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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a temperature controlled cooling system
and, more particularly, to a microprocessor controlled fluid circulating
system for medical uses.
2. History of the Prior Art
Recent clinical evidence indicates that if the temperature of a body part,
particularly a wound site, is lowered a number of therapeutic benefits
ensue. First, a lower temperature will reduce swelling and increase the
activity of the blood in the wound area to promote healing. Second, a
lower temperature at a wound site substantially reduces the pain
experienced by the patient. This not only increases the comfort level of
the patient but significantly reduces the necessity for the administration
of narcotics and other pain medication to the patient's benefit. Third,
reduction of the temperature at a wound site increases the flexibility in
that region. This is particularly true in the case of a traumatized joint
or at the installation site of an artificial joint, where a lower
temperature will greatly increase the ability of the patient to exercise
the joint. Such treatment can substantially reduce the required period of
stay in the hospital.
Initial use of cooling therapy was mainly found in the field of
orthopedics. It is now found that post surgical cooling is highly
beneficial in the reduction of trauma to the patient. It also increases
the rate of healing and reduces the length of a hospital stay. In
addition, cooling therapy is also being used in home health care for
chronic pain control and to increase joint flexibility and facilitate the
rate of healing.
Numerous prior art devices have been proposed for reducing the temperature
of a body part in order to achieve the beneficial results obtained
thereby. For example, ice packs have long been used to reduce swelling and
achieve some of these benefits. In addition, cold packs containing two
chemicals, which when mixed together absorb heat (endothermic reactions),
have also been proposed as have cooling pads through which a cooling fluid
is circulated and cooled by means of a compressor and refrigerant
condensing in evaporator coils. Such devices are very inconvenient and
contain many inherent disadvantages.
More recently, devices for circulating a cooling fluid through a blanket
applied to a patient have also been proposed. Examples of such structures
are shown in Kumar U.S. Pat. No. 3,894,213, and Brown U.S. Pat. No.
3,967,027, and Bailey U.S. Pat. No. 4,459,468. The Bailey patent discloses
an apparatus which employs a fluid reservoir for containing a substantial
volume of cooling fluid, the temperature of which is regulated by thermal
modules. The temperature of the fluid in the reservoir is monitored to
maintain a selected temperature. The fluid is pumped from the reservoir
through a hose system to a thermal blanket which is applied to the patient
and back into the reservoir for further cooling. While such a system has
been popular in medical applications, it includes numerous disadvantages.
For example, a reservoir system, such as that found in Bailey, requires a
substantial pre-cooling time in order to reduce the temperature of the
relatively large mass of fluid in the reservoir to a desired temperature
level. Secondly, such fluid reservoir type systems must also be primed or
go through a priming cycle before use to ensure that there is sufficient
fluid in the reservoir before performing the cooling operation. Thirdly,
the temperature of the reservoir fluid must be monitored and used as the
control parameter. This leads to extreme inaccuracy in attempts to
maintain a precise control over the temperature applied directly at the
wound site. The heat gained by the fluid between a fluid reservoir and a
thermal blanket may often be reflected by a temperature increase as much
as 10 to 15 degrees. This results in a very inaccurate regulation of the
actual temperature at the wound site.
Another problem associated with the applications of very cold surfaces,
such as that of an ice pack, directly to a body part is its effect on the
skin. The temperature of the ice pack is very cold and can only be left
against the skin for a short period of time. Generally, leaving it longer
than 30 minutes can result in damage to the skin. It is much more
desirable to be able to apply a temperature in a range between 50 and 55
degrees, which is relatively comfortable to the skin, and maintain that
temperature for a substantial number of days. This prolonged application
insures that the body part is cooled to the inner depth of the bone or
tissue of the traumatized area. With an ice pack, cooling only takes place
in the subdural area. In a more precisely controlled temperature
application, cooling can take place at a deep penetration for an extended
period. Thus, it is highly desirable to be able to maintain precise
control of the temperature which is actually contacting the tissue of a
wound site and then sustain that temperature for a substantial period of
time. In this manner the advantages obtained from the use of cold therapy
in a medical application can be vastly increased.
It would thus be highly desirable to be able to provide a fully
programmable temperature controller for medical applications in which the
temperature actually applied to the wound site could be very carefully
monitored and controlled. In addition, it would be desirable to be able to
produce more immediate cooling and a digital read out of that cooling to a
monitoring computer. The variations of the actual temperature of the wound
site over a substantial period of time could be used in medical studies
and other applications. Such a system could also be programmed to monitor
any anomalous conditions in the system such as insufficient amounts of
circulation fluid or losses of pressure due to leakage or defective
couplings.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a fully automatic,
microprocessor controlled system for precisely controlling the temperature
of a fluid circulated to a wound site and monitoring the variations in
that temperature over time.
Another object of the present invention is to provide a system for
circulating a fluid having precisely controlled temperatures through a
patient application blanket, which system requires no priming, has a
relatively short cool down time and provides an indication in the event of
any anomalous conditions within the system.
A further object of the present invention is to provide an electronic
controller for a temperature control fluid circulation system which is
fully programmable and has a display panel which allows periodic
reprogramming of the system and monitoring of the operating conditions
thereof.
One aspect of the present invention thus comprises an improved temperature
control fluid circulating system for automatically cooling a thermal
blanket with a thermoelectric cooling module, the system being of the type
where a temperature control fluid is cooled by the cooling module and
pumped to, through and from the blanket through first and second conduits.
The improvement comprises means for powering the cooling module with a
pulse width modulated signal and means for sensing the temperatures of
fluid flowing within the conduits. Means are provided for calculating the
mean value of the temperatures between the first and second conduits or
calculating a set off value from the temperature at the second conduit in
order to provide an approximate indication of the temperature of the fluid
within the blanket. Means associated with the powering means for modifying
the indicated temperature of the blanket are also provided. The cooling
module may comprise a thermoelectric cooling device and a thermally
conductive cooling block thermally coupled thereto.
In another aspect, the invention described above further includes coupling
the thermoelectric cooling device to a power supply, the output of which
is controlled by a pulse width modulator for precisely controlling the
temperature of the cooling block. The pulse width modulator is coupled to
a shift register for controlling the pulse width modulation of the
modulator. The cooling block may also include a unitary block having a
flow passage formed therein in flow communication with the first and
second conduits, the flow passage being of a cross section adapted for
facilitating the uniform flow of control fluid therethrough.
In a further aspect, the invention comprises a system for providing
temperature controlled fluid circulation through fluid flow circuit. The
system comprises a blanket having a fluid passageway therein for applying
a temperature to an object. The blanket includes a first conduit for
receiving flow of temperature control fluid and a second exit conduit for
discharging the flow. Means are connected to the blanket for providing a
flow of fluid through the blanket. Means are provided for modifying the
temperature of the fluid, the means including a thermally conductive
unitary block having a passageway formed therein. The block is positioned
in thermal contact with means for modifying the temperature of the block
and thereby modifying the temperature of the fluid flowing therethrough.
Means are also provided for sensing the temperature of the fluid leaving
the block and for sensing the temperature of the fluid returning to the
block. Means are provided for calculating the mean value between the
temperatures or calculating a set off value from the return temperature in
order to provide an approximate indication of the temperature of the fluid
within the blanket and means are provided for controlling the temperature
modification means in contact with the block to achieve a desired set
point value of temperature at the blanket.
BRIEF DESCRIPTION OF THE DRAWING
For an understanding of the present invention and for further objects and
advantages thereof, reference may now be had to the following description
taking in conjunction with the accompanying drawing, in which:
FIG. 1 is a perspective view of a temperature control fluid circulating
system constructed in accordance with the teachings of the present
invention;
FIG. 2 is an exploded partial perspective view of the thermal electric
cooling system incorporated in the system of the present invention;
FIG. 3 is an exploded perspective view of the arrangement for mounting
thermal electric cooling devices on the heat transfer block shown in FIG.
2;
FIG. 4 is an exploded perspective view of the heat transfer block shown in
FIGS. 2 and 3;
FIG. 5 is a block diagram of the control circuitry used in the system of
the present invention;
FIG. 6 is a flow chart showing the operation of the system of the present
invention; and
FIGS. 7A-7C are a series of graphs illustrating the improved temperature
control at the wound site obtained by the system of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, there is shown a perspective view of the
temperature control fluid circulating system constructed in accordance
with the principles of the present invention. The system includes a
mounting cabinet 11 having a pair of hooks 12 and 13 positioned along the
rear wall thereof for mounting the cabinet on the foot of a patient's bed.
As will be seen below, the features and advantages of the system of the
present invention allow it to be very quickly transported, mounted, and
put into operation so that it is useful for applying a cool temperature to
a wound site.
The cabinet 11 mounts the cooling mechanisms and control circuitry for the
fluids used in the present system. A fluid exit connection 14 and a fluid
return connection 15 are mounted in one wall of the cabinet 11. A fluid
delivery conduit 16 is connected to the exit connection 14 to conduct a
temperature control fluid from the cabinet 11 along the conduit 16 into a
patient application blanket 17. The blanket 17 is well known in the art
and can be formed of opposed sheets of vinyl material which are sealed
together at select points 18 and 19 to define a plurality of passageways
between the sheets for the circulation of cooling fluid. Preferably one of
the two sheets is transparent so that the fluid can be seen circulating
through the pad 17. The fluid enters an inlet opening 21, passes through a
convoluted path within the pad 17 and exits through a conduit 22. A handle
23 is formed of foam material to facilitate handling of the pad 17. The
inlet to the cooling pad 17 is through a bayonet type male connector 24,
and the outlet is through a similar bayonet connector 25. The inlet
conduit 16 from the cabinet 11 is coupled to the inlet conduit of the pad
24 by means of a self-sealing bayonet coupling 26. This enables the
cooling pad 17 to be easily disconnected from the hose 16 and avoid any
spillage of fluid from the system. In addition, the pad 17 is preferably
provided to the user full of fluid. This eliminates any necessity for
priming the system before operation. The fluid is returned from the pad 17
and the coupling 25 through the return conduit 20 into the coupling 15 on
the wall of the cabinet 11.
Referring to the components on the interior of the cabinet 11 shown by
cutting away the front portion of the cabinet, a peristaltic pump 31 has
an outlet opening 32 which sends fluid into an input 33 of a
thermoelectric cooling unit 34. The fluid is cooled within the unit 34 and
flows from the outlet 35 into the inlet of the connector 15 on the
sidewall of the cabinet 11 and then to the pad 17 for application to the
patient. The electronic control circuitry is mounted in a control unit 36
to which signals come from various portions of the circuitry for control
purposes.
A temperature sensor 41 is coupled in the delivery line of the fluid going
to the blanket 17 and a signal to the control unit 36 is coupled from
temperature sensor 41 via line 42. Similarly, a second temperature sensor
43 is coupled in the return line from the blanket 17 and a signal from
that sensor is coupled to the control unit 36 via the line 44. A machine
temperature sensor 45A mounted directly in the fluid path in the
thermoelectric cooler itself also senses the temperature of the fluid
there and supplies a signal via conductor 45 to the control unit 36. The
control unit 36 supplies current to the thermoelectric coolers (TECs)
mounted within the cooling unit 34 via conductors 47, 48 and 49.
Referring to the upper surface of cabinet 11, a plurality of displays,
control switches and indicator lights are mounted. A first digital display
51 shows the temperature setting of the fluid to be applied to the wound
site as set by the operator. A second display 52 displays the actual
temperature of the fluid within the thermoelectric cooling unit. The third
display 53 displays the calculated temperature of the fluid within the
blanket 17 being applied to the wound of the patient. A power cord 50
supplies operating current to the control unit 36 for the operation of the
control and power circuitry.
A first control switch 54 is touch actuated and serves to start the
operation of the system. A second touch control switch 55 raises the
temperature for which the system is set, as shown in display 51. The third
switch 56 lowers the temperature at which the system is set as shown in
the first display 51. The fourth switch 57 controls the system to switch
the temperatures used from fahrenheit to centigrade and back again.
Finally, the fifth switch 58 serves to stop the pump and the cooling
operation of the system. This function is used by the patient in the event
that the blanket 17 must be temporarily removed from the patient when the
patient leaves his bed.
The first indicator light 61 indicates the need to add fluid to the system.
This is determined by a preselected difference between the set temperature
shown in display 51 and the unit temperature shown in 52 indicating the
absence of fluid to lower that temperature. Alternatively, the system may
include a dual point conductivity probe located in either the delivery or
return fluid flow lines to measure the conductivity of the fluid flowing
therein. If a high percentage of air is contained in the fluid, the
resistance will go up indicating a need to add water to the system. The
second indicator light 62 is lit to indicate the necessity for checking a
fluid connection on the possibility that a leakage has occurred. The third
indicator light 63 is lit when the system is operating properly. The
fourth indicator light 64 is lit when the system is ready to begin fluid
circulation operation by pressing the start switch 54.
As can be seen from FIG. 1, the system operates by energizing the system
and then selecting a preselected temperature in the display 51 by
manipulation of the switches 55 and 56. Thereafter, depression of the
start switch 54 starts the pump 31 to circulate the fluid through the
thermoelectric cooling unit 34 and the conduits leading to and therefrom
and into the patient application blanket 17 for application of a cool
temperature to the patient. The control system 36 operates to energize the
thermoelectric control unit to maintain a very precise temperature of the
fluid which is actually being circulated into the blanket. The temperature
of the blanket is determined by a calculation of the mean temperature
between the temperature of the fluid at the exit conduit 16 of cabinet 11
and the temperature of the entrance fluid returning from the patient
blanket 17 at the fluid connection 15. These temperature sensors 43 and 41
provide a much more accurate determination of the actual temperature of
the fluid being applied to the patient than the prior art measurement
devices detecting fluid reservoir temperature. Alternatively, the system
may calculate an approximate blanket temperature by adding an
experimentally determined set-off value to the temperature of the fluid in
the return conduit 20 measured at sensor 43.
Referring next to FIG. 2, there is shown a exploded perspective view of the
thermoelectric cooling system 34 illustrated in FIG. 1. There it can be
seen how entrance and exit conduits 33 and 35 allow fluid to enter into
the unitary heat exchange block 71, wherein a serpentine flow pattern has
been formed in one surface thereof. The exposed surface of the block 71
will be shown in more detail below to be covered by a plate of relatively
thermally insulating material 72. Preferably, the block 71 is formed of a
highly conductive metal such as aluminum with the insulating plate formed
of a material such as plastic. One side of the block has formed thereon a
pair of raised pedestals 73 and 74. The pedestals are preferably formed
integrally with the aluminum block 71 and of the same material. The upper
surface of each of the pedestals 73 and 74 are placed in contact with the
cooling side of a pair of thermoelectric cooling devices 75 and 76.
Preferably, a silicon grease or similar material is applied between the
surfaces to maximize the heat transfer therebetween.
Still referring to FIG 2, the thermoelectric cooling devices (TECs) 75 and
76 each include a pair of electrical connections 77 and 78 in which
current flowing in one direction causes one side of the TEC to cool and
the other to heat. Current flowing in the opposite direction causes the
reverse side to cool and the other to heat. Such TECs are well known in
the cooling art and may comprise thermoelectric devices such as a Melcor
model 045-06. As shown in FIG. 2, the cool side of each of the TECs 75 and
76 is disposed adjacent the upper surface of each of the pedestals 73 and
74 of the unitary heat transfer block 71. The hot sides of TECs 75 and 76
are placed against the smooth, planar back surface of a thinned heat sink
80 that is designed to dissipate heat therefrom. The heat sink 80 includes
a plurality of elongate fins 81 along the upper surface to increase in the
convection heat transfer of heat taken from the hot surface of the TECs.
To assist the heat sink 80 in dissipating that heat, a fan 82 is provided
to draw air across the fins 81 to assist in the rate of cooling which
occurs. The fan 82 may comprise a framework 83 within which an electric
motor 84 is mounted for driving a plurality of blades 85 and providing
constant cooling to the heat sink 80. The fluid is circulated through the
blanket 17 by means of the peristaltic pump 31 which forces fluid into the
entrance cavity of the entrance port 33 of the unitary heat transfer block
71 and out the exit port 35 thereof.
As also shown in the FIG. 2, the pedestals 73 and 74 are surrounded by a
fixed sheet of foam insulating material 79 into which openings are cut to
receive the pedestals 73 and 74. This effectively insulates the cool side
surfaces of the pedestals 73 and 74 and prevents thermal inefficiencies
due to heat transfer to warmer portions of the structure.
Referring now to FIG. 3, the heat transfer assembly 34 is shown in exploded
view in substantially more detail. There it can be seen how the unitary
heat transfer surface of the unitary heat transfer block 71 is integrally
formed with the pedestals 73 and 74 extending therefrom. The upper
surfaces of those pedestals 73 and 74 are placed in direct contact with
the cool sides of the TECs 75 and 76 for efficient heat transfer
therefrom. The side surfaces 73A and 74A are insulated for undesired heat
transfer by means of the insulated foam structure 79. A pair of windows
79A and 79B are cut in the surface of the foam insulation 79 to receive
the pedestals 73 and 74 and protect the side surfaces from undesired heat
transfer. Alternatively, a wall can be placed around the pedestals 73 and
74 and an insulated layer can be foamed in place to provide thermal
insulation. Further seen in FIG. 4 is temperature sensor 45A mounted
directly in the fluid path of the unitary heat transfer block.
Referring now to FIG. 4, the unitary heat transfer block 71 is shown in
exploded perspective. There it can be seen how the fluid entrance conduit
33 is in fluid connection with a serpentine channel 70 cut directly into
the flat surface of the block 71. The channel 70 winds through the body of
the aluminum block 71 and is in fluid communication with the exit
connection 35 from the block. As can be seen, the channel 70 in the block
is formed on the opposite side of the block 71 from the pedestal 73. The
upper surface of the channel 70 is closed by means of the thermally
insulated plate 72 which is attached by means such as screws 86 to the
flat planar surface of the block 71 to form a fluid tight connection and
enable fluid to flow through the channel 70 without any leakage. In one
embodiment, the plates 72 can be made of clear plastic so that the flow
through the channel may be observed. The connections between the plate 72
and the planar surface of the block 73 containing the channel 70 is of
course fluid tight to prevent any leakage therefrom.
Referring now to FIG. 5, there can be seen a block diagram of the control
circuitry for the system of the present invention. There a microprocessor
101 receives input from a plurality of sensing devices 102-104. The
microprocessor may be of different types although a Motorola model 68HC11
microcomputer performs satisfactorily. The external input 102 comes from
the machine temperature sensor within the unitary heat transfer block via
line 45. The input 103 comes from the fluid flowing into the system as
sensed at temperature sensor 41 via line 42 while the signal on input 104
comes from the temperature of the fluid going to the patient blanket as
sensed by temperature sensor 43 and communicated via line 44. The
microprocessor 101 is connected to a read only memory 105 via a databus
106 and an address bus 107. The system also includes a RAM memory 108 for
temporary storage of data within the system. The microprocessor 101
addresses the ROM and RAM memories 105 and 108 by means of an address
decoder 109, preferably formed of programmable array logic (PAL), and
which provides memory enabling signals to the ROM memory via a bus 111 and
the RAM memory via a bus 112. The ROM memory 105 includes certain
preprogrammed instructions which are used to supply operating procedures
to the microprocessor 101 for operation of the system. An output dataline,
SPI OUT, shown at 115, is connected to a shift register 116 for the
communication of data to be shown in the various display units 51-53 of
the system. The data to be displayed is communicated by the microprocessor
101 into the shift register 116 and thereafter loaded into the display
units 51-53 through the lines 117. Similarly, the microprocessor 101
communicates data via line 115 into a second shift register 118 which
provides an actuation signal to energize each of the indication lights on
the console 11 comprising the add fluid light 61, the check connection
light 62, the system ok light 63 and the press start indicator light 64.
Data is communicated by the user to the microprocessor via a shift register
121 connected to the microprocessor via a line 122 designated as SPI IN.
Here, signals are communicated into the shift register via the input
switches on the console 11. The start switch 54, the temperature upswitch
55, the temperature downswitch 56, the mode control switch 57 and the stop
switch 58 provide inputs into the input shift register 121 and then into
the microprocessor 101. Similarly, a pressure switch within the system
provides an input at 123 in the event the pressure within the circulating
fluid system drops below a preselected value. A flow switch 124 provides
an input in the event that the flow within the system stops.
The microprocessor provides an output through a conventional RS232
communications bus 131 to or from an optional host computer (indicated but
not shown). Such a computer is particularly valuable in the case of
monitoring and research work being done with respect to the medical
effects of low temperature to a patient.
The microprocessor 101 also provides an output signal through a shift
register 132, a pulse width modulator 133 to a power supply 134 which
controls the TECs. This enables the system to very precisely control the
exact amount of power which is applied to the TECs 75 and 76. The use of a
shift register 132 to precisely control the modulation of the pulse width
applied through the power supplies 134 enables a very precise control of
the temperatures of the cooling applied by the TECs to the fluid to enable
a very precise control of the output.
A further input 110 is provided by a voltage divider to precisely calibrate
the inputs to the microprocessor at the factory so that the temperatures
sensed at the inputs 102, 103 and 104 are very precisely calibrated in the
microprocessor to be exactly that temperature based upon precise
laboratory monitors.
Referring next to FIG. 6, there is shown a flow chart of the programming
which controls the operation of the temperature control fluid circulating
system of the present invention. The program starts at 141 and at 142 the
microprocessor initializes the different variables within the system.
Next, at 143 the program reads the three temperature sensors within the
system including the sensor 41 positioned in the outgoing fluid line to
the blanket, sensor 43 in the incoming fluid line from the blanket and
sensor 45A positioned in the fluid passage in the thermo cooling module
itself. The system then calculates the mean value of the temperature
between the outgoing and incoming sensors to approximate a temperature
value at the blanket itself and stores both the read and calculated
temperature values in memory. This occurs at step 144. Alternatively, the
system may calculate an approximate blanket temperature by adding an
experimentally determined set off value to the temperature of the fluid at
the sensor 43 in the return line from the blanket.
At 145, the system sends to the display the digits to be shown in the
temperature set value in display 51, the temperature in the thermoelectric
module from sensor 45A in display 52, and the calculated value of the
blanket temperature in display 53. In addition, at step 145, the system
checks the operation of a number of system parameters including whether
the pump has turned on and pressure has built within the system below a
preselected maximum and above a preselected minimum, whether the TECs have
turned on or not because the temperature sensed is below a certain value
and whether the connectors are connected because the pressure within the
system is below a minimum value. In addition, the system at 146 checks to
see whether or not all digits have been sent to the displays 51-53. If any
of the parameters investigated at step 146 have not fallen within the
required parameter criteria, the system produces a "no" at 146 and enters
a delay stage at 147 until the system is fully operational. During this
period, the system continues to cycle through reading the temperature
sensors, calculating the values and storing them at 144, sending the
display digits and checkin | | |
