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Simple, reliable and inexpensive telemetry system for continuous monitoring of small animal core temperature
Physiology & Behavior, Vol. 19, pp. 331--333. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.
BRIEF COMMUNICATION Simple, Reliable and Inexpensive Telemetry System for Continuous Monitoring of Small Animal Core Temperature 1'2 JOHN M. DE CASTRO AND E A R L BROWER
Georgia State University (Received 3 February 1977) DE CASTRO, J. M. AND E. BROWER. Simple reliable and inexpensive telemetry system for continuous monitoring of small animal core temperature. PHYSIOL. BEHAV. 19(2)331-333, 1977.-A core temperature telemetry system is described which includes a transmitter and circuitry for signal reception, noise elimination and computer interfacing. The system is inexpensive (less than $50), easily constructed, reliable, portable, and has proven to be sensitive to rapid fluctuations in core temperature. Temperature
Telemetry
Core temperature
Computerized data acquisition
RECENT ATTEMPTS at long-term monitoring core temperature via telemetry have proven to be effective and efficient. However, these systems also have certain disadvantages not the least of which is expense, along with heavy and cumbersome design [13]. Due to technical advances, more recent attempts at building a telemetry system have escaped these problems [ 11 ]. But for a variety of reasons, including unreliability, cost, and the need for a sophisticated data reduction procedure, these techniques have not proven satisfactory. Recently, we have designed and employed a temperature telemetry system which overcomes these difficulties. This system consists of a small, inexpensive, thermally sensitive transmitter, circuits for noise elimination, computer interfacing, computer software for further noise elimination and continuous monitoring and analysis. The transmitter is a model M ($19.80) or V ($26.00) mini-mitter, (Mini-mitter Company, Indianapolis, IN), which is 15 mm in diameter, 19 mm in length and weighs just 2.3 g. It is powered by a 1.5 V hearing aid battery which is capable of 3 months continuous operation. Prior to implantation, the device is coated with a mixture of bee's wax and paraffin and with a thin outer coating of silicone to insure water tightness. Once prepared, the transmitter is implanted in the peritoneal cavity or under the skin. We have found that temperature monitoring can begin immediately following surgery and can be used to monitor recovery.
SIGNAL
RECEPTION, NOISE ELIMINATION, INTERFACING
COMPUTER
The implanted device emits a pulse, the frequency of which is correlated with temperature. Its response is linearly related to temperature over the range of physiologic temperatures. Each mini-mitter must be calibrated separately. Typically, it increases approximately 7.4 pulses/min per °C. The signal may be received on an inexpensive a.m. transistor radio of any type. We have found that the wire mesh of the animal's cage makes an excellent antenna for the system. A second a.m. radio is placed close to the first radio, but its antenna is not connected to the animal's cage. The output signals from both radios are fed into a noise elimination and interface circuit. Initially, we attempted to use a differential amplifier to cancel the noise signal. However, it was found to be impossible to exactly match the two radios. Hence, we designed the circuit depicted in Fig. 1. The signals from both radios are amplified by separate comparator circuits. The telemetry signal is then delayed by interposing a second comparator stage. The output of this second comparator triggers a one shot which outputs a signal of predetermined size and duration. The output from the one shot is easily interfaced to any of a number of digital computers. In the present application, it is interfaced to an IBM 1800 data acquisition and control system. Two
Requests for reprints should be addressed to John M. de Castro, Department of Psychology, Georgia State University, University Plaza, Atlanta, GA 30303. 2The authors gratefully acknowledge the significant contributions of M. L. Rubenstein for his assistance in the circuit design, D. Prebble for the IBM 1800 software and to M. Terman for helpful criticisms of the manuscript. 331
332
DE CASTRO AND BROWER
TEMPERATURE
I
-
-
ITRIGGER ONEV SHOT SENSITIVITY ,~
"
su~Ess,~ RAO,O
j
I
I
±
/
I ,
I 3K
©
IRESET
,--IJ.-J TIM,N~ I " I
.
n
T OUTPTU
I •
+9V ;3 13 14 L 1~-:
.lp~ 14 "~12 13 1 3 L 12
lOOK
_o 10
:i.
10
' OUTPUT
FIG. 1. Schematic (Top) and wiring diagram (Bottom) of the temperature telemetry system.
transistors are all that are needed to switch the required 36 V to the 1800. The output from the noise suppression radio, after amplification by the comparator, triggers a one shot which holds the output one shot in the reset condition. Hence, any signal in common to both radios is not transmitted to the computer since the output device is held off by the signal from the noise suppression radio. On the other hand, a signal picked up solely by the temperature telemetry radio, will be transmitted to the computer. We have found the noise suppression circuitry to be a necessity in the normal laboratory environment. It prevents noise emitted by devices such as feeders, drinkometers, and other electromechanical switching devices from being interpreted as a telemetry signal. For the noise elimination and interfacing circuitry two inexpensive intergrated circuits are sufficient - the LM339N Quad Comparator and an NE556 Dual Timer. The entire system, including the radios, is powered by a single 9 V, 1 A power supply. The entire telemetry system, including the transmitter, radios, power supply, and noise elimination and interfacing circuit, can be assembled for less than fifty dollars. The computer is not necessary since the telemetry signal can be output directly to an oscilloscope and the temperature can be determined by measuring the interpulse interval. Alternatively, it could be output to a solid state pulse rate counter with a
7-segment LED display, for a real time visual output. Computer monitoring does, however, allow greater accuracy by signal summation and eliminates the need for an observer. COMPUTER SOFTWARE The computer is programmed to further eliminate noise, and to monitor and sum interpulse intervals into 3-rain bins over the entire day. The data are output on punch cards which are used for further analysis. The software further eliminates noise by creating an interpulse interval window which is determined by the average interpulse interval occurring during the preceding 3-min interval plus or minus 20 msec. Any interpulse interval falling outside of this window is ignored. Interpulse intervals falling within the window are summed over the 3-min interval and a new average interval and window are calculated. Since the interface will, at times, cancel a true telemetry signal, a spuriously long interpulse interval will occur. Thus, an automatic recording system must eliminate this interpulse interval. The software outlined above handles this problem. In addition, this procedure facilitates the discrimination of signal from noise, yet is flexible and adapts to fluctuations in the animal's core temperature, allowing for the discrimination of relatively rapid changes in body temperature.
MONITORING CORE TEMPERATURE
=: d
333
LIGHT
ORAK
P~
,4 uJ~"
td'J~ Z3~
a_~. == ,A
oo
3"oo
6'.00 ff.oo HOURS SINCE
le.oo ]~.oo lb.oo 0800 LIGHTS ON
2'].oo
2~.oo
FIG. 2. Typical telemetry output for a single rat over one day. Temperature is expressed in pulses per minute transmitted by the mini-mitter. Figure 2 displays t h e t e m p e r a t u r e o f a t y p i c a l male rat over a 24-hr period. T h e rat was e a t i n g a n d d r i n k i n g ad lib and h a d free access t o a r u n n i n g wheel. T h e rat was o n a twelve-hr l i g h t / d a r k schedule w i t h lights o n at 0 8 0 0 h r a n d o f f at 1600 hr. Figure 2 reflects s o m e i n t e r e s t i n g t e m p e r a ture f l u c t u a t i o n s t h a t deserve m e n t i o n . First, t h e circadian r h y t h m a n d t h e overall rise in t e m p e r a t u r e associated w i t h the d a r k p o r t i o n of the cycle are readily a p p a r e n t . Second, the h i g h sensitivity o f the t e l e m e t r y s y s t e m is e v i d e n c e d b y its ability t o d e t e c t rapid f l u c t u a t i o n s in core t e m p e r a t u r e , t h a t t h e s e f l u c t u a t i o n s are n o t a r t i f a c t u a l is e v i d e n c e d b y the fact t h a t the m o r e p r o n o u n c e d peaks in t e m p e r a t u r e are c o r r e l a t e d w i t h c o n s u m m a t o r y a n d r u n n i n g wheel b e h a v i o r
(de Castro a n d Brower, in p r e p a r a t i o n ) . In a d d i t i o n , very similar f l u c t u a t i o n s have b e e n observed w i t h a t h e r m i s t o r r e c o r d i n g of b r a i n t e m p e r a t u r e ( T e r m a n , P e r s o n a l Comm u n i c a t i o n , 1977). The s y s t e m has b e e n in o p e r a t i o n for over 10 m o n t h s a n d has p r o v e d to be very reliable. O n l y o n e failure has o c c u r r e d a n d t h a t was due t o one o f t h e r a d i o ' s failing. In a d d i t i o n , t h e s y s t e m is fairly p o r t a b l e and can be easily m o v e d f r o m cage to cage. T h e noise d i s c r i m i n a t i o n capability m a k e s the s y s t e m useable even in very n o i s y e n v i r o n m e n t s a n d t h u s can be used in a variety of testing situations.
REFERENCES 1. Abrams, R.M. and H. T. Hammel. Hypothalamic temperature and sleeping.Am. J. Physiol. 206: 6 4 1 - 6 4 6 , 1964. 2. Brobeck, J.R. Food intake as a mechanism of temperature regulation. Yale J. Biol. Med. 20: 545-552, 1947-1948. 3. Brobeck, J. R. Mechanisms concerned with appetite. Pediatrics 20: 5 4 9 - 5 5 2 , 1957. 4. Brobeck, J. R. Food and temperature. Recent Prog. Horm. Res. 16: 4 3 9 - 4 6 6 , 1960. 5. Campbell, B. A. and G. S. Lynch. Activity and thermoregulation during food deprivation in the rat.Physiol. Behav. 2: 3 1 1 - 3 1 4 , 1967. 6. Canfield, R. A. and L. A. Smaha. Temperature measurement in cats with a chronically implanted sensing device. Physiol. Behav. 7: 9 2 9 - 9 3 0 , 1971. 7. Crawshaw, L.E. Effects of intraceberal 5-Hydroxytryptamine injection on thermoregulation in the rat. Physiol Behav. 9: 133-140, 1972. 8. Grossman, S.P. and A. Rechtschaffen. Variations in brain temperature in relation to food intake. Physiol. Behav. 2: 379-383, 1967.
9. Harrel, L.E., J.M. de Castro and S. Balagura. A critical evaluation of body weight loss following lateral hypothalmic lesions. Physiol. Behav. 1 5 : 1 3 3 - 1 3 6 , 1975. 10. Hulst, S. G. T. Intracerebral inplantation of carbachol in rat: Its effects on water intake and body temperature. Physiol. Behav. 8: 865-875, 1972. 11. Illingworth, G. and M. Terman. Phase locked loop: An application in temperature telemetry and a method for its evaluation. Physiol. Behav. 13: 335-338, 1974. 12. Novin, D. The relation between electrical conductivity of brain tissue and thirst in the rat. J. comp. physiol. PsyehoL 56: 145-154, 1962. 13. Rawson, R.O., A.J. Stolwijk, H. Graicben and R. Abrams. Continuous radio telemetry of hypothalamic temperatures from unrestrained animals. J. appl. Physiol. 2 0 : 3 2 1 - 3 2 5 , 1965. 14. Spector, N. H., J. R. Brobeck and C. L. Hamilton. Feeding and core temperature in albino rats: changes induced by preoptic heating and cooling. Science 161: 286-288, 1968.
BRIEF COMMUNICATION Simple, Reliable and Inexpensive Telemetry System for Continuous Monitoring of Small Animal Core Temperature 1'2 JOHN M. DE CASTRO AND E A R L BROWER
Georgia State University (Received 3 February 1977) DE CASTRO, J. M. AND E. BROWER. Simple reliable and inexpensive telemetry system for continuous monitoring of small animal core temperature. PHYSIOL. BEHAV. 19(2)331-333, 1977.-A core temperature telemetry system is described which includes a transmitter and circuitry for signal reception, noise elimination and computer interfacing. The system is inexpensive (less than $50), easily constructed, reliable, portable, and has proven to be sensitive to rapid fluctuations in core temperature. Temperature
Telemetry
Core temperature
Computerized data acquisition
RECENT ATTEMPTS at long-term monitoring core temperature via telemetry have proven to be effective and efficient. However, these systems also have certain disadvantages not the least of which is expense, along with heavy and cumbersome design [13]. Due to technical advances, more recent attempts at building a telemetry system have escaped these problems [ 11 ]. But for a variety of reasons, including unreliability, cost, and the need for a sophisticated data reduction procedure, these techniques have not proven satisfactory. Recently, we have designed and employed a temperature telemetry system which overcomes these difficulties. This system consists of a small, inexpensive, thermally sensitive transmitter, circuits for noise elimination, computer interfacing, computer software for further noise elimination and continuous monitoring and analysis. The transmitter is a model M ($19.80) or V ($26.00) mini-mitter, (Mini-mitter Company, Indianapolis, IN), which is 15 mm in diameter, 19 mm in length and weighs just 2.3 g. It is powered by a 1.5 V hearing aid battery which is capable of 3 months continuous operation. Prior to implantation, the device is coated with a mixture of bee's wax and paraffin and with a thin outer coating of silicone to insure water tightness. Once prepared, the transmitter is implanted in the peritoneal cavity or under the skin. We have found that temperature monitoring can begin immediately following surgery and can be used to monitor recovery.
SIGNAL
RECEPTION, NOISE ELIMINATION, INTERFACING
COMPUTER
The implanted device emits a pulse, the frequency of which is correlated with temperature. Its response is linearly related to temperature over the range of physiologic temperatures. Each mini-mitter must be calibrated separately. Typically, it increases approximately 7.4 pulses/min per °C. The signal may be received on an inexpensive a.m. transistor radio of any type. We have found that the wire mesh of the animal's cage makes an excellent antenna for the system. A second a.m. radio is placed close to the first radio, but its antenna is not connected to the animal's cage. The output signals from both radios are fed into a noise elimination and interface circuit. Initially, we attempted to use a differential amplifier to cancel the noise signal. However, it was found to be impossible to exactly match the two radios. Hence, we designed the circuit depicted in Fig. 1. The signals from both radios are amplified by separate comparator circuits. The telemetry signal is then delayed by interposing a second comparator stage. The output of this second comparator triggers a one shot which outputs a signal of predetermined size and duration. The output from the one shot is easily interfaced to any of a number of digital computers. In the present application, it is interfaced to an IBM 1800 data acquisition and control system. Two
Requests for reprints should be addressed to John M. de Castro, Department of Psychology, Georgia State University, University Plaza, Atlanta, GA 30303. 2The authors gratefully acknowledge the significant contributions of M. L. Rubenstein for his assistance in the circuit design, D. Prebble for the IBM 1800 software and to M. Terman for helpful criticisms of the manuscript. 331
332
DE CASTRO AND BROWER
TEMPERATURE
I
-
-
ITRIGGER ONEV SHOT SENSITIVITY ,~
"
su~Ess,~ RAO,O
j
I
I
±
/
I ,
I 3K
©
IRESET
,--IJ.-J TIM,N~ I " I
.
n
T OUTPTU
I •
+9V ;3 13 14 L 1~-:
.lp~ 14 "~12 13 1 3 L 12
lOOK
_o 10
:i.
10
' OUTPUT
FIG. 1. Schematic (Top) and wiring diagram (Bottom) of the temperature telemetry system.
transistors are all that are needed to switch the required 36 V to the 1800. The output from the noise suppression radio, after amplification by the comparator, triggers a one shot which holds the output one shot in the reset condition. Hence, any signal in common to both radios is not transmitted to the computer since the output device is held off by the signal from the noise suppression radio. On the other hand, a signal picked up solely by the temperature telemetry radio, will be transmitted to the computer. We have found the noise suppression circuitry to be a necessity in the normal laboratory environment. It prevents noise emitted by devices such as feeders, drinkometers, and other electromechanical switching devices from being interpreted as a telemetry signal. For the noise elimination and interfacing circuitry two inexpensive intergrated circuits are sufficient - the LM339N Quad Comparator and an NE556 Dual Timer. The entire system, including the radios, is powered by a single 9 V, 1 A power supply. The entire telemetry system, including the transmitter, radios, power supply, and noise elimination and interfacing circuit, can be assembled for less than fifty dollars. The computer is not necessary since the telemetry signal can be output directly to an oscilloscope and the temperature can be determined by measuring the interpulse interval. Alternatively, it could be output to a solid state pulse rate counter with a
7-segment LED display, for a real time visual output. Computer monitoring does, however, allow greater accuracy by signal summation and eliminates the need for an observer. COMPUTER SOFTWARE The computer is programmed to further eliminate noise, and to monitor and sum interpulse intervals into 3-rain bins over the entire day. The data are output on punch cards which are used for further analysis. The software further eliminates noise by creating an interpulse interval window which is determined by the average interpulse interval occurring during the preceding 3-min interval plus or minus 20 msec. Any interpulse interval falling outside of this window is ignored. Interpulse intervals falling within the window are summed over the 3-min interval and a new average interval and window are calculated. Since the interface will, at times, cancel a true telemetry signal, a spuriously long interpulse interval will occur. Thus, an automatic recording system must eliminate this interpulse interval. The software outlined above handles this problem. In addition, this procedure facilitates the discrimination of signal from noise, yet is flexible and adapts to fluctuations in the animal's core temperature, allowing for the discrimination of relatively rapid changes in body temperature.
MONITORING CORE TEMPERATURE
=: d
333
LIGHT
ORAK
P~
,4 uJ~"
td'J~ Z3~
a_~. == ,A
oo
3"oo
6'.00 ff.oo HOURS SINCE
le.oo ]~.oo lb.oo 0800 LIGHTS ON
2'].oo
2~.oo
FIG. 2. Typical telemetry output for a single rat over one day. Temperature is expressed in pulses per minute transmitted by the mini-mitter. Figure 2 displays t h e t e m p e r a t u r e o f a t y p i c a l male rat over a 24-hr period. T h e rat was e a t i n g a n d d r i n k i n g ad lib and h a d free access t o a r u n n i n g wheel. T h e rat was o n a twelve-hr l i g h t / d a r k schedule w i t h lights o n at 0 8 0 0 h r a n d o f f at 1600 hr. Figure 2 reflects s o m e i n t e r e s t i n g t e m p e r a ture f l u c t u a t i o n s t h a t deserve m e n t i o n . First, t h e circadian r h y t h m a n d t h e overall rise in t e m p e r a t u r e associated w i t h the d a r k p o r t i o n of the cycle are readily a p p a r e n t . Second, the h i g h sensitivity o f the t e l e m e t r y s y s t e m is e v i d e n c e d b y its ability t o d e t e c t rapid f l u c t u a t i o n s in core t e m p e r a t u r e , t h a t t h e s e f l u c t u a t i o n s are n o t a r t i f a c t u a l is e v i d e n c e d b y the fact t h a t the m o r e p r o n o u n c e d peaks in t e m p e r a t u r e are c o r r e l a t e d w i t h c o n s u m m a t o r y a n d r u n n i n g wheel b e h a v i o r
(de Castro a n d Brower, in p r e p a r a t i o n ) . In a d d i t i o n , very similar f l u c t u a t i o n s have b e e n observed w i t h a t h e r m i s t o r r e c o r d i n g of b r a i n t e m p e r a t u r e ( T e r m a n , P e r s o n a l Comm u n i c a t i o n , 1977). The s y s t e m has b e e n in o p e r a t i o n for over 10 m o n t h s a n d has p r o v e d to be very reliable. O n l y o n e failure has o c c u r r e d a n d t h a t was due t o one o f t h e r a d i o ' s failing. In a d d i t i o n , t h e s y s t e m is fairly p o r t a b l e and can be easily m o v e d f r o m cage to cage. T h e noise d i s c r i m i n a t i o n capability m a k e s the s y s t e m useable even in very n o i s y e n v i r o n m e n t s a n d t h u s can be used in a variety of testing situations.
REFERENCES 1. Abrams, R.M. and H. T. Hammel. Hypothalamic temperature and sleeping.Am. J. Physiol. 206: 6 4 1 - 6 4 6 , 1964. 2. Brobeck, J.R. Food intake as a mechanism of temperature regulation. Yale J. Biol. Med. 20: 545-552, 1947-1948. 3. Brobeck, J. R. Mechanisms concerned with appetite. Pediatrics 20: 5 4 9 - 5 5 2 , 1957. 4. Brobeck, J. R. Food and temperature. Recent Prog. Horm. Res. 16: 4 3 9 - 4 6 6 , 1960. 5. Campbell, B. A. and G. S. Lynch. Activity and thermoregulation during food deprivation in the rat.Physiol. Behav. 2: 3 1 1 - 3 1 4 , 1967. 6. Canfield, R. A. and L. A. Smaha. Temperature measurement in cats with a chronically implanted sensing device. Physiol. Behav. 7: 9 2 9 - 9 3 0 , 1971. 7. Crawshaw, L.E. Effects of intraceberal 5-Hydroxytryptamine injection on thermoregulation in the rat. Physiol Behav. 9: 133-140, 1972. 8. Grossman, S.P. and A. Rechtschaffen. Variations in brain temperature in relation to food intake. Physiol. Behav. 2: 379-383, 1967.
9. Harrel, L.E., J.M. de Castro and S. Balagura. A critical evaluation of body weight loss following lateral hypothalmic lesions. Physiol. Behav. 1 5 : 1 3 3 - 1 3 6 , 1975. 10. Hulst, S. G. T. Intracerebral inplantation of carbachol in rat: Its effects on water intake and body temperature. Physiol. Behav. 8: 865-875, 1972. 11. Illingworth, G. and M. Terman. Phase locked loop: An application in temperature telemetry and a method for its evaluation. Physiol. Behav. 13: 335-338, 1974. 12. Novin, D. The relation between electrical conductivity of brain tissue and thirst in the rat. J. comp. physiol. PsyehoL 56: 145-154, 1962. 13. Rawson, R.O., A.J. Stolwijk, H. Graicben and R. Abrams. Continuous radio telemetry of hypothalamic temperatures from unrestrained animals. J. appl. Physiol. 2 0 : 3 2 1 - 3 2 5 , 1965. 14. Spector, N. H., J. R. Brobeck and C. L. Hamilton. Feeding and core temperature in albino rats: changes induced by preoptic heating and cooling. Science 161: 286-288, 1968.