A bio-medical flow sensor including a packageable unit of a bottle, tubing and hypodermic needle which can be pre-sterilized and is disposable. The tubing has spaced apart tubular metal segments. The temperature of the metal segments and fluid flow therein is sensed by thermistors and at a downstream location heat is input by a resistor to the metal segment by a control electronics. The fluids flow and the electrical power required for the resisto to maintain a constant temperature differential between the tubular metal segments is a measurable function of fluid flow through the tubing. The differential temperature measurement is made in a control electronics and also can be used to control a flow control valve or pump on the tubing to maintain a constant flow in the tubing and to shut off the tubing when air is present in the tubing

Winkler, H. E.

English

NASA Technical Reports Server

United States Patent [19] [111 4,3134,5713 
Winkler [45] May 24,1983 
[54] BIO-MEDICAL n o w  SENSOR 
[75] Inventor: H. Eugene Winkler, Friendswood, 
Tex. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Adminiitration, Washington, D.C. 
[21] Appl. No.: 254,688 
[22] Filed: Apr. 16, 1981 
[51] Int. C l . 3  ............................................... A61M 5/00 
[52] U.S. c1. ...................................... 604/114; 73/204; 
128/DIG. 13; 604/151 
[58] Field of Search ............ 128/214 R, 214 E, 214.2, 
128/227, DIG. 13; 73/204,222/54 
[561 References Cited 
U.S. PATENT DOCUMENTS 
2,446,283 8/1948 Hulsberg ............................... 73/204 
2,994,222 8/1961 Laub ..................................... 73/204 
3,091,239 5/1963 Moeller ........................... 128/214 F 
3,500,686 3/1970 Bell ....................................... 73/204 
3,990,443 11/1976 Fletcher .......................... 128/214 E 
4,029,094 6/1977 Winicki ........................... 128/214 E 
FOREIGN PATENT DOCUMENTS 
604741 9/1978 Switzerland .................... 128/214 E 
Primary Examiner-Dalton L. Truluck 
Attorney, Agent, or Firm-Russell E. Schlorff; John R. 
Manning; Marvin F. Matthews 
1571 ABSTRACT 
A bio-medical flow sensor (FIG. 1) including a pack- 
ageable unit of a bottle (lo), tubing (11) and hypodermic 
needle (12) which can be pre-sterilized and is dispos- 
able. The tubing (11) has spaced apart tubular metal 
segments (18,19). The temperature of the metal seg- 
ments and fluid flow therein is sensed by thermistors 
(23,24) and at a downstream location heat is input by a 
resistor 25 (FIG. 2) to the metal segment (19) by a con- 
trol electronics (16, FIG. 2). The fluid flow and the 
electrical power required of the resistor (25) to maintain 
a constant temperature differential between the tubular 
metal segments (18,19) is a measurable function of fluid 
flow through the tubing (11). The differential tempera- 
ture measurement is made in a control electronics 16 
(FIG. 2) and also can be used to control a flow control 
valve or pump (17) on the tubing (11) to maintain a 
constant flow in the tubing (11) and to shut off the 
tubing when air is present in the tubing. 
8 Claims, 2 Drawing Figures 
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U.S. Patent May 24, 1983 Sheet 2 of 2 4,384,578 
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4,384,578 
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BIO-MEDICAL FLOW SENSOR 
tial is balanced to its pre-set condition. The advantages 
of the invention include its use as medical equipment. 
2 
ORIGIN OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS 
5 The details of my invention will best be described in 
connection with the accompanying drawing in which: 
the flow measuring system; and 
The invention described herein was made by an em- 
tured and used by or for the Government of the United 
Stated of America for governmental purposes without 
the payment of any royalties thereon or therefor. 
ployee Of the Government and may be FIG. 1 is a perspective and schematic illustration of 
FIG. 2 is a schematic illustration of the electronics for 
10 the flow measuring system. 
TECHNICAL FIELD 
_ _  
BEST MODE FOR CARRYING OUT THE 
This invention relates to flow rate measuring and 
controlling devices, and more particularly, to a system 
for accurately measuring the flow rates of fluids intro- 15 
duced intravenously . to medical _ .  patients and controlling 
INVENTION 
Referring to the drawing, in FIG. 1 the system in- 
cludes a supply bottle 10 of intravenous fluid, a plastic 
delivery tube 11 and an intravenous needle 12. Also of the flow rate of the fluids. 
Currently, intravenous fluids such as whole blood, 
plasma or drugs in isotonic solutions are introduced 
through a needle coupled by a tubing to an elevated 20 
bottle of fluid. The elevated bottle of fluid provides a 
gravity fluid feed into a patient's vein. A small pinch 
valve is used to control the flow rate which is typically 
measured by timing the frequency of the drops at the 
mouth of the bottle. Generally, the entire intravenous 25 
system including the bottle, the tubing and a hypoder- 
mic needle are disposable which eliminates the need for 
sterilizing the equipment after each use. 
The current methods of intravenous fluid injection 
have some disadvantages 'in that the flow rate varies 30 
widely as a function of the elevation of the bottle, the 
fluid level in the bottle and the temperature of the liq- 
uids. For some types of drug treatments, such as hepa- 
rin therapy or chemotherapy, the rate of the drug injec- 
tion is quite critical since excess doses can be toxic. 
Peristaltic pumps are available which deliver fluid 
from a reservoir bottle through the tubing but signifi- 
cant disadvantages exist because if the fluid pressure 
varies upstream of the pump, the flow rate can change 4o 
drastically if the tubing is not full to capacity. A drop 
35 
counter method of flow measurement is extremely inac- 
curate since the size of the drops can vary widely and 
cause a plus or minus 15% error in the flow rate deter- 
mination. 
DISCLOSURE OF INVENTION 
In accordance with the present invention I have pro- 
vided a flow measuring system for accurately measur- 
ing the flow of intravenously injected fluids. The device 
includes two metal tubing segments in the delivery tube, 
a thermal flow sensor unit, control electronics and a 
proportioning valve or peristaltic pump. The thermal 
flow sensor unit uses thermistors for accurately measur- 
ing temperature at two points in the delivery tube. Spe- 
cifically, the metal tubing segments are spaced a fmed 
distance apart from one another with a thermistor in 
thermal contact at each location. Before the fluid passes 
the downstream thermistor, a small resistor heats the 
downstream metal tubing segment sufficiently to keep 
the temperature sensed by the downstream thermistor 
at a predetermined level above that sensed by the up- 
stream thermistor. The electric power consumed by the 
resistor to maintain the predeterqined temperature 
differential between the locations is a measure of the 
flow rate. A flow control valve is regulated by the 
electrical sensing of temperature differential to increase 
or decrease the flow rate until the temperature differen- 
45 
50 
55 
60 
65 
included is a thermal flow sensor unit or container 15, 
control electronics 16, and flow control means 17. 
The plastic delivery tube 11 has a pair of metal tubing 
segments 18 and 19 incorporated along its length at a 
fixed distance from one another. The metal tubing seg- 
ments 18 and 19 are made of thin walled stainless steel 
or other highly thermal conductive metal such as silver 
or copper. The metal tubing segments 18 and 19 are 
arranged so as to be received in metal contact shells 
20,21 disposed in a housing of the thermal flow sensor 
unit 15. The metal contact shells 20 and 21 are con- 
structed of thermally conductive metal and curved to 
conform closely to the curvature of metal tubing seg- 
ments 18 and 19 so that the tubing segments is snugly 
received by metal contact shells 20 and 21. Thermally 
conductive grease may be used to enhance the thermal 
connection between the metal tubing segments and the 
metal contact shells. Each of the metal contact shells is 
encased in an epoxy or plastic casting 22 to insulate the 
metal contact shells against loss of heat. 
The upstream metal contact shell 20 is provided with 
a thermistor 23 for sensing temperature and for provid- 
ing an electrical signal in response to sensed tempera- 
ture. The downstream metal contact shell 21 is also 
provided with a thermistor 24 for sensing temperature 
and for providing an electrical signal in response to 
sensed temperature. On the upstream side of the metal 
contact shell 21, a resistor type heater 25 supplies heat 
to the metal contact shell. The power supplied to the 
resistor 25 is controlled so that the temperature of the 
tubing segment 19 is always a little higher than the 
temperature of tubing segment 18. As fluid flows 
through tubing segment 19, some of the heat is drawn 
away by the fluid and the temperature change is sensed 
by the thermistor 24. The control electronics 16, in 
response to the signal from thermistor 24 control the 
electrical power to the heater 25 to maintain a constant 
temperature difference between the two thermistors 23 
and 24. The measurement of electrical power required 
to maintain this temperature difference provides an 
indication of fluid flow on a meter 26. Thus, the control 
electronics 16 constitutes a heat control means for con- 
trolling the heating means or heater 25 to regulate the 
amount of heat to the downstream metal tubing segment 
19. 
Between tubing segments 18 and 19 and the hypoder- 
mic needle 12, a proportioning valve 17 or a peristaltic 
pump may be incorporated, in the system, the valve 17 
or pump being responsive to an electrical signal from 
the control electronics 16 to control the flow rate 
through the plastic tubing 11. Both the valve or pump 
4,3 84,518 
3 4 
17 are well known and conventional in the art and need by a temperature difference which is sensed by the 
not be further described herein. second thermistor 24. The deviation of the temperature 
The control electronics 16 receives the electrical difference measurement relative to the temperature 
signals from thermistors 23 and 24 and measures the differential for a given flow rate is used to control the 
amount of current used by resistor 25 as an indication of 5 power applied to the heater 25 to maintain a constant 
flow rate of fluid in the tubing 11. If the flow rate in the temperature differential between thermistor 23 and 
tubing 11 varies from a predetermined flow rate, the thermistor 24 for a given flow rate. 
control electronics 16 produces an electrical signal to In absence of fluid flow, the quantity of power re- 
the valve or pump 17 to adjust the flow rate to the quired to maintain a constant change in temperature is 
predetermined flow rate. 10 equal to the amount of heat loss by conduction through 
Referring now to FIG. 2, where the control electron- the surrounding material to the outside. As flow beings 
ics 16 are illustrated in schematic form, the ambient and increases, a greater quantity of power is necessary 
temperature is sensed by the thermistor 23 and an elec- to maintain the temperature difference. Since the ambi- 
trical signal is supplied to the temperature amplifier 27 ent temperature of the fluid is measured by the upstream 
which also receives an input from a reference voltage 15 thermistor 23 and a constant temperature differential is 
source 28. The electrical signal from the second, down- maintained between the two thermistors 23 and 24, the 
stream thermistor 24 is compared in a A T  amplifier 29 flow sensor response is not affected by changes in the 
with respect to the ambient temperature signal and temperature of the solution. 
supplies a comparison signal to a comparator circuit 30. This invention offers distinct advantages over the 
The comparator circuit 30 also receives a signal from a 20 prior art. It is a much more accurate, Drecise method for 
ramp generator 31. The ramp generator 31 his a control 
means 32 which adjusts the ramp signal and thus, deter- 
mines the pre-set temperature differential for the flow 
of fluid. The output of the comparator circuit 30 oper- 
ates a driver circuit 34 which controls the electrical 
current in the heating resistor 25 as a function of the 
output of the comparator circuit. To obtain an indica- 
tion of the flow rate on a meter 26, an electrical signal 
is supplied from the temperature amplifier 27 through a 
temperature compensation network 36 to an integrator 
circuit 37 which combines the electrical output of com- 
parator 30 and the electrical output of representative of 
the ambient temperature to provide resultant electrical 
signal to an amplifier 38 and output terminal 39 where 
the output is proportional to the flow rate. 
Referring again to FIG. 1, the thermal flow sensor 
unit 15 is illustrated as a box like container which con- 
tains a semi-cylindrical, lengthwise extending channel 
40 for receiving the delivery tubing 11. Disposed within 
the sensor unit 15 along the surface of the channel 40 are 
the metal contact shells 20 and 21. The cover lid 41 of 
the sensor unit 15 has a corresponding semi-circular 
channel 42 with a spaced apart pressure plates 43 and 44 
which are non-metallic and made of low thermal con- 
ductivity material. The plates 43 and 44 bear upon the 
metal tubing segments 18 and 19 when the cover lid 41 
is closed to insure thermal contact of the segments 18 
and 19 with the metal contact shells 20 and 21. To pre- 
vent heat loss, the channels 40 and 42 are sized to 
closely match the curvature of the tubing 11. A latch 45 
in the cover lid 41 is received in a recess 46 in the bot- 
tom portion of the container for locking the cover lid 41 
in a closed position. For good sensitivity and fast re- 
sponse time, the metal tubing segments 18 and 19 and 
the metal contact shells 20 and 21 should be made as 
small as is practical. Tests have shown the thermistor/- 
heater technique of measuring fluid flow described 
herein can sense fluid flows as low as 100 drops per 
hour. 
In operation of the system, the upstream thermistor 
23 measures the ambient temperature of the incoming 
fluid. The resistance heater 25 supplies heat in the re- 
gion around second downstream thermistor 24. The vide the two small metal tubing segments in ihe de1i;ery 
temperature of the downstream tubing segment 19 is tube, and the equipment can be sterilized and packaged 
always higher than the temperature of the upstream 65 exactly as is done with the conventional units. The flow 
tubing segment 18 because of the heater 25. As the fluid sensing unit into which the delivery tube is encom- 
flows by second thermistor 24, the temperature effect passed is never in contact with the fluid in the system 
on the fluid is constant for a given flow rate as reflected and therefore does not have to be sterilized. 
measuring and controlling the flow ;ate of intravenous 
fluids. The flow can be set to a precise rate and the 
device will maintain that rate constant until the therapy 
is completed. Also, since the flow rate is continuously 
25 monitored, the pump or valve 17 can be controlled 
continuously to prevent variations in flow rate due to 
changes in upstream pressure. The flow rate can be 
adjusted on the described device to a much more exact 
value than with what is currently used. It has advantage 
30 over using just a peristaltic pump since it has the capa- 
bility of shutting the pump off when the fluid reservoir 
is empty, eliminating the possibility of injecting air into 
the patient’s veins. In this instance the control electron- 
ics 16 will develop a signal representation of a no flow 
35 condition when air replaces liquid in the delivery tube 
because of the temperature measurement. This electri- 
cal signal from the temperature measurement is applied 
to the pump or valve 17 to cause an immediate shut- 
down of the pump or valve. In addition, an audible 
40 signal can be used to alert medical personnel that the 
intravenous fluid is depleted. Since a peristaltic pump is 
a positive displacement device, the tubing connected to 
the pump will remain closed against force of the pump 
rollers, thereby preventing any siphoning action. The 
45 system would, therefore, remain in this safe configura- 
tion until medical personnel remove the intravenous 
apparatus or replace the empty reservoir. 
The described invention is not affected by changes in 
fluid temperature because a temperature differential is 
50 being sensed. This is particularly important in the medi- 
cal industry, since intravenous solutions, particularly 
whole blood, are often refrigerated and may not be 
completely at room temperature when being used. 
The conventional intravenous equipment currently 
55 widely used in hospitals is completely disposable, in- 
cluding the reservoir bottle, the delivery tubing and the 
hypodermic needle. This eliminates the need for re- 
sterilization between uses. Ordinarily, the bottle, tubing 
and needle are sterilized; then the bottle is filled with 
60 the proper fluid. The complete unit is then packaged to 
prevent recontamination. The described invention like- 
wise can be disuosable. All that is necessarv is to uro- 
5 
4,384,578 
6 
I claim: 
1. A flow sensing system for biomedical application 
in measurement of low flow rate intravenous fluids, the 
improvement including an intravenous fluid source, and 3* The flow system as in 
intravenous injection unit and a delivery tubing inter- 
connecting said fluid source and said intravenous injec- 
tion unit; 
flow sensing means for sensing the rate of flow 
through the delivery tubing including spaced apart, 10 
thermally conductive tubing metal segments dis- 
posed in said delivery tubing; 
container means for enclosing said tubing metal seg- 
ments, said enclosing means having thermal sensing 
said metal tubing segments and for sensing the 
temperature at each of said metal tubing segments 
2. The flow sensing system as claimed in claim 1 
wherein said flow control means is a positive displace- 
ment pump* 
5 wherein said flow control means is a flow control valve. 
4. The flow sensing system as claimed in claims 2 or 
wherein thermal sensing means for sensing the 
temperature is responsive to air in the delivery tubing 
for closing mid delivery tubing. 
5. The flow sensing system as claimed in claim 1 
wherein said intravenous fluid source, said delivery 
tubing and said intravenous injection unit are steriliz- 
able and disposable as a unit. 
6. The flow sensing system as defined in Claim 1 
for providing a thermal connection with 15 wherein said container means has channel means which 
are adapted to releasably receive a section of delivery 
tubing containing said tubing metal segments, thermally 
conductive semi-circular shells disposed in said channel 
in said tubing; said hav- means for receiving said tubing metal segments, said 
ing heating for heat at the down- 20 thermal sensing means including thermistors for sensing 
stream metal tubing segment; the temperature of fluid in a tubing metal segment; said 
heat control means for controlling the heating means heating means including an electrical resistor element 
to regulate the amount of heat to said downstream disposed forward of the location of a thermistor, said 
metal segment as a function of the differential tem- heat control means being responsive to electrical signals 
perature between said two metal tubing segments; 25 from said thermistors for regulating the electrical 
and power used by said resistor element to maintain a con- 
for controlling stant temperature differential between said thermistors. 
the rate of fluid through said delivery tubing, said 7. The flow sensing means as claimed in claim 6 
wherein said container means has clamping plates for flow control means being located between said 30 maintaining said tubing metal segments in contact with flow sensing means and said intravenous injection said semi-circular shells. 
unit; 8. The flow sensing means as claimed in claim 1 and 
said flow control means being coupled to said heat further including means responsive to said heat control 
control means and responsive to said heat control means for visually indicating the flow rate through said 
means for controlling the flow of fluid through said 35 delivery tubing. 
further including flow control 
delivery tubing. * * I * *  
40 
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Bio-medical flow sensor

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