 12 constitutes a first blood line, the venous flow sensor 26 constitutes a first flow sensor, and the flow-restricting arrangement 28 constitutes an adjustable restriction.

[0095] The motorised clamp is responsive to a controller (controller not shown in FIG. 3) and allows the flow rate in the venous line to be prevented from exceeding a restriction threshold. For instance, the controller may issue a control signal to the motorised clamp to squeeze the venous line 12 until the flow rate, as determined by the flow sensor 26, no longer exceeds the restriction threshold. The controller of FIG. 3 may or may not be the same as the controller of FIGS. 1 and/or 2.

[0096] Due to the closed loop control, it is not necessary to know by how much the tube was squeezed, or which type of equipment was used, in order to maintain the restriction threshold.

[0097] Partially clamping the flexible tube to a sufficient extent allows the flow rate in the venous line 12 to be restricted. By gradually opening the clamp, the degree of restriction of the flow rate in the venous line 12 can be reduced until there is no flow rate restriction by the flow-restricting arrangement 28.

[0098] A controller (not shown in FIG. 3) is configured to receive as an input a restriction threshold to indicate the maximum flow rate through the venous line 12. For instance, the restriction threshold may be set via an interface. The restriction threshold may be set as an absolute value (e.g., 2 lpm) or as a relative value (e.g., half of the current flow). The current flow rate may be determined by the venous flow sensor 26 or by the main flow sensor 32. For instance, the restriction threshold may be set to half the arterial flow value.

[0099] The controller is configured to receive a venous flow value indicative of the venous flow rate, as determined by the flow sensor 26. The controller comprises decision logic to determine whether or not the venous flow rate exceeds the restriction threshold. If the venous flow value does not exceed the set restriction threshold, the flow-restricting arrangement 26 is not actuated. If the venous flow value exceeds the set restriction threshold, the controller may issue a control signal to the flow-restricting arrangement 28 to increase the flow restriction until the venous flow rate no longer exceeds the restriction threshold.

[0100] After the flow-restricting arrangement has been set, the controller continues to monitor the venous flow as determined by the flow sensor 26. If, for any reason, the flow value exceeds the restriction threshold despite a previously appropriate restriction setting, the controller issues a control signal to the flow-restricting arrangement 28 to adjust the restriction threshold.

[0101] The desired arterial flow rate and the restriction threshold may each be set independently, e.g., in absolute values, via an input interface.

[0102] The controller may be configured to adjust the arterial flow rate through the outlet 24 relative to the restriction threshold in the venous line 12.

[0103] For instance, the restriction threshold and the desired arterial flow rate may be matched. The venous flow threshold may be set to 2 lpm, and venous blood can be expected not to flow into the reservoir 10 faster than at a rate of 2 lpm. The controller may adjust the operation of the pump 20 such that the flow rate through the outlet, as measured by the main flow sensor 32, is not more than 2 lpm. This may be useful, for example, if vent line 34 is not in use (i.e. the vent flow rate is zero). If the vent flow rate is not zero, the desired arterial flow rate may be matched to the sum of the restriction threshold and the vent flow rate.

[0104] In the venous line 12, the actual venous flow rate is monitored by the first flow sensor 26. If, for any reason, the actual venous flow rate exceeds the threshold of 2 lpm, the controller is configured to respond by increasing the flow restriction, until the venous flow rate is at, or below, 2 lpm.

[0105] If the desired arterial flow rate and the restriction threshold are set independently, a change of the desired arterial flow rate will not affect the restriction threshold.

[0106] A similar process may be applied if the controller is set to match the main flow rate and the sum of the venous flow rate and the vent flow rate. For example, the venous flow restriction may be reduced by setting the venous flow threshold from 2 lpm to 3 lpm. If the vent line has a vent flow rate of, say, 1 lpm, the controller may increase the pump speed until the main flow rate is 4 lpm. Likewise, the venous flow restriction may be increased (the restriction threshold may be lowered), e.g. from 2 lpm to 1 lpm. Assuming the vent flow rate has remained constant, the controller may reduce the pump speed to reduce the main flow rate to 1 lpm.

[0107] The restriction threshold may be below or above the desired arterial flow rate. This provides a control over the blood supply during the different end phases of extracorporeal perfusion.

[0108] To initiate the end of extracorporeal perfusion support, the controller can be set to operate in the second mode, and the restriction threshold may be reduced to restrict the venous flow, e.g., to 2 lpm. At this stage, the output flow rate as determined by the pump may continue to be governed by normal perfusion requirements and the controller will no longer match the arterial flow rate to the sum of the venous flow rate and the vent flow rate. Such normal perfusion requirements may include cardiac index values and venous saturation. The arterial flow rate may be in the region of 5 lpm. As the arterial flow rate exceeds the sum of the venous flow rate and the vent flow rate, this results in a gradual filling of the vascular system.

[0109] When the vascular system is filled to a sufficient extent (this may be determined by a physiological blood pressure), the restriction threshold may be maintained and the desired arterial flow rate may be set to match the sum of the restriction threshold and the vent flow rate, by setting the controller to operate in the first mode. The output flow rate is no longer governed exclusively by normal perfusion requirements. For instance, the desired arterial flow rate and the restriction threshold may be adjusted to such that the CVP is close to, but not exceeding 15 mmHg, and/or such that the PAD is close to, but not exceeding 20 mmHg.

[0110] The restriction threshold of the venous line and the desired arterial flow rate of the main line may be adjusted synchronously. If the heart performs satisfactorily at a perfusion flow rate of 2 lpm, the restriction threshold and the pre-determined output flow rate may be reduced further, e.g., from 2 lpm to 1 lpm, to further encourage heart activity. This may affect the pressure levels, such as CVP and/or PAD. If a pressure level is too low, the desired arterial flow rate may be temporarily increased relative to the restriction threshold in order to increase the CVP or PAD value. If a pressure level is too high, the output flow rate may be temporarily decreased, and/or the restriction threshold may be partially lifted.

[0111] The restriction threshold and the desired arterial flow rate may be adjusted independently. For instance, a clinician may wish to adjust these thresholds manually according to other blood values, such as venous oxygen saturation.

[0112] If heart performance at the reduced output flow rate is insufficient, extracorporeal perfusion may be resumed by increased the output flow rate and/or by lifting the restriction threshold.

[0113] If the heart performs well with a reduced extracorporeal perfusion support, extracorporeal perfusion support may be further reduced, by setting a the desired arterial flow rate to a lower level, until a decision can be made to completely cease extracorporeal perfusion and to let the heart take over circulation.

[0114] It will be readily understood that the above-described functionality can be interchangeably applied to systems with or without an operating vent line 34. That is to say, in systems where the vent line 34 is not in use and/or the vent flow rate is zero, the arterial flow rate may be matched with or set relative to the restriction threshold or the venous flow rate. Whereas, in systems where the vent line is operational (i.e. the vent flow rate is non-zero), the arterial flow rate may be matched with or set relative to the sum of the vent flow rate and the venous flow rate, or the sum of the vent flow rate and the restriction threshold. Such logic is readily applied to the above description in relation to blood flow rate and pressure management, as well as to the filling or draining of the patient's vascular system.

[0115] In FIG. 4, steps of a control method 40 for restricting the flow rate in a blood line, such as a venous line, are shown. Such a control method may be implemented by a perfusion system such as perfusion system 3. In step 42, blood is permitted to flow through a blood line. In step 44, a blood flow sensor is provided in the blood line, to provide a blood flow value indicative of the flow rate in the blood line. In step 46, an adjustable restriction is provided to allow the flow through the blood line to be reduced. In step 48, a restriction threshold is set. The restriction threshold may be regarded as a maximum blood flow rate level. In step 50, the blood flow value (e.g., of venous blood) is determined by the blood flow sensor. In step 52, the blood flow is reduced, using the adjustable restriction, to below the restriction threshold. The restriction threshold remains responsive to the flow rate. I.e., if a blood flow value is determined to be higher than the restriction threshold, the adjustable restriction is re-adjusted to limit the flow rate to the restriction threshold.

[0116] In FIG. 5, steps of a control method 60 for controlling a plurality of blood flow rates in a perfusion system are shown. Such a control method may be implemented by a perfusion system such a perfusion systems 1, 2 or 3. In step 62, blood is circulated at an arterial flow rate in an arterial line. In step 64, blood flow is permitted in a first blood line (for example, a venous line) at a first flow rate. In step 66, blood flow is permitted in a second blood line (for example, a vent line) at a second flow rate. In step 68, the first and second flow rates are determined. In step 70, the first and second flow rates are processed to determine a desired arterial flow rate. Step 70 optionally comprises determining the desired arterial flow rate relative to the sum of the first and second flow values. In step 72, a controller is operated in a first mode to modulate operation of the arterial pump to adjust the arterial flow rate so that the arterial flow rate matches the desired arterial flow rate. In optional step 74, the controller is operated in a second mode to modulate operation of the arterial pump to maintain the arterial flow rate independently of the first flow rate and/or the second flow rate.

[0117] Threshold values described herein, such as the restriction threshold, the output flow rate, and pressure thresholds, may include a margin to avoid an overshooting response.

[0118] The methods disclosed herein can be performed by instructions stored on a processor-readable medium. For example, a processor-readable medium can comprise instructions that, when executed by a processor, cause the processor to perform any of the methods as previously described. Likewise, a processor-readable medium can comprise instructions that, when executed by a processor, cause the processor to implement the functionality of the control system disclosed herein. The processor-readable medium may be: a read-only memory (including a PROM, EPROM or EEPROM); random access memory; a flash memory; an electrical, electromagnetic or optical signal; a magnetic, optical or magneto-optical storage medium; one or more registers of a processor; or any other type of processor-readable medium. Alternatively, the present disclosure can be implemented as logic in hardware, firmware, software or any combination thereof. The control system may be implemented by dedicated hardware, such as one or more application-specific integrated circuits (ASICs) or appropriately connected discrete logic gates. A suitable hardware description language can be used to implement the method described herein with dedicated hardware.

[0119] It will be understood that the invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention.