Device for automatically controlling the infusion liquid flow in an infusion apparatus

In an infusion apparatus, the infusion liquid flow is automatically controlled by means of a control equipment which successively adjusts the actual value of said flow towards a desired value of said flow. In order to facilitate an infusion of a preselected total infusion liquid volume within a predetermined total time, the desired value of the infusion liquid flow, in its turn, is successively adjusted in response to a successively calculated value of the instantaneously remaining portion of the selected total infusion liquid volume.

The present invention relates to a device for automatically controlling the 
infusion liquid flow in an infusion apparatus by successively adjusting 
the actual value of said flow towards a desired value of said flow. 
A common feature of prior art devices of the kind above specified, such as 
those disclosed in British Pat. Nos. 1,109,175 and 1,253,817 and U.S. Pat. 
No. 3,450,153, is that they utilize a fixed desired value of the infusion 
liquid flow during the entire infusion process. This means that the total 
time for the infusion of a certain selected total liquid volume may vary 
considerably due to variations in the liquid flow, occurring in spite of 
the automatic control of said flow, and as a consequence of temporary 
breaks in the infusion, for instance in connection with another treatment 
or an examination of the patient. In practice, such variations in the 
total infusion time may be very unfavourable as it may often be of great 
importance that a patient is given the intended liquid volume within a 
certain predetermined time. 
The invention has for its object to provide an improved device of the kind 
initially specified, which eliminates the above drawback. In accordance 
with the invention, for this purpose, the device may be arranged to adjust 
the desired value of the infusion liquid flow successively in response to 
a successively calculated value of the instantaneously remaining portion 
of a preselected total liquid volume intended for infusion during a given 
total time. By adjusting the desired value of the infusion liquid flow 
successively in response to the instantaneously remaining portion of the 
total infusion liquid volume, it is possible to provide such an automatic 
control of the infusion liquid flow that the desired liquid volume will 
actually be infused within the intended time. 
The device may suitably be arranged to calculate said value of the 
instantaneously remaining portion of the selected total infusion liquid 
volume through subtraction of a total value or successive partial values 
of the infused liquid quantity from the value of the total infusion liquid 
volume. 
The invention may advantageously be applied on a device for automatically 
controlling the infusion liquid flow in an infusion apparatus wherein said 
flow is formed by a series of successive drops, the device being then 
arranged to control the infusion liquid flow by successively adjusting the 
actual value of the drop rate towards a desired value thereof. In this 
case, the device may be arranged to calculate said total value or said 
partial values, respectively, of the infused liquid quantity as well as a 
desired value of the drop rate, corresponding to the value of the 
instantaneously remaining portion of the selected total infusion liquid 
volume, with the aid of stored information about the interrelationship 
between the drop rate and the volume of each individual drop, which varies 
in response to the drop rate. 
It should be noted that, in the present specification as well as in the 
claims, the term drop rate is intended to cover various possible 
expressions for the time dependency of the drop formation. Thus, the drop 
rate may be expressed in drop frequency as well as in drop period, i.e. 
the time interval between mutually corresponding phases or stages during 
the formation of two successive drops. 
In a manner, known per se, the device may further be arranged to provide an 
alarm indication upon an inadmissibly large deviation in the actual value 
of the infusion liquid flow from the desired value of said flow. In this 
case, the device may suitably be arranged to cause an alarm indication 
only when the duration of such an inadmissible deviation exceeds a 
permitted length of time for the occurrance of such a deviation. The 
permitted length of time may be selectable. Additionally, the limits for 
admitted deviations in the actual value of the infusion liquid flow from 
the desired value may also be selectable.

In the drawing, reference numeral 10 designates a pulse generating detector 
unit, the input of which is intended to be connected to a primary drop 
detector 11, such as an electro-optical sensor, and serving to sense the 
drop rate in the drop chamber of an infusion apparatus, wherein a 
controllable infusion liquid flow is formed by a series of drops 
successively generated in the drop chamber. The general design and 
function of such an infusion apparatus is well-known in the art, for 
instance through British Pat. Nos. 1,109,175 and 1,253,817 and U.S. Pat. 
No. 3,450,153, and hence, it need not be described herein. Detector unit 
10 is arranged to deliver a short pulse over its output each time it 
receives a signal from drop sensor 11, indicating the passage of a drop 
through the drop chamber. 
The output signal from detector unit 10 is fed to a control input of a 
counter 12, the principal input of which is connected to a clock pulse 
generator 13. Counter 12 consists of an UP-counter which counts the 
supplied clock pulses in an ascending order. When counter 12 receives a 
pulse from detector unit 10 on its control input, it will deliver an 
output signal representing a number corresponding to its instantaneous 
counting state to a register 14, in which said number will be stored. 
Counter 12 is then automatically reset in order to start counting the 
supplied clock pulses in an ascending order again. Register 14 may consist 
of a latch memory. 
The number fed to and stored in register 14, which number will be 
maintained in said register until a new number is supplied from counter 
12, represents the actual value T.sub.act of the time interval between two 
successive drops formed in the drop chamber of the infusion apparatus. 
The output signal from counter 12 is also fed as a control and addressing 
signal to a function memory 15 in which values of the volume of each 
individual drop corresponding to different values of the drop rate (or the 
time interval between successive drops) are stored in different portions 
of the memory. The signal delivered from counter 12 to memory 15, which 
consists of a read-only memory, gives rise to an output signal from said 
memory. Said output signal represents a stored value .DELTA.V of the drop 
volume corresponding to the occurring drop rate, said value .DELTA.V being 
obtained from the portion of memory 15 addressed by the signal from 
counter 12. 
Reference numeral 16 designates a register of accumulating type, in which 
information about the total liquid volume to be infused during an infusion 
process is stored before starting said process. Said register 16 is 
arranged to be supplied with successive output signals from memory 15. 
Each time an input signal is received from memory 15, the number stored in 
register 16 will be reduced by the value .DELTA.V of the volume of a drop 
passing through the drop chamber of the infusion apparatus represented by 
said input signal. Hereby the information stored in register 16 will 
continuously represent the value of the instantaneously remaining portion 
of the total infusion liquid volume. The output of register 16 is 
connected to a first input of a dividing circuit 17. 
Reference numeral 18 designates a register formed by a DOWN-counter. Before 
the initiation of an infusion process, information is stored in register 
18 about a predetermined total time, during which the total infusion 
liquid volume should be infused. Register 18 has an input connected to 
clock pulse generator 13 to receive clock pulses therefrom. The received 
clock pulses will cause register 18 to count in a descending order, 
whereby the value stored in said register will be brought to represent the 
instantaneously remaining portion of the predetermined total infusion 
time. The output of register 18 is connected to a second input of dividing 
circuit 17. 
The dividing circuit 17 is arranged to generate an output signal 
representing the ratio between the remaining portion of the selected total 
infusion liquid volume and the remaining portion of the predetermined 
total infusion time. Said signal is supplied as a control and addressing 
signal to a function memory 19, in which desired values T.sub.des of the 
time interval between two successive drops, corresponding to different 
values of said ratio, are stored in different portions of the memory. 
Memory 19, which consists of a read-only memory, has an output connected 
to a further register 20. Over said output, memory 19 will deliver an 
output signal representing the desired value T.sub.des of the time 
interval between two successive drops corresponding to the desired drop 
rate, said value being obtained from the portion of memory 19 addressed by 
the signal received from circuit 17. Thus, register 20 will contain 
information about the desired value T.sub.des of the time interval between 
two successive drops while register 14 will contain information about the 
actual value T.sub.act of said time interval. 
The outputs of register 14 and 20 are connected each to one input of a 
comparator 21, which is arranged to compare said two T.sub.des and 
T.sub.act values with each other and to deliver a control signal 
corresponding to the difference between said two values to a drive circuit 
22, serving to supply drive signals to a motor 23. Said motor 23 is 
arranged to control the drop rate in the drop chamber of the infusion 
apparatus in any suitable manner. For instance, motor 23 may actuate 
clamping means adapted to provide a variable clamping action on a flexible 
tube forming a passage for the infusion liquid. Such clamping means are 
previously known, for instance through the three patent specifications 
above referred to. 
The device above described facilitates such a control of the drop rate and, 
hence, of the infusion liquid flow that it will be possible to make sure 
that the selected total infusion liquid volume will actually be infused 
during the desired total infusion time. 
Reference numeral 24 designates an error sensing circuit which is connected 
to the output of comparator 21 and adapted to sense the deviation between 
the actual value of the drop rate and the desired value of said rate. The 
error sensing circuit 24 may suitably contain a threshold-value generator 
27, adapted to generate a threshold value which the input signal to 
circuit 24 must exceed in order to give rise to an output signal from said 
circuit. Hereby the limits for an admissible deviation of the actual value 
of the drop rate from the desired value of said rate may be selected so as 
to cause circuit 24 to deliver an output signal only when the actual value 
of the drop rate deviates to an inadmissible extent from the desired value 
of the drop rate. The output signal from circuit 24 is supplied to an 
alarm control unit 25 which serves to actuate an alarm means 26. Said 
alarm means 26 may preferably be arranged to provide a visual or acoustic 
alarm. Alarm control unit 25 may contain an adjustable timing circuit 28 
operating in such a manner as to cause an actuation of alarm means 26 only 
when an error signal received from circuit 24 has a duration exceeding a 
certain, preferably selectable length of time. 
The invention is not restricted to the embodiment above described and shown 
in the drawing. Instead, many modifications are feasible within the scope 
of the invention. For instance, memories 15 and 19 may be replaced by 
suitable arithmetic logical units.