Auxiliary control for a blood pump

Abstract

An auxiliary control for a blood pump used in hemodialysis which acts upon an existing blood pump controller to continuously vary the pump rate in direct correspondence with changes in flow of a patient's blood reflected as variations in negative pressure in a blood line. The auxiliary control regulates the pump rate by producing an electrical pulse train in which the duration of the pulses corresponds to changes in negative pressure corresponding to changes in the blood flow rate. The control presents means for achieving a rapid response to changes in the flow of the patient's blood.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to an improved auxiliary control for an extracorporeal blood pump used in hemodialysis and more particularly to novel apparatus for controlling the blood pump rate in an extracorporeal hemodialysis system.

2. The Prior Art

Historically, kidney diseases have been of critical concern to human life. Many kinds of kidney diseases interfere with the function of the kidney such that the kidney ceases to remove waste and excess water from the blood. When the kidney is sufficiently impaired that a large portion of the waste products and water are not removed from the blood, the life of the patient cannot be preserved unless a way is provided for artificially performing the functions of the impaired kidney through extracorporeal hemodialysis.

Many of the presently known hemodialysis apparatus require the use of a blood pump to provide additional pressure in the withdrawn blood in order to conduct it through the hemodialysis unit. A major problem presented by the presently known blood pumps and associated control apparatus is the inability of such apparatus to provide a minimum time for dialysis while simultaneously preventing pump starvation and the resulting collapse of the supply blood lines. It is well-known that blood should be withdrawn from the patient at a rapid rate so as to reduce the time for dialysis. However, when the blood supply at the patient is insufficient to supply the blood pump, the blood lines and even the patient's blood vessels collapse which interrupts effective hemodialysis until adequate blood flow is restored. The collapse of blood lines resulting from insufficient blood supply to a continuously operating blood pump is defined herein as "pump starvation." To avoid time consuming and sometimes dangerous pump starvation, it has conventionally been necessary to adjust the pump speed well below an optimum rate to a level which provides a wide safety margin in order to avoid pump starvation.

Even with this precaution, however, it is common for the patient's blood flow rate to fluctuate significantly during the course of dialysis. Accordingly, the attending physician must choose between (a) lowering the pump rate to accommodate the lowest possible blood flow rate as a safety margin and thereby significantly extending the dialysis time or (b) risk collapse of blood lines and premature interruption of dialysis through pump starvation in the event of a drop in the patient's blood flow rate.

Several attempts have been made to produce a pump which is able to compensate for changes in the amount of available blood while the patient is undergoing dialysis. The prior art shows the use of step-wise regulation apparatus which only vary the volume of blood pumped in a series of discrete steps and do not allow for continuously variable changes in the volume of blood pumped. That type of pump and control apparatus requires a threshold level of pressure change before any responsive action is taken. One such step-wise system is shown in U.S. Pat. No. 3,698,381.

Other types of control apparatus have employed specially designed pumps which are mechanically capable of increasing the force applied to a collapsible blood reservoir in order to thereby increase the pressure of blood supplied from the reservoir. One such specialized blood pump and associated control is shown in U.S. Pat. No. 3,592,183.

A major deficiency which is observed in the attempts to solve the regulation of pump starvation is that the solution involves the replacement of all existing pump controllers and/or blood pumps. Until the present invention, it has not been possible to continuously vary the rate of a continuous flow blood pump in response to the availability of blood while retaining the existing conventional blood pump and controller.

BRIEF DESCRIPTION AND OBJECTS OF THE INVENTION

The present invention includes novel apparatus for continuously varying the pump rate of a blood pump used in hemodialysis in response to changes in blood flow from the patient so as to maximize the rate of hemodialysis while avoiding pump starvation. Furthermore, the invention provides apparatus which can accomplish the previously described function in combination with existing conventional blood pumps and control mechanisms.

It is, therefore, a primary object of the present invention to provide improved extracorporeal hemodialyzing pump control apparatus.

It is another primary object of the present invention to provide extracorporeal hemodialysis pump control apparatus which cooperates with presently known pumps and associated controls to achieve a continuously variable pump rate responsive to changes in blood flow.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram illustrating a presently preferred embodiment of the invention;

FIG. 2 illustrates a waveform taken at point A in FIG. 1, the waveform particularly showing a signal representation when the patient's blood flow has increased during the course of dialysis; and

FIG. 3 illustrates a waveform taken at point A of FIG. 1, the waveform particularly showing a signal representation when the patient's blood flow has decreased during the course of dialysis.

DETAILED DESCRIPTION OF THE INVENTION

Referring particularly to FIG. 1, an improved auxiliary control for a blood pump generally designated 20 is illustrated within the broken line. One of the features of the invention is the capability of use with existing blood pumps and associated controllers. Accordingly, for ease of illustration, the pump power supply 35, pump controller 39 and blood pump 37 have been schematically illustrated in FIG. 1, but do not constitute a part of the invention.

Blood is continuously forced from the patient to the dialyzer by blood pump 37. Accordingly, a negative pressure will exist in blood lines upstream from the pump. If outflow of the patient's blood should be limited through stricture, clotting, hypotension or any other of a variety of common circumstances, negative pressure upstream from the pump will increase proportionately. Conversely, negative pressure will decrease as blood becomes more available to the pump.

According to one presently preferred embodiment of the invention, a conventional pressure transducer 22 provides a direct conversion between negative pressure in the blood line 24 and electrical voltage. Blood line 24 connects the pressure transducer to a conduit (not shown) which carries blood from a blood vessel of a patient to the blood pump 37. The electrical qualities of the pressure transducer may be characterized as either a variable resistance or a variable voltage source. Whichever type of transducer is employed or whichever electrical characterization is used, the electrical quantity varies in proportion to the blood flow as measured by the negative blood pressure in line 24. The negative pressure is preferably observable on a conventional readout device 23.

The electrical output signal of the pressure transducer is fed into an averaging circuit 28. The averaging circuit 28 may be any one of a wide variety of known discrete or integrated circuits, the most simplified of which would merely be a capacitor in parallel with the transducer output conductors to accomplish averaging of the systolic and diastolic pressure signal from the transducer 22.

Certain types of pressure transducers which maintain a reservoir of blood and mechanically measure expansion and contraction of a chamber would not require the averaging circuit since the output signal from that type of transducer would be averaged mechanically.

The averaged transducer signal is then conducted to and appears at one of the inputs to a conventional operational amplifier 31 which forms part of the comparator 30. The initial reference control 32 provides a reference signal for the second comparing input of the operational amplifier 31. The initial reference control may be either a fixed or variable voltage divider which provides a pre-established signal level at one of at least two operational amplifier inputs.

The operational amplifier portion 31 of the comparator 30 is used in the summing mode, where the two inputs are added together to form an output to the electronic switch 36 which output is proportional to the sum of the inputs. The electronic switch 36 preferably comprises a conventional threshold trigger circuit capable of converting the output signal of the operational amplifier 31 into a pulse of duration proportional to the amplitude of the output signal of the operational amplifier. A common, readily available device for performing the function of the electronic switch would be any suitable type of current controlled current source such as a unijunction transistor with an external base to emitter timing capacitance which acts to fire a triac or the like.

The power supply for the operational amplifier portion of the comparator is a pulse generator 34 which produces a generally square wave voltage signal causing the output of the operational amplifier to turn on and off at a constant rate. Any suitable conventional pulse generator having sufficient voltage output to drive the operational amplifier would be acceptable.

It should be recognized that the signal from the operational amplifier is a periodic pulse having an amplitude proportional to the sum of the initial reference signal and the averaged transducer signal. It should be recognized that the higher the output signal from the comparator, the greater the time increment that switch 36 is on, and conversely the lower the signal from the comparator, the shorter the time increment that switch 36 is on.

As shown in FIG. 1, the regular power supply line to a conventional blood pump and controller is diverted through the electronic switch 36. The waveforms shown in FIGS. 2 and 3 are taken at point A in the diagram of FIG. 1, assuming an alternating current power supply like that available at a standard utility outlet. The solid portions of the waveforms represent that portion of the waveforms during which the electronic switch 36 is off. When the switch 36 turns on, it remains on until the AC cycle goes through zero. Because the switch 36 is open or off through most of the AC cycle in FIG. 3, the energy delivered from the pump power supply 35 to the pump controller 39 is comparatively small. Thus, the blood pump 37 operates slowly. Conversely, when the switch 36 is on through most of the AC cycle (see FIG. 2), the energy delivered to the controller 39 is comparatively high and the blood pump 37 will operate comparatively rapidly.

The existing conventional blood pump controller remains useful for the purpose of setting upper limits in the speed of the blood pump. However, the invention 20 provides for immediate and continuous compensation of the speed of the blood pump in response to changes in the patient's blood flow. When blood flow decreases, the output of the comparator 30 is reduced and therefore the electronic switch 36 allows a smaller proportion of the pump power supply signal to be conducted to the blood pump (see FIG. 3). Also, if the blood flow of the patient should increase during the course of dialysis, the amount of power supplied to the blood pump increases thereby increasing the speed of the pump (see FIG. 2). Accordingly, pump starvation caused by a vacuum-induced collapse of blood lines and blood vessels will be avoided because the pump 37 will operate only at the maximum rate accommodated by the available blood supply.

In using the invention, the patient is connected to the dialyzer in a method well-known in the art, the supply line 24 being normally in direct communication with the dialyzer blood circuit upstream from the pump. In one preferred method embodiment, the auxiliary control 20 is first switched off so as to have no effect on power delivered from the supply 35 to the pump controller 39. Alternatively, the auxiliary control 20 may remain on but the initial reference control 32 adjusted to the maximum so as not to interfere with the selection of a desirable maximum flow rate at the controller 39.

Subsequently, the blood pump 37 is energized and the speed of the blood pump is increased by adjusting the pump controller 39 to the desired maximum blood flow. The desired maximum blood flow may be ascertained by observing the negative pressure read-out 23 and increasing the speed of the blood pump until the negative pressure reaches a level prescribed by the attending physician. Alternatively, the maximum desired flow can be obtained by increasing the pump speed until the blood line or associated accumulator collapses and then reducing the speed of the blood pump 37 through the controller 39 slightly until full flow results.

Once the maximum desired flow has been established in the blood pump 37, the auxiliary controller 20 is activated by adjusting the initial reference control 32 at least until it appears from the negative pressure read-out 23 that the auxiliary control 20 is monitoring blood flow at essentially the maximum desired rate set by the pump controller 39. It has been found frequently desirable to set the initial reference control on a specific negative pressure reading representing a desirable blood flow rate.

When the initial reference control has been set, the auxiliary control 20 will continuously vary the blood pump speed so as to maintain the negative pressure reading at the preset level. Thus, if the patient's blood flow reduces, the auxiliary control 20 will reduce the speed of the blood pump 37 so that the negative pressure reading will not significantly change. Conversely, if the patient's blood flow increases, the auxiliary control 20 will increase the speed of the blood pump and prevent the negative pressure level from changing significantly.

The most advantageous physical housing for the invention has been found to be an enclosure (not shown) which provides an electrical outlet for the service plug of the conventional blood pump and controller, a meter for reflecting the negative pressure, and a dial plate and dial for setting the initial reference control. Of course, various power switches, pilot lights, or other indicators may be used in order to monitor the status of the circuit during operation.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

What is claimed and desired to be secured by United States Letters Patent is:

1. A blood pump controller responsive to changes in blood flow comprising:

a conventional blood pump for displacing blood through an extracorporeal hemodialysis system including a blood-conducting conduit;

a conventional power source and means for delivering electrical power to the blood pump, the pumping capacity of the pump being proportional to the electrical power delivered to the pump;

means electrically interposed between the power source and the blood pump said means comprising an attachment site means for detachably coupling the blood pump to the power source through the said means; sensing means in said blood-conducting conduit for monitoring the availability of extracorporeal blood to the pump upstream from the pump; and means responsive to the sensing means for selectively and continuously varying the amount of electrical power delivered to the blood pump from the power source thereby continuously varying the pumping flow rate of the blood pump, the magnitude of pumping variation being constantly proportional to extracorporeal blood flow upstream from the blood pump during the course of dialysis.

2. A blood pump controller responsive to changes in blood flow comprising:

a conventional blood pump for displacing blood through an extracorporeal hemodialysis system;

a blood conduit for conducting blood from a patient to the blood pump; and

a conventional power source and means for delivering electrical power to the blood pump;

means electrically interposed between the power source and the blood pump, said electrically interposed means comprising:

transducer means connected to the blood conduit producing an electrical signal representing the availability of blood to the pump;

comparing means for comparing the transducer signal with a pre-established reference signal and producing a proportional output signal; and

switching means responsive to the output of the comparing means for producing a periodic pulse train wherein the duration of each pulse is pro-proportional to the output signal of the comparing means, the speed of the blood pump being a direct function of the duration of the pulse.

3. A blood pump controller as defined in claim 2 wherein said transducer means comprises averaging means for averaging the systolic and diastolic blood pressures.

4. A blood pump controller as defined in claim 2 further comprising means for sensing negative blood pressure upstream from the pump and wherein the switching means comprises means for (a) producing a medium duration pulse when the proportional output signal is at an initial reference level representing a predetermined negative blood pressure, (b) decreasing the pulse duration when the proportional output signal indicates reduced patient's blood flow represented by increased negative value of the blood pressure, and (c) increasing the pulse duration when the proportional output signal indicates increased patient's blood flow represented by decreased negative value of the blood pressure.

5. A blood pump controller as defined in claim 4 wherein said pulse responsive switching means further comprises means for closing the circuit between the pump and its corresponding power supply for the duration of each pulse.

6. A blood pump controller as defined in claim 2 wherein said comparing means comprises an operational amplifier.

7. A blood pump controller as defined in claim 2, further comprising means responsive to the transducer means for terminating the operation of the blood pump when blood flow is reduced below a predetermined level.