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A controlled burning apparatus based on the weight immersion principle
A CONTROLLED BURNING APPARATUS BASED ON THE WEIGHT IMMERSION PRINCIPLE 1
By A. D. COURTEMANCHE,M.D., F.R.C.S.(C)
From the Department of Surgery Research Laboratory, University of British Columbia THE ability to produce standardised burns in the experimental animal is a prerequisite of most burn research. This necessitates being able to predict the depth of burning and the surface area involved. The depth of burning depends on the temperature and the exposure time, two factors which have always been relatively easy to control with acceptable accuracy. In predicting the surface area to be involved, investigators have been limited until recently to the use of burning irons of known surface area. This is satisfactory for producing small burns only. To achieve large surface area burns, in the region of 35 to 4 ° per cent. of total body surface area, various methods have been used, most of which did not allow accurate beforehand prediction. In I962 Bailey demonstrated that a close and predictable relationship exists between body weight and surface area in a homologous series of rats. This is represented by the formula S . A . - W 2/3 . K . The same year Bailey, Lewis and Blocker reported a burning apparatus which allowed the accurate prediction of the surface area to be burned in advance of the actual burning. This method was based on the close relationship between weight of body immersed and surface area immersed. Temperature and exposure time were carefully controlled. The writer has constructed a similar apparatus with rather extensive modifications which allows for greater ease of operation and at the same time maintains dependability and accuracy. The method is based on the weight immersion principle, and liquid conduction is used as the source of heat. As with Bailey's apparatus, the processes of measurement and scalding have been separated. The exposure time and temperature can easily be varied to control the desired depth of burning. D e s c r i p t i o n o f Apparatus.--Figures I and 3 show the apparatus mounted on a wooden frame with 3 in. rubber castors for portability. When in actual use four stabilising legs are lowered, which level the equipment. The basic difference between the writer's apparatus and that of Bailey et al. is in the technique of measuring the immersion weight of the rat. In Bailey's apparatus the measuring pan is placed on a Mettler balance and the rat is then lowered into the pan until an appropriate weight change registers. The rat rack is then raised, rotated through I8o degrees and lowered into the burning pan, the vertical travelling distance being adjusted during the measuring process. Rather than load the balance with a measuring pan and water weighing approximately 2,ooo g., in order to measure a weight change in the rat of only slightly over IOO g., it was decided to suspend the rat rack and rat from the bottom of the balance, as shown in Figure 2. A taring device on the Sartorius balance negates the weight of the rat rack and allows the weight of the rat only to register. The research for this paper was supported by the Defence Research Board of Canada, grant number 9325-20. 23
24
BRITISH JOURNAL OF PLASTIC SURGERY
The rat rack assembly is of riveted aluminium I½ in. wide with a radius o f 543 in. (Figures z, 2, and 3)- It is mounted by three slotted arcs to a hub, in such a manner that the angle may be changed relative to the weighing rod. This allows adjustment of the part of the animal's back presenting to the surface of the water. The spider assembly (Figures z, 2, 3, and 4) allows adjustment of four silk suspension lines to prevent lateral displacement of the rat rack due to buoyancy
FIG. I FIG. 2 Fig. I.--Controlled burning apparatus, front view. Fig. 2.--Elevating platform with measuring and burning pans. rack suspended from balance.
Rat mounted on
of the rat. It proved to be needless, due to the very low centre of gravity and high mass of the assembly. The measuring and burning pans are of equal size, 5 by 7 by z4 in. T h e y are mounted side by side on a circular elevating platform as shown in Figures 2, 4 and 5. The elevating platform is activated by a hydraulic lift column (Figs. 3 and 4)A compressor supplies air at 75 lb. per sq. in. Elevation is controlled by a globe valve which admits air to the oil reservoir (Figs. z, 3, and 4)- A pressure regulator controls the rate of elevation. A petcock exhausts air from the hydraulic cylinder allowing the lift column and platform to descend.
A CONTROLLED
BURNING
APPARATUS
25
An adjustable stop collar on the lift co]umn (Fig. 3) contacts the fine adjustment limit assembly, thus controlling the height of elevation and the extent of immersion of the rat in the measuring and burning pans. Fine adjustment is performed manually by rotating a large hoop fastened by three spokes to the fine adjustment limit assembly proper (Figs. 3, 4, and 5).
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FIG. 3
The stop collar at the top of the elevation stroke actuates a timer switch (Fig. 4), which in turn starts the self-setting interval timer. The timer (Fig. 2) is mounted beside the balance and a light on its face indicates the end of the preset interval. At this point the petcock on the air lift control is opened and the platform descends. Water for the burning pan is supplied by a thermostatically controlled water heater and water pump mounted at the bottom of the apparatus (Figs. I, 3, and 4)-
26
BRITISH
JOURNAL
OF P L A S T I C
SURGERY
The pump has a capacity of approximately r litre per minute and circulates the hot water through copper and tygon tubing to a coaxial water connection in the burning pan (Figs. 3, 4, and 5). Method of Controlled Burning.--In preparation for burning the following
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steps are taken. The water heater and pump are started half an hour before using the apparatus to allow the water temperature to become constant. The elevating platform is rotated so that the burning pan is below the rat rack. Using the air lift control and the fine adjustment the platform is raised until the water in the burning pan just reaches the bottom of the rat rack. The platform is then lowered and rotated until the measuring pan sits beneath the rat rack. When the platform is again elevated with the air lift control, it will stop at the preset position. The
A
CONTROLLED
27
B U R N I N G APPARATUS
measuring pan is then filled until the water reaches the bottom of the rat rack. Thus the water level will be the same in both pans. After ana~sthetising the rats with intraperitoneal Nembutal and ether by mask the entire back and flanks are dipped, depilated with Neet, washed with
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FIG. 5
alcohol and sprayed with lacquer. The animal is then fastened to the rat rack as shown in Figure 2 by means of adjustable paw damps, the tail and head being supported with small pieces of adhesive tape. By using the taring device on the Sartorius balance the weight of the rat can be read and recorded directly. The globe valve is then opened elevating the platform and measuring pan until the animal's back is partially immersed. The final elevation is controlled by manually rotating the fine adjustment limit assembly.
28
BRITISH JOURNAL
OF P L A S T I C
SURGERY
One can do this and read the balance simultaneously, thus stopping at the desired percentage weight immersion. The platform is then lowered and rotated to bring the burning pan beneath the rat. Now opening the air lift control will quickly elevate the platform the preset distance. The preset interval timer is triggered at the height of elevation and a light on its face indicates the termination of the desired exposure time. At this point the petcock on the air lift control is opened and the platform descends. The rat is then removed from the rack.
FIG. 6 Tracings of rat pelts made on X-ray film. Represent 4o and 5o per cent. weightimmersion.
<
Testing the A p p a r a t u s . - - I n order to correlate weight immersed and surface area immersed the rats were merely dipped in the measuring pan to which gentian violet had been added. This stained the immersed area quite satisfactorily. After removal from the rack the animals were skinned and the one-piece pelts spread out on heavy wrapping paper. Skinning was accomplished by incising ventrally in the midline from symphysis menti to the beginning of the tail, with transverse incisions between forepaws and hindpaws. The surface area of tail, paws, and ears was not individually calculated on all rats. The surface area of the tails o f twelve rats was calculated as for a cone and the average was then used (16"5 sq. cm.). Bailey's figures of 4"4 sq. cm. for both ears and 5"2 sq. cm. for the four paws were accepted. A total of 26-I sq. cm. was therefore added to the surface area of each pelt as skinned. A tracing of the pelt and the immersed area was made on cleared X-ray film (Fig. 6). This pattern was carefully cut out and weighed, first total peh, then stained area separately. Having calculated the weight of I sq. cm. of X-ray film it was simple to calculate the surface area of the pelt and the immersed area. This method of calculating surface area is relatively simple and accurate. It saves the expense of a planimeter with which multiple readings must be taken to achieve acceptable accuracy. Female albino rats of the Wistar strain were used. The majority weighed between I9o and 2io g., but a few weighed as much as 300 g. and as little as I7o g. Being interested primarily in larger burns for future experimental work, only 4° , 5° , and 60 per cent. weight immersions were carried out. With this apparatus the surface area immersed consistently correlated with the weight immersed. Seventy animals were stained and the averages are shown below. Percentage of Total Body Weight I m m e r s e d 4o per cent. 5 ° per cent. 60 per cent.
Percentage of Total Body Area I m m e r s e d 26. 5 ~ 2 per cent. 3I _-~2"5 per cent. 38 ~-3 per cent.
A
CONTROLLED
BURNING
APPARATUS
29
These figures agree closely with those of Bailey, Lewis, and Blocker (I962) and further confirm the validityof this method of burning. With burning there appears to be a shrinkage of the total area of the pelt and of the stained area. This is due to a generalised contracture of panniculus and, in the case of full-thickness burns, of the burned skin itself. This does not appear to change appreciably the percentage relationship between surface area immersed (burned) and the total body surface area. Bailey felt, however, that the amount of shrinkage should be added to the apparent area of burning, thus increasing the percentage of surface area burned as correlated with body weight immersed. From the writer's experience this does not seem justified. SUMMARY
A controlled burning apparatus has been constructed and tested which makes possible the accurate prediction of the body surface area to be burned. With it the investigator can reproduce the same surface area burn in any required number of animals. Liquid conduction is used as the method of burning and the temperature and exposure time may be varied as required. The basis of the method is the close relationship that exists between the weight of a body immersed and the surface area immersed. This concept is not a new one and was graphically described by Bailey~ Lewis, and Blocker in I962. While reviewing their work, prior to commencing a burn research project, it became apparent to the writer that certain modifications of their apparatus would improve its function and accuracy. These changes are described in detail and are essentially related to the method of measuring the weight change of the immersed rat. Also described is a simple method of calculating surface area of rat pelts which does not require the use of a planimeter. Testing of the apparatus revealed a consistent correlation between weight immersed and surface area immersed. Therefore the writer further advocates the use of this burning technique in the hope that experimental laboratories might use more uniform methods and make comparison of reports easier and more significant. To Mr Kenneth M. Pope the writer is indebted for the design and construction of the apparatus. REFERENCES BAILEY, B. N. (1962). Tex. Rep. Biol. Med., 20, I2. BAILEY,B. N., LEWIS, S. R., and BLOCKER,T. G. jun. (1962). Tex. Rep. Biol. Med., 20, 20.
Submitted for publication, July I964.
By A. D. COURTEMANCHE,M.D., F.R.C.S.(C)
From the Department of Surgery Research Laboratory, University of British Columbia THE ability to produce standardised burns in the experimental animal is a prerequisite of most burn research. This necessitates being able to predict the depth of burning and the surface area involved. The depth of burning depends on the temperature and the exposure time, two factors which have always been relatively easy to control with acceptable accuracy. In predicting the surface area to be involved, investigators have been limited until recently to the use of burning irons of known surface area. This is satisfactory for producing small burns only. To achieve large surface area burns, in the region of 35 to 4 ° per cent. of total body surface area, various methods have been used, most of which did not allow accurate beforehand prediction. In I962 Bailey demonstrated that a close and predictable relationship exists between body weight and surface area in a homologous series of rats. This is represented by the formula S . A . - W 2/3 . K . The same year Bailey, Lewis and Blocker reported a burning apparatus which allowed the accurate prediction of the surface area to be burned in advance of the actual burning. This method was based on the close relationship between weight of body immersed and surface area immersed. Temperature and exposure time were carefully controlled. The writer has constructed a similar apparatus with rather extensive modifications which allows for greater ease of operation and at the same time maintains dependability and accuracy. The method is based on the weight immersion principle, and liquid conduction is used as the source of heat. As with Bailey's apparatus, the processes of measurement and scalding have been separated. The exposure time and temperature can easily be varied to control the desired depth of burning. D e s c r i p t i o n o f Apparatus.--Figures I and 3 show the apparatus mounted on a wooden frame with 3 in. rubber castors for portability. When in actual use four stabilising legs are lowered, which level the equipment. The basic difference between the writer's apparatus and that of Bailey et al. is in the technique of measuring the immersion weight of the rat. In Bailey's apparatus the measuring pan is placed on a Mettler balance and the rat is then lowered into the pan until an appropriate weight change registers. The rat rack is then raised, rotated through I8o degrees and lowered into the burning pan, the vertical travelling distance being adjusted during the measuring process. Rather than load the balance with a measuring pan and water weighing approximately 2,ooo g., in order to measure a weight change in the rat of only slightly over IOO g., it was decided to suspend the rat rack and rat from the bottom of the balance, as shown in Figure 2. A taring device on the Sartorius balance negates the weight of the rat rack and allows the weight of the rat only to register. The research for this paper was supported by the Defence Research Board of Canada, grant number 9325-20. 23
24
BRITISH JOURNAL OF PLASTIC SURGERY
The rat rack assembly is of riveted aluminium I½ in. wide with a radius o f 543 in. (Figures z, 2, and 3)- It is mounted by three slotted arcs to a hub, in such a manner that the angle may be changed relative to the weighing rod. This allows adjustment of the part of the animal's back presenting to the surface of the water. The spider assembly (Figures z, 2, 3, and 4) allows adjustment of four silk suspension lines to prevent lateral displacement of the rat rack due to buoyancy
FIG. I FIG. 2 Fig. I.--Controlled burning apparatus, front view. Fig. 2.--Elevating platform with measuring and burning pans. rack suspended from balance.
Rat mounted on
of the rat. It proved to be needless, due to the very low centre of gravity and high mass of the assembly. The measuring and burning pans are of equal size, 5 by 7 by z4 in. T h e y are mounted side by side on a circular elevating platform as shown in Figures 2, 4 and 5. The elevating platform is activated by a hydraulic lift column (Figs. 3 and 4)A compressor supplies air at 75 lb. per sq. in. Elevation is controlled by a globe valve which admits air to the oil reservoir (Figs. z, 3, and 4)- A pressure regulator controls the rate of elevation. A petcock exhausts air from the hydraulic cylinder allowing the lift column and platform to descend.
A CONTROLLED
BURNING
APPARATUS
25
An adjustable stop collar on the lift co]umn (Fig. 3) contacts the fine adjustment limit assembly, thus controlling the height of elevation and the extent of immersion of the rat in the measuring and burning pans. Fine adjustment is performed manually by rotating a large hoop fastened by three spokes to the fine adjustment limit assembly proper (Figs. 3, 4, and 5).
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,, ,.,..,
FIG. 3
The stop collar at the top of the elevation stroke actuates a timer switch (Fig. 4), which in turn starts the self-setting interval timer. The timer (Fig. 2) is mounted beside the balance and a light on its face indicates the end of the preset interval. At this point the petcock on the air lift control is opened and the platform descends. Water for the burning pan is supplied by a thermostatically controlled water heater and water pump mounted at the bottom of the apparatus (Figs. I, 3, and 4)-
26
BRITISH
JOURNAL
OF P L A S T I C
SURGERY
The pump has a capacity of approximately r litre per minute and circulates the hot water through copper and tygon tubing to a coaxial water connection in the burning pan (Figs. 3, 4, and 5). Method of Controlled Burning.--In preparation for burning the following
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steps are taken. The water heater and pump are started half an hour before using the apparatus to allow the water temperature to become constant. The elevating platform is rotated so that the burning pan is below the rat rack. Using the air lift control and the fine adjustment the platform is raised until the water in the burning pan just reaches the bottom of the rat rack. The platform is then lowered and rotated until the measuring pan sits beneath the rat rack. When the platform is again elevated with the air lift control, it will stop at the preset position. The
A
CONTROLLED
27
B U R N I N G APPARATUS
measuring pan is then filled until the water reaches the bottom of the rat rack. Thus the water level will be the same in both pans. After ana~sthetising the rats with intraperitoneal Nembutal and ether by mask the entire back and flanks are dipped, depilated with Neet, washed with
8"Z~'VRYI/V6 P L R r F O R ~ - ~
••
~ - - 8UaNINa#dim CO
~7'F~UR//YG P~N--
~,'~tECT I
O~Y
pl/tVf A O J U ~ f / I ~ E N T arO~ e L - ~ ' , q T I O,*V ~ //W I T"
SE C TIO,~ ~q-,q
CO/Y[R OZ Z £ D
[
B UR/YING
[I SCALE/,~' = ' /" ~PP,qRAI7-U3
FIG. 5
alcohol and sprayed with lacquer. The animal is then fastened to the rat rack as shown in Figure 2 by means of adjustable paw damps, the tail and head being supported with small pieces of adhesive tape. By using the taring device on the Sartorius balance the weight of the rat can be read and recorded directly. The globe valve is then opened elevating the platform and measuring pan until the animal's back is partially immersed. The final elevation is controlled by manually rotating the fine adjustment limit assembly.
28
BRITISH JOURNAL
OF P L A S T I C
SURGERY
One can do this and read the balance simultaneously, thus stopping at the desired percentage weight immersion. The platform is then lowered and rotated to bring the burning pan beneath the rat. Now opening the air lift control will quickly elevate the platform the preset distance. The preset interval timer is triggered at the height of elevation and a light on its face indicates the termination of the desired exposure time. At this point the petcock on the air lift control is opened and the platform descends. The rat is then removed from the rack.
FIG. 6 Tracings of rat pelts made on X-ray film. Represent 4o and 5o per cent. weightimmersion.
<
Testing the A p p a r a t u s . - - I n order to correlate weight immersed and surface area immersed the rats were merely dipped in the measuring pan to which gentian violet had been added. This stained the immersed area quite satisfactorily. After removal from the rack the animals were skinned and the one-piece pelts spread out on heavy wrapping paper. Skinning was accomplished by incising ventrally in the midline from symphysis menti to the beginning of the tail, with transverse incisions between forepaws and hindpaws. The surface area of tail, paws, and ears was not individually calculated on all rats. The surface area of the tails o f twelve rats was calculated as for a cone and the average was then used (16"5 sq. cm.). Bailey's figures of 4"4 sq. cm. for both ears and 5"2 sq. cm. for the four paws were accepted. A total of 26-I sq. cm. was therefore added to the surface area of each pelt as skinned. A tracing of the pelt and the immersed area was made on cleared X-ray film (Fig. 6). This pattern was carefully cut out and weighed, first total peh, then stained area separately. Having calculated the weight of I sq. cm. of X-ray film it was simple to calculate the surface area of the pelt and the immersed area. This method of calculating surface area is relatively simple and accurate. It saves the expense of a planimeter with which multiple readings must be taken to achieve acceptable accuracy. Female albino rats of the Wistar strain were used. The majority weighed between I9o and 2io g., but a few weighed as much as 300 g. and as little as I7o g. Being interested primarily in larger burns for future experimental work, only 4° , 5° , and 60 per cent. weight immersions were carried out. With this apparatus the surface area immersed consistently correlated with the weight immersed. Seventy animals were stained and the averages are shown below. Percentage of Total Body Weight I m m e r s e d 4o per cent. 5 ° per cent. 60 per cent.
Percentage of Total Body Area I m m e r s e d 26. 5 ~ 2 per cent. 3I _-~2"5 per cent. 38 ~-3 per cent.
A
CONTROLLED
BURNING
APPARATUS
29
These figures agree closely with those of Bailey, Lewis, and Blocker (I962) and further confirm the validityof this method of burning. With burning there appears to be a shrinkage of the total area of the pelt and of the stained area. This is due to a generalised contracture of panniculus and, in the case of full-thickness burns, of the burned skin itself. This does not appear to change appreciably the percentage relationship between surface area immersed (burned) and the total body surface area. Bailey felt, however, that the amount of shrinkage should be added to the apparent area of burning, thus increasing the percentage of surface area burned as correlated with body weight immersed. From the writer's experience this does not seem justified. SUMMARY
A controlled burning apparatus has been constructed and tested which makes possible the accurate prediction of the body surface area to be burned. With it the investigator can reproduce the same surface area burn in any required number of animals. Liquid conduction is used as the method of burning and the temperature and exposure time may be varied as required. The basis of the method is the close relationship that exists between the weight of a body immersed and the surface area immersed. This concept is not a new one and was graphically described by Bailey~ Lewis, and Blocker in I962. While reviewing their work, prior to commencing a burn research project, it became apparent to the writer that certain modifications of their apparatus would improve its function and accuracy. These changes are described in detail and are essentially related to the method of measuring the weight change of the immersed rat. Also described is a simple method of calculating surface area of rat pelts which does not require the use of a planimeter. Testing of the apparatus revealed a consistent correlation between weight immersed and surface area immersed. Therefore the writer further advocates the use of this burning technique in the hope that experimental laboratories might use more uniform methods and make comparison of reports easier and more significant. To Mr Kenneth M. Pope the writer is indebted for the design and construction of the apparatus. REFERENCES BAILEY, B. N. (1962). Tex. Rep. Biol. Med., 20, I2. BAILEY,B. N., LEWIS, S. R., and BLOCKER,T. G. jun. (1962). Tex. Rep. Biol. Med., 20, 20.
Submitted for publication, July I964.