U.S. patent number 3,800,794 [Application Number 05/102,665] was granted by the patent office on 1974-04-02 for method and apparatus for fluid flow control.
This patent grant is currently assigned to Ivac Corporation. Invention is credited to Heinz W. Georgi.
United States Patent |
3,800,794 |
Georgi |
April 2, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
METHOD AND APPARATUS FOR FLUID FLOW CONTROL
Abstract
A method and apparatus for parenteral administration of medical
fluids, wherein a normally shut-off intravenous feeding tube is
selectively opened at a frequency and open period duration
automatically regulated by a digital control system to establish a
fluid flow rate at any selected rate over a wide dynamic range.
Measured and desired flow rates are converted to digital electrical
signals and compared, the electrical difference being used to vary
a control voltage which establishes the width of energizing pulses
controlling a member for opening the feeding tube. The frequency of
the energizing pulses is a high, preferably non-integral, multiple
of the desired drop flow rate. Appropriate alarms respond to
out-of-limit conditions indicated by the magnitude of the control
voltage.
Inventors: |
Georgi; Heinz W. (La Jolla,
CA) |
Assignee: |
Ivac Corporation (San Diego,
CA)
|
Family
ID: |
22291024 |
Appl.
No.: |
05/102,665 |
Filed: |
December 30, 1970 |
Current U.S.
Class: |
604/507;
137/487.5; 604/65; 128/DIG.13; 222/59; 604/253 |
Current CPC
Class: |
G05D
7/0635 (20130101); A61M 5/1689 (20130101); Y10S
128/13 (20130101); Y10T 137/7761 (20150401) |
Current International
Class: |
A61M
5/168 (20060101); G05D 7/06 (20060101); A61m
005/00 () |
Field of
Search: |
;128/214E,214F,213,DIG.13 ;222/59,14,76,420 ;137/486,487.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,541,363 |
|
Apr 1969 |
|
DT |
|
1,109,175 |
|
Apr 1968 |
|
GB |
|
Primary Examiner: Truluck; Dalton L.
Attorney, Agent or Firm: Fulwider, Patton, Rieber, Lee &
Utecht
Claims
I claim:
1. In the parenteral administration of medical fluids by an
intravenous set including drop forming means and fluid conduit
means coupled to said drop forming means,
a method of controlling the rate of drop flow through said fluid
conduit means, comprising the steps of:
clamping said fluid conduit to a substantially shut-off state;
producing control pulses having a frequency higher than a desired
drop flow rate through said fluid conduit: and
repetitively opening and closing said fluid conduit to flow in
response to said control pulses, the frequency of opening said
fluid conduit being at a higher frequency than the desired drop
flow rate through said fluid conduit, whereby a plurality of
control pulses and cycles of opening and closing said fluid conduit
are required to produce each individual drop of flow.
2. A method as set forth in claim 1 wherein said control pulses are
produced at a frequency that is a relatively high multiple of the
desired drop flow rate.
3. A method as set forth in claim 1, further including varying the
duration of said control pulses to regulate said drop flow
rate.
4. A method as set forth in claim 1, wherein said control pulses
are produced at a frequency that is an integral multiple of the
desired drop flow rate.
5. A method as set forth in claim 1, wherein said control pulses
are produced at a frequency that is a non-integral multiple of the
desired drop flow rate.
6. A method as set forth in claim 1, further including the steps
of:
generating a first signal proportional to the actual drop flow
rate;
generating a second signal proportional to the desired flow
rate;
comparing said first signal with said second signal to produce a
control voltage proportional to the difference between the actual
and desired flow rates; and
varying the duration of said control pulses in accordance with said
control voltage.
7. A method as set forth in claim 6, wherein said control voltage
is the integral of the difference between said first and second
signals.
8. A method as set forth in claim 6, wherein the frequency of
opening said tube is an integral multiple of the desired drop flow
rate.
9. A method as set forth in claim 6, wherein the frequency of
opening said tube is a non-integral multiple of the desired drop
flow rate.
10. In the parenteral administration of medical fluids by an
intravenous set including drop forming means and a flexible tube
coupled to said drop forming means for carrying drop flow, a method
of controlling the rate of drop flow through a flexible tube,
comprising the steps of:
clamping said tube to a substantially shut-off state;
producing control pulses at a selected frequency greater than the
desired rate of drop flow; monitoring the actual drop flow
occurring through said tube;
selectively varying the duration of each of said control pulses in
accordance with the actual drop flow; and
repetitively opening and closing said tube to fluid flow in
response to said control pulses to regulate the actual drop flow
rate so that it conforms to said desired drop flow rate.
11. A method as set forth in claim 10, wherein the frequency of
opening said tube is a relatively high multiple of the desired drop
flow rate.
12. A method as set forth in claim 11, wherein said multiple is
approximately 10 1/2 times the desired drop flow rate.
13. A method as set forth in claim 10, further including the steps
of:
generating a first signal proportional to said monitored actual
drop flow;
generating a second signal proportional to said desired flow
rate;
producing a control voltage proportional to the difference between
said first signal and said second signal; and
varying the duration of said control pulses in accordance with said
control voltage.
14. In a system for parenteral administration of liquids by drop
flow, apparatus for controlling the rate of drop flow
comprising:
drop forming means;
a feeding tube coupled to said drop forming means;
tube clamping means for closing said feeding tube to prevent liquid
flow therethrough;
flow rate setting means for designating a desired flow rate;
and
means responsive to said rate setting means for unclamping said
tube at a selected frequency higher than the desired drop flow rate
to allow repetative liquid flow through said feeding tube, whereby
a plurality of successive cycles of unclamping said tube are
required to produce each individual drop of flow.
15. Apparatus as set forth in claim 14, wherein said means for
unclamping said tube operates at a frequency that is a relatively
high multiple of the desired drop flow rate.
16. Apparatus as set forth in claim 15, wherein said frequency is
an integral multiple of the desired drop flow rate.
17. Apparatus as set forth in claim 15, wherein said frequency is a
non-integral multiple of the desired drop flow rate.
18. Apparatus as set forth in claim 14, wherein said means for
unclamping said tube at a selected frequency comprises:
drive means for said tube clamping means;
means for producing a control pulse having said selected frequency;
and
means for applying said control pulse to said drive means for
unclamping said tube at said selected frequency.
19. Apparatus as set forth in claim 18, wherein said means for
producing a control pulse includes:
variable frequency pulse generator means for generating a first
electrical signal proportional to the desired drop flow rate.
20. In the parenteral administration of medical fluids by an
intravenous set including drop forming means and fluid conduit
means coupled to said drop forming means, a method of controlling
the rate of drop flow through said conduit means, comprising the
steps of:
clamping said fluid conduit to a substantially shut-off state;
selecting a desired drop flow rate; and
repetitively opening and closing said fluid conduit to flow, the
frequency at which said conduit is opened being higher than the
desired drop flow rate through said fluid conduit, whereby a
plurality of successive cycles of opening and closing said fluid
conduit is required to produce each individual drop of flow.
21. A method as set forth in claim 20, wherein said fluid conduit
is automatically and continuously opened and closed to provide a
continuing drop flow at the desired rate.
22. A method as set forth in claim 20, wherein said frequency is a
relatively high multiple of the desired drop flow rate.
23. A method as set forth in claim 20, wherein said frequency is an
integral multiple of the desired drop flow rate.
24. A method as set forth in claim 20, wherein said frequency is a
non-integral multiple of the desired drop flow rate.
25. In a system for parenteral administration of liquids by drop
flow through a feeding tube, apparatus comprising:
clamping means for clamping said feeding tube in a normally
shut-off state;
electrical pulsing means for generating pulses at a rate greater
than the desired drop flow rate to periodically energize said
clamping means and thereby open said tube to liquid flow;
rate setting means for generating an electrical signal proportional
to desired drop flow rate;
flow monitoring means for monitoring actual drop flow through said
tube and generating an electrical signal proportional to measured
drop flow rate; and
means responsive to both said rate setting means and said flow
monitoring means for regulating the pulse length of pulses from
said pulsing means.
26. Apparatus as set forth in claim 25, wherein said means
responsive to both said rate setting means and said flow monitoring
means includes rate memory means for comparing said signals
proportional to desired drop flow rate and measured drop flow rate,
respectively, and for generating a control signal for establishing
the pulse length of said pulses.
27. Apparatus as set forth in claim 26, wherein said rate memory
means integrates the difference between said signals proportional
to desired drop flow rate and measured drop flow rate,
respectively, and varies said control signal in accordance with the
integrated difference between said signals.
28. Apparatus as set forth in claim 25, wherein said flow
monitoring means includes a drop sensing means for generating a
pulse train at a frequency proportional to measured drop flow
rate.
29. Apparatus as set forth in claim 25, wherein said rate setting
means includes a pulse generator for generating said electrical
signal as a pulse train at a higher frequency than the desired drop
flow rate.
30. Apparatus as set forth in claim 29, wherein said frequency is a
relatively high multiple of the desired drop flow rate.
31. Apparatus as set forth in claim 29, wherein said frequency is
an integral multiple of the desired drop flow rate.
32. Apparatus as set forth in claim 29, wherein said frequency is a
non-integral multiple of the desired drop flow rate.
33. Apparatus as set forth in claim 32, wherein said non-integral
multiple is approximately 10 1/2.
34. In a system for a parenteral administration of liquids by drop
flow through a feeding tube, apparatus for controlling the rate of
drop flow comprising:
tube clamping means normally maintaining said feeding tube in a
substantially shut-off state;
driver means for selectively energizing said clamping means to
unclamp said tube;
rate setting means for generating an electrical signal having a
frequency greater than the desired drop flow rate;
flow monitoring means for monitoring actual drop flow through said
feeding tube; and
control means responsive to both said rate setting means and said
flow monitoring means producing a train of control pulses at the
frequency of said electrical signal for regulating the duration of
each period of energization of said clamping means by said driver
means.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to improvements in fluid flow
control systems and, more particularly, to a new and improved
automatic, self-regulating, highly accurate drop flow control
system for parenteral administration of medical liquids over a wide
range of fluid flow rates.
The usual medical procedure for the gradual parenteral
administration of fluid into the human body, such as liquid
nutrients, blood or plasma makes use of apparatus which is commonly
referred to in the medical arts as an intravenous set. The
intravenous set usually comprises a bottle of liquid, normally
supported in an inverted position, an intravenous feeding tube,
typically of plastic, and a suitable valve mechanism, such as a
roll clamp, which allows the liquid to drip out of the bottle at a
controlled rate into a drip chamber below the bottle. The drip
chamber serves the dual function of allowing a nurse or other
attendant to observe the rate at which the liquid drips out of the
bottle and also creates a reservoir for the liquid at the lower end
of the chamber to ensure that no air enters the main feeding tube
leading to the patient.
While observation of the rate of drop flow via the drip chamber is
a simple way of controlling the amount of liquid fed to a patient
over a period of time, its utlimate effectiveness requires that a
relatively constant vigil be maintained on the drop flow, lest it
cease entirely due to exhaustion of the liquid supply or become a
continuous stream and perhaps increase the rate of liquid
introduction to the patient to a dangerous level.
By way of example, it has been the general practice in hospitals to
have nurses periodically monitor drop flow rate at each intravenous
feeding or parenteral infusion station. Such moinitoring of drop
flow rate is a tedious and time consuming process, prone to error
and associated, possibly serious consequences, and resulting in a
substantial reduction of the available time of qualified medical
personnel for other important duties. Typically, the nurse
monitoring drop flow rate will use a watch to time the number of
drips flowing in an interval of one or more minutes, and she will
then mentally perform the mathematics necessary to convert the
timed drop count to an appropriate rate, e.g., in cubic centimeters
per hour. If the calculated flow rate is substantially different
than the prescribed rate, the nurse must manually adjust the roll
clamp for a new rate, count drops again, and recalculate to measure
the new rate.
Obviously, each of the aforedescribed measurements and calculations
and flow rate adjustments usually takes several minutes time which,
when multiplied by the number of stations being monitored and the
number of times each station is monitored per day, can result in a
substantial percentage of total personnel time available. In
addition, under the pressure of a heavy schedule, the mental
calculations performed by a harried nurse in calculating flow rate
may not always prove to be reliable and, hence, errors do occur
resulting in undesired, possibly dangerous infusion flow rates.
In addition to the aforedescribed difficulties, the parenteral
administration of medical liquids by gravity induced hydrostatic
pressure infusion of the liquid from a bottle or other container
suspended above a patient is very susceptible to fluid flow rate
variation due to changes in the liquid level in the bottle, changes
in temperature, changes in the venous or arterial pressure of the
patient, patient movement, and drift in the effective setting of
the roll clamp or other valve mechanism pinching the feeding tube.
Moreover, there are a number of situations, such as in intensive
care, cardiac and pediatric patients, or where rather potent drugs
are being administered, where the desired flow rate must be capable
of precise selection and must not drift beyond certain prescribed
limits. In addition, it is extremely important in such situations
for medical personnel to be informed of undesired fluctuations in
flow rate, failure of the fluid delivery system, or exhaustion of
liquid supply when the bottle is emptied.
It will be apparent, therefore, that some of the most critical
problems confronting hospital personnel faced with an overwhelming
duty schedule and limited manhour availability are the problems of
quickly, easily, reliably and accurately monitoring and regulating
drop flow rate in the parenteral administration of medical liquids.
In recent years, a number of relatively complex and costly
electrical monitoring systems, drop flow controllers and infusion
pumps have been developed to accomplish the various tasks of
sensing and regulating drop flow rates. Some of these devices have
also been capable of activating alarms when a potentially dangerous
condition exists, thus freeing medical personnel to some extent for
other duties. However, while such monitoring and drop rate control
devices have generally served their purpose, they have not always
proven entirely satisfactory from the standpoint of reliability and
accuracy over a wide range of selected flow rates. For example,
some drop flow controllers of the prior art have been unable to
prevent passage of two drops instead of one when the feeding tube
is opened momentarily, and such controllers have also been troubled
by inconsistent drop size.
Hence, those concerned with the development and use of parenteral
fluid administration systems have long recognized the need for
relatively simple, economical, reliable, and accurate method and
apparatus for fluid flow control which would obviate the
aforedescribed difficulties. The present invention clearly fulfills
this need.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides a new
and improved method and apparatus for controlling drop flow in the
parenteral administration of medical liquids, wherein the frequency
and width of control pulses which open a normally shut-off feeding
tube are controlled by a digital system capable of sensing and
regulating drop flow rate accurately over a wide range of flow
rates.
The system for establishing control pulse frequency is an open loop
subsystem wherein the control pulse frequency representing desired
flow rate is a relatively high, preferably non-integral, multiple
of the actual drop flow rate frequency (typically expressed as DPM,
or drops per minute) which results in less drop distortion and more
consistently repeatable drop size from one drop to another.
Additional control over drop flow rate is accomplished by varying
control pulse width, i.e., the open period duration for the feeding
tube for each control pulse. Variation of control pulse width to
regulate actual drop flow rate so that it is maintained within
close tolerances at the desired flow rate is established by a
closed loop subsystem.
In a presently preferred embodiment, by way of example, a feeding
tube clamping member (normally in the tube shut-off position) is
repeatedly moved to the tube-open position by a driver which is, in
turn, energized by pulses from a variable pulse generator which
produces control pulses at a frequency which is a high multiple of
the desired drop flow rate. The width of each control pulse is
determined by the amplitude of a control voltage produced by a rate
memory which compares a pair of electrical signals proportional to
the measured and desired drop flow rates, respectively, and
integrates the electrical difference between these signals with the
proper polarity to either increase or diminish the amplitude of the
control voltage. In this way, precise regulation of the control
pulses to the proper pulse width for establishing the desired drop
flow rate is accomplished.
The control voltage amplitude is monitored so that out-of-limit
conditions calling for a flow rate in excess of system delivery
capability, or indicating a leakage flow rate which cannot be
terminated by the clamping member, trigger appropriate alarm
subsystems.
The new and improved fluid flow control system of the present
invention is extremely accurate, reliable and easy to use. The
system provides digital precision in selecting and maintaining drop
flow rates throughout a wide range, and the system is quick to
inform medical personnel of any conditions which might pose a
hazard to the patient. Hence, the system of the present invention
minimizes the time consuming and error prone aspects of human
monitoring and flow rate adjustment and frees medical personnel for
other duties.
These and other objects and advantages of the invention will become
apparent from the following more detailed description, when taken
in conjunction with the accompanying drawings of illustrative
embodiments.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a fluid flow control system in
accordance with the present invention;
FIG. 2 is an electrical schematic diagram for one embodiment of a
variable pulse width circuit suitable for use in the flow control
system of the present invention; and
FIG. 3 is a graphical representation illustrating typical drop size
as a function of a driver pulse frequency.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now particularly to FIG. 1 of the drawings, there is
shown a drop flow control system embodying the novel features of
the present invention. In the ensuing description, while reference
will be made to the term "IV" normally connoting intravenous
administration, it is to be understood that this is by way of
example only, and the flow control system of the present invention
is suitable for other forms of parenteral administration as well as
intravenous administration.
In order to control drop flow rate, it is necessary to continuously
monitor the actual drop flow as it occurs in an IV administration
set. This is accomplished in the system of FIG. 1 by a drop flow
monitor which includes a drop sensor 11 and a pulse generator 12
adapted to detect each drop as it falls and generate an electrical
pulse train at a frequency directly proportional to the drop flow
rate.
The drop sensor 11 monitors drop flow in a drip chamber (not shown)
of the IV administration set and typically may include a sensor
housing (not shown) containing a reference light source located a
fixed distance from a photocell to define an optical sensing gap
therebetween, with a reference light beam normally impinging upon
the photocell. The housing is appropriately clamped upon the drip
chamber of the IV set with the drip chamber positioned within the
sensing gap to intercept the reference beam. A falling drop of
fluid within the drip chamber interrupts the reference beam, and
the variation in the electrical response of the photocell is
communicated to appropriate circuitry indicating the presence of a
drop. One example of a suitable drop sensor is set forth in
copending U. S. Patent application Ser. No. 685,928, inventor:
Richard A. Cramer, filed Nov. 27, 1967. While a photocell
monitoring device is ideally suited for the drop sensor 11, it will
be appreciated that any drop sensing device capable of providing an
electrical indication of the presnece of a drop may be used without
departing from the spirit and scope of the invention.
The pulse generator 12 is typically a conventional Eccles-Jordan
monostable flip-flop (one-shot) which provides an output pulse with
a prescribed pulse width and amplitude each time a drop is detected
by the drop sensor 11. The pulse generator 12 provides a positive
going pulse train proportional to measured drop flow rate, as an
electrical input over line 13 to a rate memory 14.
A second electrical input to the rate memory 14 is provided over
line 15 in the form of a negative going pulse train from a variable
pulse generator 16. The pulse generator 16 is typically a variable
frequency square wave generator which generates a negative pulse
train at a frequency determined by a conventional rate selector
(not shown) which alters the control voltage that establishes the
output frequency of the pulse generator 16.
The positive pulse train from the pulse generator 12, indicative of
measured drop flow rate, and the negative pulse train from the
pulse generator 16, indicative of desired drop flow rate, are
combined and compared in the rate memory 14, the electrical
difference between the signals indicating measured and desired
rates being integrated in the rate memory with the proper polarity
to either increase or diminish the amplitude of a d.c. output
control voltage which is fed from the memory over line 18 as an
electrical input to a pulse generator 19 having a selectively
variable output pulse width.
One embodiment of electrical circuitry suitable for carrying out
necessary functions of the rate memory 14 is illustrated within the
dashed outline in FIG. 1 of the drawings. The negative pulse train
from the pulse generator 16 is directed through a current
determining resistor R1 and diode D1 as input to the negative
channel of a conventional operational amplifier 20 which, together
with a capacitor C1, is electrically wired in a conventional
integrating configuration to provide the d.c. control voltage
output over line 18. In a similar manner, the positive pulse train
from the pulse generator 12 is directed through a current
determining resistor R2 and diode D2 as an additional input to the
same negative channel of the amplifier 20 as the negative pulse
train passed by the diode D1.
If the measured and desired flow rates are the same, then the net
electrical input to the amplifier 20 is zero, since the positive
and negative pulses essentially cancel each other out, and the d.c.
control voltage output over line 18 stays constant. If the desired
rate is higher than the measured rate, the control voltage output
drifts more positive while, on the other hand, the control voltage
drifts more negative if the flow rate measured is higher than the
desired flow rate. It will also be apparent that, in the event the
electrical inputs to the amplifier 20 are disconnected, the d.c.
control voltage output of the amplifier will hold constant at its
last level prior to disconnection.
One example of electrical circuitry suitable for carrying out the
necessary functions of the pulse generator 19 having variable
output pulse width, is illustrated in FIG. 2 of the drawings.
The negative pulse train from the variable pulse generator 16 over
line 21 is first differentiated in a conventional manner by a
capacitor C2 and resistor R3 and passed by a diode D3 as trigger
pulse input to a standard Eccles-Jordan monostable flip-flop or
one-shot provided by resistors R4, R5, R6, R7, a capacitor C3, and
a pair of transistors T1, T2. The resistor R4 and capacitor C3
determine the time constant of the one-shot and, hence, the width
of the output pulses from the pulse generator 19. The latter pulse
width is dependent upon the amplitude of the negative voltage
charging the capacitor C3 through the resistor R4. Therefore, in
order to render the conventional one-shot capable of variable pulse
width output, the resistor R4 is connected to a variable control
voltage as opposed to being returned to ground in the conventional
manner. The variable control voltage is the output of the rate
memory 14 over line 18.
As the d.c. control voltage over line 18 goes more positive, the
pulse width of the one-shot increases, whereas lowering of the
control voltage (control voltage going more negative and indicative
of too high a measured drop rate) the shorter the pulse width for
electrical output from the one-shot.
It will be apparent that other variable width pulse generating
circuits susceptible to control by the control voltage from the
rate memory 14 may be utilized for the variable pulse width
generator 19 without in any way departing from the spirit and scope
of the present invention.
The output pulses from the pulse generator 19 are directed over a
line 22 as energizing pulse input to a driver 23 which, in turn,
energizes an electromagnet 24 to move a clamping member 25 away
from a flexible intravenous feeding tube 26, to thereby open the
feeding tube for fluid flow. The clamping member 25 is normally
spring-biased to a position which pinches the tube 26 in a shut-off
state.
Each output pulse over line 22 causes the clamping member 25 to be
retracted and thereby open the feeding tube 26 for the duration of
the energizing pulse width. By way of example, the electromagnet 24
and clamping member 25 may be a solenoid controlled finger normally
pressing the feeding tube 26 against an appropriate clamping
surface provided by a rigid block 27 or the like. Other selective
tube clamping expedients may be utilized, however, as long as they
are susceptible to control by the pulse output over line 22 from
the pulse generator 19.
In accordance with one aspect of the new and improved method of
controlling drop flow, the pulse output from the pulse generator 16
directed over lines 15 and 21 is a relatively high multiple of the
actual drop flow rate frequency desired. The reason for this will
be apparent from FIG. 3.
As the ratio of driver pulse frequency to actual drop flow rate
frequency increases, drop size distortion, and consequent lack of
consistent drop size repeatability, diminishes. It will also be
apparent, that best results are achieved with a high, non-integral
ratio of driver pulse frequency to desired drop flow rate
frequency, although good results can be obtained with a relatively
high integral ratio. In the preferred embodiment of the present
invention, a ratio of ten and one-half to one has proven very
satisfactory.
Hence, in accordance with the present invention, each drop which
flows through the intravenous feeding tube 26 is made up of a
multiplicity of smaller drop portions which are attached to each
other to form a contiguous fluid body making up the final drop
which is thus grown in steps under the control of the energizing
pulses from the pulse generator 19. The width of the latter pulses
is varied by the closed loop system including the drop sensor 11,
pulse generator 12 and rate memory 14 to ensure regulation of the
actual drop flow rate measured to the desired drop flow rate
indicated by the pulse output from the pulse generator 16.
The sizes of the current determining resistors R1 and R2 are
selected in accordance with conventional design practices to
compensate for the high ratio of pulse frequency over line 15 when
compared with the pulse frequency over line 13, so that the average
current flow into the summing junction 28 between the diode D1 and
D2 is not affected by the ratio of frequencies.
The control voltage output from the rate memory 14 is also directed
over a line 29 to any appropriate monitor and alarm system (not
shown) for detecting out-of-limit conditions such as an over-speed
or runaway condition indicated by an excessively high control
voltage from the rate memory 14, or an unusually low level control
voltage indicating leakage in the feeding tube 26 with the clamping
member 25 in the tube shut-off position. Such monitor and alarm
systems may take any form well known in the art, such as high and
low level discriminators for selectively triggering aural or visual
alarms.
The new and improved method and apparatus for drop flow control, in
accordance with the present invention, satisfied a long existing
need in the medical arts for an extremely accurate, relatively low
cost, reliable, easy to use system providing digitial precision in
selecting and maintaining drop flow rates over a wide range. The
system of the present invention functions to maintain selected flow
rates substantially independent of changes in temperature, crimps
in the feeding tube, variations in venous or arterial pressure of
the patient, muscular activity of the patient, or variations in the
height of the IV bottle or solution level within the bottle.
It will be apparent from the foregoing that, while particular forms
of the invention have been illustrated and described, various
modifications can be made without departing from the spirit and
scope of the invention. Accordingly, it is not intended that the
invention be limited except as by the appended claims.
* * * * *