WO1998030275A1

WO1998030275A1 - Controller for delivery of fluids

Info

Publication number: WO1998030275A1
Application number: PCT/US1998/000021
Authority: WO
Inventors: James R. Ellsworth
Original assignee: Harvest Technologies, Llc
Priority date: 1997-01-09
Filing date: 1998-01-09
Publication date: 1998-07-16

Abstract

A flow-control apparatus uses feedback to control the delivery rate of an anticoagulant to shed blood that is recovered in a blood-salvaging system. An electronic circuit (46) detects the flow rate at which an anticoagulant is added to the collected blood such that the rate of anticoagulant flow is a function of the flow rate of the collected blood. A second timing circuit (42) provides an additional flow of anticoagulant at a rate independent of the flow rate of the collected blood. The flow rate of the anticoagulant is controlled by passing a tube (8) carrying the anticoagulant through a pinch mechanism. The pinch mechanism is electrically controlled by the timing circuit and by the circuit that detects the flow rate of collected blood by sensing the pressure in the vacuum collection line (32).

Description

CONTROLLER FOR DELIVERY OF FLUIDS

TECHNICAL FIELD

This invention relates to the art of devices for controlled delivery of fluids. In the preferred embodiment, the invention provides controlled delivery of an anticoagulant for a blood recovery system.

BACKGROUND

In a known blood recovery system, shed blood is collected by a vacuum system that is carefully regulated to provide vacuum pressures that do not harm the cells of the blood being collected. An anticoagulant, such as citrate, is added to the blood as it is collected to prevent clotting. Heparin may also be used to prevent clotting by applying it to foreign surfaces or by adding it to the collected blood.

It is important to maintain a prescribed anticoagulant concentration, preferably from five to twenty parts blood to one part anticoagulant, because blood with too little anticoagulant will clot, whereas blood with too much anticoagulant requires washing to remove the excess anticoagulant. It is at present difficult to maintain a flow rate of anticoagulant that achieves this. Such is particularly true for most systems in practice because the rate of collection of shed blood generally varies as a function of time, whereas the rate of flow of the anticoagulant through a tube of give size is time invariant. One known device for controlling the flow of anticoagulant is a roller clamp that is positioned to occlude to a desired degree a tube carrying the anticoagulant. These roller clamps are not precision devices, and it is difficult to set the flow rate accurately with this device. Thus, it is common to set a high flow rate to ensure that enough anticoagulant will be present, and this generally results in adding too much anticoagulant. The excess anticoagulant must then be removed in the post-recovery process of cell washing, which involves the use of centrifugation to separate the red blood cells from other parts of the recovered fluids, including the anticoagulant. Thus, it has not been possible to maintain a fixed blood-to-anticoagulant ratio with known devices.

SUMMARY OF THE INVENTION

In accordance with the invention, a flow meter monitors the rate at which shed blood is collected through an aspiration tube in a vacuum-operated collection system. In the preferred embodiment, the flow meter employs the combination of a precision restriction in the flow path and a pressure transducer to accurately measure the flow rate. As increased volumes of blood are entrained in the aspiration tube, the flow rate of the fluids in the tube decreases, and this information is used in the system of the invention to control the supply of anticoagulant to the collected blood.

In accordance with one aspect of the invention, a pressure sensor detects the pressure differential across the precision restriction as a measure of the flow rate of the collected fluids in the aspiration tube. A first circuit includes a transducer for converting this pressure differential to a voltage, and the voltage is applied to an electrical device for controlling the flow of anticoagulant. In the preferred embodiment, the electrical device includes a solenoid that controls the amount by which a flexible tube carrying the anticoagulant is pinched. Thus, as the flow rate of collected blood increases, the pressure differential across the restriction decreases, and the solenoid is provided with an electric voltage that causes it to release and open the tube carrying the anticoagulant, whereby the flow of anticoagulant is increased.

The control mechanism preferably includes a platen that receives the tube carrying the anticoagulant and a lever for squeezing the tube against the platen. The lever is biased by a spring to occlude the tube to stop the flow of anticoagulant. The solenoid is arranged to move the lever by pushing against the force of the spring to reduce the amount by which the tube is occluded, thereby increasing the flow of anticoagulant.

A second circuit operating in parallel with the first is a timing circuit, which includes a pulse generator for applying periodic electric signals to the solenoid. These periodic signals release the pressure applied by the lever periodically to provide a constant "drip" flow rate of the anticoagulant at a rate that is independent of the rate at which blood is collected. This flow prevents drying of the passages.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of a blood collection system using a controller in accordance with the invention.

Figure 2 is a side view of a controller in accordance with the invention.

Figure 3 is a circuit diagram of a control circuit in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With references to the figures, figure 1 shows an overall schematic diagram of a system employing the invention. A blood collection system 2 includes a vacuum source that applies vacuum to an aspiration tube 4 for aspirating shed blood and carrying it to a reservoir as is known in the art. A container 6 of anticoagulant is connected to a tube 8 for supplying the anticoagulant to the collected blood or other fluids. In the embodiment shown, the anticoagulant is supplied to the blood as it flows in the aspiration tube 4. A sucker handle 10 is connected to the ends of the aspiration tube and the anticoagulant tube by a connector 12. This connector includes Y-shaped interior channels that connect the sucker handle to the aspiration and anticoagulant tubes such that the anticoagulant is drawn into the aspirated fluids as they flow through the handle into the aspiration tube. The aspiration and anticoagulant tubes are preferably provided in a dual-lumen tube as illustrated.

The anticoagulant tube 8 is directed through a flow controller 14, which is shown schematically in figure 1 and in more detail in figure 2. With reference to figure 2, an enclosure 16 supports a platen 18 and a movable element, such as a lever 20, for pressing the tube 8 carrying anticoagulant against the platen. In the preferred embodiment shown, the lever 20 is pivotally mounted to the enclosure 16 at a pin 22 such that one end of the lever engages the tube 8 and an opposite end engages a bias spring 24 and the plunger of a control solenoid 26 . One end of the bias spring is held by a bracket 28, and the other end engages the lever 20. In operation, the spring pulls on one end of the lever, which causes the other end of the lever to press the tube 8 against the platen 18 to occlude the tube. Thus, the normal condition of the mechanism is for the anticoagulant tube 8 to be pinched closed. The solenoid 26 is arranged to engage the lever such that energization of the solenoid pushes against the lever in a direction opposite to the direction of the force applied by the bias spring. Thus, energization of the solenoid releases the occlusive pressure on the tube and allows increased flow of anticoagulant into the aspiration tube through the connector 12 illustrated in figure 1.

The end of the lever 20 opposite the spring includes a ramp portion 30 which terminates adjacent the platen 18. This facilitates insertion of the tube 8 into the gap formed between the lever and the platen. During installation, the tube is placed against the ramp and urged toward the platen against the force of the spring. This moves the lever away from the platen to allow the tube to be located in the gap between these elements.

The preferred control circuit is shown in figure 3. A vacuum line 32 is connected between a source of vacuum 34 and the aspiration tube 4. In the preferred embodiment shown, the vacuum line connects to a collection chamber 36, and the aspiration line also connects to that chamber. The vacuum source and collection chamber are elements of the blood collection system 2 shown in figure 1. It will be appreciated that the collection chamber may be a disposable element. The vacuum line 32 is provided with a precision flow restriction 38, which creates a pressure differential that is a function of the flow rate of the fluids undergoing collection. A pressure transducer 40 measures the pressure drop across the flow restriction, and the output of the transducer is connected to a flow meter function circuit 42. This circuit produces a voltage that is a function of the pressure drop across the flow restriction and, hence, a function of the flow of collected blood in the aspiration tube. The voltage produced by the flow meter function circuit is applied to the solenoid 26 of figure 2 through an "or" gate 44. It will be appreciated that as the collection system collects blood, the flow rate of collected blood through the aspiration tube decreases, and the pressure differential across the restriction decreases. This decrease is detected by the pressure transducer 40, which is of known construction, and a voltage is produced that is an inverse function of the pressure across the restriction. As the voltage applied to the solenoid increases, the pressure applied to the anticoagulant tube by the lever decreases, and the flow rate of anticoagulant increases. The parameters of the circuitry are adjusted such that the increase or decrease in flow of collected blood is matched by a proportional increase or decrease in flow of anticoagulant, whereby the ratio between the two is maintained.

With further reference to the figure 3, a timing function circuit 46 produces regular pulses to the "or" gate. These pulses are provided to the solenoid irrespective of the voltage applied by the flow meter function circuit whereby a constant, small, flow of anticoagulant is provided to prevent drying of the passages.

It will be appreciated that other methods for controlling the flow of anticoagulant could be used. For example, other pinching devices could be used or the pressure applied to the anticoagulant could be controlled, as by raising or lowering the height of the bag containing the anticoagulant or by controlling a supply pump. Also, it is within the contemplation of the invention to provide the control circuit with only one of the flow meter function circuit and timing function circuit.

Modifications within the scope of the appended claims will be apparent to those of skill in the art.

Claims

I Claim:

1. A system for blending two fluids in a prescribed ratio comprising: a first flow path for carrying a first of said fluids at a variable flow rate, means for measuring the instantaneous flow rate of said first of said fluids flowing in said first flow path, means for admitting a second of said fluids to said first of said fluids, and means for controlling the admission of said second fluid to said first fluid as a function of the instantaneous rate of flow of said first of said fluids.

2. Apparatus for controlling the flow of a fluid comprising a platen configured to receive a flexible tube carrying said fluid, a movable element mounted for movement toward said platen, a biasing element applying a force to said movable element urging said movable element toward said platen, and a controllable element selectively resisting said force of said biasing element.

3. Apparatus according to claim 2 wherein said controllable element is electronically controllable, and said apparatus further comprises an electronic control circuit connected to said controllable element.

4. Apparatus according to claim 3 wherein said control circuit comprises a pressure transducer, a flow meter function circuit connected to said pressure transducer, a timing function circuit, and an OR gate connected to said pressure transducer and said timing function circuit.

5. Apparatus according to claim 3 in combination with a source of vacuum, a collection chamber for collection of a second fluid, a vacuum line connecting said source of vacuum to said collection chamber, and a pressure transducer connected between said vacuum line and said controllable element.

6. Apparatus according to claim 5 further comprising a precision restriction in said vacuum line.

7. Apparatus according to claim 5 further comprising an OR gate, and a timing function circuit, and wherein said timing function circuit and said pressure transducer are connected to said OR gate.

8. Apparatus according to claim 6 further comprising an aspiration tube connected to said collection chamber.

9. Apparatus according to claim 8 wherein said fluid is an anticoagulant, and further comprising a suction wand connected to said aspiration tube, a tube carrying said anticoagulant, and a connector in fluid communication with said tube carrying said anticoagulant and said suction wand.

10. A blood recovery system having a collection chamber, an aspiration wand connected to said collection chamber, a vacuum source connected to said aspiration wand, and a source of anticoagulant connected to said aspiration wand, characterized in that said vacuum source is connected to said collection chamber by a fluid line having a precision restriction therein, a pressure transducer measures the pressure differential across said precision restriction, and electrical signals from said pressure transducer are supplied to a controller that controls the flow of said anticoagulant.

11. A blood recovery system according to claim 10 wherein said controller comprises a fixed platen, a movable lever adjacent the platen for receiving a tube carrying said anticoagulant, a spring urging said lever against said platen, and a solenoid controlled by signals from said pressure transducer for relieving the force of said spring on said lever.