Dosing device for the volumetric dosing of a liquid additive

A dosing device for volumetric dosing of a liquid additive which is added in a certain volume ratio to a fluid, in particular withdrawn blood, flowing in a first hose line, via a second hose line feeding directly or indirectly into the first hose line. The dosing device for the volumetric dosing of an anticoagulant fluid or a sedimentation accelerator is preferably provided in a system for the collection and retransfusion of autologous blood which has a hose or tube section which extends downstream from the junction, and also a drip chamber connecting downstream from the drip tube and a light barrier, the direction of action of which is arranged transversely to the fall path of the drops. In order to avoid incorrect dosing because of changing viscosities of the liquid flowing in the first hose line, and thus of changing drop sizes, two electrically-triggerable valve means, one of which is in each case inserted into one of the two hose lines, are provided. The valve means are triggered alternately by means of a counting and control unit in such a way that in each case only one of the two named hoses is switched to "open" at the same time. The liquid remaining in the drip tube as a result of capillary action thereby brings about a volume constancy between drops falling at the lower end of the drip tube and additive which is added at the upper end of the drip tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a dosing device for the volumetric dosing 
of a liquid additive which is added in a certain volume ratio to a fluid 
flowing in a first hose line via a second hose line which feeds directly 
or indirectly into the first hose line. The dosing device of the present 
invention includes a hose or tube section, which is called a drip tube, 
which extends downstream from the junction, and has a drip chamber 
connecting downstream from the drip tube and a light barrier. The 
direction of action of the light barrier is arranged transversely to the 
fall path of the drops. Such a dosing device is used in particular within 
a system for the collection and retransfusion of autologous blood in order 
to add an anticoagulant liquid or a sedimentation accelerator to blood 
drawn, or sucked-off and intended for retransfusion, for example during an 
operation or similar. 
2. Discussion of Background and/or Material Information 
A system for the collection and retransfusion of autologous blood is, for 
example, known from EP-OS 0 483 703. In the known system, a collection 
vessel is subjected to an underpressure which is used, by means of a hose 
attached to the collecting vessel, to suck off blood from an operative 
field, i.e. from the body of a patient. The sucked-off blood, which is 
called drainage blood, flows through the hose line and passes a quantity 
dosing device before it drips into the collection container. Arranged 
upstream of the quantity dosing device is a Y-shaped branching or junction 
into which a second hose feeds which is connected to a reservoir for an 
anticoagulant liquid and/or a sedimentation accelerator. Situated between 
the reservoir for the anticoagulant liquid and the Y-shaped branching is a 
valve means which can be triggered via the previously mentioned quantity 
dosing device. 
Conventional dosing devices, known from the prior art, operate according to 
the principle of drop counting, whereby the fluid which flows in a tube 
and is to be measured or monitored, is guided to a drip chamber which is 
surrounded by a light barrier. A drop of liquid falling in the drip 
chamber breaks the light beam from the light barrier and so generates a 
counting pulse which can be fed to a microprocessor or similar means for 
further evaluation. It is a disadvantage with this type of volume 
measurement of a flowing liquid that, the greater the viscosity 
fluctuations experienced by the liquid to be measured, the more inaccurate 
is the measured result. The reason for this is that changing kinematic 
tenacity, i.e. viscosity, and changing density bring with them a change in 
the volume of an individual drop. As it is only the absolute number of 
fallen drops which can be determined by the light barrier, this leads the 
actual volumetric mixture ratio to change when a certain volume of 
additive is added to a certain number of fallen drops, for example, by a 
signal being generated by the quantity dosing device after a certain 
number of fallen drops, ascertained by means of the light barrier, by 
means of which the valve means arranged in the hose line and connected to 
the reservoir of the anticoagulant liquid is triggered and opened for a 
certain time interval. 
On the other hand, the principle of volume determination by means of a drip 
chamber and light barrier is cheap and easy to put into practice and 
operates, at least as far as the light barrier component is concerned, 
without contact, which, in particular in the case of systems and devices 
which process blood of patients, is highly desirable for reasons of 
hygiene. 
SUMMARY OF INVENTION 
It is, therefore, the object of the invention to improve a dosing device of 
a generic type for the volumetric dosing of a liquid additive which is to 
be added, as described, in a certain volume ratio to a fluid, in 
particular blood, flowing in a first hose line, via a second hose line 
which feeds directly or indirectly into the first hose line in such a way 
that, despite the use of a drip chamber and a light barrier for 
drop-counting and, therefore, indirect volume determination of the fluid 
flowing in the first hose line, a metered addition of the additive to be 
added, in particular of an anticoagulant liquid, is made possible in a 
fixed volume ratio, without the dosing being falsified by changing 
viscosities of the liquid flowing in the first hose line. 
The realization of this object is characterized in the case of a generic 
dosing device by two controllable valves or valve means which are each 
inserted into one of the two hose lines and coupled in such a way that in 
each case only one of the two valve means can be switched to "open" at a 
certain time point, and also by a counting and control unit which counts 
the drops falling through the drip chamber and after a certain number of 
drops triggers the valve means alternately. 
The present invention is based at least in part on the knowledge that, 
because of the capillary action, a certain volume of fluid always remains 
in the section of the first hose line which leads to the drip chamber, 
which can optionally also be formed in the shape of a tube and which is 
called a drip tube. 
If the second hose line, conveying the additive to be added, is connected 
by means of the valve means in such a way that additive can flow into the 
drip tube and if, at the same time, the first hose line is blocked by the 
other valve means, the volume of additive advancing into the drip tube 
corresponds to the volume of the drop leaving the drip tube. If, now, the 
mixture ratio between additive and primary fluid, for example blood, is 
expressed in integral multiples of drops, for example one drop of additive 
per seven drops of blood, a change in viscosity and a changed size of an 
individual drop resulting therefrom thus has no influence on the overall 
mixture ratio, since, for example in the case of a larger drop leaving the 
drip tube, a larger quantity of additive is correspondingly drawn into the 
drip tube. 
In a preferred embodiment or version of the present invention, the two 
valve means are combined to give a 4/2-way valve. The 4/2-way valve is 
preferably provided with a spring pre-tension, so that the valve in its 
at-rest position switches the first hose line to "open" and the second 
hose line, conveying the additive, is blocked. In the engaged state the 
situation is then reversed so that the first hose line is blocked and the 
second hose line is freed. 
In another preferred embodiment or version of the present invention the 
valve means are combined to give a 3/2-way valve, so that the second hose 
line in the valve feeds indirectly into the first hose line. To put it 
another way, the connections of the 3/2-way valve are connected such that 
the first hose line in the spring-centered resting position of the valve 
is connected directly to the drip tube, while the second hose line 
conveying the additive is blocked. In the connected state, the situation 
is again reversed so that the second hose line, conveying the additive, is 
now directly connected to the drip tube and the first hose line is 
blocked. 
In another alternative or variant of the present invention, which is 
somewhat more expensive in terms of circuitry, it is proposed to combine 
the valve means in a 3/3-way valve which has a spring-centered middle 
position in which both hose lines are blocked. This additional position 
offers the advantage that both hose lines can be blocked, for example if a 
collection vessel catching the drawn-off blood is to be replaced. 
In another preferred embodiment or version of the present invention, the 
counting and control unit of the dosing device includes a central 
processing unit (CPU) and also a freely programmable memory (RAM), and 
also inputting means in order to enter a value N representing a number of 
drops. The central processing unit (CPU) generates a control pulse for the 
alternate triggering of the valve means if the determined number of drops 
reaches the value N stored in the memory (RAM). Through the possibility of 
choice for the value N, the operator is offered the opportunity of setting 
the volumetric mixture ratio in which the additive is to be added. 
Also preferred is an embodiment or a version of the dosing device according 
to the present invention in which the counting and control unit has a 
freely programmable memory (RAM) in which is provided a storage location 
for a constant (A) which corresponds to the number of drops of additive to 
be added per switching cycle of the valve means. Through the possibility 
of choice for the value A there is provided another possibility of 
influencing the mixture ratio and setting the device to different 
additives. 
It has also proved to be advantageous for the counting and control unit of 
the present invention to have a central processing unit (CPU) and a freely 
programmable memory (RAM) in which an operating program for the processing 
unit is stored which controls the valve means alternately in such a way 
that, after a certain number of switching cycles of the valve means, a 
so-called "test switching cycle" is carried out in which the second hose 
line conveying the additive is connected through until it is ensured that 
the second hose line or the reservoir connected to the second hose line 
still contains a supply of additive. For this purpose, a large enough 
quantity of drops is admitted in the engaged position of the valve so that 
the volume of additive which has flown out, as recorded by the light 
barrier, corresponds to the volume of the drip tube and dead spaces 
possibly contained in the valve means in any case, even if only very small 
drops should fall because of viscosity influences. 
It is also preferably provided that the dosing device of the present 
invention contains disposable parts which are disposed of after use or 
contamination with blood. These individual components listed as parts 
which can be disposed of can include in particular the two hose lines, the 
two valve means, the drip tube and the drip chamber. In this way, an 
hygienically acceptable manageable device is provided in which the 
expensive components, such as the light barrier and the counting and 
control unit, which are not subjected to dirt or wear, are retained, while 
the parts coming into contact with blood can be replaced quickly and 
easily, which is very much in keeping with a quick and efficient handling 
in particular in hospitals. 
In order to simplify exchangeability, in particular of a drip chamber 
constructed as a disposable part, the drip chamber and the light barrier 
can be preferably constructed so that the drip chamber can be locked in 
the appropriately constructed light barrier. This is preferably effected 
if the drip chamber is lockable in a form-locking manner in the component 
containing the light barrier, i.e. a recess is provided in the housing of 
the light barrier in which the drip chamber, which is partially 
transparent, can be locked. The drip chamber can in particular be 
manufactured from a plastic by injection moulding. 
The invention is described in more detail below with reference to two 
preferred embodiments shown in the drawings.

DETAILED DESCRIPTION 
The embodiment or version of a dosing device according to the present 
invention which is shown in FIG. 1 is given the general reference number 
10. It has a first hose line 11 and a second hose line 12. The two hose 
lines 11 and 12 meet at a Y-shaped junction 14 and pass into a drip tube 
16. Connected to the drip tube is a drip chamber 18 which is subjected to 
an underpressure or vacuum via a draw-off or vacuum line 20. Inserted into 
the two hose lines 11 and 12 are combined valve means in the form of a 
4/2-way valve 22. The 4/2-way valve is held by means of a compression 
spring 24 in a resting position, in which the first hose line 11 is 
switched to "open" while the second hose line 12 is blocked. The 4/2-way 
valve 22 can be operated electrically by means of a solenoid 26 so that, 
in the switch position then adopted, the first hose line 11 is blocked 
while the second hose line 12 is connected to the drip tube 16. 
In the situation shown in FIG. 1, in which the valve 22 is in the resting 
position, the first hose line 11 is switched to "open". The lower pressure 
or vacuum acting in the drip chamber 18, which is achieved via the vacuum 
or draw-off line 20, acts via the drip tube 16 and the valve 22 into the 
hose line 11 which has a perforated end-section 28. The end-section 28 of 
the hose line 11 is, for example, placed in an opening in the body, such 
as an operation wound, and as described herein, withdraws or sucks off 
blood and/or wound fluid. The withdrawn or sucked-off blood is conveyed 
through the hose line 11 and the valve 22, which is switched to "open", 
and drops at the end of the drip tube 16 into the drip chamber 18. 
The descending drops break the light beam, emitted transversely to the drip 
direction, of a light barrier 30 which is constructed to surround the drip 
chamber. The light barrier 30 is constructed in traditional manner and 
includes for example a light-emitting diode (LED) 32 as the light source, 
and as the receiver element a phototransistor 34. The phototransistor 34 
illuminated by the light diode 32 is darkened by a falling drop 38, as a 
result of which a pulse is generated which is fed to a central processing 
unit (CPU). In the processing unit the pulses generated by the descending 
drops 38 are added together and compared with a set value N stored in a 
freely programmable memory (RAM). The desired set value can, for example, 
be 7. After 7 drops have fallen a control pulse is generated by the 
central processing unit (CPU) which is conveyed in a suitably amplified 
manner to the solenoid 26 of the valve 22, whereupon the valve engages and 
blocks the hose line 11, while, however, releasing the hose line 12. 
Arranged at the upper end of the hose line 12 is a reservoir 36 which 
contains an anticoagulant liquid (ACD) and optionally other additions of a 
sinking accelerator which increases the volume of the erythrocyte 
aggregates contained in the blood and thus accelerates sedimentation, i.e. 
separation of blood plasma and optionally contained wound fluid, lymph 
water, or the like. 
The hose line 12 is connected via the now-opened valve 22 directly to the 
drip tube 16 which is still filled with blood at this point in time due to 
the capillary action. As soon as another drop 38 falls at the lower end of 
the drip tube 16, a corresponding volume of anticoagulant liquid (ACD) is 
drawn up from the hose line 12 at the upper end of the drop tube via the 
switched-through valve 22. As the volume replaced at the upper end of the 
drip tube corresponds exactly to the volume which has been discharged in 
drop form at the lower end of the drip tube, the size of the drop leaving 
the drip tube has no influence on the mixture ratio, which for example in 
the present example is 7:1 in parts by volume. 
After another descending drop 38 has been detected by means of the light 
barrier and the central processing unit (CPU), the CPU generates another 
control pulse, with which the exciting current of the solenoid 26 is 
switched off, whereupon the compression spring 24 presses the 4/2-way 
valve into its resting position so that the hose line 11 is switched to 
"open" and further blood is drawn through the drainage hose 11. 
In order to ensure that the reservoir 36 for the anticoagulant liquid is 
still filled, the switch valve 22 should be kept in the engaged position, 
after a certain number of switch changes, for the duration of a descending 
drop 38. The valve should also be kept in the engaged position, switching 
through the hose line 12, for a number of descending drops which is 
measured such that the total volume of the falling drops is slightly 
greater than the internal volume of the drip tube 16 plus possible dead 
spaces in the valve 22. In these ways it can be ensured that anticoagulant 
fluid is still contained in the reservoir 36. 
To control this routine, a suitable program controlling the CPU can be 
stored in the memory (RAM). 
In order to counter an increased concentration of the anticoagulant liquid 
in the blood, which would result because of such a metered addition of 
anticoagulant liquid for test purposes, the value N can be increased for 
the normal switching cycles accordingly, so that the overall mixture ratio 
between blood and anticoagulant liquid in the collection vessel, which 
connects to the drip chamber, again corresponds to the originally intended 
mixture ratio after a finite number of switching cycles of the valve 
despite the additional input of anticoagulant fluid during the "test 
cycle". 
For this purpose, the determining influencing variable is the number of 
drops which is necessary to measure a volume which is certainly greater 
than the volume of the drip tube plus the volume of possible dead spaces 
in the valve 22. This is the case even in the most unfavourable situation 
where the smallest conceivable drop size is produced. This is due at least 
in part to the fact that, for example, the viscosity of the blood has an 
unfavourable influence. A drop which falls over and above this number or 
value N shows that ACD is still present. 
This number or value N also can be influenced through the dimensioning of 
the drip tube. Furthermore, the number of switching cycles which are 
passed through before a "test switching cycle" is undertaken is variable. 
In a test switching cycle the switch valve 22 remains in the engaged 
position longer than only for one falling drop, i.e. with switched-through 
anticoagulant liquid line 12. 
If, for example, a mixture ratio of 7:1 is desired, with a normal rhythm, 
i.e. without test cycle, the valve 22 will remain in the resting position 
for seven descending drops 38 and then switches into the engaged position 
for one drop. 
If one now assumes that every tenth switching cycle is to be a test 
switching cycle, during which a total of eleven drops fall through the 
drip chamber while anticoagulant liquid is drawn through the valve 22 
located in the engaged position, then the number of drops which fall while 
the switching valve is in the resting position at that time, i.e while the 
hose line 11 is switched to "open", is to be increased to fourteen. After 
ten complete switching cycles, a total of one hundred and forty drops of 
blood have then advanced into the drip tube, while, during the nine normal 
switching cycles, nine drops of anticoagulant liquid have been added and, 
in the tenth switching cycle, eleven drops of anticoagulant liquid. The 
overall mixture ratio is therefore 140:20, i.e 7:1, as without the test 
switching cycle. 
Because of readily comprehensible relationships, other numerical 
proportions which allow the use of a described test switching cycle 
without changing the mixture ratio can be found by appropriately 
dimensioning the drip tube or the number of normal switching cycles or the 
mixture ratios. Experience shows that a changing drop size resulting from 
changing viscosities does not influence the mixture ratio. 
For purposes of the invention, the drip chamber 18 is constructed as a 
disposable part which is coupled together with hoses 11 and 12, which are 
likewise made from plastic, and with a valve made from simple plastic 
components. 
An alternative embodiment of the dosing device according to the present 
invention is shown in FIG. 2, wherein a 3/3-way valve is used in place of 
a 4/2-way valve. The other components and elements correspond to the 
version shown in FIG. 1, the same parts having the same reference numbers 
so that their description need not be repeated. 
The 3/3-way valve 23 in FIG. 2 has two compression springs 24' and 24", by 
means of which the valve is centered in the middle. In the represented 
resting position of the 3/3-way valve 23, both the hose line 11 and the 
hose line 12 are blocked so that no fluid whatsoever can reach the drip 
tube connected to the third connection of the 3/3-way valve. In operation, 
a switching signal is generated by the CPU which, suitably intensified, is 
fed to a first solenoid 26', so that the 3/3-way valve 23 is switched into 
a first engaged position, in which the drainage line or hose line 11 is 
connected to the drip tube 16, while the hose line 12 conveying the 
anticoagulant liquid still remains blocked. In this version of the 
invention, the two hose lines 11 and 12 are thus not coupled directly to 
one another at a junction, but are connected indirectly to one another via 
the 3/3-way valve 23. After a fixed number N the CPU generates a new 
switching pulse which, suitably amplified, is this time fed to the 
solenoid 26, whereupon the 3/3-way valve is pressed into a second engaged 
position in which the hose line 12 is connected to the drip tube 16 so 
that a further falling drop 38 draws anticoagulant liquid into the drip 
tube 16. 
With reference to FIG. 2, it is evident that the dosing device according to 
the present invention can also be realized with a 3/2-way valve. If one 
imagines FIG. 2 without the middle, spring-centered resting position of 
the 3/3-way valve, then two engaged positions of a 3/2-way valve remain. 
In such a version or embodiment, the compression spring 24" and the 
left-hand solenoid 26' would not be present, with the result that the 
remaining compression spring 24' presses the 3/2-way valve into a resting 
position in which the hose line 11 is connected to the drip tube 16. After 
a corresponding number of fallen drops N, the CPU generates a 
corresponding switching pulse which is used to apply an exciting current 
to the solenoid 26", so that the 3/2-way valve is switched to an engaged 
position in which the hose line 12 conveying the anticoagulant liquid is 
connected to the drip tube 16. 
As is also shown in the figures, the light barrier 30 is incorporated in a 
housing which has a channel-type recess 40. The correspondingly 
constructed drip chamber 18 can be locked in form-locking manner into this 
recess 32. The discharge line 20, the drip chamber 18, the drip tube 16, 
the valves 22 and 23, and the two hose lines 11 and 12 can be constructed 
as disposable parts which can be simply replaced when the device, i.e. the 
parts to be reused, such as in particular light barrier 30, CPU and RAM, 
are to be used for example in another operation. 
The dosing device according to the present invention permits an accurate 
volumetric metered addition of an additive without a changing drop size of 
drops detected and counted by means of a light barrier having an influence 
on the accuracy of the dosing.